High Soil Erosion Potential Areas and Their Prioritization for Rehabilitation using a Modified Relative Erosion Potential Index In the Upper Bued River Watershed, Tuba, Benguet, Philippines.

Abstract

Evaluation of Soil Erosion Potential Measures indicates the suitability of using a rescaled Relative Erosion Potential Index (over USLE, RUSLE and MUSLE) in the Upper Blue River Watershed. 500 x 500m cell raster coding of average slope (in %, from quadrant search), land cover, and porosity (derived from soil type) enabled simple multiplication of average rainfall of the rainiest month, average slope, WRI-supplied values for soil type and land cover/use which gives rise to the Relative Erosion Potential (REP) index. Rescaling (from 0 to 1 for minimum and maximum) of the REP index facilitated statistical classification of the rescaled REP cell scores, resulting in the identification of 12 areas warranting priority work for rehabilitation.

These 12 areas are marked by steep to very steep slopes (all >50%), grassland cover, and are dominated by porous soil types. Six of these areas, in order of priority, are within the watershed, namely Camp 6, NE Camp 5, SE PMA, NW Camp 4, East Camp 3, and NE Sto. Tomas areas. The other six areas lie outside of the watershed; Philex North, Philex Minesite, NW Sto. Tomas, Banget are mostly within the Philex mining operations where reforestation is ongoing. The Saddle and Acupan Areas are astride the Philex Road.

Vegetative measures, such as tree species, especially those endemic to the area and suited to high elevation, steep slopes, thin, calcareous, lateritic or acidic soils are recommended. Vines and creeping plants, including bamboo and rattan which will hold and protect the soil from direct rainfall impact, retain moisture, provide organic matter, retard runoff, and provide products for domestic consumption and commercial use are also recommended.

Simple engineering measures at smaller scales for runoff control such as check damns, wattling, fascines and slope protection such as riprapping are recommend if proven to be cost-effective relative to the value of the downstream sites to be protected.

The methodology, as well as results of this study, can be improved with updated land cover data and consideration of soil loss potential due to mass movement. Results of this study are recommended to be disseminated and discussed with relevant stakeholders to hasten progress in mitigating soil loss in the area.