Vegetative Filter Strips Research Articles

The influence of low impact development-best management practices implementation on surface runoff reduction: A case study in Universitas Indonesia catchment area

High population growth rate will increase the infrastructure development, so the impervious land cover in a certain area will be greater. In 2016, the percentage of impervious area in UI Depok catchment area has reached 57%. This condition causes the surface runoff volume and probability of flood will increase. LID is a new paradigm for stormwater management in micro-scale areas. LID infrastructure is designed to manage stormwater for light to moderate rainfall spectrum. Previous research has produced an applied proposal of various LID-BMP infrastructure in UI catchment area, Depok, by using BMP Siting Tools. This study aims to compare the volume of surface runoff without and with the LID infrastructures on UI catchment area, Depok, and to calculate the effectiveness of LID infrastructure for various spectrum of rainfall. The LID infrastructures used are bioretention, porous pavement, infiltration trench, infiltration basin, vegetated filter strip, sand filter non-surface, sand filter surface, rain barrel and grassed swales. By applying said infrastructures, the reduction of peak flow on various rain spectrums vary from 3-30%.

AGRICULTURAL BEST MANAGEMENT PRACTICE SENSITIVITY TO CHANGING AIR TEMPERATURE AND PRECIPITATION.

Agricultural best management practices (BMPs) reduce non-point source pollution from cropland. Goals for BMP adoption and expected pollutant load reductions are often specified in water quality management plans to protect and restore waterbodies; however, estimates of needed load reductions and pollutant removal performance of BMPs are generally based on historic climate. Increasing air temperatures and changes in precipitation patterns and intensity are anticipated throughout the U.S. over the 21st century. The effects of such changes on agricultural pollutant loads have been addressed by several authors, but how these changes will affect the performance of widely promoted BMPs has received limited attention. We use the Soil and Water Assessment Tool (SWAT) to investigate potential changes in the effectiveness of conservation tillage, no-till, vegetated filter strips, grassed waterways, nutrient management, winter cover crops, and drainage water management practices under potential future temperature and precipitation patterns. We simulate two agricultural watersheds in the Minnesota Corn Belt and the Georgia Coastal Plain with different hydro-climatic settings, under recent conditions (1950-2005) and multiple potential future mid-century (2030-2059) and late-century (2070-2099) climate scenarios. Results suggest future increases in agricultural source loads of sediment, nitrogen and phosphorous. Most BMPs continue to reduce loads, but removal efficiencies generally decline due to more intense runoff events, biological responses to changes in soil moisture and temperature, and exacerbated upland loading. The coupled effects of higher upland loading and reduced BMP efficiencies suggest that wider adoption, resizing, and/or combining practices may be needed in the future to meet water quality goals for agricultural lands.

Process-Based Design Strengthens theAnalysis of Stream and Floodplain Systems under a Changing Climate

HighlightsStream-riparian interactions and preferential flow remain two “unsolved” problems in hydrology.Using mechanistic approaches enables analysis of stream and floodplain systems under future climatic extremes.Engineers should verify stream restoration designs with models that consider stream-riparian interactions.Riparian buffer design models should consider preferential flow and be more widely used for site-specific design. Keywords: . Climate Variability, Floodplain, Preferential flow, Process-based design, Riparian buffer, Stream restoration, Streambank erosion, Vegetative Filter Strip.

Vegetative filter strips—Effect of vegetation type and shape of strip on run‐off and sediment trapping

AbstractVegetative filter strips (VFSs) are a common type of off‐site method used to enhance the sustainability of catchment systems by promoting desirable soil and landscape functions. The transport of water run‐off and sediment to downstream reaches can be restricted by VFSs in the flow path. The adoption of VFSs is increasing because they have been demonstrated to be effective for trapping run‐off and sediment. Thus, an optimized design procedure for developing VFSs is required. To further understand the roles of both vegetation type and geometric size in the design of VFSs, global sensitivity analysis (GSA) within the Vegetative Filter Strip Modeling System was conducted using a traditional elementary effect test and a novel density‐based method called PAWN. The analysis involved both a uniform and a concentrated flow scenario. The GSA outcomes indicated that the inputs related to vegetation type were vital for the VFS design, especially in terms of the run‐off reduction function of the VFS, irrespective of the scenario that was used. The vertical saturated hydraulic conductivity was the main input responsible for the influence of vegetation type. The inputs related to vegetation type had limited influences on the sediment trapping performance of the VFS, which was shown to be mainly controlled by the length of the VFS. The role of vegetation type in the design of VFSs must be fully considered, especially in cases in which VFSs are established primarily for flood control or run‐off reduction purposes.

Effects of vegetative filter strip on overland flow nitrogen and phosphorus intercepting under different inflow conditions.

The vegetative filter strips can effectively intercept erosion of water and sediment on the slope, with huge potential to prevent and control soil erosion and agricultural non-point source pollution. A series of muddy water scouring experiments under different inflow conditions in the indoor soil trays were conducted to investigate the effects of vegetative filter strip (VFS) on intercepting nitrogen (N) and phosphorus (P) under different inflow conditions and its internal hydrological responses. The results showed that the VFS could effectively intercept N and P in the runoff. When the inflow was 200, 400, 600 L·h-1, the intercepting rates were 74.9%, 62.0%, 58.3% for N and 85.0%, 75.6%, 72.0% for P, respectively. The best intercepting effect occurred at the lower inflow rates. Different inflow N and P concentrations had no significant effect on N and P interception efficiency. Under different inflow conditions, the intercepting rates of N and P by VFS increased with the increases of Froude value with a significant linear positive correlation. However, there were linear negative correlations between the intercepting rate and resistance coefficient, shear stress and stream power. The relationship between the N and P intercepting rates and shear stress was the best among others, and the N and P intercepting rates could be well predicted by a formula containing shear stress.

Pollutant Runoff Reduction Efficiency of Surface Cover, Vegetative Filter Strip and Vegetated Ridge for Korean Upland Fields: A Review

Pollutant Runoff Reduction Efficiency of Surface Cover, Vegetative Filter Strip and Vegetated Ridge for Korean Upland Fields: A Review-Best management practices,Land slope,Rainfall,Soil erosion,Upland fields

Improving stormwater quality at source using catch basin inserts

Stormwater runoff transports contaminants, including gross pollutants (GPs) accumulated on surfaces to nearby receiving water bodies. These may clog storm drainage systems, seal side entry pits and increase dissolved pollutants in receiving water bodies. Best management practices (BMPs) such as oil and grit separators, grassed swales, vegetated filter strips, retention ponds, and catch basin inserts (CBIs) are implemented to reduce stormwater pollutants in urban runoff. However, the information on physicochemical characteristics of the pollutants are still few in literature but important to improve the design of BMPs, considering qualitative aspects, and their operation. CBIs are devices used to remove GPs at source without requiring any extra land use because they are typically mounted within a catch basin (e.g. side entry pit) or existing drain. In this study, improvement of stormwater quality was investigated at two different sites (Subiaco, a residential area and Hillarys Boat Harbour, a commercial-marine-recreational area; Western Australia) where a new CBI made of non-woven polypropylene geotextile was installed in side entry pits to capture GPs at source. Influent and effluent water from the CBIs was collected and analyzed for BOD, COD, TSS and PO4-P with maximum improvements in water quality of 90%, 88%, 88% and 26% respectively. The heavy metals in influent and effluent water were found very low and below the guideline values. Analysis of particle size distribution, specific surface area of solids, SEM images and heavy metal content (Cu, Fe, Ni, Pb, Zn, Cd) in solids showed that the residential area contained more finer particles than the commercial area but that solids in the commercial area contained greater concentrations of heavy metals than those from the residential area. The specific surface area was found to be higher in the residential area and particles were thought to be largely sourced from traffic. However, these characteristics may be monitored for longer term for more CBIs installed in different locations.

Innovative Sandbag Propagation Method for Giant Cane (Arundinaria gigantea (Walter) Muhl.)

ABSTRACT Vegetative filter strips have been adopted as a common best management practice to manage soil erosion and nutrient losses from cultivated fields. New species and combinations of species are constantly being assessed based on their riparian function. A unique species that is native to southern Illinois and the southeast is giant cane (Arundinaria gigantea). Giant cane's performance as an effective filter of sediment and nutrients from surface and subsurface flows has been recently documented; however, it can be difficult to establish in riparian zones. Therefore, the purpose of this study was to evaluate a new approach for restoring giant cane in riparian buffer zones and methods that provide quick protection of critical source areas in the field. This study focused on developing a low-cost method for giant cane restoration designed to give reproductive propagules an advantage in assembling a successful canebrake while protecting critical areas bordering agricultural fields and streams/ditches. T...

Field performance of two biofiltration systems treating micropollutants from road runoff

The treatment efficiency of a vegetative filter strip and a biofiltration swale treating heavily loaded road runoff are evaluated. Concentrations measured in water drained from the two systems are compared to those in untreated road runoff collected from a reference catchment for a wide range of contaminants including organic carbon, nutrients (N and P), trace metals, and organic micropollutants (polycyclic aromatic hydrocarbons (PAH), total petroleum hydrocarbons (TPH), alkylphenols, bisphenol-A, phthalates), in both total and dissolved phases. Predominantly particulate pollutants, including Pb, Zn and PAH, were very efficiently removed (around 90%) for most events. However, poor particulate removal was observed during a winter period. Relatively few pollutants were significantly removed in the dissolved phase and observed concentration reductions tended to be lower than those of suspended solids and associated pollutants; as such, lower removals were observed for total concentrations of moderately particulate micropollutants, including bisphenol-A, alkylphenols and phthalates. In addition, some pollutants appear to be emitted from various biofilter components (filter media, drainage and lining materials), as low or negative concentration removals were observed during the first months of operation of the biofiltration swale.

Predicting soil loss and sediment characteristics at the plot and field scales: Model description and first verifications

Soil loss models are useful tools for making land management decisions to prevent soil and water quality problems. Several soil loss models have been developed, including the process-based Water Erosion Prediction Project (WEPP) model and the empirical Revised Universal Soil Loss Equation (RUSLE). Although process-based models provide accurate soil loss estimates, they are infrequently used for conservation planning because of their complexity and data need. On the other hand, models such as RUSLE cannot predict the soil loss nor the sediment composition associated with individual events, both of which are critical for designing accurate soil and water conservation practices. Therefore, the objective of this study was to develop a model for estimating sediment delivery on an event scale while predicting its clay, silt and sand fractions. For this purpose, the WEPP model was implemented using measured soil and climate data from Central Chile to generate a soil loss database for many hillslope configurations and management practices. More than 200,000 erosion events were generated using data from 83 sites. Using multiple regression analysis, the main variables controlling soil loss were identified, which included rainfall erosivity, soil erodibility, hillslope geometry, antecedent soil moisture and total precipitation. These variables were incorporated into a soil loss model, which was calibrated using data from 32 sites (R2 = 0.81–0.83) and validated for the remaining 51 sites (R2 = 0.66–0.89). The model provided accurate estimates for the clay and silt fractions (R2 = 0.86 and 0.78, respectively) but showed difficulties for predicting the sand fraction (R2 = 0.31). Contour plowing and vegetative filter strip routines were also incorporated into the soil loss model, providing reliable soil loss (R2 = 0.51–0.78), clay (R2 = 0.54–0.75), and silt (R2 = 0.57–0.68) estimates. The developed model is remarkably easy to use and, due to its simplicity, allows incorporating other soil conservation routines, providing a flexible tool for soil conservation planning. This study provides a detailed description and methodology for building such a model and discusses its advantages and limitations.

Recalibration and cross-validation of pesticide trapping equations for vegetative filter strips (VFS) using additional experimental data

Vegetative filter strips (VFS) are widely used for mitigating pesticide inputs into surface waters via surface runoff and erosion. To simulate the effectiveness of VFS the model VFSMOD is frequently used. While VFSMOD simulates infiltration and sedimentation mechanistically, the reduction of pesticide load in surface runoff by the VFS is calculated with the empirical Sabbagh equation. This multiple regression equation has not been widely accepted by regulatory authorities, because its reliability has not been sufficiently demonstrated yet. A major drawback is the small number of calibration data points (n = 47). To corroborate and improve the predictive capability of the Sabbagh equation, additional experimental VFS data were compiled from the available literature. The enlarged dataset (n = 244) was used to recalibrate the Sabbagh equation, the recently proposed Chen equation and a set of “reduced” Sabbagh equations with fewer independent variables, with ordinary least squares (OLS) regression and to test an alternative, regression-free mass balance approach. The Sabbagh equation fitted the dataset slightly better than the Chen equation (coefficient of determination R2 = 0.82 vs. 0.79). The purely predictive mass balance approach performed slightly worse (Nash-Sutcliffe Efficiency NSE = 0.74), but significantly better than the Sabbagh and Chen equations with their old coefficients. In a k-fold cross validation analysis to assess the predictive capability of the various regression equations, both the full Sabbagh and the reduced Sabbagh equations with two or more variables outperformed the Chen equation. Finally, a maximum-likelihood-based calibration and uncertainty analysis were conducted for the Sabbagh equation using the DREAM_ZS algorithm and two different likelihood functions. The DREAM simulations corroborated the parameter values obtained with OLS regression. The study confirmed the suitability of the Sabbagh equation for regulatory modelling of pesticide trapping in VFS. However, the regression-free mass balance approach turned out to be a viable alternative.

Optimal allocation of nonpoint source pollution control measures using two modern comprehensive evaluation methods

Abstract Nonpoint source (NPS) pollution has been studied for many years but it exhibits random, widespread, complex uncertainties which make it difficult to manage and control. We employ group decision-making utilizing the fuzzy comprehensive evaluation method (FCE) and the analytic hierarchy process method (AHP) and comparatively evaluate the optimal allocation of NPS pollution control measures. Here, we present the top-three evaluation results ranked as follows: combination of contour tillage and vegetative filter strips (CT & VFS), vegetative filter strips (VFS), and combination of contour tillage and fertilizer reduction and vegetative filter strips (CT & FR & VFS). The fourth, fifth and sixth results by FCE method are chemical fertilizer reduction (FR), returning farmland to forest or pasture (RF), and combination of contour tillage and fertilizer reduction (CT & FR), while the corresponding results by AHP method are returning farmland to forest or pasture (RF), combination of contour tillage and fertilizer reduction (CT & FR), and fertilizer reduction (FR). The seventh results for each of the two methods are contour tillage (CT), which has a positive but limited effect on nutrient loss reduction. Our results provide new underlying insights needed to guide the resonable allocation of NPS pollution control measures.

Assessing the impact of the MRBI program in a data limited Arkansas watershed using the SWAT model

The USDA Natural Resources Conservation Service (NRCS) developed the Mississippi River Basin Healthy Watersheds Initiative (MRBI) program to improve the health, water quality and wildlife habitat within the Mississippi River Basin. Lake Conway Point Remove (LCPR) watershed was identified as one of the watersheds for the MRBI program implementation. The goal of this paper is to evaluate the effectiveness of the MRBI program in LCPR watershed using a computer simulation model. Seven best management practices (BMPs) (pond, wetland, pond and wetland, cover crops, vegetative filter strips, grassed waterways and forage and biomass planting) were modelled under four placement strategies: random placement in 30% of the watershed, random placement in 30% hydrologic response units (HRUs) of the high priority hydrological unit code (HUCs), placement in the top 30% of the high priority HUCs, and top 30% of the HRUs in the HUCs near the outlet of the watershed. The model was calibrated for flow for the period 1987–2006 and validated for the period 2007–2012. Sediment and nutrients were validated from 2011 to 2012. Out of the BMPs evaluated, grassed waterways proved to be the most effective BMP in reducing sediment and nutrient loads from row crop (soy beans) and pasture fields. Reductions at the watershed outlet ranged 0–1% for flow, 0.28–14% for sediment, 0.3–10% for TP and 0.3–9% for TN. Relatively higher reductions were observed at the subwatershed level, flow reductions ranged 0–51%, sediment reductions −1 to 79%, TP −1 to 65% and TN −0.37 to 66% depending on BMP type, placement scenario, and watershed characteristics. The results from this study provide the data to help prioritize monitoring needs for collecting watershed response data in LCPR and BMP implementation evaluations, which could be used to inform decisions in similar studies.

Effect of vegetative filter strips on the dynamics of E. coli biofilm-building potential and expression of virulence factors at Mau, Kenya

Escherichia coli (E. coli) populations could become tolerant to extreme environmental temperatures to become resident in soil and surface water habitats creating public health problems. The objective of this study was to understand the interaction between dynamics of E. coli genetic diversity, physiology, and vegetative filter strips (VFS) in overland flows and soil habitats. Pulse-field gel electrophoresis was used to establish the genetic diversity of the isolates (n = 4). Genotypic analysis showed that the runoff isolates do not form a single genetic strain, but that multiple genotype strains were capable of surviving and proliferating in these habitats. High overall unique genotypic diversity was observed in VFS II (38.5%) as compared to VFS III (9.5%) and VFS I (1.5%). Approximately 8.5% E. coli genotypes observed in the surface water and 5.5% observed in soil habitat were shared between different sampling sites, suggesting diffuse sources of E. coli in these habitats. Approximately 32.5% genotypic overlap and a limited sharing (72.5%) between soil and surface water habitats were observed. These findings inferred that certain E. coli strains might have the ability to colonize and adapt to soil and runoff surface water habitats through production of biofilms. Thus, these results confirm that biofilm formation confers competitive advantage to the E. coli environmental isolates including hardiness, versatility, higher resistance to ecological and physical impacts and higher resource availability.

Using geomorphological variables to predict the spatial distribution of plant species in agricultural drainage networks.

To optimize ecosystem services provided by agricultural drainage networks (ditches) in headwater catchments, we need to manage the spatial distribution of plant species living in these networks. Geomorphological variables have been shown to be important predictors of plant distribution in other ecosystems because they control the water regime, the sediment deposition rates and the sun exposure in the ditches. Whether such variables may be used to predict plant distribution in agricultural drainage networks is unknown. We collected presence and absence data for 10 herbaceous plant species in a subset of a network of drainage ditches (35 km long) within a Mediterranean agricultural catchment. We simulated their spatial distribution with GLM and Maxent model using geomorphological variables and distance to natural lands and roads. Models were validated using k-fold cross-validation. We then compared the mean Area Under the Curve (AUC) values obtained for each model and other metrics issued from the confusion matrices between observed and predicted variables. Based on the results of all metrics, the models were efficient at predicting the distribution of seven species out of ten, confirming the relevance of geomorphological variables and distance to natural lands and roads to explain the occurrence of plant species in this Mediterranean catchment. In particular, the importance of the landscape geomorphological variables, ie the importance of the geomorphological features encompassing a broad environment around the ditch, has been highlighted. This suggests that agro-ecological measures for managing ecosystem services provided by ditch plants should focus on the control of the hydrological and sedimentological connectivity at the catchment scale. For example, the density of the ditch network could be modified or the spatial distribution of vegetative filter strips used for sediment trapping could be optimized. In addition, the vegetative filter strips could constitute new seed bank sources for species that are affected by the distance to natural lands and roads.

Shallow water table effects on water, sediment, and pesticide transport in vegetative filter strips – Part 2: model coupling, application, factor importance, and uncertainty

Abstract. Vegetative filter strips are often used for protecting surface waters from pollution transferred by surface runoff in agricultural watersheds. In Europe, they are often prescribed along the stream banks, where a seasonal shallow water table (WT) could decrease the buffer zone efficiency. In spite of this potentially important effect, there are no systematic experimental or theoretical studies on the effect of this soil boundary condition on the VFS efficiency. In the companion paper (Muñoz-Carpena et al., 2018), we developed a physically based numerical algorithm (SWINGO) that allows the representation of soil infiltration with a shallow water table. Here we present the dynamic coupling of SWINGO with VFSMOD, an overland flow and transport mathematical model to study the WT influence on VFS efficiency in terms of reductions of overland flow, sediment, and pesticide transport. This new version of VFSMOD was applied to two contrasted benchmark field studies in France (sandy-loam soil in a Mediterranean semicontinental climate, and silty clay in a temperate oceanic climate), where limited testing of the model with field data on one of the sites showed promising results. The application showed that for the conditions of the studies, VFS efficiency decreases markedly when the water table is 0 to 1.5 m from the surface. In order to evaluate the relative importance of WT among other input factors controlling VFS efficiency, global sensitivity and uncertainty analysis (GSA) was applied on the benchmark studies. The most important factors found for VFS overland flow reduction were saturated hydraulic conductivity and WT depth, added to sediment characteristics and VFS dimensions for sediment and pesticide reductions. The relative importance of WT varied as a function of soil type (most important at the silty-clay soil) and hydraulic loading (rainfall + incoming runoff) at each site. The presence of WT introduced more complex responses dominated by strong interactions in the modeled system response, reducing the typical predominance of saturated hydraulic conductivity on infiltration under deep water table conditions. This study demonstrates that when present, the WT should be considered as a key hydrologic factor in buffer design and evaluation as a water quality mitigation practice.

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

Abstract. Vegetation buffers like vegetative filter strips (VFSs) are often used to protect water bodies from surface runoff pollution from disturbed areas. Their typical placement in floodplains often results in the presence of a seasonal shallow water table (WT) that can decrease soil infiltration and increase surface pollutant transport during a rainfall-runoff event. Simple and robust components of hydrological models are needed to analyze the impacts of WT in the landscape. To simulate VFS infiltration under realistic rainfall conditions with WT, we propose a generic infiltration solution (Shallow Water table INfiltration algorithm: SWINGO) based on a combination of approaches by Salvucci and Entekhabi (1995) and Chu (1997) with new integral formulae to calculate singular times (time of ponding, shift time, and time to soil profile saturation). The algorithm was tested successfully on five distinct soils, both against Richards's numerical solution and experimental data in terms of infiltration and soil moisture redistribution predictions, and applied to study the combined effects of varying WT depth, soil type, and rainfall intensity and duration. The results show the robustness of the algorithm and its ability to handle various soil hydraulic functions and initial nonponding conditions under unsteady rainfall. The effect of a WT on infiltration under ponded conditions was found to be effectively decoupled from surface infiltration and excess runoff processes for depths larger than 1.2 to 2 m, being shallower for fine soils and shorter events. For nonponded initial conditions, the influence of WT depth also varies with rainfall intensity. Also, we observed that soils with a marked air entry (bubbling pressure) exhibit a distinct behavior with WT near the surface. The good performance, robustness, and flexibility of SWINGO supports its broader use to study WT effects on surface runoff, infiltration, flooding, transport, ecological, and land use processes. SWINGO is coupled with an existing VFS model in the companion paper (Lauvernet and Muñoz-Carpena, 2018), where the potential effects of seasonal or permanent WTs on VFS sediment and pesticide trapping are studied.

The effects of disproportional load contributions on quantifying vegetated filter strip sediment trapping efficiencies

Vegetated filter strips (VFSs) are a best management practice (BMP) commonly implemented adjacent to row-cropped fields to trap overland transport of sediment and other constituents present in agricultural runoff. Although they have been widely adopted, insufficient data exist to understand their short and long-term effectiveness. High inter-event variability in performance has been observed, yet the majority of studies report average removal efficiencies over observed or simulated events, ignoring the disproportional effects of loads into and out of VFSs over longer periods of time. We argue that due to positively correlated sediment concentration-discharge relationships, disproportional contribution of runoff events transporting sediment over the course of a year (i.e., temporal inequality), decreased performance with increasing flow rates, and effects of antecedent moisture condition, VFS removal efficiencies over annual time scales may be significantly lower than reported per-event averages. By applying a stochastic approach, we investigated the extent of disparity between reporting average efficiencies from each runoff event over the course of 1 year versus the total annual load reduction. Additionally, we examined the effects of soil texture, concentration-discharge relationship, and VFS slope in contributing to this disparity, with the goal of revealing potential errors that may be incurred by ignoring the effects of temporal inequality in quantifying VFS performance. Simulation results suggest that ignoring temporal inequality can lead to overestimation of annual performance by as little as 20%, with the greatest disparities observed for soils with high clay content.

An Improved Representation of Vegetative Filter Strips in SWAT

Abstract. Vegetative filter strips (VFS) are popular conservation practices installed at the edges of agricultural fields to reduce losses of pollutants from agricultural areas to receiving waterbodies. The recent interest in using VFS areas as multifunctional landscapes necessitates an improved depiction of VFS in simulation models. This study is aimed to enhance the physical representation of VFS in the Soil and Water Assessment Tool (SWAT) to improve the representation of ecohydrologic processes and land management practices in VFS areas. The proposed enhancement enables routing of water, sediment, and nutrients from the source area through the VFS area and makes the infiltrated water and nutrients available for filter crop uptake. The improvements are implemented in SWAT by modifying input files through Matlab scripts and by changing SWAT subroutines to enable routing. The model improvements are tested with three paired watershed studies with and without edge-of-field VFS in central Iowa. The improved model estimated 46% runoff reduction, 91% sediment reduction, 83% total phosphorus reduction, and 54% nitrate reduction with VFS, and these estimates closely matched the measured VFS reductions. The improved model was able to represent increased infiltration, soil moisture, and denitrification in the VFS area, along with accurately capturing crop yields in the source and VFS areas. Overall, the results indicate improved physical representation of VFS in SWAT. Keywords: Conservation measures, Flexible buffer strips, Multifunctional buffers, SWAT model, Vegetative filter strips.

Assessing Surface Flowpath Interception by Vegetative Buffers Using ArcGIS Hydrologic Modeling and Geospatial Analysis for Rock Creek Watershed in Central Iowa

Abstract. Nonpoint-source (NPS) pollution is a major cause of surface water quality degradation due to the transport of chemicals, nutrients, and sediments into lakes and streams. Vegetative buffers comprise several effective landscape best management practices (BMPs) that include vegetative filter strips (VFS) and grassed waterways. However, some BMPs are less effective due to concentrated surface flow, improper cropland-to-VFS area ratios, and surface flowpaths that partially or completely bypass vegetative buffers. The overall objective of this study was to quantify the accuracy of simulated flowpaths relative to observed and global positioning system (GPS)-assisted ground-truthed surface flowpaths for improved placement of VFS and other vegetative buffers to effectively intercept surface runoff. This study was conducted on three research sites in Rock Creek watershed in central Iowa. Geographic information system (GIS) software was used for flowpath hydrologic modeling and geospatial map comparison analysis. Digital elevation model (DEM) datasets were used for flowpath simulation and included internet-available USGS 30 m × 30 m grid (typically used to design and site VFS buffers) and light detection and ranging (LiDAR) 5 m × 5 m grid DEMs. Results from this study indicate that the LiDAR 5 m × 5 m DEM generated significantly more accurate simulated flowpaths than the USGS 30 m × 30 m DEM. These results quantitatively underscore the efficacy of using high-resolution LiDAR DEM data to more accurately determine how well surface flowpaths are intercepted by VFS and other vegetative buffers. These results also demonstrate the benefits of coupling high-resolution aerial imagery with quantitative geospatial map comparison data to improve visualization and comparison of field-scale and watershed-scale hydrologic and terrestrial attributes. Ultimately, the results and procedures from this study will be applied to the development of a novel cloud-based, user-interactive, virtual-reality decision support (DS) tool that can be used to remotely assess hydrologic landscape conditions, prescribe improvements to existing BMPs, and determine new sites for enhanced BMP placement and functionality within a high-resolution 3-D imagery environment. Keywords: ArcGIS, Best management practices (BMPs), Decision support (DS) tool, Digital elevation model (DEM), Geospatial analysis, Light detection and ranging (LiDAR), Nonpoint-source (NPS) pollution, Surface runoff, Vegetative filter strip (VFS), Watershed hydrol