Clymans, Wim

Descheemaeker, Katrien

Desmedt, Florimond

Gebreyohannes, Tesfamichael

Haile, Mitiku

Haregeweyn, Nigussie

Martens, Kristine

Moeyersons, Jan

Nyssen, Jan

Poesen, Jean

Van Camp, Marc

Vandecasteele, Ine

Walraevens, Kristine

Zenebe, Amanuel

English

Ghent University Academic Bibliography

121  23. Hydro(geo)logy and impact of soil and water conservation measures on the hydrological response in May Zeg-zeg catchment (After Walraevens et al. (2009), Nyssen et al. (2010), Vandecasteele et al. (2011)) Tesfamichael Gebreyohannes1, Kristine Walraevens2, Ine Vandecasteele2,3, Wim Clymans4, Jan Moeyersons3, Katrien Descheemaeker5, Amanuel Zenebe6, Nigussie Haregeweyn6, Kristine Martens2, Marc Van Camp2, Jean Poesen4, Florimond Desmedt7, Jozef Deckers4, Mitiku Haile6, Jan Nyssen8 1 Department of Geology, Mekelle University, Ethiopia 2 Department of Geology and Soil Science, Ghent University, Belgium 3 Africamuseum, Tervuren, Belgium 4 Department of Earth and Environmental Sciences, K.U.Leuven, Belgium 5 CSIRO, Australia 6 Department of Land Resources Management and Environmental Protection, Mekelle University, Ethiopia 7 Department of Geology, V.U.Brussel, Belgium 8 Department of Geography, Ghent University, Belgium  As part of outreach accompanying research in the region around Hagere Selam, an integrated catchment programme was set up in 2004 in the 200-ha May Zeg-zeg catchment by researchers in cooperation with ADCS, a local NGO. Located at elevations between 2260 m a.s.l. and 2650 m a.s.l., the catchment stretches over the upper Antalo Limestone (Agula‘e shale is absent), the Amba Aradom sandstone and basalt. It has a sub-humid tropical mountain climate with high seasonality (Fig. 1). The main objectives were improvement of the livelihood of the communities in three adjacent villages as well as demonstrating and promoting global catchment management towards rural communities in the highlands of northern Ethiopia. This was done by the installation of a sustainable catchment management and a programme for capacity building and awareness raising regarding integrated catchment management. More specifically the project included the implementation of site-specific conservation techniques aimed at increasing water infiltration and conserving soil, i.e. the construction of dry masonry stone bunds on all land and check dams in gullies, the abandonment of post-harvest grazing, and the set aside of degraded rangelands, which results in exclosures.   Fig. 1.        Table 1 In prevision of the upcoming management programme, and in order to be able to investigate its impact, rainfall (Table 1), water table and spring monitoring were undertaken starting from 2001 122  and lasted till 2007. Intense investigations took place in the rainy season of 2006. The studies concerned the surface hydrology of the catchment, the hydrogeology, and the impact of catchment management on the hydro(geo)logy.  1. Hydrogeological studies  A geological map was produced through geophysical measurements and field observations, and a fracture zone identified in the north west of the catchment (Fig. 2). A perched water table was found within the Trap Basalt series above the laterized upper Amba Aradom Sandstones (Fig. 3). A map of this water table was compiled. Water-level variation during the measurement period was at least 4.5 m (Fig. 4). Variation in basal flow for the whole catchment was measured at the dam near the outlet in the rainy season of 2006 (Fig. 5 and 6) and varied between 12 and 276 m³/day. A groundwater flow model was produced using Visual MODFLOW using parameters for hydraulic conductivity (Table 2, Fig. 7), indicating the general direction of flow to be towards the south, and illustrating that the waterways have only a limited influence on groundwater flow (Fig. 9). The soil water budget was calculated for the period 1995– 2006, which showed the important influence of the distribution of rainfall in time (Fig. 8). Although Hagere Selam received some 724 mm of rainfall per year over this period, the strong seasonal variation in rainfall meant there was a water deficit for on average 10 months per year.  Fig. 2. 123   Fig. 3. Fig. 4.    Fig. 5. 124     Fig. 6.      Table 2. Fig. 7.   Fig. 8. Precipitation, calculated runoff and aquifer recharge (1995-2006) 125   Fig. 9.   2. Impact of catchment management Against this general background of catchment hydro(geo)logy, changes in the hydrological response of the catchment after catchment management in 2004 were investigated. Impact studies of catchment management in the developing world rarely include such detailed hydrological components. 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 (Fig. 5) 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 (Table 3). 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 (Fig. 10).  126   Table 3.   Fig. 10.  Monitoring of the ground water level indicated a rise after catchment management. The yearly rise in water table after the onset of the rains (ΔT) relative to the water surplus (WS) over the same period increased between 2002–2003 (ΔT/WS = 3.4) and 2006 (ΔT/WS >11.1) (Table 4). 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 (Fig. 11). Due to 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.  127   Table 4.      Fig. 11.  References Nyssen, J., Clymans, W., Descheemaeker, K., Poesen, J., Vandecasteele, I., Vanmaercke, M., Amanuel Zenebe, Van Camp, M., Mitiku Haile, Nigussie Haregeweyn, Moeyersons, J., Martens, K., Tesfamichael Gebreyohannes, Deckers, J., Walraevens, K., 2010. Impact of soil and water conservation on catchment hydrological response – a case in north Ethiopia. Hydrological Processes, 24(13): 1880-1895. Vandecasteele, I., Nyssen, J., Clymans, W., Moeyersons, J., Martens, K., Van Camp, M., Tesfamichael Gebreyohannes, Desmet, H., Deckers, J., Walraevens, K., Hydrogeology and groundwater flow in a basalt-capped Mesozoic sedimentary series of the Ethiopian highlands. Hydrogeology Journal, in press, online early view.  Walraevens, K., Vandecasteele, I., Martens, K., Nyssen, J., Moeyersons, J., Tesfamichael Gebreyohannes, De Smedt, F., Poesen, J., Deckers, J., Van Camp, M., 2009. Groundwater recharge and flow in a small mountain catchment in Northern Ethiopia. Hydrological Sciences Journal, 54: 739-753. 

Hydro(geo)logy and impact of soil and water conservation measures on the hydrological response in May Zeg-zeg catchment

https://biblio.ugent.be/publication/1149849/file/6747733.pdf

Hydro(geo)logy and impact of soil and water conservation measures on the hydrological response in May Zeg-zeg catchment

Abstract

Similar works

Full text

Available Versions

Ghent University Academic Bibliography