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

Abstract Submission: This study examines the impact of a bridge construction project on suspended sediment concentration in Walnut Creek, Mansfield, Texas. A water monitoring program was conducted throughout the project, using both continuous and discrete samples collected upstream, downstream, and at the construction site. Automated samplers and manual techniques captured data across varying flow and rainfall conditions. Rainfall 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 2.7 miles 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 creek’s sediment regime, particularly during storms. Several recorded rainfall events, ranging from 0.4 to 3.7 inches/day, increased downstream TSS by 7 to 38%. However, on March 16, 2024, following 0.9 inches of rainfall over a 5-hour period, TSS levels downstream of the bridge increased significantly, rising by up to 500% 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 in downstream waterbodies, especially during storm events.

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