Hydrodynamic Simulations for Trash Loading in Southern California’s Dense Urbanized Watersheds

• Published in: Journal of environmental engineering (New York, N.Y.) N.Y.), 2024-08, Vol.150 (8)
• Main Authors: Bagheri, Kian, Davani, Hassan, Biggs, Trent, McMillan, Hilary
• Format: Article
• Language: English
• Subjects: Anthropogenic factors; Calibration; Creeks; Creeks & streams; Estimates; Interceptors; Land use; Litter; Metropolitan areas; Nonpoint sources; Parameter sensitivity; Population density; Rainfall; Regional development; Rivers; Sensitivity analysis; Stormwater; Technical Papers; Urban areas; Watersheds; Waterways
• ISSN: 0733-9372; 1943-7870
• DOI: 10.1061/JOEEDU.EEENG-7474

AbstractWaterways and water bodies worldwide are impacted by anthropogenic litter (hereafter “litter” or “trash”), generated from nonpoint sources. This study analyzes litter loads across various land uses within two Los Angeles County watersheds: the Ballona Creek and the Los Angeles River. Our objective is to present a methodology to develop buildup and washoff parameters for densely populated urban areas, such as the coastal metropolitan area of Los Angeles, California. An assessment is also made to test how these model parameters perform when applied to another urbanized watershed with similar rainfall and climate patterns (i.e., the San Diego River Watershed in California). Using extensive litter collection data from small drainages (approximately 572 locations, each draining 0.05–8.5 ha), we estimate buildup and washoff model parameters. These parameters are used to simulate the buildup of litter and subsequent washoff (load) of litter in our selected watersheds. Simulated results are validated against observed data from different years in all three watersheds. To date, no study has used litter washoff data to develop these parameters for stormwater models and applied them on a regional scale. We compared linear and nonlinear power functions of litter buildup during interstorm periods. Although there were limited data to develop washoff parameters, an exponential washoff function was used and calibrated to the observed washoff. Generally, storm events with the greatest antecedent dry days had the largest litter loading. Buildup rates varied among land uses, and key calibration parameters included the maximum buildup, buildup rate constant, washoff exponent, and washoff coefficient. A parameter sensitivity analysis was conducted to reveal the washoff exponent as the most sensitive parameter. Annual litter loading estimates were 4.60  kg/ha for the Ballona Creek and 11.50  kg/ha for the Los Angeles River. Litter loading estimates for Ballona Creek were validated and calibrated to align with observed data from the Ballona Creek Trash Interceptor, resulting in an annual washoff load of 2.1  kg/ha. The estimated annual litter loading for the Lower San Diego River was 2.15  kg/ha falling between the mean (0.77  kg/ha) and the maximum (3.56  kg/ha) observed values. When applying model parameters from one watershed to another, models require extensive calibration and validation data, as extrapolating data between watersheds can introduce errors. Practical Ap