Indices for Assessing the Spatial Distribution and Functions of Riparian Buffer Zones

It is widely recognised that riparian zones can greatly reduce the movement of pollutants from hillslopes into streams. While several indices of stream condition exist, the spatial distribution of the pollutant and runoff trapping functions of the riparian zone remains poorly understood. This paper describes three indices, which quantify the spatial distribution of riparian zones that function as buffers. These indices have been developed based on a review of point-based riparian zone studies of sediment and pollutant trapping, and are designed with spatial extrapolation in mind. The indices describe the following pollutant trapping functions: 1. hillslope runoff interception, 2. hillslope sediment trapping, and 3. hillslope pollutant trapping. Each index and the spatial extrapolation techniques are described. These techniques include satellite-based remote sensing, geographical information systems, and terrain analysis. The spatial extrapolation techniques require four main products, a land use map, a riparian vegetation map, a map of soil depth and porosity, and a map of hillslope length and area. The indices are calculated using parameters from these four products. This suite of indices provides a measure of stream condition that explicitly considers buffering functions and permits a more process specific design procedure in planning catchment management.