using usbr and fao methods for sediment loads estimating in karkheh hydro-electrical dam

(Manuscript No: I12528-07)

April 18, 2012 / Accepted: April 24, 2012

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Using USBR and FAO methods for Sediment

Loads Estimating in Karkheh hydro-electrical

dam

Hashem Makenanizadeh,*

Islamic Azad University Susangerd Branch

Susangerd, Iran.

Sadegh Torfi

Department of Mechanical Engineering,

Islamic Azad University Susangerd Branch, Susangerd, Iran

Phone: (+98) 916 941 7762; fax: (+98) 612 4222324;

(Email: [email protected])

Abstract - Sediment loads and sediment formation in the rivers constitute as the major challenge in hydraulic

engineering and poses a great difficulty in the operation and maintenance of the structures constructed

downstream. Karkheh water basin is one of the areas which generate a vast volume of the loads which influence

the hydraulic behavior along the rivers and culminate in sediment formation behind the greater hydro-electrical

dam in Iran. The aim of the paper is to estimate the sediment load transport in the river upstream of the dam

using observational data from four hydrometric stations of Gamasiab, Qaresooh, Kashkaan and Seymareh using

USBR and FAO methods for a period of 29 years.

Results showed that the estimated annual suspended sediment loads by the USBR and FAO methods to be 4.7

and 7.8 million tons. Assuming an appropriate ratio of the bed load to suspended load in each of the four

stations the total annual transported sediment loads by the USBR and FAO to be 5.6 and 9.31 million tons

respectively. The comparison of the results of these two methods with the real time data observed by the

hydrometric station during 2005 estimating the total loads of 12 million tons suggests a close proximity between

the FAO showings and the real data.

Keywords: sedimentation, hydrometric stations, Karkheh hydro-electric reservoir, USBR, FAO.

Introduction

Ever increasing population and improved economic condition of a vast number of people in the developed and

developing world has boosted demands for good quality of freshwater for their food and fiber on one hand and

meeting the industrial, municipal and environmental needs on the other. This has reportedly posed a challenge

for the water users at the demand side and the water agencies and related stakeholders on the other. Permanent

rivers like the Karkheh are the major sources of water supply for the fiercely-competing stakeholders whose

livelihood depends very much on a guaranteed water supply by the river. Reliable and flexible water supply in

turn depend on systematic management of these vital renewable resources which has to consider the

anthropogenic interventions in the hydraulic behavior of the rivers and the natural phenomena like flooding,

sediment transport and draughts These factors, as Makenanizadeh [1] has observed, have considerably affected

the sustainability of the water supply regime in arid and semi-arid regions of Iran. It is observed that soil

erosion-related factors caused by water run-offs due to poor watershed management has been instrumental in

gully and sheet erosion that result in a considerable transport of the sediment loads along the rivers that

ultimately end up behind the reservoir dams such as the Dez, Karkheh and Karoon in Iran [2, 3]. This

phenomenon has not only led to gradual sediment formation along certain parts of the rivers concerned but has

resulted in the fundamental change in their morphology and hydraulic Behaviors that research [2, 4] showed to

have emerged as the major challenges by affecting abstraction at water intake structures, erosion of river banks,

sediment load entering canal networks and posing great difficulties in the O&M of irrigation and drainage

networks.

International Journal Of Structronics & Mechatronics

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Estimation of the sediment loads entry in the reservoirs of these vital hydraulic structures is one of the important

Technical considerations in hydraulic engineering which, as a matter of fact, is emerging as a major

consideration in the Karkheh which is designed to command the largest irrigation and drainage scheme in the

Middle East totaling 300,000 ha. This makes it as a vital water supply source for the strategically-located

croplands west of Greater Dezful region in the Khuzestan province of Iran. The preconditions for such

objectives is a thorough investigation and estimation of the sediment phenomenon in order to be able to institute

a sound management system to ensure the sustainability of the infrastructures on one hand and the continuity of

water supply regime on the other. The aim of the paper is to estimate the contribution of sediment load transport

by each of the four river branches constituting the great Karkheh River based on the USBR and FAO methods

and their comparison with the hydrometric data of the Karkheh reservoir.

MATERIALS AND METHOD

A. INTRODUCING THE STUDY AREA

The Karkheh water basin is located in the mid-western part of the Zagros mountain ranges comprising an area of

about 507650 km2. Because of its rugged mountains and poor vegetation cover on its slopes there are numerous

cases of gully and sheet erosions that culminate in the transport of a considerable volume of top soils by run-offs

flows particularly during rainy season [5]. There are 39 hydrometric stations upstream of the Karkheh reservoir,

the data from four of which including Gamasiab, Qeresooh, Kashkaan and Seymareh are used. The geographical

location of the river basin is shown in figure1.

Figure 1 : Geographical location of the original river branches of Karkheh

B. WORK PROCEDURE

Because of the importance of sediment formation and transport along the rivers and their effects on irrigation

and drainage networks of arid and semi-arid regions various methods of estimating these loads are presented [6].

The Most common ones are the experimental equations for transported loads and statistical regressions. The

limiting factors of these equations are their need for a wide variety of data, on geometry of the river, its

hydraulic characteristics, non-conformity with the conditions and features of the river, non-incorporation of

variation in flow, sediments and timing [11]. In the statistical regression methods the measured quantities are

simultaneously expressed in the form of power curve flow discharge (USBR method) which is known in the

Hashem Makenanizadeh, Sadegh Torfi

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literature as the suspended load curve. The sediment materials transport in this curve is merely rotated to one

variable as flow discharge. While other various other. Parameters like the natural characteristics of the basin

parameters including the sediment generation and formation during the rainfall are the influencing factors. For

these reasons there are a wide discrepancies between this relation and the measured data on suspended

sediments in such a manner which this discrepancy for a given discharge flow the suspended load varies

between 100 and 1000. Because of the lower number of observed sediment data during flooding seasons, the

frequency of data collection and their greater volume during low-discharge periods influences the power

equations. This is despite the fact that the bulk of the sediments are transported along the river where the

hydrometric stations could have otherwise recorded the loads. For this reason experts overwhelmingly agree that

the estimated sediment loads by the power equation is considerably less than the real-time data. This is based on

the fact that the annual suspended loads calculated by the power equation (USBR method) at the Talezang

hydrometric station is amounted to 7.6 million m3 whereas Makvandi et al [2006] has reported this to be 17

million m3 at the Karkheh reservoir hydrographic station. Various methods for modifying the sediment loads by

the power equation are available the most common of which are the use multi-curve power equations for each

station , the modified method of the FAO [5] , the artificial neural network[8, 9] and the fuzzy logic method [6].

Given the above-mentioned factors involved in this research, statistical regression and modified FAO methods

are used. The power equation in regression or USBR is expressed as follows:

1.

Where, Qs suspended load in tones/day and flow discharge in m3/sec and a & b are the constant quantities.

The coefficient a is proportional with inverse average discharge, average air temperature and topographic

feature of the water basin. The power b has a greater relation with average air temperature and the shape of the

basin [7].

2.

3.

Due to logarithmic nature of regression relation as well as the various measured data .The statistical data of the

periods 1971-1972 to 1999-2000 because of their comprehensiveness and their relatively long period were used

in this study. The stages by which the research was carried out to estimate the transported load are as follows:

i. Extraction of the suspended load curve from the hydraulic station of each of the river branch using the

measured data on flow discharge and suspended load by USBR and FAO methods.

ii. Drawing the flow continuity using the discharge flows in appropriate time periods.

iii. Classification of the probable flow and estimation of the discharge flows in average probable class.

iv. Estimation of transported suspended load from the station using the discharge flow gained from

previous period by USBR and FAO methods.

v. Estimating volume of the suspended load in m3/year.

vi. Adding the sediment loads from the river bed on the above calculation

vii. Comparison of the results of the FAO and USBR methods.


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RESULTS AND DISCUSSION

Results (tables 1 and 2) indicate the relation between the flow discharge and suspended sediment flow in most

stations has been accurately drawn.

TABLE1 Suspended load curves of the four tributaries by USBR method

TABLE2 Suspended load curves for the upper Karkheh tributaries by the FAO method

Figure 2 Suspended load curve river Ghareso in station Gharbaghestan


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Figure 3 Suspended load curve river Kashkan in station pool kashkan

Figure 4 suspended load curve river Gamasiyab in station Pool chehr

Figure 5 suspended load curve river Seymare in station Haliyan


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TABLE3 Suspended load transport for each Karkheh River Tributary by USBA and FAO methods

Table 3 indicate the estimation of transported suspended load from the station using the by USBR and FAO

methods. Results indicated the ration of the suspended load to bed load in the Qarbaghestan, Polekashkan,

Polechehr and Hollian based on Maddock [12] to be 20%, 20%, 15% and 15% respectively.

TABLE4 Total sedimentations estimation by USBR and FAO methods

The major criteria for the reliability and validity of data in the watershed area are the real-time annual

observational data from the hydrographic stations downstream of the dam. The method selected in this research

was based on the comparison of the observational data with the USBR and FAO methods. The hydrographic

results of the Karkheh reservoir dam with the state before water storage suggests that about 12 million m3 of

sediments are settled annually [10]. This is relatively lower than the volume of sediments in similar dams of Dez

and Shahid Abaspoor in the same province which is observed to be 17 and 20 million tons/year respectively.

This is despite the Karkheh water basin being about twice as vast as the others while Karkheh having about

twice the capacity of the others and the average annual rainfall of the Dez and Karoon being 610 and 530 mm

respectively compared with 450 mm that is reported for the Karkheh water basin. As can be observed from the

figure 6, the rate of sediments is mainly accumulated within the vicinity of the dam structure and their volume is

decreased around the river delta which is about 70 km away from the dam.

Fig. 5 Longitudinal profile of the Karkheh Reservoir prior to water abstraction and hydrographic measurements (2005).

Conclusion

Comparison of the actual sediment loads within the study area with the two sets of data obtained from the USBR

and FAO methods suggest a close proximity between the real time data observed by the hydrometric station and

the FAO method than the USBR method. The overall conclusion being that the FAO method seem to be a

relatively more accurate one that the USBR and can therefore be used as an appropriate analytical tool to model

and simulate the sedimentation processes and estimation of their loads in the hydraulic engineering projects.


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using usbr and fao methods for sediment loads estimating in karkheh hydro-electrical dam

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