Runoff Estimation and Water Management for Holetta River, Awash subbasin, Ethiopia

Mahtsente Tibebe1, Birhanu Zemadim2, Dereje Haile3 and Assefa Melesse41 Ethiopian Institute of Water Resources, Addis Ababa University, Ethiopia, 2 International Water Management Institute (IWMI), Ethiopia, 3 Institute of

Technology, Addis Ababa University, Ethiopia, 4 Florida International University, USA

IntroductionEthiopia endowed with a huge surface and ground water resources. Many perennial and annual rivers exist in the country.

Ethiopia has 12 river basins and Awash basin is one of the 12 basins in Ethiopia. Holetta River is one of the rivers found in theupper part of Awash basin and facing challenges of runoff variability and scarcity of water availability during the dry season.

Holetta River is main source of surface water in the study area, it is a perennial river having three major users, and theseare Holetta Agricultural Research Center (HARC), Tesdey Farm, and Village Farmers.

In addition to increasing water demand in the area, there is no facility to store the water in the rainy season for future usein the dry season. Therefore, the competition for water is increasing due to scarcity of water and increasing pressure byexpanding populations and increasing irrigation. In order to alleviate this challenge, integrated water resourcesmanagement, and effective water allocation system is essential.

Therefore, the aim of this research was to study the hydrology of the Holetta River and to assess the water management inthe catchment using GIS tool, statistical methods and hydrological model.

ObjectivesGeneral Objective is to study the hydrology of the Holetta River and to assess the water management in the catchment.The Specific objectives are,

To model rainfall-runoff relationship process of the catchment,To investigate the seasonal variability of runoff and water availability in the catchment,To study the water demand in the catchment, and to quantify the gap between the available river water and

demand in the catchment

MethodologyThe study conducted at Holetta catchment. The study area lies atan altitude of 2069 - 3378 meters above sea level and located ata latitude range of 8056'N to 9013'N and longitude range of38024'E to 38036' E.

Data collected Meteorological data (rainfall,

temperature, relative humidity, wind speed, and sunshine hour)

Flow data and GIS data (topographic, land use/cover data and map, soil map)

Primary data of crop type and area coverage

Based on the collected data,

Sensitivity analysis, model calibration, and validation for SWAT model performed. The most sensitive parametersidentified from sensitivity analysis and used for calibration of the model. For this study, the calibration carried outfor six years (1994 - 1999) with one-year warm up period. Then, validation of SWAT model performed for the nextfive years (2000 -2004). Statistical and graphical methods of comparing simulated with observed data used toevaluate the performance of SWAT model. The three statistical evaluation methods used were Coefficient ofDetermination [R2], the Nash-Sutcliffe Efficiency Coefficient [NSE] and Index of Volumetric Fit [IVF].

• to estimate runoff for unguaged catchmentsSWAT model

• to estimate the irrigation water demand in the areaCropWat model

• to investigate the major crops grown in the area, area coverage, and number of consumersSurvey analysis

Figure 1 - location of Holetta atchment

ResultsSWAT model analysis

Graphical performance evaluation

Figure 2 - Observed and simulated hydrograph after monthly calibration and monthly validation respectively

Statistical performance evaluation Water Demand analysis

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10.00

Ja…

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ream

Flow

(m3 /

s)

0.002.004.006.008.00

Jan-

2000

Oct

-…Ju

l-200

1Ap

r -…

Jan-

2003

Oct

-…Ju

l-200

4

Evaluation criteria

Calibration Validation

Daily Monthly Daily Monthly

R2 0.57 0.85 0.44 0.73

NSE 0.55 0.84 0.4 0.67

IVF 102.62 102.85 108.73 108.98

January February March April May

Flow (MCM) 0.749 0.419 0.829 0.623 0.471

Total Water demand (MCM)

0.313 0.583 1.004 0.873 0.341

Difference 0.436 -0.164 -0.175 -0.25 0.13

ConclusionsThe result showed, R2, NSE, and IVF were 0.85, 0.84 and 102.8 respectively for monthly calibration and 0.73, 0.67 and 108.9

respectively for monthly validation. Therefore, this indicated that SWAT model performed well for simulation of the hydrology ofthe catchment.

The overall water demand in the area was 0.313, 0.583, 1.004, 0.873, and 0.341 MCM for January, February, March, April, andMay respectively.

The available flow was 0.749, 0.419,0.829, 0.623 and 0.471 MCM for January, February, March, April, and May respectively.Comparing the available flow and water demand in each month, it showed a gap during February, March and April. Therefore,

there is shortage of supply during these months with a total of 0.59 MCM.In addition to shortage of water supply, the analysis of the questionnaire indicated that there is a conflict between users at

diversion points and during water allocation.

RecommendationsEven though the SWAT model performs well in the study area, the accuracy was highly dependent on quality of data. The

Holetta catchment has only one gauging station. In order to improve data quality, it is better to have at least two gauging stationin the catchment. In addition to this, in poorly gauged areas, use of satellite data is very advantageous. For future studies, SWATmodel can apply to estimate sediment yield in the area and to evaluate the effect of different catchment changes on the river.

The water demand analysis showed that there was shortage of river water supply during February, March, and April. Theanalysis also showed there is conflict between users. In order to solve water shortage, alternative source of water supply shouldbe studied and integrated water management system should be implemented.

AcknowledgementsAt first, I want to express my deepest thank for Holetta Research Center, Ministry of Water and Energy, and United StatesAgency for International Development (USAID) /HED for all their support. Next, my heartfelt thank goes to all my family andfriends for their encouragement and wonderful support.

This document is licensed for use under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 UnportedLicense July 2013

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