Catchment management in the developing world rarely include detailed hydrological components. Here, changes in the hydrological response of a 200-ha catchment management in north Ethiopia are investigated. The management included various soil and water conservation measures such as the construction of dry masonry stone bunds and check dams, the abandonment of post-harvest grazing and the establishment of woody vegetation. Measurements at the catchment outlet indicated a runoff depth of 5 mm or a runoff coefficient (RC) of 1.6 % in the rainy season of 2006. Combined with runoff measurements at plot scale, this allowed calculating the runoff Curve Number (CN) for various land uses and land management techniques. The pre-implementation runoff depth was then predicted using the CN values and a ponding adjustment factor, representing the abstraction of runoff induced by the 242 check dams in gullies. Using the 2006 rainfall depths, the runoff depth for the 2000 land management situation was predicted to be 26.5 mm (RC = 8 %), in line with current RCs of nearby catchments. Monitoring of the ground water level indicated a rise after catchment management. The yearly rise in water table after the onset of the rains (∆T) relative to the water surplus (WS) over the same period increased between 2002-2003 (∆T/WS = 3.4) and 2006 (∆T/WS >11.1). Emerging wells and irrigation are other indicators for improved water supply in the managed catchment. Cropped fields in the gullies indicate that farmers are less frightened for the destructive effects of flash floods. Due to an increased soil water content, the crop growing period is prolonged. It can be concluded that this catchment management has resulted in a higher infiltration rate and a reduction of direct runoff volume by 81 % which has had a positive influence on the catchment water balance.

Dar es Salaam Quaternary coastal aquifer is a major source of water supply in Dar es Salaam City used for domestic, agricultural, and industrial uses. However, groundwater overdraft and contamination are the major problems affecting the aquifer system. This study aims to define the principal hydrogeochemical processes controlling groundwater quality in the coastal strip of Dar es Salaam and to investigate whether the threats of seawater intrusion and pollution are influencing groundwater quality. Major cations and anions analysed in 134 groundwater samples reveal that groundwater is mainly affected by four factors: dissolution of calcite and dolomite, weathering of silicate minerals, seawater intrusion due to aquifer overexploitation, and nitrate pollution mainly caused by the use of pit latrines and septic tanks. High enrichment of Na+ and Cl- near the coast gives an indication of seawater intrusion into the aquifer as also supported from the Na-Cl signature on the Piper diagram. The boreholes close to the coast have much higher Na/Cl molar ratios than the boreholes located further inland. The dissolution of calcite and dolomite in recharge areas results in Ca-HCO3 and Ca-Mg-HCO3 groundwater types. Further along flow paths, Ca2+ and Na+ ion exchange causes groundwater evolution to Na-HCO3 type. From the PHREEQC simulation model, it appears that groundwater is undersaturated to slightly oversaturated with respect to the calcite and dolomite minerals. The results of this study provide important information required for the protection of the aquifer system

The sustainable development of water resources includes retaining some amount of the natural flow regime in water bodies to protect and maintain aquatic ecosystem health and the human livelihoods and wellbeing dependent upon them. Although assessment of environmental flows is now occurring globally, limited studies have been carried out in the Ethiopian highlands, especially studies to understand flow-ecological response relationships. This paper establishes a hydrological foundation of Gumara River from an ecological perspective. The data analysis followed three steps: first, determination of the current flow regime—flow indices and ecologically relevant flow regime; second, naturalization of the current flow regime—looking at how flow regime is changing; and, finally, an initial exploration of flow linkages with ecological processes. Flow data of Gumara River from 1973 to 2018 are used for the analysis. Monthly low flow occurred from December to June; the lowest being in March, with a median flow of 4.0 m3 s−1. Monthly high flow occurred from July to November; the highest being in August, with a median flow of 236 m3 s−1. 1-Day low flows decreased from 1.55 m3 s−1 in 1973 to 0.16 m3 s−1 in 2018, and 90-Day (seasonal) low flow decreased from 4.9 m3 s−1 in 1973 to 2.04 m3 s−1 in 2018. The Mann–Kendall trend test indicated that the decrease in low flow was significant for both durations at α = 0.05. A similar trend is indicated for both durations of high flow. The decrease in both low flows and high flows is attributed to the expansion of pump irrigation by 29 km2 and expansion of plantations, which resulted in an increase of NDVI from 0.25 in 2000 to 0.29 in 2019. In addition, an analysis of environmental flow components revealed that only four “large floods” appeared in the last 46 years; no “large flood” occurred after 1988. Lacking “large floods” which inundate floodplain wetlands has resulted in early disconnection of floodplain wetlands from the river and the lake; which has impacts on breeding and nursery habitat shrinkage for migratory fish species in Lake Tana. On the other hand, the extreme decrease in “low flow” components has impacts on predators, reducing their mobility and ability to access prey concentrated in smaller pools. These results serve as the hydrological foundation for continued studies in the Gumara catchment, with the eventual goal of quantifying environmental flow requirements.

The hydrodynamic behaviour of a sloped phreatic aquifer in the Tigray Highlands in northern Ethiopia is described. The aquifer is situated in the soils of a plateau on top of a basalt sequence and lies on steep slopes; the latter lead to hydraulic gradients that can cause high discharge fluxes. Distinct wet and dry seasons characterize the climate of the Tigray Highlands and recharge is absent during the dry season. Because of the fertile vertisols that have developed, the plateau is heavily cultivated and thus has great local economic, and hence social, importance. Water for land irrigation is almost exclusively delivered by rainfall, which is largely restricted to the period June-September. During the dry season, the water table drops dramatically and the aquifer drains nearly completely, under the strong gravity-driven, sustained discharges. This study strives to give insights into recharge and discharge mechanisms of the aquifer, in order to improve the effectiveness of the implemented water conservation measures.Key words groundwater recharge; integrated water balance; water management; runoff; soil moisture balance; MODFLOW; Ethiopia Recharge et écoulement hydrogéologiques dans un petit bassin versant de montagne en Ethiopie du nordRésumé L'article décrit le comportement hydrodynamique d'un aquifère phréatique incliné dans les Tigray Highlands en Ethiopie du nord. L'aquifère se situe dans les sols d'un plateau aux pentes raides, au sommet d'une séquence basaltique. L'escarpement cause des gradients hydrauliques conduisant à des écoulements importants. Les saisons humide et sèche bien différenciées caractérisent le climat des Tigray Highlands, et la recharge est nulle pendant la saison sèche. A cause des vertisols fertiles, le plateau est intensément cultivé et présente par conséquent une valeur locale économique et sociale importante. L'eau d'irrigation provient presque exclusivement de la pluie, qui est largement limitée à la période Juin-Septembre. Pendant la saison sèche, la nappe descend énormément, et l'aquifère est presque complètement drainé, en raison des flux gravitaires continus importants. Cette étude continue à la compréhension des mécanismes de recharge et d'écoulement de l'aquifère, dans le but d'améliorer l'efficacité des mesures implémentées de conservation de l'eau.

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Mendae Plain at Abraha Atsbaha (Tigray Region, northern Ethiopia) is an agricultural area, which has been very drought-prone in the past. In the last decade, agricultural development has boosted because of the intensive use of large diameter wells that tap the phreatic aquifer. Pumped water is used for irrigation during the long dry season (October to May). Since 15 years, water harvesting measures have been implemented, mainly in the form of infiltration ponds and trenches that enhance local infiltration of rainfall runoff from hillslopes. To investigate the sustainability of the groundwater exploitation and the efficiency of the measures, the different recharge and discharge components of the water balance of data-scarce Mendae Plain have been identified and quantified, using different methods. Diffuse aquifer recharge is calculated from a soil moisture balance, based on meteorological data, and with the chloride mass balance method, based on groundwater analyses. Diffuse recharge is much higher on cultivated land plots than on non-cultivated bare soils. Rainfall infiltration in ponds and trenches is estimated based on the inflow catchment derived from the topography. Groundwater flow to a nearby river is obtained by balancing inflow and outflow by the other components over an 11 year period. The balance components are integrated into a lumped parameter model that was run for the period from 2000 to 2010. The results show that infiltration in ponds and trenches contributes between 30 and nearly 50% of total aquifer recharge, with the highest values in dry years. Changes in aquifer storage over time are an indicator for the evolution of groundwater levels in the aquifer and confirm the occurrence of two dry periods in

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