INFLUENCE OF RAINFALL ENERGY AND OVERLAND FLOW ON SOIL LOSS FROM TERRACED PLANTATION ON STEEP TERRAIN OF DOI ANGKHANG HIGHLAND PROJECT, CHIANG MAI

The influence of rainfall energy and overland flow on soil loss within a plantation of 6 exotic tree species from Taiwan, planted  with narrow terracing on steep terrain was determined. Data were collected from 4×15 m, runoff plots 2, 3 and 7 years after the plantation were established. One hundred and seventy six storm events of rainfall, runoff and soil loss from each of the tree-covered plots were incorporated in to this study. A linear regression relationship between storm rainfall and rainfall energy (Rs or EI30 index) was found to be highly correlated with R2 ranges from 0.86 to 0.99. Narrow-bench terraces helped to reduce overland flow and led to a low correlation between soil loss and surface runoff. R2 which indicates the influence of surface flow on soil loss was less than 0.5 in all plantation plots in year 2 and 3, however, it was 0.92 in the bare plot. A very small R2 was obtained when Rs was added in the analysis. It can be concluded that narrow-bench terracing and the vegetation recovery greatly reduced both rainfall and runoff energy on the steep terrain.

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