Sediment Collection and Analysis of Sediment Contributing to State Storm Sewer Facilities

Authors

Document Type

Article

Citation

Dvorak, B. I., Admiraal, D. M., & Shrestha, P. (2026). "Sediment Collection and Analysis of Sediment Contributing to State Storm Sewer Facilities", NDOT Research Report FY24(031).

Abstract

The Nebraska Department of Transportation (NDOT) must manage sediment, and pollutant loads from roadway runoff to meet stormwater regulations. The SAFL Baffle, a hydrodynamic separator used by NDOT, depends on reliable estimates of total suspended solids (TSS) and particle size distribution (PSD). However, limited data exists for Nebraska roadways. In this study stormwater runoff was monitored at four NDOT-maintained sites, two in Lincoln and two in Beatrice, over 1.5 years to characterize TSS and PSD and to evaluate SAFL Baffle performance using the SHSAM model. Results showed large variability across sites and seasons. Median TSS ranged from 158 to 580 mg/L, and median particle size (d50) from 16 to 322 µm. Finer particles dominated at most sites, likely due to runoff from gravel or exposed soils off the roadway and especially outside of the NDOT right of way. Higher TSS in spring was observed and reflected low vegetation cover and winter sediment buildup. SHSAM modeling showed that the SAFL Baffle alone may not achieve 80 percent TSS removal, as it is less effective for fine particles. However, if off-site sediment loads are credited toward compliance, performance goals could be met. The study highlights the need for local sediment data and for accounting for off-site sources in NDOT stormwater design.