Two systems are being monitored in Nebraska, a sloped VTA and a level VTA system. The level VTA, surrounded by a 1-foot high berm, impounds any runoff from the sloped VTA. We have a water level logger in the level VTAs and know the berm elevation with respect to the logger elevation. We also log the rain events at each site, so we compare the precipitation event to the depth logger and know when, and if, the level VTA is inundated (water goes over the berm). While we don’t know the volume, it is a simple way to evaluate our design for potential discharges.
Iowa State University is monitoring CAFO sites, and those systems are being monitored for inflow and outflow, using flumes and pipe flow sensors to measure flow. They are also measuring nutrient content of the flow with ISCO samplers and with these data can estimate nutrient mass going into and out of the VTA. For the Iowa sites, we can differentiate from a discharge related to direct rainfall runoff from the VTA and runoff coming from the feedlot because our settling basin valves are normally closed during rainfall events. And the monitoring equipment puts a time stamp on all collected flow data.
Because the permitted CAFOs are required to record and sample all discharges, the ISU project includes development of a low-cost method for meeting this need.
Author: Chris Henry, Biological Systems Engineering, University of Nebraska
