A design aid for sizing filter strips using buffer area ratio

Abstract

Nonuniform field runoff can reduce the effectiveness of filter strips that are a uniform size along a field margin. Effectiveness can be improved by placing more filter strip where the runoff load is greater and less where the load is smaller. A modeling analysis was conducted of the relationship between pollutant trapping efficiency and the ratio of filter strip area to upslope contributing area, i.e., buffer area ratio. The results were used to produce an aid for designing filter strips having consistent effectiveness along field margins where runoff load is nonuniform. Simulations using the process-based Vegetative Filter Strip Model show that sediment and water trapping efficiencies of a filter strip increase nonlinearly as the buffer area ratio gets larger. Site characteristics, including slope, soil texture, and upslope soil cover management practices, help to define this relationship more accurately. Using the Vegetative Filter Strip Model simulation results, a graphical design aid was developed for estimating the buffer area ratio required to achieve specific trapping efficiencies for different pollutants under a broad range of agricultural site conditions. A single graph was produced showing simulation results for seven scenarios as a family of lines that divide the full range of possible relationships between trapping efficiency and buffer area ratio and into fairly even increments. Simple rules guide the selection of one line that best describes a given field situation by considering slope, soil texture, and field cover management practices. Relationships for sediment-bound and dissolved pollutants are interpreted from the Vegetative Filter Strip Model results for sediment and water. 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. The use of this design aid will enable a more precise fit between filter size and runoff load where runoff from agricultural fields is nonuniform.Key words: models-nonpoint source pollution-precision conservation-surface runoffvariable-width buffers-vegetative buffers-water quality-watershed planning Filter strips are commonly installed for improving and protecting water quality in agricultural watersheds. Filter strips (Code 393) reduce the load of sediment, nutrients, and other pollutants in overland runoff from fields by promoting infiltration and sediment deposition (Haan et al. 1994;USDA 1997). Typically, they are designed to have a constant width (parallel to flow) along a field margin, and maximum pollutant trapping efficiency is achieved when field runoff is uniformly dispersed across the entire filter strip (USDA 1997). Several design methods have been developed for determining the appropriate width for a filter strip treating spatially uniform runoff (see review in Dosskey et al. 2008). However, researchers have observed that surface runoff commonly concentrates in fields and flows mainly through only small portions of filter strips...

Recent advances and future directions in soils and sediments research

“…While such features are no doubt useful, in many situations they may not be in optimal locations or of suitable design (e.g. Dosskey et al 2011). Much guidance on buffer design and location has been based on research undertaken in temperate environments, such as the UK and USA.…”

Shallow water table effects on water, sediment, and pesticide transport in vegetative filter strips – Part 1: nonuniform infiltration and soil water redistribution

“…In spite of the potentially important environmental impacts of the presence of shallow water under VFS, there is a dearth of studies addressing this problem either experimentally or mechanistically. Several authors suggest the importance of this factor in VFS experimental studies (Lacas et al, 2005;Arora et al, 2010) or when designing or implementing this field BMP (Simpkins et al, 2002;Dosskey et al, 2006Dosskey et al, , 2011, but they do not provide a mechanistic interpretation. Some authors suggest that the reduction of infiltration and VFS efficiency can be problematic for seasonal WT depths above 2 m, typical of hydromorphic soils (Dosskey et al, 2006(Dosskey et al, , 2011Lacas et al, 2012).…”

“…Several authors suggest the importance of this factor in VFS experimental studies (Lacas et al, 2005;Arora et al, 2010) or when designing or implementing this field BMP (Simpkins et al, 2002;Dosskey et al, 2006Dosskey et al, , 2011, but they do not provide a mechanistic interpretation. Some authors suggest that the reduction of infiltration and VFS efficiency can be problematic for seasonal WT depths above 2 m, typical of hydromorphic soils (Dosskey et al, 2006(Dosskey et al, , 2011Lacas et al, 2012). As cited by Salvucci and Entekhabi (1995), the importance of accounting for areas of WT effects in water balance and runoff studies has been recognized for a long time, and specialized analysis and simulation approaches have been proposed by numerous authors (for example, Vachaud et al, 1974;Srivastava and Yeh, 1991;Salvucci and Entekhabi, 1995;Chu, 1997;Basha, 2000).…”

AgBufferBuilder: A geographic information system (GIS) tool for precision design and performance assessment of filter strips

“…Methods for doing so include grading the field or constructing spreaders, but these activities can add substantial cost. A more cost-effective design would simply vary the dimensions of filter strip according to the amount of runoff receivedlarger where runoff is greater and smaller where runoff is less (Dosskey et al 2005).A design method has been proposed for sizing filter strips that can account for spatially nonuniform overland runoff (Dosskey et al 2011). This method sizes different segments of a filter strip along a field margin in relation to the size of field area that drains to each segment (i.e., buffer area ratio).…”

“…This procedure would use the same input data as the design methodology, with the addition of a digital map indicating the location of the existing or hypothetical filter strip, and utilize the same quantitative relationships between buffer area ratio and trapping efficiency as used for design. The results could be used to estimate the trapping efficiency of past installations and to evaluate comparative performance of alternative future designs.The objectives of this study were to (1) develop a GIS-based procedure for designing and assessing performance of filter strips based on the methodology of Dosskey et al (2011), (2) validate results produced by the GIS procedure by comparing them to field measurements, and (3) demonstrate the utility of the GIS procedures by comparing performance of spatially variable designs to that of constant-width configurations of the same overall size. …”