Ground Water- Surface Water Interaction and Impact Assessment, In the Case 0f Western Ziway-Meki River Catchment
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Date
2021-07
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Addis Ababa University
Abstract
As the combined pumping rate of the water supply and irrigation of the towns and rural areas ,were the cause of the depletion of groundwater resources in the groundwater basin and the drying up of stream water. The goal of this research was to enhance the current understanding of the interaction of surface water-ground water and impact assessment using a numerical model. Initially, to measure the natural recharge of the aquifer and to model streamflow, the surface water hydrology of the sub basin was researched using the HEC-HMS (SMA)model. The ground flow mechanism was analyzed by using 3D numerical groundwater flow model (Processing Modflow Pro (Version 5.3.0.1)). The required model inputs were obtained from the results of field observation, secondary data and previous work carried out in the area. As calibration parameters, horizontal hydraulic conductivity from 0.1 m/day to 15 m/day and ground water recharge 64.6 mm/year, which constitute the main groundwater model parameters, were considered. The HEC-HMS(SMA) model was used to measure the recharge rate for the sub-basin in order to achieve a recharge. Model calibration was subsequently carried out using the process of trial-and-error calibration using groundwater contours formed from heads collected at 56 observation points. Therefore, the average RMSE for simulated hydraulic heads was approximately 20.65m. The calibrated model is used to assess the groundwater-surface water interactions, and groundwater system activity under various potential use scenarios. Simulated water levels in the model were more sensitive to decreases in recharge values and sensitive to decreases in hydraulic conductivity values. However, relative to recharge and hydraulic conductivity, the model is not as sensitive to decreases or increases in pumpage. According to the simulation, groundwater flows from the western escarpment to the east eventually join Lake Ziway. Lakes and rivers are significant sources of aquifer recharge. Increased pumping rate results substantial regional groundwater level decline, which leads to the drying of springs and shallow hand dug wells, according to simulations conducted under various potential future use scenarios. Finally, the model's water budget results showed that groundwater recharge comprised 81.48%, through river leakage 3.28 % and constant head was 15.24% of the total water input for the entire study region. Because of this, it can be noted that the surface water impacts to the water budget of the sub-basin.
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Keywords
Meki River, SMA, Hec-Hms, Modflow, Hec-GeoHms, Surface Water-Ground Water Interaction