Deckers, J

Descheemaeker, K

Haile, Mitiku

Muys, B

Nyssen, Jan

Poesen, J

Raes, D

Terryn, L

English

Ghent University Academic Bibliography

Geophysical Research Abstracts,Vol. 11, EGU2009-1626, 2009EGU General Assembly 2009© Author(s) 2008Water harvesting and sediment trapping in exclosures - A gully diversionexperiment in the Tigray Highlands, EthiopiaK. Descheemaeker (1,2), J Nyssen (3), J Poesen (1), D Raes (1), L Terryn (), M Haile (4), B Muys (1), and JDeckers (1)(1) Department of Earth and Environmental Sciences, K.U.Leuven, B – 3001 Heverlee, Belgium, (2) International WaterManagement Institute / International Livestock Research Institute, Addis Ababa, Ethiopia, (3) Department of Geography,Ghent University, B – 9000 Gent, Belgium, (4) Department of Land Resources Management and Environmental Protection,Mekelle University, Mekelle, EthiopiaDue to rapid vegetation restoration, exclosures (i.e. areas protected from grazing) are an effective and efficientmeasure for soil and water conservation. As a result, exclosures have become a widespread measure to combatthe severe soil erosion and to rehabilitate the degraded land in the Tigray highlands of northern Ethiopia. Giventhe high infiltration rates and sediment trapping capacity of exclosures, this study investigates to what extent thesecharacteristics can be optimized through the diversion of runoff water from an eroding gully into a well-restoredexclosure.A representative exclosure of 20 years old was selected for the gully diversion experiment. The exclosure waslocated on a steep limestone escarpment and was cut by a strongly eroding gully. The runoff from the gully wasdiverted into the exclosure by three diversion structures and canals, which led the runoff about 50 – 100 m into theexclosure and allowed it to infiltrate gradually. At the bottom of the exclosure, a cut-off drain served to evacuatethe excess water back into the gully. The aim of the experimental set-up was (1) to supply additional water to therestoring vegetation in the exclosure so as to increase biomass production, (2) to decrease sediment and runoffoutput from the catchment, (3) to decrease gully erosion rates. The experiment was evaluated using a sedimentbudget and a water balance.The sediment budget of the gully diversion system was drawn up based on records of the sediment load in therunoff water of the gully and measurements of the volumes of sediment deposited in the exclosure. The waterbalance of the exclosure system was developed based on measurements of the additional runoff input at thethree inlet canals and of the outflow of excess runoff water in the cut-off drain. Runoff discharge measurementswere made using v-notches in the canals. Weekly soil water content measurements allowed for calibration andvalidation of the BUDGET soil water balance model. This model was then used to determine the contribution ofthe additional water input to groundwater recharge and to biomass production for different rainfall scenarios.The gully diversion experiment indicated that sediment deposition rates of 60 Mg ha-1 y-1 can be easily achievedin well-restored exclosures. Infiltration of runoff water from gullies in exclosures resulted in water harvesting,as 1100 mm extra water can infiltrate in normal rainfall years. This had important beneficial effects for theexclosure as fertile sediment was trapped and extra water infiltration resulted in water stress alleviation, increasedtranspiration and therefore a far higher biomass production. The gully diversion also resulted in a huge increasein deep percolation of water (up to 850 mm of water) and thus recharge of the groundwater, which is expected toresult in spring formation downstream. Finally, the trapping of runoff and sediment from the gully in the exclosuredecreased runoff and sediment discharges downstream of the exclosure, which resulted in smaller runoff erosivityand hence smaller sediment yield from the gully.

Water harvesting and sediment trapping in exclosures: a gully diversion experiment in the Tigray Highlands, Ethiopia

https://biblio.ugent.be/publication/849127/file/857684

Water harvesting and sediment trapping in exclosures: a gully diversion experiment in the Tigray Highlands, Ethiopia

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