SEDIMENT DISPERSAL AND TRANSPORT THROUGH FIRST-ORDER STREAMS AND ASSOCIATED WETLANDS

Three stream gauges were placed along 1st-order streams downgradient of a substantial construction project in sout central Mississippi. A fourth gauge was placed along a relatively undisturbed stream to act as a control. The automated gauges take readings every 20 minutes of temperature, depth, conductance, and turbidity, and were installed 2-years before construction commenced.

This study looks at the impact of large construction projects on the physical aspects of the streams including cross-sectional shape, turbidity, temperature, conductivity, and the ability of the associated wetlands to collect and retain sediment. The longitudinal transport of the sediment is also focused on to ensure downstream ecosystems are not negatively impacted.

The streams studied are housed in relatively extensive riverine wetlands characterized with a shallow gradient. The girth of the wetlands allow for substantial storage capacity, and help protect the downstream areas from inundation with sediment. One stream is characteized by hardwoods/pines with little ground vegetation, and the other initially flows through similar conditions, but then is surrounded by forested grasslands with sparse clusters of pines and shrubs.

Abnormally high turbidity values were observed before and after construction began. Large amounts of sediment have been transported, at different times, through two of the streams and deposited along their floodplain directly downstream of the construction box. The first inundation of sediment showed little to no impact on reaches of the stream only a half mile downstream. The stream that is currently undergoing a heavy sedimentation event, shows impacts that reach further downstream, but do not seem to impact any stream of 3rd order and above.