Impact of soil and water conservation measures on catchment hydrological response—a case in north Ethiopia

Abstract

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.

Rehabilitation of degraded dryland ecosystems – review

“…Moreover, the conversion of land fully covered by grasses to one covered by scattered bushes creates greater bare soil surfaces alongside 'fertility islands' around shrub canopy patches, which encourages increased runoff and reduce resources redistribution, resulting in higher soil erosion (Millennium Ecosystem Assessment 2005a; Field et al 2012). Hence complementing tree planting with physical soil conservation measures (terraces, bunds, and check dams) may reduce soil erosion more effectively (Nyssen et al 2010). As a whole, reforestation as dryland soil reclamation measures should be site specific and take into considerations, among others, site history, the type and degree of soil degradation, microclimatic conditions and broad socio-economic factors.…”

Targeting of intervention areas to reduce reservoir sedimentation in the Tana catchment (Kenya) using SWAT

“…Several studies have assessed actual sediment budgets at the catchment scale, stressing the importance of distributed approaches (e.g. Lenhart et al 2005, Haregeweyn et al 2013), but only a few studies on the regional impact of soil conservation measures have been made (Bellin et al 2009, Lesschen et al 2009, White and Arnold 2009, Nyssen et al 2010, Tuppad et al 2010.…”

Impact of conservation agriculture on catchment runoff and soil loss under changing climate conditions in May Zeg-zeg (Ethiopia)

“…Indeed, overland flow could not be produced through saturation, since water tables never reach the surface at the steeper slopes. Nyssen et al (2010) show that even in the lowest places of the catchment the water , their values can be adjusted for CA with the conversion parameter ε = 0.963 (Table 5). The effect of CA on runoff from cropland is more pronounced than the effect of other conservation measures, such as stone bunds, as for example CN of a PT farmland with 'zero' grazing and good stone bunds is 77.3 but CN of a CA farmland with 'zero' grazing and no stone bunds is 75.8.…”