INFLUENCE OF ROADS AND CANALS ON GROUNDWATER-SURFACE WATER INTERACTIONS IN A CHANNELIZED WETLAND

The goal of this study was to investigate the effect of a canal and adjacent road on groundwater-surface water interactions in a channelized wetland. The study was conducted in the Emily and Richardson Preyer Buckridge Coastal Reserve in North Carolina, which is boarded on three sides by the Alligator River. The Reserve has a network of canals leading into the Alligator River that was excavated to allow the construction of access roads to facilitate logging activities that have now ceased. We undertook a detailed investigation by installing monitoring wells in the stream bed and banks of the canal. Water level loggers and temperature sensors were then deployed at various depth intervals in the wells to record groundwater levels and temperature. Stilling wells and specific conductivity loggers were also installed to measure electrical conductivity in the canal water. Sediment characteristics were then recorded from samples derived from holes drilled into the banks of the canal and across an adjacent dirt road and wetland. Finally, electrical resistivity surveys were conducted to assess salt levels in the sediments underlying the road, wetland and adjacent to the canal. The specific conductivity and electrical resistivity records were used as a measure of salt content in ground and surface water. Results show that there were periodic salinity pulses in the canal. Electrical resistivity was relatively low next to the canal and wetland, but was high beneath the road. This implies that there was a high concentration of salts underneath the wetland, in the canal and adjacent to the canal. However, the salt concentrations beneath the road were relatively low. These observations therefore suggest that the canals may facilitate movement of brackish surface water into the reserve from the Alligator River whereas the roads may act as barriers to shallow subsurface flow. The relative location of wetlands, roads and canals may therefore play a role in facilitating how quickly brackish water is flushed from the wetland system. If a road lies between a wetland with high salt concentrations and a canal, the high salt levels may still persist in the wetlands even though groundwater flow is towards the canal. The results of this study may therefore have implications for management strategies that may be developed in the Reserve.