Buffer Width Tool
1
In Table A select the reference line
number that most closely resembles the
field conditions and the type of pollutant
the buffer will address.
2
Locate the curve below that
corresponds with the site conditions
selected in Step 1.
3
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.
Table A – Conditions Corresponding to Each Line in the Graph
1.
2.
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.
FSL = Fine Sandy Loam; SiCL = Silty Clay Loam
Reference condition definitions
Pollutant Type
Dissolved pollutants include nitrates, dissolved P, and soluble
pesticides
Field Length
Length of contributing area to buffer
Table B – Line Selection Adjustment Rules
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 = 0.003
Forest, full canopy = 0.0001
Construction site, no mulch = 1.0
Construction site with secured mulch = 0.1
4
• Add up the pluses and
minuses to get the
total adjustment.
• 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.
Adapted from - Dosskey, M.G., Helmers, M.J., Eisenhauer, D.E. 2008. A design aid for determining width of filter strips.
Journal of Soil and Water Conservation 63(4): 232-241.
5
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.
7
6
Example 1 begins with Reference
Line 5. The goal is 60% trapping
efficiency of sediment.
Example 2 begins with Reference
Line 4. The goal is 8% trapping
efficiency of dissolved nutrients.
Example 1 - Sediment
Example 2 - Nitrate
9
7
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.
Adapted from - Dosskey, M.G., Helmers, M.J., Eisenhauer, D.E. 2008. A design aid for determining width of filter strips.
Journal of Soil and Water Conservation 63(4): 232-241.