Sediment Load Calculation by Using the Universal Soil Loss Equation with a Geographic Information Software

Water erosion within rural basins is mainly caused by rains and runoff phenomena.The mentioned water erosion, reduces crop zones yields and produces soil loss, which, for academic purposes is a non-renewable resource. On the other hand, the sediment load produced, reduces the water quality and it is a good way of transportation for chemical pollutants. This is, without forgetting that on a yearly basis, it is necessary to use several economic resources to water canals cleaning, reservoirs flushing and sediment removal actions within estuaries and ports.

This document provides a methodology to calculate water erosion within a rural basin located in Central Mexico, Mexico. These methodology is based on the Universal Soil Loss Equation (USLE) but applied to a Geographic Information System (GIS), in this case the ArcGIS software.

One of the main problems in Mexico is the lack of reliable data, when it comes to sediment load estimation. This has become a major challenge once a dam is designed, because there are no data to design an accurate capacity of silts in within the reservoirs and, hence, the water storage capacity gets lost as time goes by, due to a deficient design criteria.

This paper approaches one of the most used methods to calculate the sediment load within rural basins, and that is the Universal Soil Loss Equation. The USLE method is developed by using a Geographic Information System (GIS), in this case the ArcGIS software.

ArcGIS has a specific tool called “Map Algebra”; this tool was used to solve the USLE for two possible scenarios. The first one is for the Potential Erosion, and the second one is for the Current Erosion within the studied basin. This two scenarios are reached by using different data maps such as maps for the “C” factor (Land use), “K” factor (Soil type), “R” factor (potential erosion by rainfall activity), and the “LS” factor (obtained with the DEM raster).

Once the USLE is calculated, the results are displayed as a map for both Potential Erosion and Current Erosion within the basin, these results were calculated in ton/hectare/year.

Finally, this paper also presents the hypothetical possibility of building a dam within the basin. This leads to the sediment load calculation that would get into the dam`s reservoir, as well as the time that would take for the dam to get silted to the 100% of its capacity.