Establishing irrigation potential of a hillside aquifer in the African highlands

Abstract

Feeding 9 billion people in 2050 will require sustainable development of all water resources, both surface and subsurface. Yet, little is known about the irrigation potential of hillside shallow aquifers in many highland settings in sub-Saharan Africa that are being considered for providing irrigation water during the dry monsoon phase for smallholder farmers. Information on the shallow groundwater being available in space and time on sloping lands might aid in increasing food production in the dry monsoon phase. Therefore, the research objective of this work is to estimate potential groundwater storage as a potential source of irrigation water for hillside aquifers where lateral subsurface flow is dominant. The research was carried out in the Robit Bata experimental watershed in the Lake Tana basin which is typical of many undulating watersheds in the Ethiopian highlands. Farmers have excavated more than 300 hand dug wells for irrigation. We used 42 of these wells to monitor water table fluctuation from April 16, 2014 to December 2015. Precipitation and runoff data were recorded for the same period. The temporal groundwater storage was estimated using two methods: one based on the water balance with rainfall as input and baseflow and evaporative losses leaving the watershed as outputs; the second based on the observed rise and fall of water levels in wells. We found that maximum groundwater storage was at the end of the rain phase in September after which it decreased linearly until the middle of December due to short groundwater retention times. In the remaining part of the dry season period, only wells located close to faults contained water. Thus, without additional water sources, sloping lands can only be used for significant irrigation inputs during the first 3 months out of the 8 months long dry season. K E Y W O R D SEthiopia, groundwater, highlands, irrigation, Lake Tana, water budget, water storage, water table fluctuation method

Experimental Evaluation for the Impacts of Conservation Agriculture with Drip Irrigation on Crop Coefficient and Soil Properties in the Sub-Humid Ethiopian Highlands

“…However, from the field observation during harvest, the maximum rooting depths for onion, garlic, cabbage, and pepper are less than 60 cm. On the other hand, the depth of groundwater level varies spatially and temporarily; in the dry season 4-15 m in Dangishta and 8-20 m in Robit was observed [52]. Gao et al [53] explained that the upward capillary rise is negligible when the groundwater depth is more than 2.5 m.…”

Hydrogeology of Volcanic Highlands Affects Prioritization of Land Management Practices

“…Performing the annual water budget with the data in Table 3 assuming that evapotranspiration between June and September is 416 mm [67], the excess rainfall that cannot be accounted for is 465 mm in 2015, 492 mm in 2016, and 547 mm in 2017. Some of the water which is unaccounted for would have evaporated during the dry phase, but according to observations in other watersheds within 100 km from the study area, this would constitute less than 200 mm a −1 [16,92]. Field evidence ( Figure 6a) suggests that the remainder of the unaccounted water flowed out of the watershed via the subsurface through the faults and lineaments.…”

“…The water levels in the piezometers in the Gomit watershed were nearly independent of rainfall once they reached their maximum levels ( Figure 7). In other watersheds like Debre Mawi, the water table fluctuated with the amount of rainfall [13,16,58]. In addition, Alemie et al [13] observed for a few hand-dug wells that the groundwater level remained constant during the wet phase.…”

“…Muñoz-Villers and McDonnell [9] in Mexico and Iwagami et al [10] in Japan reported that runoff was directly related to the percentage of highly permeable, strongly weathered, and fractured volcanic rocks. Another difference between volcanic derived andosols and sediments is that despite the large percentage of clay particles in andosols, volcanic experimental watershed studies in Ecuador [11,12], in Oregon's Cascade Range [8], in Ethiopia [13][14][15][16], and in Honduras [17] exhibited high hydraulic conductivities and water flows, mainly via the subsurface to the valley bottoms where they surface. Finally, unlike most low lying watersheds, subsurface transfer of flow from one surface basin to another has been reported in volcanic watersheds in the southern Rio Grande Valley, USA [18], the Andean basins in Chile [3,[19][20][21], a Costa Rican rainforest [22,23], and the Ethiopian Highlands [24,25].…”

Connecting hillslope and runoff generation processes in the Ethiopian Highlands: The Ene-Chilala watershed

“…In addition to surface runoff, interflow is a major component of the discharge at the watershed outlet in humid highlands (Gurtz et al, 2003;Jackson et al, 2014;Setegn et al, 2010;Whipkey, 1965). Interflow occurs when the soil at the hillside is above field capacity and a saturated layer develops above the hardpan (Alemie et al, 2019;Tilahun et al, 2014Tilahun et al, , 2019. The water table depth above the hardpan increases from the divide to the saturated area (Bayabil et al, 2010;Betson, 1964;Guzman et al, 2017a, b).…”