higher institute of agriculture and animal husbandry
TRANSCRIPT
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REPUBLIC OF RWANDA
MINISTRY OF EDUCATION
HIGHER INSTITUTE OF AGRICULTURE AND ANIMALHUSBANDRY
(INSTITUT SUPERIEUR D’AGRICULTURE ET D’ELEVAGEISAE-Busogo)
FACULTY OF AGRICULTURE
DEPARTMENT OF SOILS AND AGRICULTURAL ENGINEERING
OPTION: WATER RESOURCE MANAGEMENT
EVALUATION OF RICE CROP WATER REQUIREMENT IN THE DEVELOPPEDSWAMP OF RWASAVE HUYE –GISAGARA DISTRICTS,
SOUTHERN PROVINCE
Memoire presented by:NZAMWITAKUZE AugustinFor the fulfillmentIr A0 Degree in Agricultural Engineering
Director:Ir SURESH KUMAR PANDE ( MSc)
Busogo, January 2009
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CERTIFICATION
This is to certify that this research was undertaken by me under the supervision of my Director ofMemoir,
Ir SURESH KUMAR PANDE ( MSc)
Signature of the candidate: NZAMWITAKUZE Augustin
………………………………………………………………………………………..
Signature of the Director: Ir SURESH KUMAR PANDE ( MSc)
……………………………………………………………………………………….
Signature of the Head of Department: SURESH PANDE…………………………………………………………………………………
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DEDICATION
TOAlmighty God
Friends and acquaintance
all farming community
our classmates of Soil and Agricultural
Engineering
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ACKNOWLEDGEMENTS
First and foremost, I owe my thanks to the Almighty God, for his abundant blessings guidance
and protection during my studies. I am grateful to Mr. SURESH KUMAR PANDE, project
supervisor and Head, Soils and Agriculture Engineering Department for his inspiration, valuable
suggestions and painstaking efforts throughout the period of our project work.
Author is highly indebted and full of gratitude to Dr. KAREMANGINGO Charles, the Rector,
ISAE for his support and encouragement given to me.
I am grateful to Professor Dr. Antoni Joseph Rayar, Dean, faculty of Agriculture for his
valuable guidance during my course of study. I am thankful to Dr. Sankaranarayanan, Mr. N.
Kannan and all academic staff of the department of Soils and Agricultural Engineering for their
constant support and encouragement given through out my project studies
I shall always remember my classmates, with whom I shared happiness and hardships at institute
during my memorable five years stay in ISAE, Busogo.
At last, I express my heartfelt gratitude to my brother and colleagues, whose affection and
encouragement has been a driving force for achieving my project work.
Lastly may anybody who assisted me, in one way or the other, find through this work, an
expression of sincere gratitude.
NZAMWITAKUZE Augustin
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EXECUTIVE SUMMARYThe agriculture in Rwanda represent about 40 % of gross domestic product (GDP),more
than 80% of total exportation incomes (tea and coffee) and occupy about 90 % of country
population . However, the Rwanda is unable to satisfy food need of its population with national
production. That is the necessity of increasing the agricultural production through irrigated area.
Due to inefficiency use of water, the present study have been necessary with the ultimate purpose
of evaluating rice crop water requirement in Rwasave developed swamp, located between Huye
and Gisagara Districts of the southern Province of Rwanda. As such, it will assist the scheme
management at all levels in determining whether the efficiency is satisfactory and, if not, which
and where corrective actions need to be taken in order to improve the situation.
The study revealed the low conveyance efficiency with an average of 56.36% of the
irrigation channels with (87.27% for the right main channel and 56.36% for the left main
channel) and a very low water use efficiency (3.39 kg/ha-mm of water) in Rwasave developed
swamp. However, the water application efficiency is very poor (21.88% in right irrigation
channel and 21.26% in left irrigation channel) which indicate the over use of water and high
deep percolation losses to the tune of 1.56 cm/day. There is clear cut evidence to show that the
scheme management is not good and there is a need of participatory irrigation management by
the farmers/water users who ought to own this action. The overall irrigation efficiency has been
estimated as 48%. This clearly shows the water losses to the tune of 52%. The total water
requirement with existing agro-climatic conditions and irrigation efficiency was estimated as
2152.25 mm. The average water use efficiency was also determined and found to be 3.25 Kg/ha-
mm. Based on the CROPWAT programme, a peripheral channel of 0.425 sq. m cross section is
recommended. As the existing channels can not be changed or replaced, the only alternative is to
put lining and regular maintenance of existing channels.
Good water management practices can increase the efficient use of irrigation water, but the
participatory irrigation management by farmers themselves is of paramount importance. There is
no doubt that further researches have to be undertaken on the efficiency of water use in all
developed swamps of Rwanda. In fact, it is one of the key factors to increase and sustain crop
production for the rapid growing population.
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RESUMEAu Rwanda l’agriculture représente environ 40% de la production intérieur brut, plus de
80% du revenues total exportation (café et thé) et occupe environ 90% de sa population.
Cependant le Rwanda ne satisfait les besoins alimentaires de sa population avec sa production
agricole interne. D’où la nécessite d’augmenter la production agricole a travers différents
aménagement y inclus ceux des marais. Suite à l inefficience d’utilisation de l’eau, cette étude a
été menée pour évaluer les besoins en eau du riz dans le marais aménagé de Rwasave, districts de
Huye et Gisagara de la province du Sud. L‘étude consiste à évaluer la gestion du marais à tous
niveau pour déterminer si le rendement est satisfaisant afin de proposer les corrections à
envisager et les endroits à corriger.
En effet l’étude a révélé une faible efficience de conduite dans les canaux d’irrigation
avec une moyenne totale de 56.36 %. Pour les canaux principaux elle est de 57.27% au côté
droit et de 56.36% au côté gauche. L’efficience d’application est de 21.88% et 21.26% pour
canal d’irrigation du côté droit et de la côté gauche respectivement. L’efficience d’utilisation est
aussi faible, elle est de 3.39 kg-ha/mm. Cela occasionne l’utilisation massive de l’eau sur la
petite superficie et la grande percolation en profondeur qui est de 1.56 cm/jour. Il a été constaté
que la gestion du marais n’est pas authentique car la participation des agriculteurs, utilisateurs de
l’eau, n’est pas intégrale ; ils devraient être responsabilisés pour prendre cette action comme la
leur. L’efficience d’irrigation a été estimée à 48% ceci montre clairement la perte de 52% de
l’eau. Les besoins en eau total avec les conditions agro-climatique existantes et efficience d
irrigation est estime à 2152.25 mm l’efficience moyenne d utilisation de l’eau est de 3.25 kg-
ha/mm. En se basant sur les résultants obtenues par le logiciel CROPWAT on recommande la
section du canal de ceinture de 0.425 m2 comme les canaux existants ne peut pas être remplacé
la seul alternative est de les paver et les maintenir régulièrement.
Ces mesures seront efficaces si les agriculteurs eux-mêmes participent dans la gestion
régulière de l eau dans le périmètre rizicole. En cas de crise ils chercheront les solutions qui leur
conviennent. En fin, plus d études doivent être conduite sur l efficience d utilisation de l eau dans
les marais du Rwanda pour augmenter la production de façon durable.
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LIST OF ABREVIATIONS AND ACRONYMS
Ca : CalciumCOAIRWA : Coopérative ya Abahinzi b’ Igishanga cya RwasaveFAO : United Nations Food and Agriculture OrganizationGDP : Gross Domestic ProductsIFAD : International Fund for Agriculture DevelopmentISAR : institut des sciences agronomique du RwandaK : PotassiumMINAGRI : Ministry of Agriculture, Animal Resources and ForestryMINALOC : Ministry of Local Government and Social AffairsMg : MagnesiumN : NitrogenNGOs : Non-Governmental OrganizationsP : PhosphorusRADA : Rwanda Agriculture Development AuthorityRSSP : Rural Sector support ProjectRwf : Rwanda FrancSSA : Sub-Saharan AfricaUNDP : United Nations Development ProgrammeUSDI : United States Department of Interior Bureau of ReclamationWUAs : Water Users’ AssociationsEICV :Enquête Intégrale sur les condition de vie des ménages (householer living
conditions survey)
MINECOFIN : Ministry of Finance and Economic Planning
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Table of contentsTitles Pages
CERTIFICATION ........................................................................................................................... iDEDICATION................................................................................................................................ iiACKNOWLEDGEMENTS........................................................................................................... iiiEXECUTIVE SUMMARY ........................................................................................................... ivRESUME ........................................................................................................................................ vLIST OF ABREVIATIONS AND ACRONYMS ......................................................................... viTable of contents........................................................................................................................... viiCHAPTER-1 ................................................................................................................................... 1INTRODUCTION .......................................................................................................................... 11.1. Problem Statement ................................................................................................................... 21.2. Principal objectives .................................................................................................................. 21.2.1. Specific objectives ................................................................................................................ 21.3. Justification of study ................................................................................................................ 21.4. Hypothesis................................................................................................................................ 31.5. Plan of work............................................................................................................................. 31.6. Delimitation of the study ......................................................................................................... 3CHAPTER – 2 ................................................................................................................................ 4REVIEW OF RETERATURE........................................................................................................ 42.1.Swamps development in Rwanda ............................................................................................. 42.1.1.Classification of the swamps in Rwanda ............................................................................... 42.1.2.Management and use of swamps ........................................................................................... 62.2. Constraints of agricultural production in swamps ................................................................... 62.3. Suitability and utilization of swamps....................................................................................... 62.3.1.Legal aspects of swamps........................................................................................................ 72.4. Irrigation .................................................................................................................................. 82.4.1 Importance of irrigation ......................................................................................................... 82.4.2. Harmful effects of over-irrigation......................................................................................... 92.4.3. Classification of irrigation methods .................................................................................... 112.4.4Some technical terminology on irrigation............................................................................. 122.4.4.1. Water requirement of crops ............................................................................................. 122.4.4.2. Available Water (AW)..................................................................................................... 132.4.5. Project irrigation efficiency ................................................................................................ 132.4.5.1. Water Conveyance Efficiency ......................................................................................... 132.4.5.2. Water Application Efficiency .......................................................................................... 142.4.6. Efficiency of irrigation practices and water use ................................................................. 142.4.6.1. Water Storage Efficiency................................................................................................. 142.4.6.2. Water Distribution Efficiency.......................................................................................... 142.4.6.3. Water Use Efficiency....................................................................................................... 142.5. Movement of water into soil .................................................................................................. 152.5.1. Infiltration ........................................................................................................................... 152.5.2. Infiltration rate calculation.................................................................................................. 152.5.3. Factors affecting infiltration rate ........................................................................................ 162.5.4. Measurement of infiltration ................................................................................................ 162.5.4.1. Permeability ..................................................................................................................... 16
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2.5.5. Irrigation requirement of rice.............................................................................................. 18CHAPTER-3 ................................................................................................................................. 19MATERIALS AND METHODOLOGY...................................................................................... 193.1. Study zone description........................................................................................................... 193.2. Materials ................................................................................................................................ 203.3. Methodology .......................................................................................................................... 203.3.1. Exploratory survey.............................................................................................................. 203.3.2. Flow discharge measurement.............................................................................................. 213.3.3. Water losses measurements ................................................................................................ 213.3.4 Hydraulic conductivity tests ................................................................................................ 223.3.5. Crop water requirements..................................................................................................... 22CHAPTER-4 ................................................................................................................................. 24ANALYSIS AND RESULTS INTERPRETATION.................................................................... 244.1. Exploratory survey............................................................................................................. 244.1.1. Identification of respondents............................................................................................... 244.1.2. Management of the swamp ................................................................................................. 254.1.3. Organization of farmers ...................................................................................................... 264.2. Hydraulic conductivity calculation ........................................................................................ 264.3. Crop water requirements........................................................................................................ 274.3. Determination of discharge and water conveyance efficiency .............................................. 334.4. Determination of water losses in the rice fields..................................................................... 35CHAPTER-5 ................................................................................................................................. 38CONCLUSION AND RECOMMENDATIONS ......................................................................... 38BIBLIOGRAPHICAL REFERENCES ........................................................................................ 40APPENDICES .............................................................................................................................. 42APPENDIX-A: SURVEY QUESTIONNAIRE ........................................................................... 42Appendix-B: LIST OF COAIRWA FARMERS’ ASSOCIATIONS ........................................... 46ANNEX-C : CLIMATOLOGIC DATA....................................................................................... 47
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List of table
Pages
Table-1: Approximate Available Moisture Holding Capacity of Soils ........................................ 13
Table-2 permeability classes based on hydraulic conductivity of soil ......................................... 17
Table-3: Distribution of the respondents according to their age................................................... 24
Table-4: Distribution of the respondents according to their sex ................................................... 24
Table-5: Climate data for Rwasave general area .......................................................................... 28
Table-6: Crop water requirements for the rice using CROPWAT season A ................................ 29
Table-7: Crop water requirements for the rice using CROPWAT season B ................................ 30
Table-8: Mean velocity measurements in irrigation channels ...................................................... 33
Table-9: Discharge measurements in irrigation channels ............................................................. 34
Table- 7: Water losses in five plots of Rwasave swamp .............................................................. 35
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CHAPTER-1
INTRODUCTION
Rwanda is a mountainous country with total geographical area of 26338 sq. km. Agriculture is
the most important economic activity of ordinary households in Rwanda. According to the 2002
national census (RGPH), over 90 % declared their engagement in farming. In town and suburban
areas, 9,3% of ordinary households are interested in marshland cultivation and other farming
activities. At the current employment level, according to the integral survey on household living
conditions (EICV) in 2000-2001, farming is the main income source in rural areas and in 2003;
the agriculture share of the GDP was 46 %.
The population density is with more than 324 inhabitants/km2 one of highest in Africa. Rwanda
receives a considerable good amount of rainfall through annual cycle of four seasons: two rainy
seasons and two dry seasons, however the poor distribution of rainfall in space and time pose
significant problems to predominantly rainfed agriculture:
Due to undulating topography, uncertainty of rainfall in space and time and lack of appropriate
conservation and production technology no doubt the agricultural production is very poor.
Out of the total arable land of 825000 ha, hillside constitutes about 80% (660000 ha). Due to the
decline of soils fertility on hill slopes and overall climate change, swamps are the most important
remaining land resource for the development of agriculture in a country like Rwanda whose
backbone is agriculture. Therefore, irrigated agriculture will remain to be important for providing
food and livelihood security to the fast growing population. The key question is what strategies
will ensure such sustained effective and productive water use. That’s why Rwanda has prepared
and published the National Master Plan for the Development and Management of Marshlands.
The total area occupied by swamps in Rwanda has been estimated to be 165,000 hectares of
which only 94,000 hectares have been exploited for agriculture (MINAGRI, 2004). Among those
exploited swamps 88,000 hectares are not properly managed due to traditional practices that
result into poor production. From 9,000 hectares of swamps that were developed through
adequate irrigation and drainage infrastructures, only 5,000 hectares are being properly
maintained, and the remaining 4,000 hectares need rehabilitation for good water management
(IFAD, 2007).
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1.1. Problem StatementThough the total amount of rainfall in most part of Rwanda is sufficient, however its ill
distribution in space and time poses great problems of soil erosion in hill slopes, floods and
deposition of sediments in swamps during rainy season. On the other hand lack of moisture
during dry season on hills and swamps remains a stark reality. To exploit the potential swamp
areas, appropriate land and water management activities have to be undertaken. Among others,
the major causes of decreased water productivity in irrigation have been largely attributed to low
irrigation (20-50%) and water use efficiency, especially in Sub-Saharan Africa where surface
irrigation is the commonly used method of irrigation (Magayane and Makarius, 2005).
However the swamps in Rwanda represent almost a complex system whose surroundinghydrographical net work system is directly depended on the condition of catchments area(HYDROPLAN, 2002).
In order to study the problem and prospects of swamp development in RWASAVEswamp rice perimeter, a case study was conducted during 2008. The RWASAVE swamp islocated in HUYE District . The area of developed swamp is about 120 hectares, where rice cropis grown. The study was undertaken with the following objectives:
1.2. Principal objectivesThe principal objective is evaluation of rice crop water requirement in RWASAVE swamp inorder to propose solution and suggestions for its improvement.
1.2.1. Specific objectivesFor achieving the principal objectives the specific objectives are as follow:
To investigate the actual situation in water distribution in RWASAVE developed swamp;
To determine flow discharges in the irrigation scheme and water losses;
To determine rice crop water requirement for better water management. To investigate the level of organization of local water users (i.e. farmers) associations in
the developed swamp of RWASAVE.
To provide solutions and suggestions for efficient water management in rice perimeter.
1.3. Justification of studyDetermination of rice crop water requirement in RWASAVE swamp, present situation of watermanagement and efficiency of water use will help to find out the present problems of riceproduction. It will also help to come out the potential solution for efficient water use to optimizethe production.
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1.4. HypothesisThe following hypotheses were made before undertaking the study:
a. The poor irrigation efficiencies are the main cause of low irrigated area under command;
b. Good water management can improve water use efficiency resulting in increased
production, productivity and area under irrigation;
c. The determination of rice crop water requirement is the main source of avoiding the
scarcity of water in dry season.
d. There are some problems in farmers’ organization in the developed swamp of
RWASAVE.
1.5. Plan of workThe present work is subdivided into three chapters which are:
Introduction
Review of literature
Materials and methods
Results and discussions
And the work is ended by conclusion and recommendation.
1.6. Delimitation of the studyThe present study has as objective of checking if the water in the swamp is sufficient and
properly used to meet rice crop water requirement. The study have been conducted in all area of
this swamp but for clarifying the problems in order to propose the solution and suggestion for
better economic rentability of the swamp the following study will be conducted:
Exploratory survey for knowing the management of the swamp and Organization of
farmers
Rice crop water requirements.
Determination of discharge and water conveyance efficiency.
Determination of water losses in the rice fields.
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CHAPTER – 2
REVIEW OF RETERATURE
2.1. Swamps development in RwandaThe word “swamp” denotes the whole soils of low landscape including humid parts and
marshy soils. Swamps are ecosystems, which have recently caught attention, though the need for
their sustainable development deserves further concern. The importance of swamps is related to
their potential to retain large volumes of water, which can be used for system maintenance and
for dry season agriculture. Agricultural production in Rwanda is extremely dependent on the
rainfall pattern and the climatic uncertainty contributes to wide variations in crop production.
Wherever there are swamps there are people, mainly small farmers and fishermen. This close
association between people and swamps draws attention to the remarkable strategic importance
of these ecosystems in the rural economy and the need for an effective planning, management
and conservation strategy.
The arable area is about 825,000 ha, hillside slopes (about 660,000 ha) are not exploited
in the dry season and marshlands (about 165,000 ha) are partially exploited in the rainy seasons
depending on their degree of flooding. About 94,000 ha of marshlands are currently exploited
(HYDROPLAN, 2002), mostly the ones called mineral, whereas the remaining being large
marshlands made up of peaty or organic soils covered by Papyrus are not cultivated. However,
only 4,000 ha of swamps are fully equipped with irrigation and drainage systems and 1,200 ha
are partially equipped.
2.1.1. Classification of the swamps in RwandaTherefore each swamp and its catchments area should be considered for development. Thehydrology of swamp in Rwanda is defined basically on hydrological conditions which exist oncatchments area. According to HYDROPLAN 2002, the swamps of Rwanda are classified inthree categories:
The swamps of high altitude which are in general narrow in shape and under certaincondition can develop the organic soils in peat. They can be used for water storage, butsome area can be used for cultivation. This kind of swamps is found in BYUMBA,GIKONGORO and RUHENGERI Provinces. Example of these swamps isKAMIRANZOVU and RUGEZI.
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The intermediate swamps or swamps of middle altitude. These swamps are oftenmore large in size. They are essentially situated in central plateau (BUTARE,GITARAMA and KIGALINGALI Provinces).
The big swamps of low altitude or collectors swamps. They are present in centralpart of country or along the primary hydrographical network (NYABARONGO,AKANYARU and AKAGERA).
According to the Ramsar Convention (1971), the definition of wetlands considers a very wide
range of inland, coastal and marine ecosystems, including lakes, flood plains, freshwater
marshes, peatlands, estuaries and mangroves (Dungan, 1991). In Rwanda, semi-detailed
characterization and classification studies of swamps have been carried out. There are different
types of classification as follows:
a. Classification according to Cambrezy;
b. Classification according to the size of the swamp;
c. Classification according to the natural vegetation;
d. Classification based on the utilization and stages of the development;
e. Hierarchical classification according to the hydrology.
The hydrology of swamps in Rwanda is basically defined on hydrological conditions which
exist on catchments areas. According to HYDROPLAN (2002), the swamps of Rwanda are
classified in three categories:
a. The swamps of high altitude which are in general narrow in shape and under certain
conditions can develop the organic soils in peat. They can be used for water storage, but in some
area they can be used for cultivation. These kinds of swamps are for example Kamiranzovu and
Rugezi swamps.
b. The intermediate swamps or swamps of middle altitude which are often more large in
size. They are essentially situated in Central Plateau.
c. The big swamps of low altitude or collectors swamps which are found in the central part
of Rwanda or along the primary hydrographical network composed by rivers Nyabarongo,
Akanyaru and Akagera.
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2.1.2. Management and use of swampsWater management is the key issue in the use and management of swamps. While
drainage is not so problematic in hydromorphic sandy soils, it can be dangerous in peat soils.
Under improved drained conditions, main cultivated crops are rice, maize, beans and vegetables.
Rice is considered as the main crop to be grown on these soils due to its rooting system which is
well adapted to waterlogged conditions and to its growing cycle during the rainy season, where
the peat soils are likely to be flooded. These soils are, however, quite fragile due to the absence
of the mineral component. Therefore, mismanagement of peat soils can lead to its degradation
and permanent loss for agriculture.
The major constraints in the swamps development are among others the lack of
experience and technical skills of farmers to manage water. The fragile ecosystem of the swamp
to be developed is the major problem of a drastic decrease of agricultural production. The
consequences of those problems are very harmful if care is not taken by those water users.
2.2. Constraints of agricultural production in swampsThe major constraints are:
a) Lack of experience of farmers to manage water and insufficient technical framework;b) High intensity rainfall, peak flows coming from catchments area, rise in ground water
table, lack of appropriate production and conservation technology.c) Finally technical constraints: The fragile ecosystems of swamp to be developed. The
problem can appear and cause drastic decrease of agricultural production. Theconsequences of those problems are very harmful if care is not taken by user.
These problems are:
Not easily workable; Problem of irreversible moisture stress; Problem of water erosion; Problem of soil mass movement; and Decrease in soil fertility.
Water management in the swamps should be properly done without disturbing the ecosystem(MINAGRI / National Bank, 2001).
2.3. Suitability and utilization of swampsEach swamp development and their utilization should consider the problems of swamp inRwanda. Four principal factors are to be considered before any development of swamp:
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Analysis of existing situation; Diagnosis of problems present in the swamps; Basic problem in agricultural production; Major constraints to the swamps (HYDROPLAN, 2002)
The suitability and utilization is given below :
1. Analysis of existing data;2. Collection of complementally data;3. Explanation of classification criteria and the classification;4. Hydrology of the area;5. Selection and evaluation of development techniques;6. Standardization and normalization of development techniques;7. Elaboration of development methods and techniques.
The above aspects are very important for establishing. the following criteria which should not beneglected during the planning and development of swamp.
Geomorphological criteria: Characteristics of catchments area; Physical criteria: Area of swamp and that of catchments, length, width of area
and slope of main drain; The present land use: Type of crop and vegetation as well as other activity. Socio-economic criteria: Density of population on catchments area, land holding
and the crops grown by the farmers; activities done out of swamps, financialcapacity and time management;
Ecological and environmental criteria; Presence of market and consumption of commodities; Availability of extension services; Study of existing development.
2.3.1. Legal aspects of swampsThe necessity to develop legislation on marshlands was perceived very early by the
Government of Rwanda, due to the acuteness of land shortage which characterizes the
country. That situation makes swamps the only alternative to reduce pressure on the fragile
slopes as well as to increase production in order to ensure food security for the population.
Since 1988, the Rwandan Government began to work out legislation for the
exploitation of swamps with assistance from various partners such as FAO. In those legal
texts, are defined the status and definition of marshlands, their delimitation, classification,
rules of exploitation, institutions in charge, modalities of management, maintenance and
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production, contracts of the utilization of the marshlands, etc. According to the Organic
Law of 14/07/2005 (MINIJUST, 2005) determining the use and management of land in
Rwanda as it is stipulated in Article 14, swamps belong to the State private domain and
can be given to associations/cooperatives or private people according to defined
modalities. However, the uplands are personal or for the family. The social implication of
this fact is that the farmer will give more priority and much care to the uplands than the
swamps which do not belong to him. That is why many swamps are not efficiently and
properly managed.
2.4. Irrigation
2.4.1 Importance of irrigationIrrigation is the artificial application of water, with good economic return and no damage to
land and soil, to supplement the natural sources of water to meet the water requirement of crops
(Majumdar, 2004). A crop requires a certain amount of water at some fixed interval throughout
its period of growth. If the water requirement of the crop is met by natural rainfall during the
period of growth, there is no need of irrigation. Crops receive water from natural sources of
water in forms of precipitation, other atmospheric water, ground water and flood water. Since the
amount, frequency and distribution of precipitation which is the principal source of water for
crops are unpredictable, may be insufficient, unevenly distributed, untimely, and the ground
water may be too deep in the soil profile, irrigation becomes necessary for successful crop
growing. Irrigation should, however, be profitable and applied in times of crop need and in
proper amount. Adequate and timely irrigation leads to high yields. The excess or under
irrigation may damage lands and crops. Irrigation applied earlier to the actual time of crop need
results in ineffective irrigation and waste of water, while delayed irrigation may cause water
stress to crops and reduce the yield (Majumdar, 2004).
Irrigation is the key input in crop production. Full benefit of crop production technologies
such as high yielding varieties, fertilizer use, multiple cropping, crop culture and plant protection
measures can be derived only when adequate supply of water is assured on one hand. High
yielding varieties usually have a higher water requirement than ordinary varieties. The yield
potential of these varieties can be fully exploited if an adequate amount of water is made
available, besides other inputs (Gautam and Dastane, 1970). On the other hand, optimum benefit
9
from irrigation is obtained only when other crop production inputs are provided and technologies
applied. With adequate supply of water and other inputs, crop production technologies such as
multiple cropping can be profitably applied to boost up growth and yield of crops (Majumdar
and Mandal, 1984).
2.4.2. Harmful effects of over-irrigationIrrigation is beneficial only when it is properly managed and controlled. Faulty and
careless irrigation does harm to crops and damages lands, besides causing waste of valuable
water. Rice is the exception and it is grown under soil submergence. When plenty of water is
available, most of inexperienced irrigation farmers are tempted to over-irrigate their lands
because they assume that with more water, they will get higher yields without being conscious of
the harmful effects. If the water is used judiciously and scientifically, there would be practically
no ill-effects. Therefore, wide knowledge and experience are required for efficient water
management. These following ill-effects can be effectively reduced and sometimes altogether
eliminated by exercising economical and scientific use of water.
The following are some harmful effects of faulty and excess irrigation (Majumdar, 2004):
a. Impaired soil aeration. Excess irrigation fills all soil pores expelling soil air completely.
This leads to deficiency of Oxygen in the soil and disturbs seriously the root respiration and root
growth. However, in rice, the supply of Oxygen to roots is made from leaves through
aerenchyma cells which are continuous from leaves to roots.
b. Imbalance in nutrient uptake. Plants derive energy by root respiration and the energy is
needed for nutrient uptake. Reduced and lack of root respiration owing to improper soil aeration
under excess soil water condition greatly disturbs the nutrient uptake. The decline in uptake
occurs in the order of K > N > Ca > Mg > P. The Potassium uptake is affected the most and the
Phosphorus uptake, the least. Some nutrients such as Manganese and Iron become more soluble
and their increased availability may reach the toxic level to plants, whereas Boron and
Molybdenum become less available.
c. Physiological imbalance in plants. Physiological activities of plants get seriously
disturbed due to lack of adequate Oxygen in poorly aerated soils under excess soil water
condition. An imbalance in nutrient uptake that may occur due to reduced or excess availability
of nutrients under impaired respiration disturbs the physiological activities of plants greatly.
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d. Restricted root system. Excess water and lack of adequate Oxygen in soil restrict the
root development and feeding zone of plants. Roots do not grow in wet soils and usually remain
shallow particularly where water table rises and encroaches the normal root zone of crops. With
restricted feeding area the availability and uptake of nutrients decline. Consequently, crop
growth and yields are affected. Shallow root system exposes the crop more to the risk of low
yields from drought.
e. Toxicity of nutrients. Under of excess soil water condition and in water logged soils,
some nutrients like Manganese and Iron get reduced in the soil and their solubility increases.
Their increased availability leads to their toxic uptake by plants.
f. Loss of soil fertility. Uneven and excess irrigation leads to leaching of nutrients beyond
plants root zone. Often, careless and heavy irrigation causes erosion of fertile surface soil and
run-off that washes out plant nutrients into drains.
g. Soil erosion. An uncontrolled heavy irrigation in sloping and undulated lands may cause
erosion of surface soil. The stream size and amount of irrigation applied should be decided based
on water intake rate, hydraulic conductivity, textural class, and water retentive capacity of soil,
land slope and soil water depletion status.
h. Destruction of beneficial soil structure and soil aggregates. Water logging and excess
soil water conditions for a long period destroy the crumb structure and soil aggregates and
encourage the development of platy structure. Crumb structure and soil aggregates favour crop
growth and yield.
i. Production of harmful gases. Under excess soil water and water logging conditions,
harmful gases such as Ethane, Methane, Hydrogen Sulphide, Carbon Monoxide and Hydrogen
gas are produced due to anaerobic decomposition of organic matter present in the soil. These
gases are toxic to crop plant. Under water logged condition it is often observed that plants turn
yellowish and become stunted and diseased.
j. Rise of water table. Faulty and over-irrigation in a farm if continued over a long period
leads to rise of water table. This occurs particularly in lands where the root zone is underlaid by
an impervious soil or rocky layer. Rise of water table restricts the root and feeding zones of
crops. Growing of fruit trees and deep rooted crops is very much restricted in areas where the
water table rises high up and gets near to the soil surface.
11
k. Water logging. When irrigation is done with a large stream and if that is not turned off in
proper time, water accumulates in the lower part of the field and causes water logging. Farmers
have the tendency to use more water than actually required by the crops. The excess water
percolates into the ground and raises the water table. Water logging occurs when the water table
reaches near the root zone of crops. The soil pores become fully saturated and the normal
circulation of air in the root zone of the crops is stopped and the growth of the crops is decreased.
Thus, the crop yield is considerably reduced. When the water table reaches the ground surface,
the land becomes saline (Arora, 2004). The ground water brings salts with it and these salts are
deposited on the ground surface after the water evaporates. The land ultimately becomes unfit for
cultivation.
l. Activities of micro-organisms. Excess soil water due to excess irrigation causes
deficiency of Oxygen in soil. Useful aerobic bacteria such as ammonifying, nitrifying and
Nitrogen fixing bacteria cannot function well or at all under Oxygen deficiency on one hand.
Decomposition and mineralization of organic matter, atmospheric Nitrogen fixation and
availability of nutrients to plants are hampered. On the other hand, anaerobic bacteria are
activated causing loss of Nitrogen as gas, evolution of harmful gases and appearance of plant
diseases.
m. Mosquitoes nuisance. Due to excessive application of water and due to leakage from
canals, the pits and depressions get filled up with water. These stagnant pools of water act as
breeding places for mosquitoes and the region becomes malaria prone (Arora, 2004).
2.4.3. Classification of irrigation methodsWater management pertains to optimum and efficient use of water for best possible crop
production keeping water losses to the minimum. Serious water losses occur unless it is properly
monitored while irrigating fields. Various methods are adopted to irrigate crops and the main aim
is to store water in the effective root zone uniformly and in maximum quantity possible ensuring
water losses to the minimum. Each method of irrigation has certain advantages and
disadvantages based on certain principles. Factors such as the water supply; the type of soil; the
topography; the land and the crop to be irrigated; socio-economic, health and environmental
aspects, determine the correct method of irrigation to be used. Whatever the method of irrigation,
it is necessary to design the system for the most efficient use of water by the crop.
12
According to Majumdar (2004), the common methods of irrigation are broadly grouped
under:
(1) Surface irrigation methods;
(2) Subsurface or sub-irrigation methods;
(3) Overhead or sprinkler irrigation methods;
(4) Drip or trickle irrigation method.
As it is stated above, irrigation is an artificial application of water for creating favorable
conditions for plant growth. The right quantity of water at appropriate time plays an important
role in crop production. The control of water losses during irrigation is an important aspect to
save this priceless commodity. Irrigation water may be applied to crop by flooding it on the field
surface, by applying it beneath the soil surface, by spray it under pressure or by applying it in
drops. The surface irrigation method refers to irrigating lands by allowing water to flow over the
soil surface from a supply channel at upper reach of the field (Majumdar, 2004). The subsurface
irrigation, also designated as sub-irrigation, involves irrigation to crops by applying water from
beneath the soil surface either by constructing trenches or installing underground perforated pipe
lines or tile lines. The sprinkler irrigation refers to application of under pressure water to crops
in form of spray from above the crops like rain and that is the reason why it is also called the
overhead irrigation. The drip irrigation, also called trickle irrigation, refers to the application of
water at a slow rate drop by drop through perforations in pipes or nozzles attached to tubes
spread over the soil to irrigate a limited area around the irrigation (Majumdar, 2004).
2.4.4 Some technical terminology on irrigation
2.4.4.1. Water requirement of cropsWater requirement of a crop refers to the amount of water required to raise a
successful crop in a given period (Majumdar, 2004). It comprises the water lost as
evaporation from crop field, water transpired and metabolically used by crop plants, water
lost during application which is economically unavoidable and the water used for special
operations such as land preparation, puddling of soil, salt leaching and so on. The water
requirement is usually expressed as the surface depth of water in millimeters or
centimeters. Crop water requirement may be mathematically formulated as:
CWR = ET + Wm + Wu + Ws or CWR = CU + Wu + Ws where, CWR = Crop water
requirement, cm; ET = Evapo-transpiration from crop field, cm; Wm = Water
13
metabolically used by crop plants to make their body weight, cm; Wu = Economically
unavoidable water losses during application, cm; Ws = Water applied for special
operations, cm and CU = (ET + Wm) is the consumptive use of water by the crop, cm.
2.4.4.2. Available Water (AW)The available water is defined as the difference between the moisture content of a soil at
the field capacity (FC), and its moisture content at the permanent wilting point (WP) and it is
usually expressed in millimetres. These quantities are often described as constants, but this is
misleading, because they are only constant for a given soil, and vary with the texture and
composition of the soil. The following Table–1 gives typical values for the soil moisture.
Table-1: Approximate Available Moisture Holding Capacity of Soils
Soil texture Available water(cm/m depth)
Coarse texture - coarse sands, fine sands, loamy sands. 6 – 10Moderately coarse texture - sandy loams and fine sandy loams. 10 – 14Medium texture - very fine sandy loams, loams, and silt loams. 12 – 19Moderately fine texture - clay loams, silty loams, and sandy clay loams. 14 – 20Fine texture - sandy clays, silty clays, and clays. 13 – 20Source: Michael and Ojha (1966)
2.4.5. Project irrigation efficiencyIrrigation efficiency is usually expressed as the percentage ratio of the amount of water
stored in crop root zone for crop use in the project command area to the amount of water diverted
from the project source (Majumdar, 2004). It is expressed as, Ep = 100 ,
where Ep = Project irrigation efficiency in percent;
Ws = Amount of water stored in crop root zone soil;
Wd = Amount of water diverted or pumped from the source.
2.4.5.1. Water Conveyance EfficiencyWater conveyance efficiency may be defined as the percentage ratio of the amount of
water delivered to fields or farms to the amount of water diverted from sources. It is expressed
as, Ec = 100 , where Ec = Water conveyance efficiency in percent;
Wf = Amount of water delivered to fields or farms (at the head of field supply channel or farm
distribution system);
Wd = Amount of water diverted from sources.
14
2.4.5.2. Water Application EfficiencyThe water application efficiency may be defined as the percentage ratio of the amount of
water stored in the crop root zone to the amount of water delivered to fields. It is expressed as,
Ea = 100 , where Ec = Water application efficiency in percent;
Ws = Amount of water stored in the crop root zone soil;
Wf = Amount of water delivered to fields.
2.4.6. Efficiency of irrigation practices and water use
2.4.6.1. Water Storage EfficiencyWater storage efficiency refers to the percentage ratio of the amount of water stored in
effective root zone soil to the amount of water needed to make up the soil water depleted in crop
root zone prior to irrigation (Majumdar, 2004). It may be expressed as, Es = 100 , where
Es = Water storage efficiency in percent;
Ws = Amount of water actually stored in root zone soil from the water applied;
We = Amount of water needed to meet the soil water depleted in the crop root zone soil prior to
irrigation.
2.4.6.2. Water Distribution EfficiencyWater distribution efficiency measures the extent to which water is uniformly distributed
in the effective root zone soil along the irrigation run (Majumdar, 2004). It is described as,
Ed = 100 (1 - ), where, Ed = Water distribution efficiency in percent; ȳ = Average numerical
deviation in depth of water stored in root zone soil along the irrigation run from the average
depth of water stored during irrigation; đ = Average depth of water stored during irrigation along
the water run.
2.4.6.3. Water Use Efficiency(i) Field water use efficiency
This may be defined as the ratio of the amount of economic crop yield to the amount of
water required for crop growing (Majumdar, 2004; Hillel, 1998). It is obtained as follows,
Eu = , where Eu = Field water use efficiency expressed in kilogram of economic yield per
hectare-cm or hectare-mm of water; Y = Economic crop yield in kilogram per hectare;
WR = Water requirement of the crop in hectare-cm or hectare-mm
15
(ii) Crop water use efficiency
This may be defined as the ratio of the amount of economic yield of a crop to the amount
of water consumptively used by the crop. It is found out as follows, ECU (or WUE) =
where, ECU or WUE = Crop water use efficiency in kilogram of economic yield per hectare-cm
or hectare-mm of water; Y = Economic yield of crop in kilogram per hectare;
CU = Consumptive use of water in hectare-cm or hectare-mm;
ET = Evapo-transpiration in hectare-cm or hectare-mm.
2.5. Movement of water into soil
2.5.1. InfiltrationThe movement of water from the surface into the soil is called infiltration. The infiltration
characteristics of the soil is the one dominant variables influencing irrigation. Infiltration rate is a
soil characteristic determining the maximum rate at which water can enter the soil under specific
condition including the presence of excess water. It has the dimension of velocity
The actual rate at which water is entering the soil at any given time is called infiltration rate. The
infiltration rate decreasing during irrigation. The rate of decrease is rapid initially and tends to
approach a constant value. Cumulative infiltration is the total quantity of water enters the soil in
a given time(Israelson,1962)
2.5.2. Infiltration rate calculationFor the design purposes, the relationship between accumulated infiltration and elapsed time are
usually expressed by the following :
………………………(1)
…………………….(2)
Z=0 where =accumulated infiltration in time t.
T=elapsed time,minute.
A,b, ,are characteristic constents.
Field experimental data on accumulated infiltration versus time, when plotted on an ordinary co-
ordinate paper give a parabolic curve. When the data are plotted on log-log paper a linear
relationship is indicated.
16
But some data on the initial stage of the experiment usually fall along slight curved line. Since
the constant but rectifies this slight deviation from linear log-log relationship, equation (1)is
considered superior to equal (2)to express the accumulated infiltration-time relationship.
The value of a,b, and usually range between 0 and 1. The infiltration rate at any time t is
obtained by differentiating equation (2)as follows
2.5.3. Factors affecting infiltration rateThe major factors affecting infiltration rate are:
1. Initial moisture content,
2. Condition of soil surface,
3. Hydraulic conductivity of the soil profile,
4. Texture,
5. Porosity,
6. Degree of swelling of soil colloid and organic matter,
7. Vegetative cover,
8. Duration of irrigation or rainfall,
9. Viscosity of water (Michel,1978)
2.5.4. Measurement of infiltrationThree methods of estimating infiltration characteristics of soil are used. The use of cylinder
infiltrometers, measurements of subsidience of free water in large basin and estimation of
accumulated infiltration from the water in advance data. The use of cylinder [infiltrometer] is the
most common method.
2.5.4.1. PermeabilityPermeability may be defined as the characteristics of porous medium of its readiness to transmit
a liquid. The equation expressing the flow considers the fluidity of the liquid and the
permeability factors called intrinsic permeability.
Darcy’s law according to the definition of permeability may be written as:
17
Where Q:volume of flow,cm3/sec2
K:intrinsic permeability,cm3/sec2
ρ= density of liquid.
μ=viscosity of liquid
ΔH=loss of hydraulic head,cm2.
L=length of tube area, cm2.
From the expression, we find that the hydraulic conductivity K is:
Where :f= fluidity of liquid
Again,
The intrinsic permeability has the physical dimension of L2T-1
Only the size and shape of soil particles and pare influence it. Intrinsic permeability is same as
the hydraulic conductivity expect that it is independent of the fluid properties such as specific
weight and conductivity is dependent on the fluid properties and the change with quality of
water.
Table2 permeability classes based on hydraulic conductivity of soil
Permeability classes Hydraulic conductivity of soil(cm/hr)
Extremely slow
Very slow
Slow
Moderate
Rapid
Very rapid
<0.0025
0.0025-0.025
0.025-0.25
0.25-2.5
2.5-25.0
>25.0
Source:Smith and Browning(1975)
18
2.5.5. Irrigation requirement of riceRice is a semi-aquatic plant and hence its water requirements are many times more than
most other food crops. It is, therefore, a major consumer of the water resources of the country
and thus needs careful water management in order to increase its efficiency of water use. Rice is
grown under varied soil and climatic conditions and its effective root zone depth is 60 cm.
Though rice could be grown on a variety of soils, it grows best on clay loams to clays since these
are retentive of moisture and have low percolation rates of 1-5mm/day (Michael, 1981). The
cultural practices of rice vary widely, depending upon the variety and the local soil and climatic
conditions. However, the condition under which rice is grown could broadly be grouped into
two, namely, low land rice and upland rice. Under low land conditions, rice is generally
transplanted on puddled soils and land is kept under submerged conditions by rain or irrigation
water. The practice of puddling and land submergence, in general, has been found to reduce the
percolation losses, check weed growth, increase the availability of plant nutrients, regulate soil
and water temperature, favour the fixation of atmospheric Nitrogen in soil through algal growth
and improve photosynthesis in the lower leaves due to reflected light from the water surface
(Michael, 1981).
The practice of shallow submergence directly save considerable amount of water as
compared to deep submergence. The practice of continuous shallow submergence, however, is
possible only when the water supplies are adequate and assured. Land also needs to be
scrupulously leveled to facilitate uniform spreading of water. Weeds, especially the grassy types,
also need to be controlled. Experimental results are available to show that it is not always
necessary to follow the practice of continuous submergence, especially in the rainy season when
the humidity is high and evaporative demands are low (Michael, 1981). He also added that under
these conditions, the practice of intermittent submergence, i.e. submergence during the critical
stage of initial tillering and/or flowering and maintenance of saturation to field capacity during
the rest of the stages give yields comparable to those obtain under continuous shallow
submergence. The water supplies, if limited, could safely be curtailed during the non-critical
stages of crop growth. The shortage of water during initial tillering and flowering reduce the
yield considerably while the stages of tillering, grain formation and maturity tolerate water stress
to a great extent.
19
CHAPTER-3
MATERIALS AND METHODOLOGY
3.1. Study zone descriptionWith the area estimated about 862ha, Migina swamp constitutes of many complex swamp
of 30ha to 120ha. The main swamps of Migina are 14: Rwasave, Nyarigira, Ndobogo,
Nyamugari, Migina, Munyazi, Rwuya, Kihene, Rwibona, Mukura, Rwamamba, Rwabisemanyi,
Nyabuyogera and Akagera. These swamps occupy the area of Huye and Gisagara districts
(MINAGRI,1992)
From Kigali city, at 136km left there is first swamp Migina and Nyarigina a Rwasave
branch of Rwasave swamp between Huye and Gisagara districts. At many intervals of distances,
the stream flows along and takes name of the swamp through which it flows. That is why it is
called Nyarigina, Rwasave, Mukura, Rwibona, Kihene,…
Rwasave swamp is swamp of flat bottom commonly called <<large vally>> flooded or
very humid during the rain seasons. It has a mean altitude of 1621.5m, mean rainfall of 1215
mm, the mean annual temperature is 19,60c. the area has the climate of two dry seasons and two
rainy seasons. The physical and hydrodynamic characteristics of Rwasave soil are the
followings:
With the loamy clay soil with its permeability of 0.25cm/hour from 50cm depth
Water retention capacity of 95 to 200mm for 50 and 100cm thickness respectively
(MINAGRI)
.
Rwasave swamp has a barrage with the following characteristics:
Height on earthen barrage - 8m
Length - 100m
Bottom width of bund - 20 to 27m
Top width of earthen bund - 4m
Total storage capacity of the dam ;10000m3
And live storage - 8700m3 (BIZUMUREMYI 2006)
Various climate data were collected from the Kigali National Meteorological Centre and
computed by CROPWAT as presented in Table-5
20
3.2. MaterialsIn order to collect different data in the field, the following materials have been used:
a. Note-book, pen/pencil, ruler, calculator,
b. Stakes/nails;
c. Bottle, stopwatch;
d. Books;
e. Measuring tape and
f. Meteorological data.
g. Bucket.
3.3. Methodology
3.3.1. Exploratory surveyIn order to gather the general information about the swamp, an exploratory survey has
been conducted within the cooperative COAIRWA composed of 9 farmers’ associations. The
survey consisted on the identification of the respondents, the historical background of the
swamp, its management and the farmers’ organization. In accordance with the location of the
farmers’ associations, two of them have been used as a sample: KUNDADUKORE and
RWANYINZARA located respectively upstream and downstream command area of the swamp.
The sample has been taken in the two farmers’ associations by using Alain Bouchard
(Perrien et al., 1984) formula as follows:
n = where, N0 = = Sample size;
N = Universe size (< 106 individuals);
p = Frequency (p = 0.5);
d = Error (10%);
tα = Student value (tα = 1.65 in Student table).
N = 26 + 34 = 60 is the universe sample.
N0 =
n = ; this was the number of the respondents to the open-ended questions.
21
3.3.2. Flow discharge measurementThe velocity of a canal or stream and hence its discharge, may sometimes be determined
approximately by the use of surface floats. To use floats a relatively straight reach of a channel
20 to 30 metres long with a fairly uniform cross section along its length is selected (Stern, 1994;
Arora, 2004). To reduce the effects of wind on the float, a long-necked bottle partly filled with
water was used as a float. The velocity of the stream is determined by running the float and
noting the time the float takes to cross the channel section. The float is placed in the centre of the
channel 1 or 2 meters upstream of the start of the measured length L, and the time t taken to
cover the measured is noted. A number distance of three or four readings are recorded and the
mean is taken. Care is taken to see that the float does not touch the channel sides (USDI, 1953).
The distance L divided by the time t gives the velocity V of the float, which corresponds to the
velocity of the water at its surface.
It has been found that for regular channels flowing in a straight course under favorable
conditions, the mean velocity of a strip in the channel is approximately 0.85 times its surface
velocity for small streams (Stern, 1979; Majumdar, 2004; USDI; 1953). Since the velocity of
water is the highest on the surface, a constant factor equal to 0.85 is used to multiply the arrived
value of velocity to come to the correct value. The formula for estimating the stream discharge
may be written as, Q = 0.85 ( ) H.V, where Q = Discharge, cm3/s; a = Width of the channel at
flow surface level, cm; b = Bottom width of the channel, cm; H = Flow depth in the channel, cm
and V = Flow velocity, cm/s.
3.3.3. Water losses measurementsUsually, water consumption is expressed in water depth. Water consumption in depth is
obtained by measuring the change of water level in the paddy field when both water supply and
outflow from the paddy field are controlled. Daily water consumption is defined as water
consumed in the paddy field. For this purpose, the “stake and nail” method has been used for its
easiness and applicability in saturated conditions. Plots for this measurement were sampled
depending on location in the swamp, reliability to inflow and outflow measurement of water and
farmers’ willingness to allow experiments to be conducted in their rice fields. The field plot
experimentation was conducted in one crop season of B season (2008). The sample farm plots
were monitored for water losses due to paddy transpiration, evaporation from standing water in
the fields, and lateral and deep percolation.
22
The procedure is as follows:
(i) Install a stake on which a nail is attached at exactly the level of the water;
(ii) Close inlet and outlet of water in the plot;
(iii) Measure and record water level and rainfall at a regular time basis;
(iv) Calculate daily change of water level.
3.3.4 Hydraulic conductivity testsIn fact, hydraulic conductivity calculation helped us to know the permeability of the soil of our
case study as an important parameter into irrigation to decide the spacing of the channels.
Select and level the site;
Collect water to fill the hole using the a bucket until is saturated ;
Determine initial height using a ruler;
Using a stopwatch; record a final height after a certain time interval;
Calculate K using Lewis following formula.
K=1.15 x r [ ]
Where.K: Hydraulic conductivity cm/secho:initial height of water,cm
ht:final height of water,cm
r : radius,cm
t : time interval,cm
3.3.5. Crop water requirementsIn order to calculate the water requirements for the rice I used the program CROPWAT 4
WINDOWS version 4.3. After collecting various climate data, the program automatically
calculates the reference crop evapotranspiration of the rice using the Penman-Montheith formula.
After entering the rainfall data, the program will calculate automatically the effective rainfall.
Then, we have to enter the crop data for rice because the program does not have this crop. The
duration of every development stage of rice is entered: the planting date is 15 February, seedling
stage of 40 days, vegetative growth stage of 60 days, reproductive growth stage of 40 days and
the maturing growth stage of 40 days. The effective root zone depth of rice was taken as 60 cm
and the crop coefficient Kc according to the growth stage of 1.05 for the seedling stage, 1.2 for
the vegetative and reproductive stages and 0.8 for the maturing/ripening stage. As the irrigation
23
practices are not well known by the farmers, the field irrigation efficiency of 50% was generally
used in earth channels (AAA, 2005). The program does not take into account the amount of
water necessary for the puddling operation for the paddy rice and the percolation losses, which
amount is respectively estimated to 100 mm and 30 mm per month (AAA, 2005). Therefore, this
quantity of water will be added to the crop water requirements for the rice during calculations.
24
CHAPTER-4
ANALYSIS AND RESULTS INTERPRETATION
4.1. Exploratory surveyThe following results have been found by discussing with about 32 persons actively
involved sampled from the two farmers’ associations KUNDADUKORE and RWANYINZARA.
4.1.1. Identification of respondentsTable-3: Distribution of the respondents according to their age
Age Total number Percentage (%)
Less than 35 years 10 31.25
Between 35 and 50 years 16 50.00
More than 50 years 06 18.75
TOTAL 32 100.00
Table-4: Distribution of the respondents according to their sex
Sex Total number Percentage (%)
Male 15 46.875
Female 17 53.125
Total 32 100.00
The data presented in Table-1 reveal that the respondents aged less than 35 years and
those aged between 35 to 50 years are 31.25% and 50 % respectively. It indicates that people
who are physically active are engaged in land activities. A little number of people older than 50
years (18.75%) is engaged in paddy rice cultivation. In fact, although the paddy rice field works
are heavy and they are especially done by those who are strong enough it is found that the
women are more actively engaged in rice cultivation than men. The women, children and old
family members are engaged in guarding the field from birds, cooking food, etc. The Table-2
shows that females are very few (53.125%) compared to males (46.875%). It is because the
males like to go to the city when in the beginning, it was desired to balance the gender but only
seven (07) women willingly came forward to assist the study. The reason is culturally man-
dominated society.
25
4.1.2. Management of the swampAll the respondents revealed that the swamp has been developed by the French company
LOIET during the year 1980 and they started its exploitation since 1981. In addition to that, it
was informed that the swamp was not exploited before its development due to the excess of
water and because there was no need to cultivate the swamp since there were enough and fertile
hillside lands during that period. They also added that the main crop they are now used to
cultivate in this swamp is rice, except in some parts where there is not enough water for
irrigation, vegetables and maize are grown.
The farmers said that there is no river irrigating the swamp apart from the dam which
receives water from different springs and rainfall. According to the respondents, there is always a
shortage of water during July and August and high water table is observed in the swamp during
rainy seasons (March and April). The total developed area is developed but in some party where
there is problems of water they cultivate other crop than rice. The farmers in the upstream side of
the swamp have the problems of water during the driest seasons than downstream due to the
streams contributing to the irrigation water. In fact, a number of small barrages have been
constructed along the main drain in order to get enough water for downstream users. Due to lack
of water supply from the barrage, farmers often open the upstream gates at night and sometimes
even steal the wooden shutters used for closing the gates. It clearly shows the problem of
organization and management of water use in Rwasave developed swamp.
The farmers having sufficient water take two paddy crops during every year with an
average production of 4tons/hectare/season. However, farmers don’t change the rice varieties
because the seeds is selected at harvest by the farmers. Lack of capacity building in water
management is also an important cause of less area coverage under irrigation and conflict of
interest between upstream water users. Some of the respondents informed that some training an
field visit was organized by RADA, ISAR, RSSP, on rice technical aspects only. It is so obvious
that they are traditionally managing the swamp. In order to fight against diseases, the
cooperatives arrange for spraying and the farmer reveal that they don’t use fertilizers. There is no
irrigation schedule and there is no taxation of irrigation water. That is the reason why farmers do
the over-irrigation. There is no “water master” to monitor the use of water and they take it ad
libitum (they take as much water as they can while they can). The primary, secondary and
26
tertiary irrigation canals are maintained once a month by the farmers during the community
working/umuganda in the swamp. Only the main drain is maintained with funds collected from
the farmers every season (1,000 Rwf per plot of 500 square metres). The respondents also
revealed that maintenance was done during last year and this is the reason why the main drain is
presently full of weeds/grasses.
4.1.3. Organization of farmersThe respondents said that after the development of the swamp, every person who wanted a plot
could ask for it and get it. One plot is 500 square metres but some are smaller . Farmers are
organized in 9 associations (enclosed in Appendix-B) which are grouped in one cooperative
(COAIRWA). Farmers were complaining about the prices of the rice which are very low and
fixed market overall factory. The farmers have to sell a big portion of their production through
the local markets and another part will be used for family food needs. Basically, irrigation water
management that covers the management of irrigation networks and irrigation water has to be
implemented on the basis of participatory, integrated, transparent, accountable and sustainable
principle. They also informed that their production varies between 3 and 4 tons per hectare
according to the climatic conditions.
4.2. Hydraulic conductivity calculation
0.0077cm/sec
27
K=0.0048325Cm/sec
The K measured was 4.8 10-3 cm/sec.
According to the table 1,this shows that the soil on which hydraulic conductivity has been
measured was4.8 10-3 cm/sec means that this soil is very pervious, and care should be taken in
order to avoid losses and this improve puddling operations.
4.3. Crop water requirementsThe crop water requirement for the rice (Table-6-7) was obtained by the use of the
program CropWat 4 Windows Ver 4.3 and according to the climate data (Table-5). In order to
get the total water requirements for the rice, we had to add 100 mm for the puddling operation
and 30 mm per month for the percolation losses (AAA, 2005). However, the actual
measurements were also made to estimate the deep percolation losses in actual field conditions.
The 30 years climatic data viz. rainfall, maximum and minimum temperature,
humidity, wind speed, sunshine, solar radiation and pan evaporation, were collected from Kigali
National Meteorological Service (Table-5). The data were analysed and used for CROPWAT
presented in Table-5.
28
Table-5: Climate data for Rwasave general area12/23/2008 CropWat 4 Windows Ver 4.3
******************************************************************************
Climate and ETo (grass) Data
******************************************************************************
Data Source: C:\CROPWATW\METEO.PEM
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Country : RWANDA Station : NGOMA
Altitude: 1760 meter(s) above M.S.L.
Latitude: -2.36 Deg. (South) Longitude: 29.44 Deg. (East)
------------------------------------------------------------------------------------------------------------------
Month MaxTemp MiniTemp Humidity Wind Spd. SunShine Solar Rad. ETo
(deg.C) (deg.C) (%) (Km/d) (Hours) (MJ/m2/d) (mm/d)
-------------------------------------------------------------------------------------------------------------
January 24.6 14.4 74.2 172.8 5.6 17.8 3.78
February 24.9 14.5 73.8 169.3 5.5 18.1 3.87
March 24.8 14.6 75.2 187.5 5.7 18.5 3.93
April 24.0 14.8 79.4 178.8 5.5 17.5 3.53
May 23.9 14.9 77.8 173.7 5.4 16.2 3.31
June 24.5 14.1 68.9 170.2 7.2 18.0 3.71
July 25.1 13.9 60.8 185.8 7.9 19.2 4.19
August 26.2 14.7 59.4 191.8 7.6 20.0 4.56
September 26.0 14.5 66.9 185.8 6.2 18.9 4.28
October 25.2 14.4 71.9 192.7 5.7 18.4 4.05
November 24.1 13.1 76.4 197.0 5.5 17.7 3.73
December 24.1 14.3 75.9 178.8 5.1 16.8 3.56
-----------------------------------------------------------------------------------------------------------
Average 24.8 14.3 71.7 182.0 6.1 18.1 3.88
----------------------------------------------------------------------------------------------------------
Pen-Mon equation was used in ETo calculations with the following values
for Angstrom's Coefficients:
a = 0.25 b = 0.5
*********************************************************************
29
Table-6: Crop water requirements for the rice using CROPWAT season A12/25/2008 CropWat 4 Windows Ver 4.3******************************************************************************
Crop Water Requirements Report******************************************************************************- Crop # 1 : rice- Block # : [All blocks]- Planting date : 5/1- Calculation time step = 10 Day(s)- Irrigation Efficiency = 50%---------------------------------------------------------------------------------------------------Date ETo Planted Crop CWR Total Effect. Irr. FWS
Area Kc (ETm) Rain Rain Req.(mm/period (%) ---------- (mm/period) ---------- (l/s/ha)
---------------------------------------------------------------------------------------------------5/1 37.00 100.00 1.05 38.85 36.99 30.68 8.17 0.1915/1 36.86 100.00 1.05 38.70 36.60 30.47 8.23 0.1925/1 36.71 100.00 1.05 38.55 37.17 30.75 7.80 0.184/2 36.59 100.00 1.05 38.42 38.94 31.67 6.74 0.1614/2 36.49 100.00 1.05 38.31 41.98 33.27 5.04 0.1224/2 36.43 100.00 1.05 38.26 46.08 35.46 2.80 0.066/3 36.43 100.00 1.05 38.25 50.82 37.98 0.27 0.0116/3 36.48 100.00 1.05 38.30 55.54 40.48 0.00 0.0026/3 36.58 100.00 1.05 38.41 59.45 42.50 0.00 0.005/4 36.75 100.00 1.05 38.59 61.67 43.55 0.00 0.0015/4 36.97 100.00 1.05 38.82 61.36 43.12 0.00 0.0025/4 37.25 100.00 1.05 39.11 57.85 40.82 0.00 0.005/5 37.57 100.00 1.05 39.45 50.80 36.43 3.02 0.0715/5 37.94 100.00 1.05 39.83 40.40 30.00 9.83 0.2325/5 38.33 100.00 1.05 40.25 27.56 21.99 18.26 0.424/6 38.75 100.00 1.05 40.69 14.16 13.19 27.50 0.6414/6 39.18 100.00 1.05 41.14 3.35 3.35 37.79 0.8724/6 39.61 100.00 1.05 41.59 0.23 0.23 41.36 0.96-----------------------------------------------------------------------------------------------------Total 671.93 705.53 720.97 545.94 176.82 [0.23]-----------------------------------------------------------------------------------------------------
* ETo data is distributed using polynomial curve fitting.* Rainfall data is distributed using polynomial curve fitting.
30
Table-7: Crop water requirements for the rice using CROPWAT season B
************************************************************************12/25/2008 CropWat 4 Windows Ver 4.3************************************************************************
Crop Water Requirements Report
************************************************************************
- Crop # 1 : rice- Block # : [All blocks]- Planting date : 15/7- Calculation time step = 10 Day(s)- Irrigation Efficiency = 50%
------------------------------------------------------------------------------------------------------Date ETo Planted Crop CWR Total Effect. Irr. FWS
Area Kc (ETm) Rain Rain Req.(mm/period) (%) ---------- (mm/period) -------------- (l/s/ha)
-----------------------------------------------------------------------------------------------------15/7 40.46 100.00 1.05 42.49 0.00 0.00 42.49 0.9825/7 40.82 100.00 1.05 42.86 3.89 3.71 39.14 0.914/8 41.12 100.00 1.05 43.17 7.96 7.54 35.63 0.8214/8 41.36 100.00 1.05 43.43 12.24 11.55 31.88 0.7424/8 41.53 100.00 1.05 43.60 17.14 15.82 27.78 0.643/9 41.61 100.00 1.05 43.70 22.51 20.14 23.56 0.5513/9 41.61 100.00 1.05 43.69 28.06 24.26 19.44 0.4523/9 41.52 100.00 1.05 43.60 33.42 27.96 15.64 0.363/10 41.33 100.00 1.05 43.40 38.18 31.05 12.34 0.2913/10 41.04 100.00 1.05 43.10 42.02 33.40 9.70 0.2223/10 40.67 100.00 1.05 42.70 44.69 34.93 7.77 0.182/11 40.20 100.00 1.05 42.21 46.07 35.63 6.58 0.1512/11 39.66 100.00 1.05 41.65 46.19 35.59 6.06 0.1422/11 39.07 100.00 1.05 41.02 45.20 34.93 6.09 0.142/12 38.43 100.00 1.05 40.35 43.38 33.84 6.51 0.1512/12 37.78 100.00 1.05 39.67 41.14 32.56 7.11 0.1622/12 37.15 100.00 1.05 39.01 38.91 31.34 7.67 0.181/1 37.06 100.00 1.05 38.91 37.31 30.85 8.06 0.19-----------------------------------------------------------------------------------------------Total 722.42 758.55 548.32 445.10 313.44 [0.40]------------------------------------------------------------------------------------------------
* ETo data is distributed using polynomial curve fitting.* Rainfall data is distributed using polynomial curve fitting.
31
Total crop water requirement for two seasons of year=758.55+705.53=1464.08mmTotal Water Requirements for the rice growing seasons = 1464.08 mm + 200 mm + (30 x 12) =
2024.08 mm per 360days
Effective rainfall for all year =445.10+545.94=991.04 mm per 360days
Average effective rainfall per month=991,04 mm *30/360=82.58 mm
Average ETo per month=(722.42+671.93) / 12=116.195mm
Average water requirement per month=2024.08mm/12=168.67mm
Net irrigation requirement of the crop per month=168.67mm- 82.58mm=86.09 mm
According to the irrigation efficiency of 50%, the following monthly Gross Irrigation will be
required by the crop at the field head during the all seasons=86.09mm*100/50=172.18mm
Therefore, the gross Irrigation Requirement=1,721.80m3/month/ha because 1 mm of water is
equivalent to10 m3/ha.
The Gross Irrigation Requirements of the crop for the whole A and B seasons (12months) for 80
hectares (whole perimeter) is equal to GIR = 1,721.80*12*80=1652928m3
This crop water requirement shows that with 10000m3 volume of the dam cannot irrigate all area
of the swamp. But with the down stream of the dam two streams contribute to the irrigation:
Migina with 0.0051m3/sec which give 158630.4 m3 per year and Munyazi combined with
Ndobogo which have discharge of 0.19055m3/ sec equivalent to 5926867.2 m3 per year this
shows that this stream can irrigate all the swamp but the problem is that it is located about 30
hectares down stream of the dam the only way of using this stream is to pump its water to the
dam.
The area which can be irrigated the dam=10000*80/1652928=0.484ha
Area irrigated by Migina=158630*80/1652928=7.68ha
Table-7 shows the peak flow water supply of 0.98 l/s/ha in July for the considered B
Season. It is also known that the present irrigated area of the swamp is 80 ha instead of 120 ha;
and also assuming that each main irrigation channel will irrigate a half of the field, the discharge
to be conducted in each main irrigation channel is 0.98 l/s/ha x 1.2 x 40 ha = 47.04 l/s, equivalent
to 47.04 x 10-3 m3/s, where 1.2 is the safety coefficient for the design of the irrigation channels.
From the figures presented in Table-7, the peak Irrigation Requirement computed by
CROPWAT is equivalent to 42.49 mm in 10 days during July. Therefore, for the whole area to
be irrigated, it becomes (42.49*80*10,000)/1,000=33,992m3 in 10 days. For the design of each
32
irrigation channel and if continuous discharge is to be given, the irrigation requirement is
equivalent to 33,992/2*10*24*3600=0.019675 m3/s. But, for the good water management, 10
hours of water supply every day can be ensured, i.e.0.19675 * 10/24=0.0082 m3/s. Therefore,
the required discharge for the 10 hours of irrigation every day with approximately 50% of
conveyance efficiency is equivalent to 0.0164 cumecs. Considering the deep percolation losses
as 1.56 mm day, the total loss of irrigation water from 40 hectares would be 1.56 * 40 * 10000
/1000 = 624 cu.m. Therefore additional water is to be supplied by irrigation channel every day.
This will amount to a continuous discharge of 0.0722 cumec for 10 hours. Hence the total
capacity of irrigation channel would be 0.0164 + 0.0722 = 0.0886 cumecs . Considering the most
economical trapezoidal section of open channel, where bottom width b was determined by the
equation b = 2d x tanθ/2 (where d is the depth of flow and θ is side slope). Assuming channel
depth d = 0.35 m; bottom width b = 0.35 m; the top width B = 1.05 m; the side slope 1:1 (H:V);
the hydraulic gradient S = 0.003 and the value of Manning’s roughness coefficient 0.035
(Majumdar, 2004). The following calculations have been made.
The cross section of the designed irrigation channel (A) is equal to A = ( ) x d = 1.05+0.35 x
0.35/2 = 0.245 m2. The wetted perimeter P = 1.34 m.
The hydraulic radius R = = 0.182 m
The velocity V = R2/3 x S1/2, where n is the Manning’s roughness coefficient; R is the hydraulic
radius and S is the hydraulic gradient. Therefore, the mean velocity of the open channel is
V = 0.50 m/s and the discharge Q = V x A = 0.50 x 0.245 = 0.123 cumecs. Therefore, the
designed channel has a sufficient capacity to carry the required discharge of 0.088 cumecs.
However, a free board of 0.15 m is also proposed to take care of run-off coming from
surrounding catchments area above channel and damage due to trampling and siltation.
Therefore, the final cross section of peripheral channels would be 0.425 m2. The present cross
section of 1.1 sq. m seems to be over designed. However, this section serves as the disposal
channel for excess runoff which can be directly connected to main drain with the shortest route.
From these irrigation channels openings with gates are given to supply water directly to the field.
Better water management needs timely opening and closing the gates. However many times,
gates are not closed and water moves through field and lost as deep percolation losses and runoff
to main drain. Main drain water is stopped at various points and used for irrigating down stream
33
fields, however deep seepage losses may lead to reduction in irrigated area particularly during
dry season.
From the total water coming from streams, it is evident that 80 hectares area can easily be
irrigated. For irrigating the upstream 20 hectares land which can not be irrigated from dam or
Migina stream. Based on earlier calculations 40 hectares area needs a discharge of 0.886 cumecs
for a duration of 10 days at rate of 10 hour/ day, therefore to irrigate 20 hectares down stream
land of dam a pumping system can be installed to supply water from Ndabogo stream at the rate
of 0.0443 cumecs .
4.3. Determination of discharge and water conveyance efficiencyTo determine the channel discharge and water conveyance efficiencies, the gate valve of
the main channel was fully opened and velocities of flow at different locations were measured.
Four locations were selected for the measurements of the discharge: near the dam gate in the
main channel, in the peripheral irrigation canals both on the two sides of the swamp and at the
entrance of the upstream field from the left main irrigation canal. In order to get reliable results,
four repetitions have been done for each part. The velocity is determined by dividing the distance
L of the considered segment by the time t recorded. The details of average velocity at different
points and discharge are presented in Table-8 and Table-9.
Table-8: Mean velocity measurements in irrigation channels
Surface velocity
(cm/s)
Correction
factor
Corrected
velocity (cm/s)
At the farm dam gate right side 66.8 0.85 56.8
At the farm dam gate left side 56.8 0.85 48.3
Right main irrigation channel 62 0.85 52.7
Left main irrigation channel 43 0.85 36.55
At the entrance of the u/s field 32 0.85 27.2
The formula for estimating the discharge is as follows:
Q = 0.85 d.V, where Q is the discharge (cm3/s); B (cm) and b (cm) are Top and bottom
width of channel respectively; d (cm) is the flow depth in the channel and V (cm/s) is the mean
velocity of water in the channel.
34
Table-9: Discharge measurements in irrigation channels
Velocity(
cm/s)
d
(cm)
B
(cm)
b (cm) Q
(cm3/s)
Remark
At the farm dam gate right
lined rectangular serves also
as spillway
56.8 20 100 100 113600
At the farm dam gate left 48.3 20 180 100 135240
Right main irrigation
channel
52.7 30 80 60 110670 About 30% leakage
Left main irrigation channel 36.55 30 80 60 76755 About 30% leakage
At the entrance of u/s right
field
40.37 20 40 20 24222
At the entrance of u/s left
field
27.2 20 40 20 16320
Since the discharge required to be conducted in each main irrigation channel which is of
0.088 m3/s and the present measured discharge is greater than the required discharge in the two
main irrigation channels, the designed irrigation channel is suitable for carrying the required
water during irrigation. This means also that the crop water needs will be met. Water
Conveyance Efficiency Ec = 100( ), where Wf is the amount of water delivered to the fields or
farms (at the head of field supply channel or farm distribution system) and Wd is the amount of
water diverted from sources. Therefore, Water Conveyance Efficiency is as follows:
For Left irrigation channel Ecf in % = 100 x 16320/76755 x0.7 = 30.54 %For right irrigation channel Ecf in % = 100 x 24222/110670x0.7 = 31.27%
The conveyance efficiency for consideration of main channel to the right peripheral irrigationchannel, EcR = 100 x 110670/113600 = 97%%. However, conveyance efficiency for consideration of main channel to the left peripheral
channel, EcL = 100 %
From the above results, it is evident that due to lining the conveyance efficiency in right
peripheral channel is more, how ever left main channel is not lined and conveyance efficiency is
only 56.36%. Due to low water conveyance efficiencies I unlined channels, huge amount of
35
water is lost through evaporation, seepage, and transpiration by undesired vegetation and leakage
through water control structures in the conveyance system. It indicates that the water conveyance
system is very poor and proper maintenance is needed. According to Majumdar (2004), the
losses may vary from 25 to 60 percent of water diverted for irrigation. He also added that in the
unlined canals, water ways and channels, the water loss is usually heavy and the same is
attributed mainly to seepage. In fact, growth of undesirable vegetation along and in canals and in
channel beds and sides is also responsible for additional losses. In addition to that, there were
many cracks in channel beds and bunds which may lead to water losses by seepage. In fact, the
canals are not well maintained and old enough to be efficient in conveying irrigation water.
Field water use efficiency (Eu) = , where Y is the economic crop yield in kilogram per
hectare and WR is the water requirement of the crop in hectare-cm or hectare-mm. Therefore,
Eu = (7000kg/ha)/2066.16=3.39 kg/ha-mm of water. The above water use efficiency has been
found while
considering overall irrigation efficiency of 50% and 280 mm water losses taken for puddling
(200 mm) and percolation (30 mm per month) for the estimation of water requirements through
CROPWAT. However, during the study water application losses in the field were also measured.
4.4. Determination of water losses in the rice fieldsIn five plots of rice, the water levels and the corresponding time are recorded according
to a fixed and regular time interval which is 24 hours in our case. The water losses through
evaporation, evapotranspiration, percolation and infiltration in the five experimental plots of
(2500) square metres are as follows:
Table 7: Water losses in five plots of Rwasave swampPlots D1 & T1 H1
(cm)
D2 & T2 H2
(cm)
ΔH1
(cm)
D3 & T3 H3
(cm)
ΔH2
(cm)
Plot 1 14/12 at 08AM 11.50 15/12 at 08AM 9.90 1.60 16/12 at 08AM 8,40 1.50
Plot 2 14/12 at 08AM 9.80 15/12 at 08AM 7.20 2.60 16/12 at 08AM 6.00 1.20
Plot 3 14/12 at 08AM 12.30 15/12 at 08AM 11.00 1.30 16/12at 08AM 9.90 1.10
Plot 4 14/12 at 08AM 11.70 15/12 at 08AM 10.00 1.70 16/12 at 08AM 8.50 1.50
Plot 5 14/12 at 08AM 13.00 15/12 at 08AM 11.30 1.70 16/12 at 08AM 9.90 1.40
D: Day; T: Time; ΔH: Water level difference
36
Total water losses for five plots = (1.6+2.6+1.3+1.7+1.7+1.5+1.2+1.1+1.5+1.4) cm
Total losses for five plots are equivalent to 15.60 cm.
Average water losses per plot 15.6/5=3.12cm
cm = 3.12cm/plot / 48 hours = 3.12 cm /2500 m2 / 48 hours.
Daily average water losses = 3.12/2=1.56 cm/dayThe average water depth maintained was equal to (8.4+6+9.9+8.5+9.9)/5 = 8.54 cm. The average
water losses in the field through ETO and deep percolation are 1.56 cm/day.
The losses through ETO from Table-5 and are 1394.35 mm/360 days which equal to average
ETO of 3.8732 mm/day. The average water losses including ETO and deep percolation are 1.56
cm/day.
Therefore, considering the depletion of water from root zone as 3.87 mm, then the total water
applied to compensate water depletion from root zone and deep percolation would be 15.6 – 3.87
= 11.73 mm deep percolation losses
Hence, water application efficiency Ea = 100 * 3.87/15.6 = 24.80%.
The overall efficiency would be average of water conveyance and water application efficiencies.
Therefore, the average irrigation efficiency = (97 +56.36 +30.54 + 31.27 + 24.8 ) / 5 = 48%,
leading about 52% of water losses. In fact, the deep percolation loss in wet rice is exceptionally
very high and ranges from 38.3% to as much as 80% of the water applied in various soils
(Mandal and Majumdar, 1983). With an average irrigation efficiency of 48%, about 2152.25 mm
water is required for meeting the irrigation requirement of 1033.08 mm along with 200 mm
puddling.
Hence, the water use efficiency would be Eu = 7000/2152.25 = 3.25 Kg/ha-mm. From this
figure, it is evident that to grow 1 ton of paddy, about 3076.92 tons of water is required. This
comes when it is considered that 200 mm and 11.73 mm water are required for puddling and
deep percolation losses respectively. Agriculture is the largest consumer of water, using an
average of 80 percent of total water consumption in developing countries. Irrigation direct
contribution to world agricultural growth has been substantial, because both the irrigated area
and the yield from it have expanded rapidly. However, irrigation is extremely water intensive. It
takes about 1,000 tons of water to grow one ton of grain and 2,000 tons to grow one ton of rice
(Postel, 1996, quoted by Karyabwite, 2000).
37
In Rwasave swamp, the water application is very poor and it shows that the area under crops is
less due to huge water losses. There is lack of knowledge of farmers in rice water requirement
and its management. Besides, absence of water measuring devices and ignorance of farmers in
deciding the time of irrigation and water required for irrigation often pose problems. The type of
soil with high percolation rates and low level of puddling and levelling is the main cause of
lower efficiency. In addition to that, during the dry season, there is water scarcity in the swamp
and the “water master” sometimes opens the dam gate when he wants and many times he is not
there to allow the farmers to get irrigation water at adequate moments. Therefore, the farmers
have to manage well the small amount of water received in their rice fields by uniformly
applying it and preventing the deep percolation and run-off losses. And they must use
agricultural inputs to increase production for meeting international water use efficiency. The
efficiency may be very low in a badly managed farm and higher in a well managed farm.
Majumdar (2004) stated that the application efficiency can be increased to approach 80% if crops
are under-irrigated by applying lower amount of water than needed because of water scarcity or
high-priced water. Under-irrigation may completely prevent deep percolation and run-off of
water, but it is undesirable as crops suffer from water stress and give lower yields. Proper land
levelling and grading is a prerequisite for efficient water application. This is needed to avoid
accumulation of excess water in lower spots leading to deep percolation loss and under-irrigation
of higher spots, and to achieve uniform run and distribution of water in the field. In addition to
that, one of the major reasons for large water consumption and decreased water productivity in
irrigation has been largely attributed to low (20-50%) irrigation and water use efficiency
especially in Sub-Saharan Africa where surface irrigation is the commonly used method of
irrigation (Magayane and Makarius, 2005
38
CHAPTER-5
CONCLUSION AND RECOMMENDATIONS
The detailed discussions made in Chapter-4 show that farmers’ organizations are not strongenough for efficient water management in Rwasave developed swamp. In addition, the farmershave also a feeling that it is the Government responsibility to repair and maintain theinfrastructures. To meet out the irrigation requirement of paddy, appropriate quantity of water isnot supplied and always higher depth of water around 10-12 cm is maintained in the paddy fieldsof Rwasave swamp.
. It has been observed that irrigation and drainage channels are manifested with weeds
and the lined main and peripheral channels are in bed shape full of cracks.
Currently, the overall irrigation efficiency is 39.44% leading about 60% of water losses.The total water requirement with existing agro-climatic conditions and irrigation efficiency hasbeen estimated as 1,473.62 mm. The average water use efficiency worked out to be 5.09 Kg/ha-mm. As water charges are not recovered from users and free supply is made, which leads to overirrigation by upstream farmers resulting in low water availability to tailEnders. It has been foundthat the scarcity of water results in dissatisfaction to downstream users, causing harm toirrigation infrastructures. In Rwasave developed swamp, the mismanagement of water results inirrigating less area under project command. There is obviously a room to improve the irrigationefficiency by the proper water management resulting in increased production, productivity andarea under irrigation.
With the above conclusions drawn during this study, following recommendations areproposed:1. Thorough puddling and leveling of fields should be done regularly;2. Farmers should be organized and sensitized for effective and efficient irrigation
management;3. Capacity building programmes on efficient water and other inputs management must be
organized by the MINAGRI in coordination with the Ministry of Natural Resources,agricultural research and educational institutions;
4. Like tea and coffee, an agency to promote rice production, processing and marketingshould be established to safeguard the interest of rice growers;
5. Policies of water charges, i.e. irrigation service fee, must be put in place for futuremaintenance and management of irrigation and drainage infrastructure;
6. Water users’ associations should be responsible of collecting the prescribed watercharges, timely maintenance of infrastructures and management of the irrigation scheme;
39
7. Reservoir water can also be used for fish production and revenue can be generated bygiving it on lease for this purpose to private investors;
8. Lining of peripheral canals and regular maintenance of irrigation and drainage channelsand other infrastructures should be done for long time benefits;
9. Irrigation schedule and appropriate quantity of water use can improve the irrigationefficiencies and enhancement of command area;
10. The participatory irrigation development and management approach has to involve thefarming community and all stakeholders, with special consideration of gender issues,from the initial decision making, throughout the entire process of planning, operation,maintenance, as well as rehabilitation and management of the irrigation scheme and thewhole rice chain.
40
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Smith,1975 et al.: swampland soil properties in tropical humid regions, Washington D.C.
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APPENDICES
APPENDIX-A: SURVEY QUESTIONNAIRE1. RESPONDENT IDENTIFICATION
a. Names:
b. Age:
c. Sex:
d. Marital status:
e. Number of children (if married):
f. District:
g. Sector:
2. HISTORICAL BACKGROUND OF CYIMPIMA SWAMP
a. When did the development of this swamp start?
b. By whom?
c. Were you cultivating this swamp before the development?
d. What were the main problems related to the cultivation of the swamp?
e. What were the infrastructures made before the development of this swamp?
f. Did you ask for the development of the swamp?
g. Why did you prefer to cultivate the swamp?
h. When did the cultivation of the swamp begin?
i. Which kind of crops did you cultivate after the swamp development?
j. Do you cultivate only rice in this swamp? Why?
k. What kind of crops do you like to grow in this swamp?
l. How much was the production before the development of this swamp? And after the
development, how much is it now?
3. MANAGEMENT OF THE SWAMP
a. What are the sources contributing water to this swamp?
b. Have you ever seen any reduction of water level in this swamp?
c. In which months do you see the maximum flow discharge in this swamp?
d. In which month do you see the minimum flow discharge in this swamp?
e. What happen when water becomes more in the swamp? Any flooding is there?
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f. Do you find enough water for irrigation during dry season?
g. What happen when water becomes less in the swamp?
h. Do you do any crop rotation?
i. How do you expect the maintenance of hydro-infrastructures?
j. Do you need any training? Which kind of training do you need?
k. Do you get any training? Which kind of training and by whom?
l. Do you use any fertilizers or pesticides in your cultivation? How do you get them?
4. Do you get any support from local government or any local NGO? Which kind of
support? ORGANIZATION OF FARMERS
a. How many plots do you have in the swamp? What are their sizes?
b. How did you get them?
c. Are you organised in any association or cooperative? Which ones?
d. How do you distribute irrigation water?
(1) On the demand
(2) By rotation
(3) Continuously
e. Is there any coordination in the management of irrigation water? How? By whom?
f. What are the disadvantages due to the lack of the irrigation water management?
g. Do you do the operation and management of hydro-infrastructures? How?
h. How do you measure the necessary amount of irrigation water in your plot?
i. Do you have any irrigation schedule? How is it?
j. What are the effects of over-irrigation?
k. What are the effects of the lack/shortage of irrigation water?
l. Is the water stored in the reservoir enough to irrigate the whole swamp?
m. If not, what are the alternative measures?
n. How do you manage or solve conflicts related to irrigation water management?
o. Who are other users of this water?
p. What are other uses of this water?
q. How much of your production is for the market? And the other part for your own
nutrition?
r. What are problems do you encounter in the management of this swamp?
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s. How many women are there in your association?
1. UMWIRONDORO
a. Amazina:
b. Imyaka:
c. Igitsina:
d. Ni ingaragu cyangwa arubatse:
e. Afite abana bangahe:
f. Akarere:
g. Umurenge:
2. AMATEKA Y’IGISHANGA
a. Iki gishanga cyatunganijwe ryari?
b. Nande?
c. Mbere yo gutunganywa, iki gishanga mwagihingagamo?
d. Guhinga muri iki gishanga kitaratunganywa byari bibateje ibihe bibazo?
e. Mwabigenza gute kugirango amazi abagereho cyangwa ngo atabangiriza imyaka?
f. Ni mwebwe mwasabye ko iki gishanga gitunganywa?
g. Ni izihe mpamvu zabateye kuza guhinga iki gishanga?
h. Mwatangiye kugihingamo ryari?
i. Kimaze gutunganywa mwagihinzemo iki?
j. Ese muhinga umuceri wonyine muri iki gishanga? Kuki?
k. Ni ibihe bihingwa mwifuza kuba mwahinga muri iki gishanga?
3. IMIKORESHEREZE Y’IGISHANGA
a. Amazi muyakura he yo kuvomerera imyaka yanyu?
b. Hari igihe mubura amazi cyangwa amazi akababana make?
c. Ni mu kuhe kwezi mubura amazi?
d. Ni mu kuhe kwezi mugira amazi menshi mu gishanga?
e. Mubigenza gute iyo muhuye n’ikibazo cy’amazi menshi? Hajya haba umwuzure?
f. Mu gihe cy’izuba ryinshi, mukurahe amazi yo kwuhira ibihingwa byanyu?
g. Mu gihe amazi ababanye make mubigenza gute?
h. Mujya muhinduranya imyaka muhinga cyangwa muhinga igihingwa kimwe gusa?
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i. Mujya mukorera imiyoboro y’amazi cyangwa se ibindi bikoresho byo kubagezaho
amazi?
j. Hari amahugurwa mubona? Ayahe?
k. Mukoresha ifumbire mvaruganda n’imiti mu mirima yanyu? Mubikurahe? Mubibona
gute?
l. Ni izihe ONG zibatera inkunga? Nkunga ki? Ubuyobozi bw’ibanze bubatera inkunga ki?
4. AMASHYIRAHAMWE Y’ABAHINZI
a. Ufite uturima tungahe mu gishanga? Ubuso bungana iki kamwe kamwe?
b. Utwo turima watubonye gute?
c. Mwibumbiye mu mashyirahamwe y’abahinzi? Ni ayahe mashyirahamwe?
d. Amazi muyatanga mu mirima gute?
e. Hari abashinzwe gukurikirana imitangire n’imicungire y’amazi? Ni bande? Babigenza
gute?
f. Ni izihe ngaruka z’imicungire mibi y’amazi yo kuvomera imyaka?
g. Mujya mukorera isuku imiyoboro cyangwa inyubako z’amazi? Mubigenza gute?
h. Mumenya gute igipimo cy’amazi akenewe mu murima?
i. Mufite ingengabihe y’ivomera? Iteye ite?
j. Ni izihe ngaruka z’amazi menshi mu myaka?
k. Ni izihe ngaruka z’amazi adahagije mu myaka?
l. Amazi ari mu kigega arahagije kuvomerera igishanga cyose?
m. Nimba adahagije muri icyo gihe mubigenza gute cyangwa ni izihe ngamaba mwafashe?
n. Mu gihe havutse amakimbirane akomotse ku mikoreshereze y’amazi muyakemura gute?
o. Nta bandi bakoresha aya mazi badahinga iki gishanga?
p. Aya mazi muyakoresha gusa mukuvomera imyaka? Muyakoresha iki kindi?
q. Umusaruro wanyu ungana iki? Mujyana uwo musaruro wose kw’isoko?
r. Ni izihe nzitizi muhura nazo mu mirimo yanyu yo muri iki gishanga?
s. Mw’ishyirahamwe ryanyu mufite abari n’abategarugori bangahe?
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Appendix-B: LIST OF COAIRWA FARMERS’ ASSOCIATIONSS/N0 Name of association Total number of
membres
1 KUNDADUKORE 84
2 JYAMBEREMUHINZI 96
3 TURWUBAKE 92
4 DUKUNDUMURIMO 97
5 RWANYINZARA 95
6 DUTERIMBERE 108
7 ABAKUNDUMURIMO 120
8 ABASHYIZEHAMWE 105
9 ABAHUZUMURIMO 110
TOTAL 907
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ANNEX-C : CLIMATOLOGIC DATARainfall in mm
January February March April May June July August September October November December120 119 142 213 122 27 9 32 84 118 153 115
Wind speed in m/secJanuary February March April May June July August September October November December
2 1.96 2.17 2.07 2.01 1.97 2.15 2.22 2.15 2.23 2.28 2.07
Maximum temperatureJanuary February March April May June July August September October November December24.59 24.85 24.83 24.02 23.9 24.51 25.09 26.17 26 25.16 24.06 24.11
Minimum temperatureJanuary February March April May June July August September October November December14.43 14.5 14.65 14.81 14.86 14.11 13.89 14.67 14.46 14.39 14.13 14.29
Relative humidityJanuary February March April May June July August September October November December74.15 73.75 75.19 79.36 77.8 68.93 60.83 59.38 66.89 71.9 76.37 75.93
Solar radiation hoursJanuary February March April May June July August September October November December
5.61 5.48 5.62 5.51 5.41 7.19 7.92 7.57 6.18 5.66 5.51 5.12
Source: National Meteorological Centre Kigali.