Comparison of Soil Loss Estimation based on USLE, MMF and RMMF Models in Nam Chun Watershed, Lom Sak District, Phetchabun Province

Abstract

Soil loss estimation was conducted in the Nam Chun watershed, Lom Sak district, Phetchabun province.  The experimental plots on the soil loss were constructed on different land uses consisting of 1 plot of up-and-down plowing, 2 plots of sweet corn, 2 plots of sweet tamarind and 3 plots of mixed forest plantation. The observed sediment was examined in the area for 6 months from 1 May to 31 October, 2006. The results showed that the observed sediment from the plots of up-and-down plowing, sweet corn, sweet tamarind and mixed forest plantation were 9.04, 2.09, 3.41 and 0.40 t/rai/6 months respectively. Estimation comparison among the USLE, MMF and RMMF models was analyzed using the C-factor from different sources such as LDD (2002), the EI_30max and the ratio method.  USLE, the most correct estimation of sediment for the mixed forest plantation plot when using C-factor from LDD (2002), estimated the sediment as 0.81 t/rai/6 months (SSE = 0.04).  For MMF, the most correct estimation of sediment for the mixed forest plantation plot when using the C-factor from the EI_30max method and the ratio method estimated sediment as 0.21 t/rai/6 months (SSE = 0.04).  For RMMF, the most correct estimation of sediment for the mixed forest plantation plot when using the C-factor from the EI_30max method and the ratio method estimated sediment as 0.21 t/rai/6 months (SSE = 0.04).  However, the MMF and RMMF methods needed more complicated parameters and more steps in the calculation than those of USLE.  The estimated sediment regarding MMF and RMMF showed that sediment was not found on the 75^th day and 90^th day in the sweet tamarind plot and there was no sediment on the 60^th day, 75^th day, 105^th day and 120^th day in the mixed forest plantation plot, whereas, observed sediment was still found on every observation.  Therefore, it can be concluded that the USLE method is the most appropriate for soil loss estimation in this study area.

Keywords: Soil loss Estimation, Observed Sediment, USLE MMF and RMMF model, Nam Chun Watershed