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Open AccessArticle

Hydrological Foundation as a Basis for a Holistic Environmental Flow Assessment of Tropical Highland Rivers in Ethiopia

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Amhara Design and Supervision Works Enterprise, Bahir Dar, P.O. Box 1921, Ethiopia
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Faculty of Civil and Water Resources Engineering, Bahir Dar Institute of Technology, Bahir Dar University, Bahir Dar, P.O. Box 26, Ethiopia
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School of Fisheries and Wildlife, Department of Aquatic and Wetland Management, Bahir Dar University, Bahir Dar, P.O. Box 26, Ethiopia
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Basin Information System Directorate, Abbay River Basin Authority, Bahir Dar, P.O. Box 1376, Ethiopia
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Department of Biological and Environmental Engineering, Cornell University, Ithaca, NY 14850, USA
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Laboratory for Applied Geology and Hydrogeology, Ghent University, Pietersnieuwstraat 33, 9000 Gent, Belgium
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Department of Water Resources and Ecosystems, IHE Delft Institute for Water Education, Westvest 7, 2611 AX Delft, Países Baixos, The Netherlands
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Faculty of Civil Engineering and Geosciences, Delft University of Technology, Mekelweg 5, 2628 CD Delft, Países Baixos, The Netherlands
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Author to whom correspondence should be addressed.
Water 2020, 12(2), 547; https://doi.org/10.3390/w12020547
Received: 16 December 2019 / Revised: 11 February 2020 / Accepted: 13 February 2020 / Published: 15 February 2020
(This article belongs to the Special Issue A Systems Approach of River and River Basin Restoration)
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. View Full-Text
Keywords: environmental flow component; Ethiopia; holistic environmental flow assessment; hydrological foundation; indicators of hydrologic alteration software; Lake Tana environmental flow component; Ethiopia; holistic environmental flow assessment; hydrological foundation; indicators of hydrologic alteration software; Lake Tana
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Abebe, W.B.; Tilahun, S.A.; Moges, M.M.; Wondie, A.; Derseh, M.G.; Nigatu, T.A.; Mhiret, D.A.; Steenhuis, T.S.; Camp, M.V.; Walraevens, K.; McClain, M.E. Hydrological Foundation as a Basis for a Holistic Environmental Flow Assessment of Tropical Highland Rivers in Ethiopia. Water 2020, 12, 547.

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