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

John Gannon,David Kinner,Mark Lord

doi:10.3390/w8120607

Abstract

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.

Highlights

The 2015 update to the U.S Clean Water Act (CWA) expanded the definition of “waters of the United States” to include headwater streams, including those classified as intermittent and ephemeral [1,2]
In this study we show that a drainage ditch draining a paved road in an otherwise forested upland catchment in western North Carolina affects water chemistry in the stream network and contributes disproportionally high discharge to the system
Decreases in Si and Ca2+ concentrations were observed below the confluence of the drainage ditch and the stream network, as well as an increase in SO24−

Summary

Introduction

The 2015 update to the U.S Clean Water Act (CWA) expanded the definition of “waters of the United States” to include headwater streams, including those classified as intermittent and ephemeral [1,2]. This broadened definition of waters within the jurisdiction of the CWA, still explicitly excludes stormwater drainage ditches in upland areas [2]. It has been estimated that annual costs of increased sediment influx to rivers alone is in the tens of billions of dollars [10] These costs are likely to increase for regions with continued development, such as the Southern Appalachian Mountains of North Carolina [11]

Results

Discussion

Conclusion