Gravel Inlet Effects on Runoff Losses of Solids, Organic Matter, and Phosphorus on a Field Scale

Managing water in depressional areas with surface intakes is important for crop production, but can result in downstream impacts to lakes, rivers, and streams. In a recent study a gravel filter reduced losses of sediment, particulate P, and chemical oxygen demand by 20-28%. Soluble forms of N and P were a small part of the total and increased by passing through the gravel filter with previously deposited sediment. Based on the precipitation during this study, considered in a Minnesota historical climatic context, it is estimated that untilled gravel filters will have a life span of at least ten years. This study has also shown that gravel filters preferentially trap sediment with higher P concentrations. Tilling through gravel filters greatly increases sediment deposition, this reduces water flow but increases sediment filtration due to reduced gravel pore space.