Alternative Tile Intake Design for Tile Drainage: A Case Study

The overall goal of this study is to demonstrate the effectiveness of an alternative tile intake (ATI) at reducing runoff, sediment, and nutrient loads from agricultural fields during extreme storm events through an ongoing demonstration project in the Clear Creek, IA watershed. An ATI is a best management practice (BMP) consisting of a modified gravel intake atop a layer of wood chips. Gravel intakes have been shown to be highly efficient at trapping sediment and sediment-bound particulates, like phosphorus, by enhancing settling through ponding and filtration, while the addition of the wood chips is to facilitate denitrification, similar to a bioreactor. Additionally, these intakes can help attenuate runoff relative to conventional intakes by reducing the flow rate of runoff into the subsurface. In this study, which will ultimately utilize a mixture of numerical, analytical, laboratory, and field methods, a three-part control volume is conceptualized consisting of the contributing hillslope, the ATI, and the subsurface pipe below the ATI. To date, the Water Erosion Prediction Project (WEPP) has been used to simulate the field conditions at the demonstration site for calculating runoff volumes and sediment fluxes to the ATI for different magnitude events. A physical model of the installed ATIs at the demonstration site is currently being used in the laboratory to quantify the saturated hydraulic conductivity and filter efficiency of different combinations of pea gravel and wood chips. These laboratory experiments will also be complemented with analytical exercises and infield monitoring of the installed ATIs. Preliminary measurements suggest that ATIs have a filtering efficiency of about 80%.