Implementation of shallow water table effects on pesticide runoff mitigation efficiency by vegetative filter strips within SWAN-VFSMOD

2021 ◽  
Author(s):  
Robin Sur ◽  
Rafael Muñoz-Carpena ◽  
Stefan Reichenberger ◽  
Klaus Hammel ◽  
Horatio Meyer ◽  
...  
Keyword(s):  
Surface Water ◽  
Shallow Water ◽  
Water Table ◽  
Shallow Water Table ◽  
Vegetative Filter Strips ◽  
Worst Case ◽  
Filter Strips ◽  
Pesticide Runoff ◽  
Selection Of

<p>Quantitative mitigation of pesticides entering surface water using vegetative filter strips (VFS) is currently available within the regulatory SWAN tool for EU FOCUS STEP 4 simulations. For the VFSMOD model option, field estimates of surface runoff, sediment and pesticide loads simulated with the model PRZM are routed through the VFS where VFSMOD estimates the reductions of total inflow (dQ), eroded sediment (dE) and pesticide (dP) loads before the remaining runoff enters the waterbody. The reduced runoff is handed over to the TOXSWA aquatic model to calculate predicted environmental concentrations in surface water (PECsw). Brown et al. (2012) proposed VFSMOD parametrization rules including the selection of VFS soils and other characteristics for use in the FOCUS R1 to R4 (Rx) SWAN scenarios. The rules apply to free-draining soils, described in VFSMOD by the Green-Ampt model extended for unsteady rainfall. However, in some EU regions, the presence of a seasonal shallow water table (sWT) is common. In these cases, the VFS efficiency can be limited, depending on water table depth (WTD) and soil type. VFSMOD incorporates a sWT mechanistic infiltration component that has proven successful to predict sWT effects in VFS experiments. This component requires soil hydraulic characteristics, described by e.g. the Mualem-van Genuchten (MvG) equations.</p><p>The main objective of this study is to identify Rx representative VFS soils to study the effects of sWT on pesticide mitigation for a combination of illustrative storms and pesticides, as well as on PECsw from long-term SWAN simulations.</p><p>The selection and testing of the Rx VFS soils seeks to reflect a 90<sup>th</sup>-percentile worst case in space of dP. The multicriteria adopted in the soil selection evaluate not only dP, but also the percentile of important soil parameters for noWT (K<sub>s</sub>, S<sub>av</sub>) and sWT infiltration conditions (fillable pore volume f<sub>pv</sub>). The framework consisted of 4 steps: (a) soil spatial soil database analysis for VFS Rx mitigation scenarios; (b) selection of VFS candidate soils; (c) analysis of effects of sWT and sorption on dP for individual storm events; (d) Effect of sWT on long-term STEP 4 SWAN VFS mitigation simulations. For (a), representative soil profiles and area coverage for each of the EU Rx were obtained by combining the latest EU JRC soil profile databases SPADE2 and SPADE14. Each multilayer soil was aggregated into single-layer depth-weighted profiles, and MvG parameters were estimated using HYPRES pedotransfer functions (PTF). Water table depths (WTD) were set at equilibrium with TOXSWA median surface water level, and S<sub>av</sub> and f<sub>pv</sub> were calculated by numerical integration from MvG characteristics. For (b), 10644 VFSMOD simulations were run for all combinations of soils, T=1 and 10 yr storms, high/low Koc pesticides, and sWT/noWT conditions. Candidate Rx VFS soils were selected for the most conservative case (low Koc=100 Kg/L pesticide, T=10 yr storm) and noWT to achieve the target spatial 90<sup>th</sup> percentile worst case of pesticide load reduction by the VFS. </p><p>The implementation of the new sWT VFS mitigation component provides a more realistic description of pesticide reduction in accordance with STEP 4 EU FOCUS objectives.</p>

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

2018 ◽  
Vol 22 (1) ◽  
pp. 53-70 ◽  
Author(s):  
Rafael Muñoz-Carpena ◽  
Claire Lauvernet ◽  
Nadia Carluer
Keyword(s):  
Shallow Water ◽  
Water Table ◽  
Surface Runoff ◽  
Rainfall Intensity ◽  
Initial Conditions ◽  
Companion Paper ◽  
Soil Infiltration ◽  
Shallow Water Table ◽  
Vegetative Filter Strips ◽  
Filter Strips

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.

scholarly journals Shallow water table effects on water, sediment and pesticide transport in vegetative filter strips: Part A. non-uniform infiltration and soil water redistribution

2017 ◽  
Author(s):  
Rafael Muñoz-Carpena ◽  
Claire Lauvernet ◽  
Nadia Carluer
Keyword(s):  
Shallow Water ◽  
Water Table ◽  
Rainfall Intensity ◽  
Initial Conditions ◽  
Pollutant Transport ◽  
Soil Infiltration ◽  
Shallow Water Table ◽  
Vegetative Filter Strips ◽  
Filter Strips ◽  
Infiltration Excess

Abstract. Vegetation buffers like vegetative filter strips (VFS) are often used to protect water bodies from surface runoff pollution from disturbed areas. Their typical placement in bottomland 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 analyse 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 5 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 non-ponding conditions under unsteady rainfall. The effect of a WT on infiltration under ponded conditions was found effectively decoupled from surface infiltration/excess runoff processes for depths larger than 1.2 to 2 m, shallower for fine soils and shorter events. For non-ponded 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 behaviour with WT near the surface. The features and good performance of SWINGO support its coupling with an existing VFS model in the companion paper, where the potential effects of seasonal or permanent WTs on VFS pollutant transport and control are studied.

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

2018 ◽  
Vol 22 (1) ◽  
pp. 71-87 ◽  
Author(s):  
Claire Lauvernet ◽  
Rafael Muñoz-Carpena
Keyword(s):  
Hydraulic Conductivity ◽  
Shallow Water ◽  
Water Table ◽  
Overland Flow ◽  
Silty Clay ◽  
Relative Importance ◽  
Shallow Water Table ◽  
Vegetative Filter Strips ◽  
Filter Strips ◽  
Pesticide Transport

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.

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