Impact of Bridge Construction on Suspended Sediment Concentrations in Walnut Creek, Texas

This study examines the impact of a bridge construction project on suspended sediment concentration in Walnut Creek, Mansfield, Texas. A monitoring program was conducted during the project, using both continuous and discrete samples collected upstream, downstream, and at the construction site. Water samples were collected from the creek manually, using automated samplers to collect data during various flow and rainfall conditions. Data from four nearby stations were used to calculate rainfall at the bridge location, employing the inverse distance squared (IDS) precipitation model. The flow records from the USGS station, located 4.3 km downstream of the construction site, were adjusted to account for the difference in watershed area between the construction site and the station. Total suspended solids (TSS) and turbidity were measured, and the results indicated that construction activities influenced the sediment transport and deposition pattern in the creek, particularly during storms. Several recorded rainfall events, ranging from 10 to 94 mm/day, increased downstream TSS by 7%–38%. However, on March 16, 2024, following 23 mm of rainfall over a 5-h period, TSS levels at the bridge site and downstream increased significantly compared to upstream levels, rising by up to five times at the construction site. This spike in sediment concentration was largely attributed to runoff from the construction area. The study highlights that bridge construction can have a measurable impact on sediment levels downstream of the construction site, especially during storm events.