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Subject: search.filters.subject.WetSpass model

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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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    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.