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Subject: search.filters.subject.Groundwater recharge

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    GIS BASED GROUNDWATER POTENTIAL MAPPING AND RECHARGE 1 ESTIMATION: A CASE STUDY IN MELKAODA WATERSHED RIFT VALLEY LAKES 2 BASIN, OROMIA, ETHIOPIA
    (Hawassa University, 2021-10-24) ADEM BUTA DEKEBO
    The groundwater potential zones of the Melkaoda Watershed were demarcated with the help of remote sensing and Geographic Information System (GIS) techniques. The parameters that were considered for identifying the groundwater potential zone like geology, slope, drainage density, geomorphic units, and lineament density were generated from satellite data and they were then integrated with weighted overlay in ArcGIS. Suitable ranks were assigned for each category of these parameters and weight factors were decided for them based on their capability to store groundwater using AHP approach and then the groundwater potential zones were classified into four categories as very low, low, high & very high. In addition, the groundwater recharge was estimated with the help of the WetSpass model using water balance approach. The parameters considered for this case generally included three types: hydro-meteorological (rainfall, temperature, wind speed, PET, and GWD), bio-physical (soil, landuse, topography, and slope), and attribute lookup (soil lookup, landuse lookup, and rain day lookup) tables. All the hydro-meteorological parameters were interpolated in ArcGIS for grid map preparation of each parameter and the prepared grid map was converted to ASCII file format for the effective model run. The model performance was checked through calibration and the obtained groundwater recharge result ranges 0.45 to 65.5 mm/year with the mean value of 32.87 mm/years and 3.4% contributed to groundwater as recharge. finally, the changes in groundwater recharge between two simulation period was stated again with help of WetSpass model using the LULC images of 1989 and 2018 to quantify the impacts of the LULCC. The parameters used for this analysis were the same as those used for groundwater recharge estimation except for the satellite image of 1989 and the LULCC analysis depicted that there was the expansion of built-up land and agricultural land. Agricultural land and built-up land were increased by 0.046, 2.56 rate per a year from 1989 to 2018 respectively. This paper finalized that there was access to the groundwater potential in the Melkaoda Watershed and this could overcome the water scarcity challenging the community in and around the area. The recharge which has been the main source of groundwater is decreasing from time to time as the result of this paper is indicating. Thus, to get sustainable groundwater potential, the recharge has to be well treated by increasing groundwater recharge
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    GROUNDWATER IRRIGATION POTENTIAL ASSESSMENT OF THE LAKE HARAMAYA WATERSHED, OROMIYA, EASTERN ETHIOPIA
    (Hawassa University, 2021-10-20) ASHENAFI BERHANU TEFERI
    There is growing concerned about food security in Africa and especially in sub-Saharan Africa, Ethiopia. Even in good years, Ethiopia cannot meet its large food-deficit through rain fed production. Irrigation in Ethiopia is considered a basic strategy to alleviate poverty and hence food security. Most of the traditional irrigated lands in Ethiopia are dominantly supplied by surface water sources; while groundwater is smaller, this means that there is significant potential to increase irrigation sources from the groundwater. This paper focuses on further developing groundwater irrigation potential in the Lake Haramaya watershed. The concept of the approach is to identify the irrigation potential of the groundwater by comparing monthly and annual groundwater availability and crop irrigation requirements after satisfying the human and environmental groundwater needs. A GIS-based MCE technique was used to identify potential land suitable for surface irrigation using groundwater. Key factors that significantly affect irrigation suitability evaluated in this study include the slope, land use, soil depth, soil texture, soil drainage, and road proximity and town proximity factors. The suitability of individual factors was analyzed separately and assigning the weight to each factor then overlaid using the weighted overlay tool in Arc GIS to get the overall suitability based on the criteria set by FAO for surface irrigation using groundwater. The available groundwater potential for irrigation was quantified by allocating some fraction of groundwater recharge that is in excess after satisfying other human needs and environmental requirements. The groundwater recharge was estimated using spatially distributed physical based models called WetSpass. WetSpass-M model has been simulated the monthly and annual water balance components of Lake Haramaya watershed successfully. The key components WetSpass-M model analyzing include rainfall, groundwater depth, wind, temperature, PET, land use, soil, slope, topography, soil look up table, and land use lookup table data. The human water demand was estimated by multiplying the total projected population of three towns (Harar, Haramaya, and Bate) with 20l per capita per day. Due to the high uncertainty of groundwater environmental needs, three scenarios, leaving 30, 50, and 70 % of recharge for the environment, were implemented. And finally, crop irrigation water requirements were computed using the CROPWAT model. The key components of the CROPWAT model input include climate data, crop data, and soil data. The irrigation potential of the groundwater was identified by comparing groundwater availability and crop irrigation demand after satisfying the human and environmental groundwater needs. The result of the suitability analysis revealed that around 56.33% (7031ha) of the total watershed area (12,481.3 ha) was in the range of high to marginally suitable for surface irrigation development using groundwater. Results of the analysis show that average annual renewable groundwater availability for irrigation ranges from 174165268.8 to 321036480m3depending on the scenario. The CROPWAT8.0 model result revealed that crop irrigation requirements vary due to climatic station and type of major crops selected. The total crop irrigation requirements irrigable with groundwater ranges from 15531349.6 to 2274841.40 m3/year over the watershed. By comparing monthly groundwater available in m3/s at all scenarios with monthly crop gross irrigation demand in m3/s, the obtained total irrigation potential of the study area was 12,012.57ha. To conclude, this indicates that there is significant potential to increase irrigation sources from the groundwate
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    Estimation of Groundwater Recharge Using GIS Based Wetspass-M Model: The Case of Dedaba Watershed, Rift Valley Lakes Basin, Ethiopia
    (Hawassa University, 2024-10-18) JIBRIL WAKEYO WARIO
    The Dedaba watershed, located within the Rift Valley Lakes Basin in Oromia, Ethiopia, is experiencing significant changes driven by agricultural expansion, land use and land cover (LULC) changes, and a growing population. These dynamics, combined with insufficient watershed management, have resulted in water resource depletion, pollution, and environmental degradation. The escalating demand for groundwater, driven by the population increase, present a considerable challenge in this region. This study utilized the WetSpass-M (Water and Energy Transfer between Soil, Plants, and Atmosphere under quasi Steady State – Monthly) model, a spatially-distributed water balance model, to assess seasonal and annual groundwater recharge, actual evapotranspiration, and surface runoff in the Dedaba watershed. The model integrates spatially distributed data on precipitation, potential evapotranspiration, temperature, wind speed, soil types, LULC, and topography. These datasets, processed using GIS techniques, allowed for the generation of detailed spatial water balance components. Calibration and validation of the model were conducted using observed groundwater levels and streamflow data, ensuring accurate simulations. The calibrated WetSpass-M model revealed groundwater recharge estimates ranging from 0.46 to 65.4 mm/year, with an average of 37.47 mm/year, representing 3.4% of the total recharge. To understand the impacts of LULC changes on groundwater recharge, the model was applied using LULC data from 1990 and 2020. Results indicated a continuous decline in recharge rates over this period, underscoring the significant influence of LULC on groundwater resources. Specifically, the model estimated recharge at 3.29 mm in January 1990, peaking at 6.03 mm in September, and dropping to 0.13 mm in December. By 2005, these values had decreased, with January at 2.84 mm, September at 5.2 mm, and December at 0.12 mm. The downward trend persisted into 2020, with recharge starting at 2.61 mm in January, peaking at 4.52 mm in September, and reaching 0.12 mm in December. The study highlights the critical need to consider temporal variability and long-term trends in groundwater recharge for sustainable water management in the Dedaba watershed. The analysis of LULC changes shows a rapid urban expansion, reduction of forests and grasslands, and consequent threats to groundwater recharge. Mitigating these risks requires collaborative efforts, including promoting afforestation, water-conserving urban farming, sustainable agricultural practices, and artificial recharge techniques. Future research should incorporate climate change projections to enhance groundwater recharge predictions and improve water resource management strategies.