University of Twente Student Theses


Water balance modeling with swat for integrated water resources assessment in Raya valley (Tigray, Ethiopia)

Gebregziabher, Assefa (2010) Water balance modeling with swat for integrated water resources assessment in Raya valley (Tigray, Ethiopia).

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Abstract:The study focused on the water balance modelling of Raya Valley (Ethiopia). The modelling software package SWAT2005 with the Map Window interface was applied to the water balance modelling in the study area which is in the southern part of Tigray region, northern Ethiopia. Raya Valley lies at an altitude of about 1500 m between the lower Afar Depression in the east and the high mountain range in the west. Water availability in the study area is highly variable both in time and space and overexploitation can cause depletion of the water resources. The demand of the water resources for irrigation and domestic use is increasing. Therefore the need for a better understanding of hydrological processes has become critical. The hydrological and hydrometeorological data in the area are scarce and generally poor in quality. There are large data gaps. In this study, the SWAT daily weather generator algorithm used the monthly climate data for ten years (1996-2005) to generate the missing daily climatic data for the same period. The Map Window SWAT 2005 (MWS) interface has built-in GIS data processing capabilities such as required for watershed delineation, input map characterization and processing, stream and outlet definition, the computation of the different geomorphologic characteristics and characterization of land cover and soil. Surface runoff was modelled based on the SCS- curve number approach. The SWATCUP2 package was used for calibration and uncertainty analysis of the SWAT model parameters. Modelling of the area was carried out in two phases. An initial model simulation was made for the Golina catchment for the period from 1996 – 2005. This was followed by modelling of the Alamata catchment, just north of the Golina catchment, for the same period. It was necessary to first model the discharges of the Golina River, because no river gauge has ever been operational in the Alamata Basin. In the Golina River model two weather stations – with precipitation and temperature data - were used as a source for the weather generator package. Calibration of the Golina River proved to be difficult because of the poor quality of the discharge data. It was only possible to construct an approximate monthly runoff curve after correcting for outliers and systematic errors. The calibration with SWAT-CUP therefore has to be considered strictly indicative. The conceptual model was then applied to the neighbouring Alamata Basin, using the same parameter values as determined for the Golina Basin. The results of the conceptual SWAT model correspond with those reported previously. The indicative water balance is also in good agreement with groundwater studies of the area. The daily runoff curves show very fast daily and possibly sub-daily runoff after heavy rains, suggesting a reason why hydrometric analysis of these catchments has proved to be difficult.
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Programme:Geoinformation Science and Earth Observation MSc (75014)
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