Field-Monitoring Sediment Basin Performance during Highway Construction

Abstract

Stormwater regulations require erosion and sediment control practices to be implemented during construction to prevent discharging polluted water offsite and mitigate downstream effects. Sediment basins are a common sediment control practice used to detain suspended sediment from stormwater runoff by providing residence time and storage to promote gravitational settling. Sediment basin design, and thus pollutant removal efficiency, vary regionally due to local design standards and preferences. Traditional sediment basins require a dedicated excavation pond with various mechanisms for dewatering. This manuscript presents the results of a case study where two sediment basin systems were created within a conveyance channel by constructing an earthen berm across the channel to detain sediment-laden stormwater. A dewatering riser pipe was routed through the earthen berm to provide primary dewatering. The in-channel sediment basin was constructed with a 3% slope and a 10 ft. bottom width. The first system consisted of one basin created by a single earthen berm damming sediment-laden runoff, whereas the second system included two earthen berms, creating two in-channel sediment basins in series. The two systems were independently field monitored during Highway U.S. 30 construction in Tama County, Iowa. Prior to this field campaign, there was no documented performance data on the in-channel sediment basin design. Field monitoring was conducted by deploying a rain gauge and automated water samplers positioned at the inflow and discharge points of a (a) single basin and (b) two basins in series within a roadside channel. Instrumentation was completed on in situ basins constructed per Iowa Department of Transportation standards before the start of site earthwork. During the monitoring period, no maintenance or dredging was recorded. The retrieved water samples were taken from the monitored basins and analyzed for turbidity. Inflow turbidities often reached magnitudes up to the 103 NTU. Water quality samples from the basin indicated negligible turbidity reduction after residence. During monitoring, there were several occurrences where discharge turbidity was higher than inflow turbidity, indicating that the basin was serving as a sediment source. This manuscript describes the in-channel sediment basin design, field-monitoring site and sampling regimen, and discusses potential design technique and component improvements to achieve enhanced performance.

Large-Scale Performance Evaluation of Various Woven Silt Fence Installations under Nebraska Highway Conditions

“…Additionally, offsetting the trench at the toe of the silt fence by 15.2 cm (6 in.) reduced undermining at no additional cost and was recommended to be put into practice [24].…”

Water Quality Modeling and Monitoring

“…To prevent the discharge of polluted stormwater offsite and mitigate the downstream effects on the water quality of the receiving waterbody, stormwater regulations in the USA require erosion and sediment control practices to be implemented during construction. Schussler, Perez, Whitman, and Cetin [2] implemented a field monitoring program on two in-channel sediment basins along Highway U.S. 30 construction sites in Tama County, Iowa, USA, using automated water samplers to study sediment concentrations at the inflow and discharge of the basins to quantify sediment removal efficiency. Sediment basins are typically employed on the edge of disturbed watersheds to capture and detain suspended sediment from stormwater runoff by providing residence time and storage to promote gravitational settling.…”

“…Sediment basins are typically employed on the edge of disturbed watersheds to capture and detain suspended sediment from stormwater runoff by providing residence time and storage to promote gravitational settling. The limited right-of-way in the construction site led to the creation of in-channel basins from existing roadside channels to treat stormwater [2]. Inflow turbidities in the monitored sediment basins reached magnitudes of up to 103 NTU, and discharge turbidity monitoring indicated negligible turbidity reduction or even turbidity increase on several occasions.…”

“…Inflow turbidities in the monitored sediment basins reached magnitudes of up to 103 NTU, and discharge turbidity monitoring indicated negligible turbidity reduction or even turbidity increase on several occasions. Throughout the study, they recommended [2] several potential design improvements and techniques (e.g., implementing an upstream forebay, geotextile lining, baffles, floating surface skimmer, and flocculant dosing) to enhance in-channel sediment basin performance.…”