Buffer Width Tool

1
Buffer Width Tool
Locate the curve below that corresponds with the
site conditions selected in Step 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.
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

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.
Reference condition definitions
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 0.003 Forest, full
canopy 0.0001 Construction site, no mulch
1.0 Construction site with secured mulch 0.1
Table B Line Selection Adjustment Rules

• 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 ones
  site.

2
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
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 90 trapping efficiency of dissolved nutrients.
Example 1 - Sediment
Example 2 - Nitrate
9
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.