|STEENHUIS, TAMMO - Cornell University - New York|
|SCHNEIDERMANN, ELLIOTT - New York City Department Of Environmental Protection|
|GUZMAN, CHRISTIAN - Cornell University - New York|
|TEBEBU, TIGIST - Cornell University - New York|
|MOGES, MAMARU - Bahir Dar University|
|TILAHUN, SEIFU - Bahir Dar University|
Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 9/25/2015
Publication Date: 9/25/2015
Citation: Steenhuis, T.S., Schneidermann, E.M., Guzman, C.D., Tebebu, T.Y., Moges, M., Langendoen, E.J., Tilahun, S.A. 2015. Integrated watershed management for saturation excess generated runoff, erosion and nutrient control. In: Proc. 3rd International Conference on the Advancement of Science and Technology (ICAST-2015), May 8-9, 2015, Bahir Dar, Ethiopia. 8 pp.
Interpretive Summary: The governing hydrological processes have to be properly understood to effectively manage water resources and soil conservation measures across an eroding landscape. For example, soil erosion control practices in the (sub)humid Ethiopian Highlands, where excess-saturation generated runoff dominates, have been ineffective as they were developed for infiltration-excess generated runoff processes. Scientists from the USDA-ARS National Sedimentation Laboratory in collaboration with researchers at Bahir Dar University (Ethiopia), Cornell University, and New York City Department of Environmental Protection used watershed studies in both temperate and monsoon climates across three continents to present a similarity of saturation-excess runoff quantity and spatial distribution. Source areas are degraded soils where a less permeable layer has formed at depth and lands at the bottom of hillslopes. Thus priority in landscape interventions in the (sub)humid Ethiopian Highlands should be given to re-vegetation of the degraded areas so as to reduce the sediment concentration contributions originating from these source areas. Additionally, efforts should be directed to gully rehabilitation in the saturated bottom landscape. Finally for nutrient control application of fertilizers and manure should be avoided on the source areas.
Technical Abstract: Understanding the basic hydrology and erosion is vital for effective management and utilization of water resources and soil conservation planning. An important question for judging effectiveness of soil and water conservation practices is whether runoff erosion and nutrient loss is affected by infiltration excess (affected by land use) or saturation excess (affected by topography). To examine this, we use watershed studies on three continents. Several of these watersheds had long-term records of rainfall and discharge. In other watersheds water tables were monitored and infiltration rates were compared with rainfall intensities. The results show that in well vegetated in (sub) humid watersheds independent of location, the surface soil had generally greater infiltration rates than the prevailing rainfall intensities. This implies that in both temperate and (sub) humid monsoonal climates direct runoff can only be generated from locations where the soil is saturated near the surface either by a regional high groundwater or by a perched water table on shallow soils over a hardpan. However, despite the similarity, the variation in incoming solar radiation (affecting both temperature and evaporation) and rainfall distribution, the runoff pattern was opposite between monsoon and temperate climates with respect to the dormant season. The runoff in the temperate climate is the greatest in the dormant season, while in a monsoon climate the runoff is the greatest in the wet season. In both climates erosion was directly linked to the runoff processes with much greater erosion rates from the degraded areas and the bottom of the slope than from the upper parts. This was especially true when large gullies formed in the saturated bottom lands where the soil had very little strength and water pressures were great when the water table was above the gully bottom. These bottom lands were also the source of the dissolved phosphorus in the stream. Thus priority in landscape interventions should be given to re-vegetation of the degraded areas so as to reduce the sediment concentration contributions originating from these source areas. Additionally, efforts should be directed to gully rehabilitation in the saturated bottom landscape. Finally for nutrient control application of fertilizers and manure should be avoided on the source areas.