A Comparison of Electromagnetic Induction Mapping to Measurements of Maximum Effluent Flow Depth for Assessing Flow Paths in Vegetative Treatment Areas

Vegetative treatment systems (VTSs) are one type of control structure that has shown potential to control runoff from open feedlots. To achieve maximum performance, sheet-flow over the width of the vegetative treatment area (VTA) is required. Tools, such as maps of flow paths through the VTA, are needed to aid producers in locating concentrated flow paths and in determining the most effective approach to redistribute flow. Members of the USDA-ARS USMARC laboratory have developed remote sensing techniques using Electromagnetic Induction (EMI) to measure spatial nutrient distribution, and identify possible flow paths, within VTAs. The objective of this study was to determine whether apparent soil electrical conductivity maps can be used to locate concentrated flow paths in the VTA. Effluent flow paths in the VTA were determined by measuring the maximum height of flow at different locations within the VTA. In this study, PVC stakes were coated with a water sensitive paint and located throughout the treatment area during effluent release from solid settling basin to the VTA. The maximum depth of flow at each stake was recorded following a release event from the settling basin. The flow maps generated from the data were compared to ECa maps measuring salt build-up in the soil due to basin discharge. The flow paths identified in the EMI maps were generally in agreement with measured water depths in the VTA. Therefore, techniques that use EMI technology can be used by regulators to monitor VTS performance, by design engineers to improve system performance, and by producers to better manage their systems.