sustprop water group 150509

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Sustainable water resources management of Chennai basin

Introduction

The International Council for Local Environmental Initiatives (1994) gave the following

practical and local interpretation of the concept of sustainability as it applies to urban

areas: "Sustainable development is development that delivers basic environmental, social

and economic services to all residents of a community without threatening the viability of

the natural, built and social systems upon which the delivery of these services depends."

Water infrastructure not only provides essential services to enable economic and social

development in densely populated areas but also strongly affects the way society handles

water as one of the most precious and limited resources. This is covered by ASCE's

(1998) and UNESCO's (1999) definition of "sustainable water resource systems" beingthose water resource systems "designed and managed to fully contribute to the objectives

of society, now and in the future, while maintaining their ecological, environmental and

hydrological integrity." Sustainable development is not about looking back at our

accomplishments to defend or criticize but about using this platform of existing

infrastructure as a springboard for the future. The task is to look ahead and ask ourselves

how we can make it even better, taking into account that the world transforms with

increasing population, changing values and technological progress.

Background of Chennai Basin Surface and Ground Water Resources

Chennai basin is located in the Northern most corner of Tamil Nadu (Figure 1). It

consists of four topographically independent rivers draining into Bay of Bengal, 1)

Araniar, 2) Kosasthalaiyar 3) Couum and 4) Adyar. The combined drainage area of these

rivers is about 7,282 km2; off these 5,542 km2 is located within the state of the Tamil

Nadu and the remaining area lies in Andhra Pradesh. Although topographically

independent, these rivers are well connected by a network of canals, pipelines, barrages

(Anicut) and reservoirs for drinking, irrigation, industrial water supplies and flood water

diversion. Because of their interconnectivity, these river basins are considered as single


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unit while conducting water potential studies by the Public Works Department,

Government of Tamil Nadu.

Chennai city and its metropolitan area (CMA) with a total population of 7.5 million

sprawl across (1,177 km2) the downstream end of Couum and Adyar rivers. The

upstream portion of the Chennai basin is dominated by agriculture (40% of the basin

area). According to the Indian meteorological department, Chennai receives an average

annual rainfall of about 1,266 mm. Although most part of India receives rainfall mainly

during the South-west monsoon (June to September), Chennai receives only about 30%

of its annual rainfall during this season. More than 60% of the annual rainfall is received

during the north-east monsoon (October to December) as tropical depressions

(occasionally developing into cyclones) with medium rainfall intensities. January to May

is considered as dry season receiving only about 10% of annual rainfall.

Being a monsoonal climate, a considerable amount of rainfall occurs within a short time

span of one or two weeks. Hence, water has to be conserved and stored for longer

periods for round the year availability. After filling the tanks and reservoirs upstream,

still a significant portion of the high runoff generated during this time is lost to the sea

after causing flooding and inundation in the CMA. It is desirable that some part of the

surplus water is stored within the basin so that the water supply and ecological needs can

be met during the dry periods; on the same note flooding could be reduced in the CMA.

For the sustainable development and utilisation of water resources in the Chennai basin,

several water resources development, planning and management issues such as, water

supply sources and the estimation of their sustainable yield, equitable distribution of

water among various stakeholders, water conservation technologies for irrigation and

municipal water use, watershed management through soil and water conservation

measures, flood and storm water management need to be addressed in a holistic manner.

This requires an integrated water resources management (IWRM) approach leading to

sustainable river basin planning and management. This would involve a systems

approach considering different possible current and futuristic scenarios of water


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availability, water demand including climate change effects, technology and

infrastructure development, land use modifications. The multiple objectives and the

corresponding priorities need to evolved, considering the social, economic and

environmental dimensions of the problem, in line with the overall goals of sustainable

development. Appropriate measures/indicators of sustainability have to be employed to

evaluate the level of sustainability of the various alternative plans and scenarios.

In the next few paragraphs, the key water resources issues of Chennai basin are discussed

briefly. Following that, the five topics listed below that will be addressed by the Centre

for Sustainable Development in the next three years, is dealt in detail.

i) Assessment of Surface and Ground water resources

ii) Estimation of sustainable yield of surface and ground water resources

iii) Demand estimation for municipal and industrial water supply, irrigation and

instream (environmental) flows

iv) Evaluation of the level of sustainability of the existing urban water systems

and suggest plans for improvement

v) Evaluation of the current flood mitigation system and suggest plans for

integrated flood management.


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Figure 1. Chennai basin with four rivers and their connectivity (Source: Tamil Nadu Public Works Department).

State of Tamil Nadu

River Basins of Tamil Nadu


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Water Resources Issues:

Municipal Water Supply

The primary sources of municipal water supply from surface water are the reservoirs at

Poondi, Redhills, Cholavaram, Chembarambakkam, and Porur Lake located within

Chennai basin (200 MLD). The lakes are mostly fed by North East Monsoon, which is

active only for a few months in a year between October and December. A system of lakes

connects and collects the catchment run-off on the northwest of CMA to the Red hills.

Water from Red hills is conveyed through closed conduits to Kilpauk water works,

treated therein and distributed to various parts of the city. Large well fields are also

located in Poondi, Tamaraipakkam, Panjetty, Minjur, and Kannigaiper which supply

about 100 MLD of water. Water is also brought from Kandaleru Reservoir in Andhra

Pradesh (Telugu Ganga Project) and Veeranam tank (230 km south of Chennai).

Telugu Ganga Project supplies water from Kandaleru reservoir in Andhra Pradesh

through an open canal and conveys to the lakes of Poondi, Redhills, Cholavaram and

Chembarambakkam lakes for further treatment and distribution to the city. The additional

supplies from this project are estimated to be 930 MLD.

From Veeranam tank (Chennai Water Supply Augmentation Project-I) an additional

180MLD of water is supplied to Porur lake and finally distributed through the

distribution network system.

In addition to the above, plans are on the anvil to augment the water supply through

construction / rehabilitation of check dams across Couum, Adyar and Palar Rivers to the

tune of 20 MLD (Chennai Water Supply Augmentation Project-II (CWSAPII)) and

through desalination of sea water (100 MLD plant at Minjur).

The forecast water requirement for domestic, commercial and industrial uses in the year

2026 is expected to be 2,248 MLD (Table 2). While the full potential of the existing and


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the ongoing source works is only 1,535 MLD (Table 1), thus leaving a deficit of 713

MLD. Towards meeting this shortage, desalination plants with a capacity of 700 MLD

are proposed in two phases. It is to be noted that during dry years excessive pumping of

ground water is being done to offset the deficit from other sources. According to some

estimates ground water is being pumped at a rate of over 200 MLD while the sustainable

yield seems to be only 100 MLD. This has resulted in sea water intrusion in certain

pockets of the coastal aquifers.

Table 1. Safe Yield of Existing and Proposed Sources for Water Supply (Source:

Development plan for CMA, JNNURM; http://jnnurm.nic.in/).

Sl. No. Name of Source Safe Yield in

MLD1 Poondi-Cholavaram Red Hills Lake system

(including

200

diversion of flood flow from Araniar to Korataiyar

2 Ground Water from Northern Well Field 100

3 Southern Coastal Aquifer 5

Sub Total (A) 305

4 Krishna Water I Stage 400

5 Krishna Water II Stage 530

6 New Veeranam (CWSAP-I) 180

7 CWSAP-II (Proposed) 208 Sea Water Desalination (Proposed) 100

Sub Total (B) 1230

Grand Total (A) + (B) 1535

As noted from table 2, industrialization also contributes to the water stress in the Chennai

basin. This demand is projected to increase in the coming years and put pressure on the

already fragile water resources of the region. Although some industries adopt water

conservation and recycling measures, more concerted efforts need to be done to

effectively manage the available water. In addition to source augmentation i) losses due

to leakage and pilferage are to be minimized (currently estimated to be about 40%); ii)

strengthening and expansion of the existing water distribution system including repair /

rehabilitation need to be addressed in a more scientific manner.


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Table 2. Forecast water demands for municipal use (Source: Development plan for CMA,

JNNURM; http://jnnurm.nic.in/).

Sl.

No

Name of category Year

2011 2016 2021 2026

MLD1 Water requirement for the resident 1165 1284 1431 1606

. population

2 Water requirement for office,

commercial, industrial premises and

other places of employment,

education

349 385 429 482

etc.

3 For industrial use 116 128 143 160

Total Water requirement 1630 1797 2003 2248

Irrigation demand:

Prior to the urban explosion in the 1900, these river basins were dominated by

agriculture. Currently, the upstream portions of these rivers are still dominated by

agricultural crops (about 40% of the basin area). Water intensive crops such as paddy,

sugarcane, banana and vegetables are grown in wide tracts of agricultural lands in

Chennai basin. About 60% of the cultivated area is under paddy, 10% in groundnut, 5%

in sugarcane, and 5% in banana. Pulses, vegetables, and non-food crops such as cotton

are grown in rest of the area. Hence, depending on the region, season and crop, about 80

to 90% of the net area sown is irrigated at least once in a year. In Tiruvallur district about

30% of the net sown area is irrigated through tanks and canals and 70% from open wells

and tube wells; while in Kancheepuram district 50% of land is irrigated from tanks and

the other 50% from open wells and tube wells. (Source: Tamil Nadu Agriculture

Department, 2005-06 Crop Statistics)

Ground water is being increasingly used to overcome the vagaries in monsoon and

improve the reliability of water supply for agriculture. Instead of using wells to provide

supplementary irrigation only when the monsoon fails, they are being used continuously

round the year to raise water intensive crops such as paddy and commercial crops such as


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sugarcane and banana. Further, former irrigation tanks such as Poondi, Red Hills and

Cholavaram lakes are presently being used to meet the drinking water needs of Chennai

city, thus affecting irrigated agriculture and aggravating ground water mining in the

region.

In order to improve the reliability of water for agriculture, 100s of recharging tanks

called Ooranies were dug in ancient times all across the basin to capture the runoff

during the short rainfall season. However, siltation, poor maintenance, and urban

encroachment have rendered many of these tanks currently unusable. Further, high

pumping rate for irrigation and drinking water supply for Chennai Metropolitan Area

have considerably depleted the aquifers, as much as 80% in some regions, triggering salt

water intrusion. The rate of siltation of major reservoirs is also of major concern in this

basin. According to some preliminary studies about 0.5 to 1% of the storage capacity per

annum of the reservoirs is lost due to siltation. Some of the reasons include catchment

degradation due to deforestation and urbanization, intensive farming practices,

uncontrolled grazing and lack of soil conservation measures. These landuse/landcover

changes have altered the runoff pattern, exposed the top soil to the direct impact of high

intensity rainfall events thus triggering more erosion and siltation of the reservoirs.

Alternate cropping practices that minimize water use and improve the soil vegetative

cover could be promoted among the farmers. Basin wide assessment of deficit irrigation

and other water conservation measure should be studied to improve surface and ground

water yield.

Environmental flows:

Most the surface water, except for storm water flows, in these river basins are captured

by irrigation tanks and water supply reservoirs located upstream. Hence, very little to no

baseflow (dry weather flow) exist in these rivers. At present for all practical purposes we

can assume that no environmental flow is available at the downstream section for the

sustenance of riparian vegetation, mangroves, aquatic plants and marine species. A major


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portion of the current baseflow in Cooum and Adyar River within the Chennai

metropolitan area consists primarily of treated, partly treated and untreated sewage

outflows. Operational strategies are to be arrived at in order to maintain a minimum

desirable environmental flow at identified river reaches so that the overall health of the

river basin and ecosystem can be improved.

Flood management:

Whenever there is heavy downpour resulting from depressions or cyclones of the North-

east monsoon, first the upstream tanks fill up and surplus water results in successive

breaching of tanks and causes flood in the CMA. Inadequate storm water drainage

system, siltation and poor maintenance of tanks, encroachment of tank beds and flood

plains, urbanization in the lower reaches, and blockade of the river mouths due to sand

bar formation and tidal backwaters are the major reasons for flooding and inundation in

the CMA. There have been some limited attempts in the past by the PWD and the

CMDA to tackle the flood problems in terms of desilting of waterways and storm drains,

building levees, flood walls and diversion channels. However, an integrated flood

management incorporating both structural and non-structural measures needs to be

formulated within the sustainability paradigm.

Topics to be addressed by the Centre for Sustainable Development

Assessment of Surface and Ground water resources

Surface Water Assessment: Due to non-uniform distribution of rainfall, variation in

topography, soil and land use patterns, the availability of water will vary across the basin.

The current spatial and temporal distribution of water availability of the basin can be

assessed using historical records and/or hydrological modelling. Historical records of

stream flow, reservoir levels, and ground water levels are measured at few discrete

locations by the PWD and other government entities. Historical records of daily water

levels at the five major tanks/reservoirs are available from PWD. However, there are

hundreds of small tanks distributed across the basin on which measurements of water

levels are not available. Similarly, measure records of stream flow are available only at


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few locations in the main limb of the rivers. Hence, these observations have to be

integrated within a hydrological/water balance modelling approach to derive a

comprehensive estimate of spatial and temporal distribution of water availability.

The Institute for Water Studies, PWD has recently published a Micro-level watershed

study for Chennai basin (IWS, 2005) as a precursor to the IAMWARM project funded by

the World Bank. This Micro-level study could be used as a base for the current study. A

hydrological model such as Soil and Water Assessment Tool (SWAT) can be calibrated

and validated using observations at discrete locations (Arnold et al. 1998). For

hydrological modelling, fifty to hundred years of weather data will be needed for a

comprehensive assessment. Further, topography, soil and landuse parameters will be

needed to assemble the hydrologic model.

The hydrological model will provide a spatial and temporal estimate of various water

balance components such as surface runoff, potential and actual evapotranspiration,

infiltration and ground water recharge. This assessment could be made in two stages: 1)

Without any human interventions (virgin flows) and 2) with human interventions such as

irrigation diversions, land use modifications, watershed management practices and

storage structures. These two scenarios would help us in quantifying the natural water

yield of the basin and the amount of water stored in surface detention structures during

different times of the year. This can further help us in determining the environmental

flows needed to meet the ecosystem demands in certain sections of the stream and the

operational procedures to meet this demand.

Disturbances in weather patterns due to global climate change will influence the spatial

and temporal distribution of various water balance components. In the peninsular India,

the day time and night time temperatures are projected to increase in the coming years

(Srivastava et al. 2008). Further, the extreme rainfall events that would cause floods are

also projected to increase in frequency (Joshi and Rajeevan, 2006). Hydrological models

could be used to simulate the impact of several such weather perturbations, suggested by

the IPCC, on the spatio-temporal distribution of water balance components. Ensemble of


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several such simulations would provide a range (band) of values for the various water

balance components, which could be used to comprehensively assess the water resources

of the basin.

Ground water Assessment: The subsurface geological formations of Chennai city vary

from ancient Archaeans to recent Alluviums, which can primarily be grouped into (i)

Archaeans Crystalline Metamorphic rocks (ii) Upper Gondwanas comprised of

sandstones, siltstones and shoals, tertiary sandstones and (iii) coastal and river Alluvium.

The groundwater resources for Chennai city include the sources from well fields, coastal

aquifers, brackish water based Reverse Osmosis Plants and Neyveli aquifers. The major

aquifers are at Minjur, Panjetty and Tamaraipakkam located in the north and northwest of

the city and the aquifers along the coastal belt from Thiruvanmiyur to Kovalam. In

addition, well fields have been developed at Tamaraipakkam, Panjetty, Minjur, Poondi,

Flood Plains and Kannigaiper. The recent well yield statistics for Chennai city have

clearly brought out the depletion of ground water source during the last 30 years due to

increase in demand resulting in overdraw of ground water. In addition, due to severe

scarcity, CMWSSB has hired private agricultural wells from 2000 to augment water

supplies. In order to regulate and control the extraction, use of transport of ground water

and to conserve ground water, the Chennai Metropolitan Area Ground Water

(Regulation) Act, 1987 was enacted. The current projections indicate that the overall

water demand for the year 2026 is of the order of 2,248 MLD as against the full potential

of the existing and presently ongoing source works totalling to 1,535 MLD, thus leaving

a deficit of 713 MLD (The details can be referred from Development Plan for Chennai

Metropolitan Area April 2006). Due to frequent and recurrent deficit monsoon in

Chennai, there is uncertainty on the availability of ground water during such periods.

Hence, it is pertinent to create additional reliable sources of ground water supply

(particularly in hard rock terrains), in addition to the precise assessment of presently

available ground water sources. Also, the role of coastal ground water resources

assessment indirectly influences the groundwater quality as well significantly. For

example, the chemical quality of ground water in Chennai City is mostly brackish and not

suitable for drinking purposes. In general it is alkaline with pH value from 7.8 to 9.0 and


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many pockets have high chloride and sulphate; very few selected pockets have potable

quality at Besant Nagar, Greenways Road, Nungambakkam, Kilpauk etc. and also good

fresh water aquifer is found in the stretch between Thiruvanmiyur and Uthandi along the

coast. In areas like K.K. Nagar, Ashok Nagar, Sastri Nagar, Mylapore, Anna Nagar etc.

excess iron has been found resulting in reddish colour of water, chocking pipes with

yellowish-brown precipitate and also disagreeable taste. The quality changes due to

seawater intrusion in the past are evident in Triplicane, Mandaveli and other areas along

the coast. Mandatory provision of rainwater structures within the city has marginally

improved the recharging potential for the ground water and also the water quality and

Ground Water table in the recent past. Thus, a detailed study needs to be carried out on

the assessment of groundwater and its associated socio-economic impact on Chennai city.

Groundwater resources development occupies a key place in the irrigation and municipal

water supply sectors in India and especially in Chennai basin, complementing the surface

water contributions. The dependence on groundwater resources has increased

significantly over the last two decades due to population growth, industrial development

and a heavy migration of population to the city and the suburbs, which, in turn, has

necessitated over-exploitation of the ground water resources to cater to the municipal and

industrial demands of the metropolitan area and sustain the agriculture in the peri-urban

areas. The ground water yield assessment is a primary task in any sustainability study of a

basin in connection with the utilization of water resources.

The present proposal to address a large scale groundwater assessment which involves the

entire Chennai city covering as many as four major river basins inevitably consists of

interdependencies of factors and processes affecting the groundwater resources.

Groundwater being an essential part of the hydrological cycle and a valuable natural

resource, it is vital forsustainingagriculture, industrial uses, streams, lakes, wetlands,

and eco-systems, particularly in the context of Peninsular India, which consists of highly

heterogeneous formations. The use of groundwater has particular relevance to the

availability of many potable-water supplies. Groundwater enhances water supply because

it has a capacity to meet water needs during periods of increased demand, particularly


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during drought and when surface-water resources are close to the limits ofsustainability.

Thus, groundwater is not an isolated or independent resource. It is a primary component

of the hydrological cycle connected to the land surface and terrestrial eco-systems.

Thinking holistically about groundwater systems in terms of connections to the

hydrologic cycle illuminates a number of interdependencies that need to be considered

when assessing groundwater availability and long term aquifersustainability. These

interdependencies can exert substantial controls on the balance of in-flows and out-flows

to the groundwater system (the groundwater budget), and the controlling factors can be

greatly influenced by human activities along the river basins. The water fluxes affecting

the groundwater budget include land-surface infiltration, evapo-transpiration, and flow

within the vadose zone; flow into and through the saturated zone, aquifer losses to deeper

strata, and the many forms of groundwater discharge and abstraction. Similarly, many

factors influence the groundwater movement. Important controlling factors include local

variations in climatic conditions, hydro-geologic setting (including vadose zone

processes), vegetative cover, land use, and institutional approaches to water management;

and all the above factors ultimately influence groundwater recharge, groundwater storage,

aquifer sustainability, and socio-economic stability. Many of these factors vary over

space and time, which makes quantifying the groundwater budget complex.

Estimation of sustainable yield of surface and ground water resources

Sustainable Yield of Surface Water: There are several definitions for sustainable yield.

But the definition provided by Australian Governments National water commission

seems to be very comprehensive. According to the Australian Governments National

Water Initiative (http://www.water.gov.au/), Sustainable yield is broadly defined as the

level of extraction that if exceeded, would compromise key environmental assets, or

ecosystem functions and the productive base of the resource. In spite of general

definitions such as the above there is not a standardized method for determining

sustainable yield in the literature. In the current study, sustainable yield of surface water

(major tanks and stream segments) will be calculated as the amount of water that could

be safely extracted after accounting for instream (environmental) flow requirements.


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Sustainable Yield of Ground Water: All groundwater reservoirs of economic importance

are temporarily holding water in transit from a place of recharge to a place of discharge.

Any amount of water extracted from the ground water by mechanical means (through

pumping) would have to be eventually replaced by the same amount coming from the

surface waters. Also, the natural discharge from ground water supports riparian, wetland,

and other groundwater-dependent ecosystems, as well as the base flow of streams and

rivers. All pumping comes from capture, and all capture is due to pumping. The greater

the intensity of pumping, the greater the capture. Capture comes from decreases in

natural discharge and increases in recharge, the latter coming either from increased

ground surface recharge or from the surrounding areas. In cases of depletion of aquifer,

capture is augmented with decreased storage, i.e., with a permanent lowering of the water

table.

The water that seeps below the ground surface can follow one of three paths:

1. Return to the atmosphere via evaporation and evapotranspiration;

2. Return to the ocean via base flow and subsequent stream flow; or

3. Return to the ocean through deep percolation.

Of these three, only deep percolation is completely independent of the surface waters.Therefore, it is the only component of precipitation (or recharge) that may be potentially

subject to sequestering (capture) by pumping. Studies are needed on a local, sub regional,

and regional basis to determine deep percolation as a percentage of precipitation, or

alternatively, as a percentage of recharge. For groundwater basins in close proximity to

the ocean, the possibility of salt-water intrusion must be examined carefully.

A groundwater reservoir is essentially a leaky, porous natural geologic container. In

nature, precipitation P separates into direct runoff Q, evaporation and evapotranspiration

ET, and natural recharge NR. All natural recharge eventually flows out as either natural

discharge ND or deep percolation DP, at various spatial scales, from small to large

watersheds. Natural discharge can return to the atmosphere via evaporation and

evapotranspiration ET or to the ocean via base flow BF. The deeper the ground water, the


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larger the spatial scale of natural discharge, from the local to the regional scale. The

portion of natural discharge that returns to the atmosphere via evaporation and

evapotranspiration is mostly already committed. Only a small fraction of it (the water that

evaporates directly from the ground) may be subject to capture, if deemed necessary to

satisfy socioeconomic needs. The case for the sequestration of the other two fractions (the

evaporation from bodies of water and the evapotranspiration from vegetation) is usually

less defensible. Not all water pumped is lost from the groundwater system; only the water

consumed and not returned to the aquifer. Thus, a precise water balance, which takes into

account all uses, is needed to assess sustainability.

Sustainable yield does not depend on the size, depth, or hydro geologic characteristics of

the aquifer. Current practice notwithstanding, sustainable yield does not depend on theaquifer's natural recharge, because the natural recharge has already been appropriated by

the natural discharge. Sustainable yield depends on the amount of capture, and whether

this amount is socially acceptable as a reasonable compromise between little or no use,

on one extreme, and sequestration of all natural discharge, on the other extreme.

Sustainable yield is seen to be a moving target, to be determined after a judicious study

and appraisal of all issues regarding groundwater utilization. These include

hydrogeology, hydrology, ecology, climatology, social and economic development, and

the related institutional and legal aspects, to name the most relevant.

In practice, sustainable yield may be taken as a suitable percentage of precipitation. A

reasonably conservative estimate would take up to the deep percolation amount as

sustainable yield, provided that it does not lead to excessive salt-water intrusion. On a

global basis, deep percolation amounts to about 2% of precipitation. In the absence of

basin-specific studies, this figure may be used as a point-of-start on which to base

sustainable yield assessments. A fraction of evaporation and evapotranspiration (ET) is

seen to be part of discharge (ND), which originates in recharge (NR). A detailed water

balance is required to evaluate the components of precipitation and recharge, so that the

fractions of deep percolation, evaporation, evapotranspiration and base flow that may be

candidates for capture can be ascertained. Sustainable yield can also be expressed as a

percentage of recharge. Globally, if recharge can be assumed to be approximately 20% of


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precipitation, then deep percolation would be about 10% of recharge. Thus, a reasonably

conservative estimate of sustainable yield would be 10% of recharge. Limited experience

indicates that average values of this may be around 40%, while less conservative

percentages may exceed 70%. The current concept of sustainable yield represents a

compromise between theory and practice. In theory, a reasonably conservative estimate

of sustainable yield would be about 10% of recharge. In practice, values higher than 10%

may reflect the need to consider other factors besides conservation.

Considering the complexities involved at the regional scale in evaluating the groundwater

assessment and its associated sustainable yield in the long term for Chennai city, the

following components are to be estimated:

1. Estimation of Base-Flow2. Estimation of Regional Aquifer Parameters using Base-Flow Recession Data

3. Estimation of Evapo-transpiration from groundwater

4. Estimation of Safe Yield

5. Estimation of Regional Specific Yield

6. Estimation of Groundwater Recharge & Discharge components for Groundwater

Balance

7. Estimation of Exploitable Dynamic Groundwater Reserve

8. Estimation of Regional Groundwater Budget

Demand estimation for municipal and industrial water supply, irrigation and instream

(environmental) flows

The municipal water demands are well documented by the PWD and other government

agencies. However, the irrigation water demand and the return flows are not well

quantified in the Chennai basin. Field visits will be undertaken to survey the irrigation

practices in various parts of the basin. Current crop statistics and cropping practices in

various villages of the river basin will be collected from the agriculture and statistics

departments. The amount of effective irrigation water demand will be quantified using

the hydrologic modelling framework discussed in the previous section.


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Tamil Nadu Agriculture University (TNAU) has developed a policy paper on

Alternative Cropping Practices in Tamil Nadu and presented it to the Govt. of Tamil

Nadu in 2006 (TNAU, 2006). It was developed with an overall objective of reducing the

cropping area under paddy by 20% and sugarcane by 40% (both water intensive crop) to

grow other high demand, less water intensive, crops such as oilseeds, pulses, cotton, and

maize. Reduction in area under paddy and sugarcane was proposed not only due to

reduced water availability but also to avoid their surplus production, and get better

economic returns. Such alternate cropping practices could also be simulated to

comprehensively quantify the irrigation water demand across the basin.

Increased temperatures and alteration in rainfall patterns due to climate change will also

influence the irrigation water demand. As discussed previously, this increased

evaporative demand could be quantified using the hydrologic model such as SWAT.

There are models such as IWR-MAIN which could provide a forecast of increased urban

water use due to climate change.

Environmental flow to meet the ecosystem demand is an important aspect of IWRM.

Several methods are available in the literature for estimating this demand. In the current

study, the method developed and adopted in British Columbia, Canada (Hatfield et al.

2003) could be used for estimating the instream flow requirement in Chennai basin. In

British Columbia, the instream flow thresholds were calculated based on whether it is a

fishless steam or a fish-bearing stream. For fishless streams, the minimum instream flow

release is equivalent to the median monthly flow during the low flow month. For fish-

bearing stream, the minimum flows are adjusted as percentiles of mean natural daily

flows for each calendar month. In order to estimate flows based on the above criteria, at

least 20 years of continuous natural daily stream flow records with minimum

interventions to flows due to man made structures and diversions are needed. The

hydrological model results from the previous section could be used in lieu of observed

data where such long-term measured data are not available. Further, in the current study,

the ecosystem needs of sensitive regions such as Pallikarani Marsh and similar such

regions across the basin need to be established from literature and field studies.


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Evaluation of the level of sustainability of the existing urban water systems and suggest

plans for improvement

Conflicting objectives and expectations of various stakeholders have led to increasing

interests in the consideration and resolution of multiple social, economic, environmental

and supply sustainability objectives in the management of water supply systems,

especially during extended dry periods. The International Council for Local

Environmental Initiatives (1994) gave the following practical and local interpretation of

the concept of sustainability as it applies to urban areas: "Sustainable development is

development that delivers basic environmental, social and economic services to all

residents of a community without threatening the viability of the natural, built and social

systems upon which the delivery of these services depends." With respect to the

sustainability of metropolitan and urban areas but also to the sustainability of water

resources management the urban water infrastructures play a central role. Water

infrastructure not only provides essential services to enable economic and social

development in densely populated areas but also strongly affects the way society handles

water as one of the most precious and limited resources. This is covered by ASCE's

(1998) and UNESCO's (1999) definition of "sustainable water resource systems" being

those water resource systems "designed and managed to fully contribute to the objectives

of society, now and in the future, while maintaining their ecological, environmental and

hydrological integrity." Almost immediately water and wastewater engineers raise the

question whether sustainable development is different from what has been practiced to

date. Obviously, water and sanitary engineering has provided substantial social benefits

and helped to protect the environment from impacts.

Sustainable development is not about looking back at our accomplishments to defend or

criticize but about using this platform of existing infrastructure as a springboard for the

future. The task is to look ahead and ask ourselves how we can make it even better,

taking into account that the world transforms with increasing population, changing values

and technological progress.


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Literature Review - Evaluation of Sustainability of Urban Water Supply and Distribution

Systems

With the practical advances in science and technology, such as modelling and data base

availability and access, the water resources mangers and the stakeholders are now able to

evaluate the sustainability of complex urban water systems considering the individual

preferences of the stakeholders and a large number of performance measures (PMs) over

longer time frames (Loucks and Gladwell, 1999). In the field of water supply

planning, Jabor and Mohsen (2001) used Analytic Hierarchical Process

(AHP) to evaluate four non-conventional water supply sources in

Jordan, namely, (i) using treated wastewater, (ii) rainwater harvesting,

(iii) importing water, and (iv) desalination of brackish water under five

performance measures (PMs) related to technical, availability,

environmental, reliability and economical aspects. Joubert et al. (2003)

employed multi-attribute utility theory (MAUT) and additive utility

functions to evaluate and prioritize water supply augmentation and

water demand management options for the City of Cape Town in South

Africa where the water demand was rapidly reaching the potential

yield and also severe water restrictions had to be imposed in summer

to regulate the demand. Fourteen alternatives, including 4 supplyaugmentation alternatives, 6 demand control alternatives and 4 water

reuse alternatives were evaluated using nineteen PMs under five main

objectives.

Perera et al. (1999) used a water supply simulation software (REALM)

and a multi-criteria decision analysis software (Logical Decisions 1997)

in a DSS to derive optimum operating rules for the Melbourne water

supply system in Australia. The inputs and information required for the

simulation-optimization model were: system inflow details and climatic data, seasonally

adjusted monthly demands forecast, the unrestricted demands for each demand zone in

the water supply system, the information on nodes and carriers in the network (such as

capacity constraints, transfer priorities) and long-term operating rules controlling inter-


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reservoir transfers and demand restrictions. Four objectives, namely, i) ensuring a safe

and reliable water supply to Melbourne by maximizing the level of service to the water

users; ii) maintaining an acceptable cost for water by minimizing the pumping/treatment

costs and maximizing the hydropower revenue; iii) minimizing the adverse effects on the

environment; and iv) maintaining supply sustainability by maximizing total system

storage volume and eight system PMs have been considered.

The relative sustainability of operations under different planning scenarios has been

evaluated by Lundie et al. (2004) for the Sydney Water Systems in the year 2021,

considering environmental issues along with financial, social, and practical

considerations in strategic planning. Life Cycle Assessment (LCA) tool, being holistic,

quantitative, comparative, and predictive, was chosen to examine the potential

environmental impacts. Assessment of a greenfield scenario incorporating water demand

management, on-site treatment, local irrigation, and centralized biosolids treatment

indicated that significant environmental improvements would be possible relative to the

assessment of a conventional system of corresponding scale.

For the Chinese city of Tianjin, a framework of sustainable urban water resource

management has been developed that provides a holistic picture of the issues and their

relationships, while offering alternative choices for municipal decision makers to choose

from. The framework follows an integrated watershed management approach,

considering the physical, biological, political and socio-economic factors and adopts a

contextual holism. Four strategies, namely, supply management, demand management,

efficiency management and emission management have been adopted to achieve the

overall goal. It is shown that water usage systems with various levels of integration and

cascading can lead to significant reductions in domestic water consumption and thus

lower the environmental impact of domestic water usage.

Hiessl et al. (>>>) have questioned the suitability of the traditional engineering concept

characterized by high initial costs of centralized structures, mixing of wastewater streams

of various qualities, and open loop design to fulfill the new requirements of urban water


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infrastructure from sustainability point of view. Using the scenario approach, they have

developed three long-term scenarios and have evaluated their sustainability using a total

of 44 criteria that are structured using the Analytic Hierarchy Process. The results of an

interdisciplinary analysis and assessment performed for two German municipalities as

case studies indicate that infrastructure scenarios with decentralized components, closed

loops of water and localized treatment options for wastewater are preferable to the

traditional systems.

Criteria for the Assessment of Sustainability

Sustainability of urban water supply and distribution systems are usually assessed using

criteria such as water supply system reliability, reversibility and vulnerability;environmental system integrity; equity in water allocation and socio-economic

acceptability. Water supply and distribution systems, in a long-term view, are subject to

substantial risk due to inherent stochastic variability of supply and demand and a

fundamental lack of knowledge. The traditional measures of system performance are

insufficient to capture the risk behaviour of water supply and distribution systems, and

additional criteria must be used to quantify recurrence, duration, severity and other

consequences of the non-satisfactory system performance. These criteria include

reliability, reversibility and vulnerability (Kundzewicz and Kindler, 1995). Reliability

represents the probability of a system success state, and it is complementary to risk,

which represents the frequency of system failure. Two kinds of reliability are commonly

used: i)Occurrence reliability, calculated as the ratio of the number of periods of system

success to the number of periods of operation; and ii) Volumetric reliability, often defined

as the ratio of the volume of supplied water to the total demanded volume (complement

of shortage ratio). Reversibility (also called resilience) is the probability of recovery of

the system from failure to some acceptable state within a specified time interval. Fiering

(1982) proposed several alternative indices of resilience, including the duration of the

system's residence in the satisfactory state, steady state probability of the system being in

the satisfactory state. Hashimoto et al. (1982a, b) developed a mathematical definition of

resilience, suggesting that resilience could be a measure of the probability of being in a


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period of no failure in the current period when there was a failure in the last period. Moy

et al. (1986) incorporated a formulation of resilience into mathematical programming for

reservoir operation where resilience was measured as the maximum number of

consecutive periods of shortages that occur prior to recovery. Vulnerability represents the

severity or magnitude of a system failure. Hashimoto et al. (1982a, b) developed a metric

for overall system vulnerability as the expected maximum severity of a sojourn into the

set of unsatisfactory states. Emphasis was placed on the maximum severity (how bad

things are) for each unsatisfactory state. Moy et al. (1986) defined a vulnerability

criterion as the magnitude of the largest water supply deficit during the period of

operation. Reliability, resilience and vulnerability of a system are not independent, and

trade-offs among them are to be evaluated. These criteria may be insufficient for

non-stationary and uncertain conditions due to changing economic and social contexts,

and therefore, the appropriate treatment of the uncertain and the unknown is imperative

(Kundzewicz and Kindler, 1995).

Environmental impacts often put the sustainability of water resources systems at risk. A

guiding criterion for sustainable water resources management is to minimize the

interference of the water supply and distribution systems with the integrity of the

associated environmental system. To meet this criterion, we must at least ensure the

following: i) Sufficient water regimes to maintain and restore, if applicable, the health of

aquatic and floodplain ecosystems; ii) No long-term irreversible or cumulative adverse

effects on the environment and ecosystems; iii) Water quality that meets certain

minimum standards that may vary over time and space; and iv) Integrated consideration

of water quality and quantity when designing and operating water supply and distribution

systems. To reflect the environmental system integrity in a modeling framework, first the

environmental impacts, especially the long-term environmental consequences resulting

from water uses, must be simulated and expressed in some quantitative forms, for

example, salt concentration in groundwater, soil salinity in the crop field. Second, those

environmental impacts need to be assessed in some forms that can be comparable with

other criteria. One of the common direct forms is economic damage from environmental

degradation, which, is often difficult to evaluate. Generally, indirect forms are used to


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calculate these effects, including normative forms related to water quality standards or

institutional environment water supply quantum.

Equity is one of the basic concepts within the primary definition of sustainable

development (WCED, 1987). In view of equity, sustainable water resources systems must

allow people, "now and then" and "here and there" to share the water use right (both

benefit and cost) in such a way that no one should be disadvantaged or inadequately

compensated (ASCE, 1998). Equity can be described as an even distribution of beneficial

water use related benefits in both spatial and temporal domains. Factors that affect either

temporal equity or spatial equity in water resources development can be either

anthropogenic or natural, or both. Temporal equity is associated with long term

cumulative consequences, which may lead to damages or even disasters in the future.

One typical case related to spatial inequity is the conflict between upstream and

downstream areas in a river basin. Conflict may arise when upstream users release

excessive pollutants into the river, and as a consequence, downstream users suffer

damage due to the poor water quality. Temporal equity concerns the equity in

supply/distribution to a specified user over different years. In long-term studies, inter-

generational equity is also evaluated. Since equity in water resources management

involves complex natural, political and socio-economical factors, there is no general

expression for this term.

Similar to the metric natural capital that describes the optimal scale of a sustainable

economy, in the field of water resources planning and management,socioeconomic

acceptability is used. When the marginal cost associated with water resources

development and management is greater than the marginal benefit, the water resources

development activities lose their socio-economic acceptability, and the water resources

system enters an unsustainable state at this point. An example would be the water

resources management problem in the Aral Sea basin in Central Asia. The withdrawal of

water for irrigation has created great profits for that region, but at the same time the

environmental disaster due to excessive water withdrawal has caused huge damage.


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Methodology

The harvesting and the bulk distribution of water resources are to be modeled within a

water supply and distribution system. Mass-balance accounting procedures are to be used

at nodes, while the movement of water within carriers is subjected to capacity constraints.

A robust optimization algorithm is to be used to optimize the water allocation within the

system for each time step of a simulation period using pre-defined penalties and

operating rules. The operating rules are usually defined by rule curve restrictions, target

storage curves, satisfying pressure and demand requirements at various nodes of

consumptive use and other priority releases such as environmental flows. During each

simulation time step, the water assignment criteria need to be satisfied by the model

based on priorities of allocation decided by the water supply managers considering the

stakeholder preferences. Some of the typical examples of the water assignment criteria

are: satisfying evaporation losses in the reservoirs, satisfying transmission losses in

carriers; satisfying all demands (which may be restricted) to maximize supply reliability;

minimizing spills from the system, maximizing the yield; satisfying instream

requirements defined by minimum capacity of carriers; ensuring that the end-of-season

storage volume targets are met.

The scenario approach is especially suited to deal with complex planning situations and

high degree of uncertainties as it is the case for urban water infrastructure systems. The

scenario approach stimulates the imagination of those involved, provides a common

language for multidisciplinary teams, supports a shared understanding of the problem

under consideration by structuring the group thinking processes in interdisciplinary

project teams, and finally, enables the appropriation of the results by the decision makers.

Evaluation of the current flood mitigation system and suggest plans for integrated flood

management.

Destructive abundance of water may be caused due to one or more of the following: river

floods caused by intensive and/or long-lasting precipitation, fast snowmelt, precipitation-


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triggered landslide into a lake, storm surges and development-related failures such as

dam breaks. Devastating floods destroy human heritage and undermine the development.

Sustainable development should have a built-in mechanism of maintenance of resilience

against surprises and shocks owing to such destructive effects caused by the abundance

of water. This calls for the preparedness for tackling events of low probability and

random timing of incidence but vulnerable in terms of the severity of the damage. In case

of developing countries such as India, human poverty is an important factor aggravating

flood hazard. The desire to overcome poverty in addition to the fertility of the soil, leads

to the encroachment of flood plains by way of informal and/or illegal urban settlements

(as squatters), as found in the coastal city of Chennai. These areas are often uninhabited

precisely because they are flood-prone, and hence are available for informal settlement

by squatters.

The traditional definition of flood risk was often conditional upon a set of assumptions

about how the flooding system will behave in the future. Typically, it will be assumed

that random processes are stationary in statistical terms and that a change in

environmental phenomena will occur at some steady rate. However, flooding systems

will be subject to changes that do not coincide with such assumptions made in the

estimation of risk. In fact, these changes may impact upon the loads on the flooding

system, its response, or the potential impacts of flooding arising out of natural

environmental processes or evolution in ecosystems or intentional and unintentional

human interventions in the flooding system. Moreover, social and economic changes will

have a profound influence on the potential impacts of flooding and the way they are

valued.

Typically, some of the most common risk management actions (some structural measures

and some non-structural measures) and their perceived effects can be listed as:

i) Development control in floodplains that limit the development activity within the flood

plains and hence reduce the vulnerability; ii) Improving flood resistance of buildings

resulting in a reduction of flood damage; iii) Increasing public awareness of temporary

measures to reduce flood impact on building contents; iv) Flood insurance that attempts


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to distribute the costs of flood damage across different communities and over time; v)

Increasing storage in catchments and reducing the rate of runoff (source control) that

reduces the flood severity, vi) Flood defense planning, design, construction, operation,

and maintenance including improving the urban drainage that reduces the probability

(frequency) and the severity of flooding (upto a limit); vii) Efficient Real-time flood

forecasting and warning that would reduce the impact of flooding; viii) Emergency repair

of flood defenses that would reduce the probability of flooding; ix) Evacuation of people

in flood events to reduce risk related to public safety and health; x) Post-flood recovery

and reconstruction that would reduce social, health and economic impacts due to

flooding. In order to implement the various activities mentioned, the coordinated action

among a number of public and private organizations involved and active participation of

the multiple stakeholders is essential.

Non-structural measures such as source control (watershed/landscape structure

management), flood plain zoning and regulation, building policy frameworks, economic

instruments, public awareness raising, creation of flood-related data bases and an

efficient decision support system with capabilities of flood risk assessment and well

supported by a state-of-the-art flood forecast-warning system, would go well with the

spirit of sustainable development than structural measures that involve huge initial

investments but yield limited flood protection and less reversible thus unduly affecting

the welfare of the future generations. Moreover, since sustainability requires thinking

about the future generations, the threat due to climate change becomes important. It is to

be understood that non-structural measures of flood mitigation, being flexible, lend

themselves well to the implementation of adaptation strategies with regard to climate

change, the assessment of which has significant uncertainty. However, given the existing

urban infrastructure and the rate of growth of population and economic development in

the Chennai city, it is not possible to eliminate the option of structural measures entirely,

but they can be minimized and localized in scale. Hence, it would be wise to arrive at an

optimal site-specific mix of structural and non-structural measures that would be

sustainable.


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Flood risk management is the process of data and information gathering, risk assessment,

appraisal of options, and making, implementing, and reviewing decisions to reduce,

control, accept, or redistribute risks of flooding. Integrated flood risk management

explicitly recognizes the interrelationships between all risk management measures, and

their analysis, costs, and effectiveness, within changing social, economic, and

environmental contexts. It can be helped by improving access to data and models, sharing

and communicating risk analyses, involving a wider range of stakeholders, and

coordinating risk management actions (Hall et al., 2003). Integrated flood risk

management in practice requires decision-making ability that is beyond the information

processing capacity of any individual or a single organization. It therefore requires a

framework within which diverse activities can be enacted, which will help to ensure that

they are complementary and based on a common understanding of key principles. This

requires a close cooperation and interaction of the stakeholders and the organizations

involved in planning and management.

A definition of sustainable flood defence schemes given by the UK Environment Agency

(1998, p. 9) describes them as taking "account of natural processes (and the influence of

human activity on them), and of other defences and developments within a river

catchment ... and which avoid as far as possible committing future generations to

inappropriate options for defence". In order to measure and monitor the progress of flood

management towards sustainable development, a set of suitable criteria and indicators are

essential that would enable planning of strategies and implementation of decisions.

Kundzewicz (2000) used the following four conceptual criteria, fairness (or equity),

reversibility, risk and consensus recommended by Simonovic (Takeuchi et al., 1998) for

the assessment of the sustainability of flood protection systems. Fairness or equity is to

ensure that flood protection should be extended to all members of the society, although

the difference in vulnerability to floods between even neighbouring households can be

considerable. Reversibility measures the potential degree of mitigation of impacts. This

may be viewed as an entropy-related criterion, quantifying the time, the energy, and the

cost involved in the transformation of an engineered system to its original unengineered

(natural) state (cf. Nachtnebel, in press). Large structural flood defences such as flood


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mitigation reservoirs are practically irreversible, while levees, flood walls and dikes can

be considered to be reversible but at a high cost as in case of the renaturalization of

regulated rivers in Germany. Risk in the context of flood management is perceived in

terms of the likely damage that may be caused due to the occurrence of the uncertain

flood events. The concept of risk in the context of structural flood defences, such as

levees or flood walls is explained below. These structural measures may provide

excellent protection against more frequent small to medium floods. At the same time,

their existence creates a false feeling of absolute safety which often results in intensive

development of low-lying areas. When a major flood occurs, the levee or the flood wall

may fail and instead of acting as a flood defence, it may amplify the destruction and

losses. Thus, in this context, risk is typically understood as a product of low exposure

(probability of failure) but high consequences (vulnerability). Consensus means that

involved and affected parties should agree on the programme of flood protection and

management. General agreement should be based on equitable compromise. One could

add to these criteria a measure of efficiency and synergism; e.g. a multipurpose reservoir

may also have a number of other functions related to sustainability such as water supply,

recreation, in-stream flow requirement.

Gardiner (1995) suggested using four groups of criteria to compare options of flood

defence and assessed their performance from the viewpoint of sustainable development.

They are related to global environment (resilience to climate change, energy efficiency,

biodiversity), inter-generational equity (retention of strategic adaptability/future options),

natural resources (quantity and quality of surface water and groundwater, wildlife habitat)

and local environment quality (morphological stability, landscape and open land,

recreation and amenity and enhancement of river environment).

Resilience is another essential characteristic of a sustainable urban system. It describes

the capability of an urban system to withstand and recover quickly from shocks such as

natural or man-made disasters. Godschalk (2003) describes a resilient city as one that

would be capable of withstanding severe shock without either immediate chaos or

permanent harm. Designed in advance to anticipate, weather, and recover from the


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impacts of natural or man-made hazards, resilient cities would be built on principles

derived from past experience with disasters in urban areas. While they might bend from

hazard forces, but would be flexible enough not to break. Such systems tend to be

redundant, diverse, efficient, autonomous, strong, interdependent, adaptable and

collaborative. Composed of networked social communities and lifeline systems, resilient

cities would become stronger by adapting and learning from disasters, and would be able

to mitigate the risks arising out of a wide range of hazards and from their own multiple

vulnerabilities owing to the creation of complex infrastructure systems and buildings to

telecommunications, transport, and energy and resource supply lines. One of the typical

examples for such a resilient city in the present times is that of Tulsa, located in the

Oklahoma state of the USA. Spurred to action by a long series of repetitive floods during

the 1970s and 1980s, Tulsa established a floodplain clearance effort, followed by a stable

program funding through a storm water utility fee, watershed-wide development

regulations, an aggressive public awareness program, master drainage plans supported

with a capital funding program, and floodplain recreation and creation of open space

areas. As a result, Tulsa has reduced losses from repeated flooding, enhanced quality of

life by expanding open space recreation areas, and created a better environment by

returning floodplains to wetlands and reclaiming wildlife habitat, thus becoming a

sustainable city (Godschalk, 2003).

Deliverables

1. Flood inundation map of the Chennai basin

2. Hydro-information system based on GIS data base, including water balance

3. Strategies for irrigation water management through scheduling, alternative

cropping pattern without affecting the environmental flow to the downstream

reaches of the basin

4. Identification of tanks and reservoir for rehabilitation

5. Flood management plans for the basin

6. Procedures for combined reservoir operation for water supply (industrial and

drinking water)


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7. Estimates of deficit in water availability, if any, and suggest alternative sources to

augment the supply (desalination etc.)

8. Identify and quantify all recharge and discharge components of Groundwater

covering the four major rivers crossing the Chennai city;

9. Calculate the average annual groundwater balance;

10. Prepare recommendation for sustainability of groundwater use for various

scenarios over the time horizon considered, accounting for the social, economic

and environmental dimensions.

sustprop water group 150509

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