Buffer Width Tool In Table A select the reference line number that most closely resembles the field conditions and the type of pollutant the buffer will address. 1 Using Table B, compare the site conditions to each of the 5 adjustment factors. Follow the Adjustment Rules to select a line number that is higher or lower than the reference line number selected in Step 1. Add up the pluses and minuses to get the total adjustment. 3 Reference condition definitions 2 Locate the curve below that corresponds with the site conditions selected in Step 1. 4 Add the total adjustment number to the reference line number. The result is the appropriate line number to use for determining a buffer design width at one’s site. Pollutant Type Dissolved pollutants include nitrates, dissolved P, and soluble pesticides Field Length Length of contributing area to buffer Slope Average slope of the buffer and contributing area Soil Texture Categories Coarse = Sandy loam, sandy clay loam, and fine sandy loam Medium = Very fine sandy loam, loam, and silt loam Fine = Clay loam, silty clay loam, and silt C-Factor (from Universal Soil Loss Equation) Cropland, clean tillage = 1.0 Cropland, plow tillage, low residue = 0.8 Pasture, permanent grass = Forest, full canopy = Construction site, no mulch = 1.0 Construction site with secured mulch = 0.1 Table A – Conditions Corresponding to Each Line in the Graph 1.C-Factor of 0.5 represents plowed and disked row crops with moderate residue returned to the soil surface. C-Factor of 0.15 represents conservation tillage and no-till with high residue returned to the soil. C-Factor values for other soil cover management conditions can be found on the next page. 2.FSL = Fine Sandy Loam; SiCL = Silty Clay Loam Table B – Line Selection Adjustment Rules Adapted from - Dosskey, M.G., Helmers, M.J., Eisenhauer, D.E A design aid for determining width of filter strips. Journal of Soil and Water Conservation 63(4):

Utilizing the newly determined line on the graph determine the appropriate buffer width to achieve the desired sediment or nutrient trapping efficiency. See examples below. Example 1 begins with Reference Line 5. The goal is 60% trapping efficiency of sediment. Can other site factors be accounted for in the design tool? Yes, any site condition that would double or halve the field runoff load should dictate an adjustment of one line below and one line above the initial reference line, respectively. To account for different size design storms, a 3.6 inch per hour and 1.5 inch per hour storm would roughly double or halve, respectively, the runoff load compared to the 2.4 inch per hour storm used to generate the reference lines. 7 Example 2 begins with Reference Line 4. The goal is 8% trapping efficiency of dissolved nutrients. Example 1 - SedimentExample 2 - Nitrate Adapted from - Dosskey, M.G., Helmers, M.J., Eisenhauer, D.E A design aid for determining width of filter strips. Journal of Soil and Water Conservation 63(4):