Application of GeoWEPP model in simulating runoff and soil loss of Mapawa watershed in Bukidnon, Philippines

The study aimed to apply the geospatial interface of Water Erosion Prediction Project (GeoWEPP) model in simulating runoff and soil loss of the Mapawa watershed in Songco, Lantapan, Bukidnon, Philippines. The study was conducted from April 2007 to January 2009. Primary data collected included watershed surveys and soil sampling. Secondary data collection included from MSEC [Management of Soil Erosion Consortium], NAMRIA [National Mapping and Resource Information Authority], and SANREM through the PPDO [Provincial Planning and Development Office] of Malaybalay City. Moreover, because the study is methodological in nature, familiarization with the applied models, preparation of data input files, simulation implementations, calibration of input parameters, final model implementation and model outputs analyses and validation were undertaken. In GeoWEPP erosion modelling, four basic input files corresponding to local climate, slope, land management, and soil were generated. Climate input file was generated within BPCDG [breakpoint climate data generator] program using a one year and standard weather dataset. Slope input file was derived from the created spurius-free 3-meter resolution DEM [digital elavation model] of the study site. Soil and management input files were generated based on primary data from the study site and supplemented with the built-in databases of the WEPP program. In addition, database files were created to link WEPP with GIS application software through its geospatial interface. After series of adjustments made to the input parameters, WEPP simulated sediment yield from the 5 weirs of respective main and subwatersheds with an average RMSE [root mean square error] of 5.32 and IA of 0.96. On a per rainfall event basis, WEPP predicted runoff and soil loss of the entire watershed with an average RMSE of 12,154 and 5.0, and IA [index of agreement] of 0.55 and 0.95, respectively. Based on a per cropped area, the observed and predicted sediment yields of 80.5 t/ha/yr and 89.2 t/ha/yr, respectively for the entire watershed far exceed the tolerable limit of 10 t/ha/yr. This indicates that the sustainability of the soil in the cultivated parcels within the watershed may be difficult to attain under the observed and predicted sediment yield scenarios. The results indicate that with appropriate calibration of parameters, GeoWEPP can be applied in simulating runoff and soil loss volumes of a small and agricuturally active watershed in Bukidnon. Despite limited number of datasets for validation, the model performed satisfactorily with promising results. Recommendation for further studies were offered.