Implications of Streamflow Changes Following Timber Harvesting for TMDL Development in Low-Gradient Forested Headwaters

The impacts of timber harvesting on headwater streamflow and water quality have been well-established in mountainous regions, but fewer studies have examined low-gradient headwaters of the Gulf Coastal Plain, which display highly variable hydrology. In addition, a knowledge gap exists between plot- and watershed-scale impacts of harvesting. In this study, paired-watershed and Before-After-Control-Impact (BACI) designs were utilized to quantify changes in streamflow for 27 months after clearcut harvesting with and without BMPs in a low-gradient forested 3rd order watershed draining 369 km2 of North Central Louisiana. No difference was found in monthly baseflow measurements at any site or in peak water level response to storm events. Post-harvest baseflow decreased at most of the monitoring locations. Poor stage-discharge relationships complicated the quantification of changes in hydrology post-harvest. Beaver dams complicated stream hydrology in this low-gradient landscape. Streamflow was minimal during the summer months and annual discharge was dominated by storm events. Therefore, Total Maximum Daily Load (TMDL) development for nutrient and sediment loading should focus on storm events.