Beyond the Clean Water Rule: Impacts of a Non-Jurisdictional Ditch on Headwater Stream Discharge and Water Chemistry

Ephemeral drainage ditches in upland areas, such as those draining roads, are excluded from the jurisdiction of the U.S. Clean Water Act (CWA). While several studies have shown that road drainage and/or development in forested watersheds can impact water quality, the direct physical and chemical impacts of a single drainage ditch have not been identified. In this study, we measured water chemistry (silicon, calcium, and sulfate) and magnitude of discharge from one such feature and at the outlet of the catchment it is within. We found that discharge from the drainage ditch was sometimes over 10% of the larger stream into which it drains, despite the small relative size of the ditch catchment (1.1 ha) compared to the main catchment (43 ha). Furthermore, we observed sharp decreases in silicon and calcium and increases in sulfate concentrations downstream from the drainage ditch across longitudinal sampling of the stream network. This illustrates the impacts of a common feature in high relief, forested areas that when aggregated over the landscape are likely responsible for regional water quality impacts.