Sediment export from a highway construction site in Central North Carolina.

摘要

Sediment export and turbid runoff from active construction sites continue to be a source of impairment to surface water resources. Few studies have been published that include monitoring data from construction sites, particularly highway construction sites. In this study, water quality monitoring of runoff originating from three sections of a highway construction corridor was conducted during a 4.5-year period. Two unnamed tributaries, referred to as Tilly and Ellery for this study, were monitored at two locations downstream of the highway corridor, and one tributary, referred to as King's Mill, was monitored upstream and downstream of the highway corridor. At each station, discharge was continuously monitored and flow-proportional samples were collected. Samples were analyzed for total suspended solids, total solids, and turbidity. A recording raingauge was also maintained at one of the highway monitoring stations. Monitoring data at all stations documented increased sediment export and turbidity levels during the construction period as compared to the pre- and post-construction periods. During construction, sediment export rates ranged from 2.7 to 17.7 Mg ha-1 year-1, while mean turbidity levels ranged from 466 to 1,607 NTU for the five stations downstream of the highway corridor. For the station with the greatest sediment export, about 32% of the export occurred during two back-to-back tropical storms. At this time, one section of the highway was particularly susceptible to erosion because more than 6 m of fill material had recently been added to bring the road surface to near grade and vegetation had not yet been established. Increases in sediment export and turbidity at the other four downstream stations during highway construction were less pronounced. Mean turbidity levels during construction at all downstream stations were greater than 50 NTU. Post-construction mean turbidity levels were much less than during construction but were still greater than pre-construction at four of the five stations. Post-construction turbidity levels on the King's Mill tributary downstream of the highway were not significantly different from upstream.