Evaluation of Groundwater Level Variations Under Surface Irrigated Scheme:

Abstract

The present study attempted to evaluate groundwater level variations under surface irrigated scheme of Wonji-Shoa Sugar Estate (WSSE), Upper Awash Valley of Ethiopia. The recent level of GWTD was measured at the field from May to July. Groundwater table depth measuring in 2018, using previous installed piezometer tubes and the infiltration rates of the soil in the study area is estimated using double ring infiltrometer and also the soil texture of the field was analyzed using hydrometer method. This study clearly showed that the GWTD at WSSE was extremely shallow. From the current studies the mean average GWTD of the study area ranged between 0.54 m and 0.62 m; thus, all plantation fields were classified to be shallow (waterlogged). From current soils result analyzed, shallow ground water table can be observed mostly in the field having clay soil which is southern part of the study area especially F-163 (Figure 3.1).Compared to local precipitation, irrigation water has a major impacts in groundwater recharging in the irrigated area. The monthly ground water table depth responses of the 8 piezometers, observed at different parts of the plantation field were recorded during the observation period and the GWTD varies from 0.1 m (F-133) and 1.85m depth (F-135). The irrigated fields F-50 and F-135 have relatively deep GWT depths; whereas the irrigated fields F-24, F-63, F- 207, F-66, F-101 and F-163 have relatively shallow GWT (Appendix table 8). GWTD during rainy season was increased by 5% from May to June and 8% from June to July. As a result, the major causes of groundwater levels came from the excess irrigation water especially absence of proper central drainage structures, an old earthen canals and over irrigation water without considering the infiltration capacity of the soil and soil texture. The measuring of GWTD with estimated soil infiltration rates area, indicated in the current study, is believed to provide a tool for water management and, hence, crucial for the decision making and actions taking processes. In most field, unfunctional piezometers have been abandoned, but, these piezometers would have substantial importance for groundwater levels study. Thus, protection and management of piezometers is highly recommended.