Sensitivity Analysis of MPSIAC Model

Abstract

MPSIAC is currently known as an appropriate method to measure sediment of<br />Watershed basins of the country while there has not been any sensitivity analysis so far for<br />this method. In this study, required data for MPSIAC model were gathered from six basins;<br />Amame-Kamarkhani, Kand-Golandok, Tang Kenesht (from two different references), Nojian<br />(from three different references), Pegahe sorkh katvand (from one reference) and Ivanaki<br />(authors' research). Eleven sensitivity analyses were conducted and the amount of sediment<br />was calculated using the sum of nine factors. Each input parameter was increased or<br />decreased by 20% using a computer program in Visual Basic in Excel. Then sensitivity of the<br />model for the parameters was analyzed. The less sediment has the basin, the less sensitivity<br />has the input parameters in the model. MPSIAC model has twenty input variables that<br />resulted in nine main factors. Erosion parameter (R) was calculated by adding nine main<br />factors and the quantity of sediment was calculated by an exponential function. By evaluation<br />of nine main factors, it was concluded that land use and Gully development were the most<br />sensitive factors. As a result, based on the area and sensitivity of main factors, more<br />investments must be done on the most sensitive factor to reduce soil erosion. In the<br />assessment of nine main factors occurred errors are reduced due to adding operation.<br />Regarding all items, each factor that has more input quantity has the highest sensitivity. As a<br />result, if score of each factor grows more than six, more attention must be paid to score<br />assignation. If occurred errors in assessment of nine factors did not neutralize each other and<br />have additive or decreasing on the R, by addition of 20% to R, it showed that this factor was<br />the most sensitive factor to run the model. If R is equal to 60 and 20% related to the error<br />occurred in calculation of it, 54% error occurs in estimating the amount of sediment and<br />sensitivity reaches to 2.7. This evaluation indicated that MPSIAC model for evaluation of<br />basins with the amount of sediment more than 2.2 ton/hectare must be used more preciously<br />because the model is so sensitive in this status and possible error may get over 50%.