Civil and Environmental Engineering, Department of
Department of Civil and Environmental Engineering: Dissertations, Theses, and Student Research
First Advisor
Dr. Bruce Dvorak
Second Advisor
Dr. David Admiraal
Committee Members
Dr. Arron Mittelstet
Date of this Version
Fall 10-22-2025
Document Type
Thesis
Citation
A Thesis Presented to the Faculty of Graduate College at the University of Nebraska In Partial Fulfilment of Requirements For the Degree of Master of Science
Major: Civil Engineering
Under the Supervision of Professors
Bruce I. Dvorak and David M. Admiraal
Lincoln, Nebraska
July 2025
Abstract
The Nebraska Department of Transportation (NDOT) must manage sediment and pollutant loads from roadway runoff to meet stormwater regulations for discharges into impaired waters. The SAFL Baffle, a hydrodynamic separator used by NDOT, depends on accurate estimates of total suspended solids (TSS) and particle size distribution (PSD). However, existing studies show large variability in these characteristics, limiting their relevance to Nebraska roadways.
This study monitored stormwater runoff for 1.5 years at four NDOT-maintained sites—two in Lincoln and two in Beatrice—that received runoff from areas outside the roadway right-of-way. The SAFL Baffle was evaluated using the SHSAM (Sizing Hydrodynamic Separators and Manholes) model following NDOT permit requirements.
Results showed high variability in sediment characteristics among sites and seasons. Median TSS ranged from 158 to 580 mg/L, and median particle size (d50) from 16 to 322 µm. Three sites exhibited finer particles, likely from gravel surfaces and exposed soils outside the right-of-way, while coarser sediment was associated with impervious cover and steeper slopes. Higher spring TSS concentrations suggested seasonal effects from limited vegetation growth and winter sediment buildup.
SHSAM modeling indicated that the SAFL Baffle alone is unlikely to meet the 80% TSS removal target because of reduced efficiency for fine particles. However, since much of the sediment originated from off-site areas, permitting credit for off-site treatment could allow compliance. The study underscores the importance of region-specific sediment data and accounting for off-site sources in Nebraska roadway runoff management.
Comments
Copyright 2025, Pavel Shrestha