A Riparian Buffer Design for Cropland

Purpose: • Present a general, multi-purpose, riparian buffer design suitable for most cropland situations • Provide some guidelines for adjusting this general design to better fit site-specific conditions or landowner need

Concentrated runoff flow : implications for buffer design and water quality benefits

Paper presented at the 13th North American Agroforesty Conference, which was held June 19-21, 2013 in Charlottetown, Prince Edward Island, Canada.In Poppy, L., Kort, J., Schroeder, B., Pollock, T., and Soolanayakanahally, R., eds. Agroforestry: Innovations in Agriculture. Proceedings, 13th North American Agroforestry Conference, Charlottetown, Prince Edward Island, Canada, June 19-21, 2013.Non-uniform or concentrated flow of surface runoff from agricultural fields can reduce the pollutant trapping effectiveness of buffer strips having constant width along a riparian zone or field margin. Effectiveness and cost-effectiveness might be improved by reconfiguring the buffer to be larger where more runoff flows and smaller where runoff is less. A GIS tool has been developed that accounts for non-uniform patterns of runoff flow which can be used for assessing performance of buffers and for designing them. This tool was used to assess the effect of nonuniform runoff on sediment trapping efficiency of constant-width buffer designs and to compare performance of constant-width and variable-size configurations. The tool is an ArcGIS extension based on the design model of Dosskey et al. (2011). It employs a digital elevation model (DEM) to divide the riparian area or field margin into many segments, determine contributing area and slope to each one and, then, design for a buffer area ratio that provides a specified level of trapping efficiency. The assessment procedure employs these same algorithms, but in a different order; first, determining the existing buffer area ratio and, then, calculating it's trapping efficiency. Results using this tool on a sample of fields in the Midwestern U.S. suggest that variable-size designs can be more than twice as effective per unit buffer area as conventional constant-width designs. Producing cost-effective designs and accurate performance assessments of buffers requires accounting for detailed spatial patterns of runoff flow from agricultural fields.Mike Dosskey (1), Matt Helmers (2), Dean Eisenhauer (3), and Tom Mueller (4) ; 1. USDA National Agroforestry Center, 1945 North 38th Street, Lincoln, NE, USA 68583. 2. Department of Biosystems Engineering, Iowa State University, Ames, IA, USA 50011. 3. Department of Biological Systems Engineering, Univ. of Nebraska, Lincoln, NE, USA 68583. 4. Department of Plant and Soil Sciences, University of Kentucky, Lexington, KY, USA 40546.Includes bibliographical references

A Design Aid for Determining Width of Filter Strips

Watershed planners need a tool for determining width of filter strips that is accurate enough for developing cost-effective site designs and easy enough to use for making quick determinations on a large number and variety of sites. This study employed the process-based Vegetative Filter Strip Model to evaluate the relationship between filter strip width and trap¬ping efficiency for sediment and water and to produce a design aid for use where specific water quality targets must be met. Model simulations illustrate that relatively narrow filter strips can have high impact in some situations, while in others even a modest impact cannot be achieved at any practical width. A graphical design aid was developed for estimating the width needed to achieve target trapping efficiencies for different pollutants under a broad range of agricultural site conditions. Using the model simulations for sediment and water, a graph was produced containing a family of seven lines that divide the full range of possible relationships between width and trapping efficiency into fairly even increments. Simple rules guide the selection of one line that best describes a given field situation by considering field length and cover management, slope, and soil texture. Relationships for sediment-bound and dissolved pollutants are interpreted from the modeled relationships for sediment and water. Interpolation between lines can refine the results and account for additional variables, if needed. The design aid is easy to use, accounts for several major variables that determine filter strip performance, and is based on a validated, process-based, mathematical model. This design aid strikes a balance between accuracy and utility that fills a wide gap between existing design guides and mathematical models

A design aid for determining width of filter strips

Watershed planners need a tool for determining width of filter strips that is accurate enough for developing cost-effective site designs and easy enough to use for making quick determinations on a large number and variety of sites. This study employed the process-based Vegetative Filter Strip Model to evaluate the relationship between filter strip width and trapping efficiency for sediment and water and to produce a design aid for use where specific water quality targets must be met. Model simulations illustrate that relatively narrow filter strips can have high impact in some situations, while in others even a modest impact cannot be achieved at any practical width. A graphical design aid was developed for estimating the width needed to achieve target trapping efficiencies for different pollutants under a broad range of agricultural site conditions. Using the model simulations for sediment and water, a graph was produced containing a family of seven lines that divide the full range of possible relationships between width and trapping efficiency into fairly even increments. Simple rules guide the selection of one line that best describes a given field situation by considering field length and cover management, slope, and soil texture. Relationships for sediment-bound and dissolved pollutants are interpreted from the modeled relationships for sediment and water. Interpolation between lines can refine the results and account for additional variables, if needed. The design aid is easy to use, accounts for several major variables that determine filter strip performance, and is based on a validated, process-based, mathematical model. This design aid strikes a balance between accuracy and utility that fills a wide gap between existing design guides and mathematical models

Filter strip performance and processes for different vegetation, widths, and contaminants

Filter strips are widely prescribed to reduce contaminants in surface runoff from agricultural fields. Tbis study compared performance of different filter strip designs on several contaminants and evaluated the contribnting processes. Different vegetation types and widths were investigated using simulated runoff event on large plots (3 m X 7.5 or 15 m) having fine-textured soil and a 6 to 7% slope. Filter strips 7.5 and 15 m wide downslope greatly reduced concentrations of sediment in runoff (76-93%) and contaminants strongly associated with sediment (total P, 55-79%; permethrin, 27-83% [(3-phenoxyphenyl) methyl (±)-cis, trans-3-(2,2-dichloroethenyl)-2,2-dimethylcyclopropane carboxylate ]). They had less effect on concentrations of primarily dissolved contaminants [atrazine, -5-43% (2-chloro-4-ethylamino-6- isopropylamino-s-triazine); alachlor, 10-61% [2-chloro-2\u276\u27 -diethylN-( methoxymethyl) acetanilide]; nitrate, 24-48%; dissolved P, 19- 43%; bromide, 13-31 %]. Dilution of runoff by rainfall accounted for most of the rednction of concentration of dissolved contaminants. Infiltration (36-82% ofrunoffvolume) substantially reduced the mass of contaminants exiting the filter strips. Doubling filter strip width from 7.5 to 15 m doubled infiltration and dilution, but did not improve sediment settling. Y onng trees and shrubs planted in the lower onehalf of otherwise grass strips had no impact on filter performance. Compared with cultivated sorghum [Sorghum bicolor (L.) Moench] grass clearly reduced concentrations of sediment and associated contaminants in runoff, but not volume of runoff and concentration of dissolved contaminants. Settling, infiltration, and dilution processes can explain performance differences among pollutant types and filter strip designs

A Design Aid for Determining Width of Filter Strips

Watershed planners need a tool for determining width of filter strips that is accurate enough for developing cost-effective site designs and easy enough to use for making quick determinations on a large number and variety of sites. This study employed the process-based Vegetative Filter Strip Model to evaluate the relationship between filter strip width and trap¬ping efficiency for sediment and water and to produce a design aid for use where specific water quality targets must be met. Model simulations illustrate that relatively narrow filter strips can have high impact in some situations, while in others even a modest impact cannot be achieved at any practical width. A graphical design aid was developed for estimating the width needed to achieve target trapping efficiencies for different pollutants under a broad range of agricultural site conditions. Using the model simulations for sediment and water, a graph was produced containing a family of seven lines that divide the full range of possible relationships between width and trapping efficiency into fairly even increments. Simple rules guide the selection of one line that best describes a given field situation by considering field length and cover management, slope, and soil texture. Relationships for sediment-bound and dissolved pollutants are interpreted from the modeled relationships for sediment and water. Interpolation between lines can refine the results and account for additional variables, if needed. The design aid is easy to use, accounts for several major variables that determine filter strip performance, and is based on a validated, process-based, mathematical model. This design aid strikes a balance between accuracy and utility that fills a wide gap between existing design guides and mathematical models