Monitoring the performance of vegetative treatment systems across subhumid and semiarid rainfall zones

Abstract

Hydraulic loading of a vegetative treatment system (VTS) is an important factor of its performance. Water is the carrier of the nutrients from the feedlot onto the other components of the system. If a VTS can contain all applied water within a vegetative treatment area (VTA) then it will be able to control the nutrients as well. To determine the performance of VTS designs, four feedlots were studied across the state of South Dakota. Precipitation, VTA inflow, and VTA outflow were measured directly. Evapotranspiration (ET) was estimated using locally-measured weather parameters. Measurements showed that in six of the twelve site-years, VTS were able to prevent water from leaving the VTA. Two of the years that did have VTA releases were due to rainfalls in excess of a 25-year, 24-hour storm. This leaves four of the site years with releases under the 25-year, 24-hour storm limit and showed some of the possible design flaws that could be improved. Seasonal water releases from the VTA were all 5% or less of the seasonal inflow and precipitation that was applied to the VTA. To increase the performance of VTS, solids settling basins should have adequate size to contain runoff from a 25-year, 24-hour storm, a water restriction system to reduce the volume flow rate or delay the flow from the basin, and a water distribution system that spreads water evenly and slowly across the VTA.