Designing erosion and nutrient control practices in watersheds in humid regions: lessons learned

Authors: STEENHUIS, TAMMO - Cornell University; ZIMALE, FASIKAW - Bahir Dar University; BOLL, JAN - Washington State University; TILAHUN, SEIFU - Bahir Dar University; BROOKS, ERIN - University Of Idaho; GUZMAN, CHRISTIAN - Washington State University; HOANG, LINH - New York City Department Of Environmental Protection; SCHNEIDERMAN, ELLIOT - New York City Department Of Environmental Protection; MUKUNDAN, RAJITH - New York City Department Of Environmental Protection; Langendoen, Eddy

Submitted to: ASABE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 1/31/2017
Publication Date: 7/16/2017
Citation: Steenhuis, T.S., Zimale, F.A., Boll, J., Tilahun, S.A., Brooks, E., Guzman, C.D., Hoang, L., Schneiderman, E.M., Mukundan, R., Langendoen, E.J. 2017. Designing erosion and nutrient control practices in watersheds in humid regions: lessons learned. In Proc. 2017 ASABE Annual International Meeting, July 16-19, 2017, Spokane, WA. Paper No. 1701316. pp. 11. DOI: 10.13031/aim.201701316.

Interpretive Summary: Soil erosion and nutrient management is most effective when conservation practices are applied to runoff source areas. Conventional control practices developed for areas where rainfall intensity exceeds the soil infiltration rate have been unsuccessful in reducing sediment and nutrient concentrations in the (sub)humid region of Ethiopia. In collaboration with researchers of Bahir Dar University, Ethiopia, Cornell University and the New York City Department of Environmental Protection, scientists at the USDA, ARS, Watershed Physical Processes Research Unit conducted watershed studies on three continents (Africa, Central America, and North America) to show the prevalence of runoff generation caused by soil saturation processes in both temperate and (sub) humid monsoonal climates. Watershed runoff was generated at degraded areas with a perched water table over a slowly permeable layer and the bottom lands with a high regional ground water table. The bottom lands are also the source of gullies and dissolved phosphorus in the stream. Thus priority in landscape interventions should focus to re-vegetation of the degraded areas and 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: For close to a century, governments have encouraged soil and water conservation measures on farmers’ fields using universal technologies independent of environmental and social context. Most of these conservation technologies-based infiltration-excess runoff mechanisms were beneficial over an extended time in the drier climates for water conservation and erosion control, but only for short times in humid areas and in neither climate for nutrient control. The objective of this presentation is to document the hydrological and management factors that should be considered in the optimum performance of soil and water conservation practices in humid regions and then use them to find more effective practices. We are using the humid and sub humid Ethiopian highlands landscape and the New York City source watersheds in the Catskill Mountains as case studies. We show that since infiltration-excess hardly occurs in these humid regions, direct runoff is generated from areas that become saturated on valley bottoms, near rivers, and on hillsides with the most severely degraded soils and perched water. Only practices that consider the saturation runoff mechanisms are effective in reducing non-point source pollution and erosion. This includes protecting areas and limiting nutrient additions in areas near streams that generate surface runoff.