DESIGNING EROSION AND NUTRIENT CONTROL PRACTICES IN WATERSHEDS IN HUMID REGIONS: LESSONS LEARNED

摘要

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-excessrunoff 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 Ethiopianhighlands 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 andlimiting nutrient additions in areas near streams that generate surface runoff.