Sediment Basin Outflow Influence on Stream Water Quality During Highway Construction

Can we tell if turbid water has been discharged into a stream by monitoring the stream? This presentation will cover how sediment basin discharge and stream water quality (turbidity and total suspend solids) are related. The water quality of sediment basin discharge and stream water quality (upstream and downstream of the construction site) were monitored for three years. Water quality basics and stream flow interpretation will be covered.

Full Abstract: Sediment discharge from construction sites can have harmful effects on aquatic life. Sediment basins are often used to capture runoff with high loads of sediment to settle out the suspended sediments (SS) prior to discharging into adjoining waters. The objective of this monitoring was to see if construction of I-540 impacted the water quality (turbidity and total suspended solids [TSS]) of Swift Creek. Swift Creek was chosen since a bridge was going to be built over the creek, and it is home to an endangered freshwater muscle. Monitoring happened at one location upstream and two locations downstream of the construction site. The water quality of several sediment basins on I-540 were additionally monitored. Turbidity and TSS were samples taken by automatic samplers during storm events in the basins and creek. An automatic sampler also took a daily water quality sample for the creek as a baseline. Turbidity and TSS of the creek and sediment basins were influenced by rainfall intensity. The creek water quality fluctuated over time. The level of the creek fluctuated a lot during the monitoring and increased 1.8 to 2.2 m during storm events. Water being discharged into the creek often exceeded the turbidity and TSS of the creek. However, the creek turbidity and TSS did not increase as much as expected or compared to other sampling campaigns. Swift Creek is in a highly suburban watershed. It is possible that construction of suburbs has led to more water flowing into the creek and the dilution of turbid water being discharged from the construction site.