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1. Application of SWAT in Natural Wetland Catchments. A Case of Rugezi Catchment in Rwanda , P.M. Ndomba, D. Magoma, F. W. Mtalo, and J. Nobert

   Abstract | Full Paper

   Hydrologic models are increasingly used to support decisions at various levels and guide water resources policy formulation, management and regulations. In this study the Soil and Water Assessment Tool (SWAT) was examined for its applicability in wetland catchment of Rugezi in Rwanda covering an area of, approximately to, 197 Km2. The study adopted SWAT model as recommended by others workers in the region in order to extend its testing. The application of SWAT model entailed setting up the model using readily available data, sensitivity analysis and calibration. In this study wetland model physical parameters such as width, depth, length, slope and area were generated by GIS based SWAT interface. The ground photos available from literature supplemented and validated the GIS data. An independent simulation was also conducted without implementing the wetlands in order to study its impacts on the hydrology. Sensitivity analysis indicated that Channel effective hydraulic conductivity (CH_K2), Surface runoff lag time (Surlag), SCS runoff curve number under moderate moisture condition (CN2), and Manning’s n value for main channel (Ch_n) are the most sensitive parameters. Comparable results between simulated and observed streamflows at the catchment outlet, Rusumo gauging station, were obtained. The Nash and Sutcliffe coefficient values (CE) and Index of Volumetric Fit (IVF) were 49.15% and 95.6% for calibration and 51.4% and 98.6% for validation periods, respectively, indicating a satisfactory simulation. It was evident from this study that the wetland was a major hydrological controlling feature in the basin and should be safeguarded. These results suggest that SWAT model is potentially useful in studying the hydrology of natural wetland catchments with limited data. Besides, the authors would like to recommend extensive testing of the model in other wetland catchments in the region.

   
   Key words :Hydrology, Modelling, Natural Wetland, Rugezi Catchment, SWAT

2. Aquifer Storage and Recovery and Surface Basins for a Greener Kilifi District, Caroline Onyancha, Alexander Khaemba and Bernadette Sabuni

   Abstract | Full Paper

   Kilifi District experiences 5-6 months of continuous dry weather and in some instances years of continuous dry periods. When the rains fall, they are short and intense causing ground erosion and siltation of surface water sources. Most of rainwater is discharged to the Indian Ocean through the numerous intermittent streams within the area. Currently, majority of the inhabitants of the district depend on food rations and perform no economic activities because of the harsh climatic conditions. The aims of this study were to investigate the suitability of the subsurface materials for storing the rainwater that is lost through run-off, to determine the methods that can deliver the water to the subsurface and to evaluate the expected performance of the storage structures. The process of conveying and storing water in the subsurface during times of abundance, and recovery of the stored water during times when it is needed is commonly referred to Aquifer Storage and Recovery (ASR). When executed well, ASR can recover and maintain groundwater levels thus making it available for domestic use and for agriculture. Several factors that control successful operation of ASR were analysed in a Geographical Information System (GIS) to pinpoint suitable areas. After pinpointing the sites, extensive fieldwork was carried out to compare the results of GIS analyses and the conditions on the ground. The results show that more than 50% of the pinpointed sites are hydrogeologically suitable for recharge. Storage zones comprise of a broad variety of aquifer lithologies at depths ranging from 10 to 100 m. The most notable characteristics of the subsurface are: the presence of salty formations; irregular aquifer system physical properties; sensitive and collapsing fine materials. There is also insufficient information on physical properties of some aquifers, ASR will need to commence in form of pilot projects. Once ASR projects are successful, crop production through irrigation and regeneration of indigenous trees will turn Kilifi District to a green environment.

   
   Key words :Kilifi District, Aquifer Storage and Recovery, Agriculture, Green Environment

3. Bed Form Types and Dimensions at El Ekhsas Gauge Station From Field Measurements, Mohamed Ali, Karima Attia, and Aly El Bahrawy

   Abstract | Full Paper

   The study of bed form formation in river beds is a complex process. The formation process results from the interaction between the sediment and flow characteristics. The bed forms are responsible for increasing bed roughness. In sediment transport, depending on the condition of the bed form, the fraction of the total shear stress that is responsible for bed load transport changes. Therefore, knowledge of bed form characteristics and geometries are very essential in alluvial system integrated management. In natural rivers, the bed form types and dimensions differ along the river cross section as the depth variation results in different hydraulic characteristics. This research represents the analysis of detailed field measurements at El Ekhsas gauge station in two different dates. Bed form types and dimensions were extracted, analyzed, and compared with the dimensions calculated from the most common bed form predictors. Also, the measured bed form dimensions were compared with the corresponding dimensions resulted from formulas developed for Nile River. It was concluded that some bed form predictors are valid and reliable for Nile River. Also the current research developed new relationships which help in predicting bed form dimensions in the Nile. The study recommends that the other gauge stations should be applied for such research to validate the developed relations.

   
   Key words :Bed form, River Nile, Field Measurements, Formulas, and El Ekhsas.

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