Development and Validation of a Geographic Information System (GIS)- Assisted Soil Erosion Model in a Watershed Scale

Abstract

The study was done to develop erosion model, test, and validate its capability in mapping soil erosion and runoff and predicting the amount of sediment and water discharges at the outlet of a watershed; identify areas with high erosion risk potential within the watershed; and formulate recommendation for management strategies that would reduce soil erosion in the watershed. Named Predicting Catchment Runoff and Erosion for Sustainability (PCARES) Model, it predicted accurately the runoff heights and sediment concentration in a watershed in each single rainfall event. The erosion “hot spots” were predicted to occur in areas with steeper slope and agricultural land with less ground surface cover and no conservation measures, roads, and footpaths.  Net depositions were located in areas with thick crop cover, riparian buffer strips, and gentle slopes. The results demonstrate both the ability of the PCARES model in predicting the runoff and soil erosion in a watershed in a given erosive rainfall event, assess the impacts of land use change and soil conservation activities in a watershed on the rate of soil erosion and the significant influence of surface cover in reducing runoff and soil erosion in a watershed. The model can thus be used as a tool in assessing the impact of any development undertakings in a watershed prior to its implementation for sustainable watershed resource management. Absence of surface cover during land preparation stage contributed significantly to an increase amount of runoff water and soil loss. Thus, areas that are not used for agriculture purposes should be maintained as grassland or be planted with forest or fruit trees. Soil loss and runoff height decreased from land preparation to early crop establishment stage and further decreased at maturity. To mitigate the negative impact of thorough land preparation, minimum tillage if not zero tillage should be adapted where it is applicable.  Adapting an extreme condition (bare surface) resulted to highest simulated runoff and soil loss. Very low if not almost absence of soil loss was predicted from the grassland and the forest land uses. Soil loss in the cropland is dependent on the soil and crop residue management, the type of crop grown, and the soil conservation strategies employed by the farmers. If farmers will continue to destroy the surface cover, soil loss will always be a continuous threat to soil degradation and crop production sustainability in the catchment.