Predicting Shallow Groundwater Tables for Sloping Highland Aquifers

• Published in: Water resources research 2019-12, Vol.55 (12), p.11088-11100
• Main Authors: Alemie, Tilashwork C., Tilahun, Seifu A., Ochoa‐Tocachi, Boris F., Schmitter, Petra, Buytaert, Wouter, Parlange, J‐Yves, Steenhuis, Tammo S.
• Format: Article
• Language: English
• Subjects: Aquifer models; Aquifer recharge; Aquifers; Barriers; Developing countries; Dikes; Dry season; Dug wells; Embankments; Ethiopian highlands; Evaporation; Evaporation rate; Food; Food cans; Foods; Groundwater; groundwater hydrology; Groundwater levels; Groundwater recharge; Groundwater table; Highlands; Households; Hydrology; Irrigation; Irrigation water; LDCs; Livestock; Method of characteristics; modeling; Porosity; Potential evaporation; Rain; Rainfall; Rainy season; Rivers; Satellite imagery; Seasons; Soil; Soil porosity; Soil surfaces; Spaceborne remote sensing; Subsurface flow; Sustainable development; Travel; Travel time; vadose zone; Water resources; Water table; Watersheds; Wet season
• ISSN: 0043-1397; 1944-7973
• DOI: 10.1029/2019WR025050

While hydrological science has made great strides forward during the last 50 years with the advance of computing power and availability of satellite images, much is unknown about the sustainable development of water for irrigation, domestic use, and livestock consumption for millions of households in the developing world. Specifically, quantification of shallow underground water resources for irrigation in highland regions remains challenging. The objective is to better understand the hydrology of highland watersheds with sloping hillside aquifers. Therefore, we present a subsurface flow model for hillside aquifers with recharge that varied from day to day. Recharge to the aquifer was estimated by the Thornthwaite Mather procedure. A characteristic time was identified for travel time of water flowing from the upper part of the hillside to the river or well. Using the method of characteristics, we found that the height of shallow groundwater level can be predicted by determining the total recharge over the characteristic time divided by drainable porosity. We apply the model to farmer‐dug wells in the Ethiopian highlands using observed rainfall, potential evaporation, and a fitted travel time. We find that the model performs well with maximum water table heights being determined by the soil surface and minimum heights by the presence or absence of volcanic dikes downhill. Our application shows that unless the water is ponded behind a natural or artificial barrier, hillslope aquifers are unable to provide a continuous source of water during the long, dry season. This clearly limits any irrigation development in the highlands from shallow sloping groundwater. Plain Language Summary The population in the Ethiopian highlands, similar to other developing countries, is rapidly increasing. In order to have enough food during the year, most families grow their food crops during the rainy season. More food can be grown by irrigation during the dry season. We mathematically tested and observed data of eight wells as to whether shallow aquifers on the sloping lands can store sufficient water during the rainy season so it can be used for irrigation after the rains have stopped. We found that groundwater on sloping soils is only available during the whole year when volcanic‐derived subsurface barriers prevent flow downslope. Key Points A novel parsimonious model was developed for shallow hillslope groundwater tables Shallow groundwater depth in wells can be predicted fr