Locating Potential Sites for Nutrient Interception Practices in a Tile-Drained Watershed Using Lidar Data.

Practices that reduce nutrient loadings from tile-drained watersheds can improve water quality, if sited and managed optimally. Reconstructed wetland and two-stage ditches are two practices that efficiently intercept nutrients, but are expensive to install and must be sited where geomorphic and economic criteria are both met. In this study, we identified potential locations for these practices in Lime Creek (Illinois) using LiDAR topographic data. A 1-m grid elevation model was processed to remove false impoundments where roads intersected channels. Depths of drainage ditches were estimated and mapped. This provided maps with elative estimates of excavation spoil volumes generated by developing two stage ditches throughout the watershed. To site wetlands, a shallow impoundment 2.4 m deeper than the ditch was simulated above each road crossing; sites were dropped if surface drainage would be impeded upstream to the next road. A second impoundment 0.9 m deeper than the drainage ditch was then simulated. The 0.9 m impoundment estimated the wetland area, and the 2.4 m impoundment estimated a buffer zone where the wetland would impede drainage. After ensuring infrastructure would not be inundated, a field review was conducted. The approach was successful and eleven sites were identified as possible wetland reconstructions. About 30% of Lime Creek watershed could be serviced by nutrient removal wetlands covering less than 2% of the contributing area. Including buffers, up to 6.2% of the land could be removed from row cropping but buffers would support bioenergy crops, forage, or wildlife habitat. LiDAR data can provide new tools to screen sites for multiple conservation practices within watersheds.