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Egerton University (2021)

Modelling Surface Water Flows for Ungauged Sites within the Upper Mara River Catchment using Geomorphologic Characteristics

Kinyanjui, Samuel Muhoro

Titre : Modelling Surface Water Flows for Ungauged Sites within the Upper Mara River Catchment using Geomorphologic Characteristics

Auteur : Kinyanjui, Samuel Muhoro

Université de soutenance : Egerton University

Grade : Master of Science Degree in Agricultural Engineering 2021

Résumé
Remote sensing and GIS techniques allows the use of advanced catchment-scale hydrological models for addressing challenges of the scarce water resource. Scarcity of gauged data is a major constraint therefore, alternative techniques such as geomorphological characterization can provide insight on catchment hydrological characteristics. The objective of this study was to evaluate spatial distribution of surface water flows using geomorphological derived model parameters in the Upper Mara River Catchment. A semi-distributed ArcGIS based SWAT was calibrated and validated, based on gauged data, using Sequential Uncertainty Fitting Index algorithm on SWAT-Calibration and Uncertainty Program. The performance of the model was evaluated and reported. The catchment morphometry was derived from Digital Elevation Model in ArcMap using Spatial Analyst tool. The morphometry in nexus with mathematical map equations were used to derive geomorphological characteristics such as bifurcation ratio, rho coefficient, drainage density, infiltration number, form factor among others. Using formulated regressions SWAT model parameters were estimated from catchment geomorphology. A geomorphological-based SWAT model was setup, its performance compared to the generic model, and used to carried out for spatial surface water flow analysis over the Amala River catchment. The study found that, Amala River catchment was predominately covered by rainfed croplands ( 64.7%) and Mollic Andosols soil ( 73.6%). CN2 was the most sensitive parameter (t-stat=33.82 & P-value=0). SWAT model performed satisfactorily ; NSE, R2 and RSR values for calibration (validation) are 0.80 (0.51), 0.81 (0.73) and 0.45 (0.45), respectively. The catchment exhibits a dendritic drainage pattern with an average bifurcation ratio of 4.26 which is closer to the upper bound value of 5. The surface runoff yield efficiency was low and non-uniform with an average drainage density of 1.07 km/km2. The geomorphological based model had NSE of 0.77 and R2 of 0.78 which was a satisfactory performance. The study concluded that generic calibration using observed data gave a better model but where such data is unreliable geomorphological characteristics can be used to estimate model parameters and give a satisfactory model. The spatial flow analysis showed that surface water flows are the overall predominant component with an average of 372.3 mm annually and sub basins outlets derived are potential sites for water harvesting. Thus, the outcomes provide a baseline for informed siting of water pans, dams and other water harvesting structures

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Page publiée le 14 mai 2022