Segments of the buffer that were forested for the entire 14 m width were assumed to be completely buffered. Segments without any forest cover were assumed to be nonbuffered. For segments of the buffer that contained both forest and other land uses, we determined the fraction of forest cover. The fraction was calculated as the forested area of the segment divided by the total area of the segment. This fraction, which varied between 0 to 1, was then used to calculate the corresponding filter strip width in SWAT.