Fluvial Wetland Reconstruction Strategies in the Southeastern USA

Keywords: geomorphology, floodplain, alluvium
Abstract Type: Paper Abstract

Abstract

Fluvial wetlands commonly occurred on alluvial bottomlands in the southeastern USA prior to the 19th century. However, 19th-20th century infrastructure for agriculture and silviculture (drainage ditches and roads), along with human-induced rapid sedimentation, eliminated or reduced functionality of most wetlands. Current interest in wetland restoration is gaining momentum, but target (pre-disturbance) conditions often are unclear, which leads to difficulty in identifying restoration strategies. This process can benefit from knowledge of the fluvial geomorphic and hydrologic settings, including pre-disturbance conditions. We present key elements to consider in wetland selection and restoration from practical experiences. Sites well suited for wetland restorations include floodbasins, back-levee swales, and paleochannels. Such geomorphic settings and infrastructure can now be easily characterized using very high-resolution (1-m) light detection and ranging (LiDAR) topographic images. In bottomland geomorphic settings, connectivity to groundwater and streamflow from nearby hillslopes best ensures long-standing water within wetlands. Seasonal wetlands benefit from connectivity to channels during overbank events (crevasse channels, paleochannels, ditches). Road crossings and culverts that provide inadequate flow and connectivity commonly need to be removed, and pre-existing ditches and drainage tiles may need to be blocked, filled, or removed. LiDAR imagery streamlines the wetland restoration process, but it is inadequate for identification of current water tables and thickness mapping of 19th-20th century human-induced sediment top-strata that may need to be removed to fully restore wetlands. Therefore, field observations and coring remain necessary. Example scenarios are presented from recent wetland restoration activities in the North Carolina Blue Ridge and the Georgia Coastal Plain.