Methods
RUSLE estimates average annual soil loss (A) by taking into account rainfall erosivity (R), soil erodability (K), topography and hydrology (LS), land cover (C), and conservation practices (P). RUSLE values can be used to establish a relative ranking system of nonpoint source pollution potential among agricultural fields.
RUSLE has been successfully employed as a tool to control nonpoint source pollution for decades. Factors used to calculate annual soil loss (A) can be derived from existing geospatial data. Once the layers integrated within a GIS, overlay analysis facilitates the computation of annual soil loss.
Once annual soil loss is computed for agricultural fields, the next step is to remove those areas that are already protected by existing buffers. By identifying those areas that flow into “natural vegetation,” the agricultural areas that are already buffered can be excluded. The final output of our model consists of all agricultural areas that are in need of riparian buffers ranked based on their RUSLE values.
Mapping the presence or absence of riparian buffers adjacent to agricultural fields cannot be used to solely determine the need for buffer establishment. The perspective on the right, generated using an IKONOS satellite image (© Space Imagine, 2001), demonstrates how topography influences the local hydrologic conditions and ultimately determines a how effective a buffer is. In this example field “1” has relatively poor riparian buffer coverage, yet all of the flow on that field is directed to the buffer. Conversely, field “2” has reasonably sized riparian buffer on virtually its entire border with the river, yet flow is directed to the section that lacks the buffer. Flow modeling using GIS software, can help to isolate those buffers that are actually effective and determine the respective areas they buffer.