ESTIMATION OF SPATIAL DISTRIBUTION OF GROUNDWATER RECHARGE AND CROPWATER REQUIREMENT OF POTATO IN HOLETTA WATERSHED, UPPER AWASH RIVER BASIN, ETHIOPIA

Abstract

Sustainable groundwater management requires knowledge of recharge. Recharge is also an important parameter in groundwater flow and transport models. Spatial variation in recharge due to distributed land-use, soil texture, topography, groundwater level, and hydrometeorological conditions should be accounted for in recharge estimation. Estimation of temporal and spatial distribution of recharge is a key factor for a long-term water resource planning. Therefore, this study strives to estimate spatial ground water recharge and crop water requirement of potato in holetta watershed, upper Awash River basin, Ethiopia. In this study the long term seasonal and annual groundwater recharge of Holetta Watershed (415.7 km2) was estimated and recharge map were developed through a grid based physically distributed model, WetSpass. Long term average hydro-meteorological data and spatial pattern of watershed physical grid maps were used as main inputs for the model. All input maps for the model were prepared using ArcGIS 10.4 spatial analysis tool. Soil, land use and runoff coefficient parameters in dbase files, season independent gridded base map of topography, slope, and soil were used in the model. Also, precipitation, potential evapotranspiration, temperature, wind speed, groundwater depth and land use map were prepared and employed by the model, in ASCII grid format for both winter and summer seasons. From the result, it is found that the long-term temporal and spatial average annual rainfall of 1,035mm was distributed as: surface runoff of 157 mm (15.1%), evapotranspiration of 770 mm (74.3%), and recharge of 109.45 mm (10.6%). Thus, an average of 45.5Mm3 of groundwater recharged per year was estimated from the total watershed area. Reference evapotranspiration, effective rainfall, crop pattern data, and soil data are required to run the CROPWAT model. After all, data is analyzed the crop water requirement of potato (Solamum tuberosum L.) was calculated. The crop water requirement and irrigation requirement of potato crop was vary from month to month in this watershed. The monthly crop water requirements are 42.3, 94.8, 170.3, 141.8 and 33.8mm for Jan, Feb, Mar, Apr and May respectively. The monthly irrigation requirements are 42.3, 94.7, 161.8, 127.2 and 25mm for Jan, Feb, Mar, Apr and May respectively. The total crop water requirements and irrigation requirements are 483 mm/crop season and 451 mm/season respectively. Therefore, the volume surface water recharges in this watershed was satisfactory for irrigation requirements of potato crop in this watershed.