Implications of a kinematic wave model for first flush treatment design

A deterministic model was developed to predict pollutant mass first flush and to utilize it for better design of best management practices (BMPs) that focus on treating the first flush. The model used the kinematic wave equation to calculate flow and mass transport, and erosion equations to calculate pollutant concentrations, which were assumed to be from a short and a long term source. The model parameters were calibrated with a parameter estimation procedure using three years’ monitoring data from a highway runoff site in west Los Angeles. The simulation results showed that there exists an optimum watershed size to maximize first flush. Contours of watershed length, developed from simulations for different conditions of rainfall and watershed geometry, can be used to design runoff collection systems for highways and parking lots to maximize first flush.     

Storm water quality of first flush urban runoff in relation to different traffic characteristics

Storm water quality was monitored at four sites in a middle-sized Swedish town. The objective was to compare storm water pollution in the first flush storm water runoff between sites with different traffic intensities within a town. Flow proportional storm water runoff samples were collected. The samples were analyzed for suspended solids, conductivity, total nitrogen, total phosphorus, oil index, lead, cadmium, copper, chromium, nickel, and zinc.

The results showed that the levels of heavy metals and total phosphorus in storm water were highest at the site with the highest traffic intensity (7000 vehicles/day). A strong linear dependence between suspended solids (SS) and total phosphorus and heavy metals was observed. SS was the dominant explanatory variable for these parameters and a suitable predictor. The observed correlation between SS, heavy metals, and total phosphorus means that reducing levels of suspended solids in storm water would contribute to a substantial decrease of particle-bound heavy metals and total phosphorus in storm water. No samples were taken during winter; however, results indicate that de-icing material used in winter may affect surface runoff quality during other seasons. The results can be used as a reference for storm water quality management for traffic-related sites in towns with similar land use and climatic characteristics.     

Modeling effectiveness of agricultural BMPs to reduce sediment load and organophosphate pesticides in surface runoff

Quantifying effectiveness of agricultural BMPs at the watershed scale is a challenging issue, requiring robust algorithms to simulate not only the agricultural production system but also pollutant transport and fate. This research addresses the challenge to simulate performances of BMPs in reducing organophosphates (OPs) runoff at the watershed scale. The SWAT model is calibrated and validated following a sensitivity analysis combining Latin Hypercube sampling and One-factor-At-a-Time simulation. The calibrated model is then applied in the Orestimba Creek Watershed to simulate BMPs including buffer strips, sediment ponds, vegetated ditches, use reduction, and their combinations. BMP simulation suggested that sediment ponds trap 54-85% of sediment from field runoff, but less than 10% of dissolved diazinon and chlorpyrifos. Use reduction can reduce pesticide load in a close-to-linear fashion. Effectiveness of vegetated ditches and buffers depends on their physical dimension and vegetation cover. Combining individual BMPs provides enhanced mitigation effects. The combination of vegetated ditches, buffer strips and use reduction decreases diazinon and chlorpyrifos load by over 94%. This study has suggested that the SWAT model reasonably predicts BMP effectiveness at the watershed scale. Results will assist decision making in implementing BMPs to reduce pesticide loads in surface runoff.     

国外雨水管理理念与实践

近年来,城市暴雨内涝问题得到各界广泛关注,城市雨水管理的重要性日益凸显。本文研究了国外雨水管理的发展历程,概述了"最佳管理实践"、"低冲击开发"、"水敏城市设计"和"可持续性城市排水系统"等国际主流城市雨洪管理策略,同时对近年来世界先进城市防治内涝方面的管理措施进行了归纳总结;最后,在思想意识、排放体制、措施等方面与中国目前排水体制进行了对比,并归纳了三种理念的适用范围,希望根据国内实际条件的不同,因地制宜地制定适合中国特色的雨水管理理念。     

城市暴雨处理及分析集成模型系统(SUSTAIN)介绍

暴雨的管理与控制已经成为制约城市可持续发展的重要议题之一,最佳管理实践(BMP)和低影响开发(LID)策略的提出,对于改变传统观念、建立新型的城市暴雨管理体系具有积极意义,但缺乏有效的设计与评估工具,制约了该理念的工程推广与应用。美国国家环保局(USEPA)支持开发的城市暴雨处理及分析集成模型系统(SUSTAIN),以ArcGIS为基础平台,综合应用了水文、水力和水质分析模型,可以对BMP和LID的措施类型、安置地点和实施效果进行科学有效的设计与评估,对于在我国开展暴雨管理措施的模型分析与设计评估具有很好的借鉴意义。     

Quantification of stormwater runoff using a combined GIS and curve number approach: a case study for an urban watershed in the Ozark Highlands,USA

Managing stormwater runoff is crucial to preserving water quality in rapidly developing urban watersheds. The objective of this study was to develop a methodology to test existing stormwater drainage infrastructure, identify potential areas of improvement, and estimate potentially contaminated runoff by combining two widely used stormwater runoff prediction models. A watershed containing much of the University of Arkansas-Fayetteville campus was targeted for this study because stormwater from this watershed drains into a local river designated as an impaired water body due to siltation. The curve number method was used to estimate runoff for various flood-return periods and antecedent moisture conditions, while a flow-direction model integrated topography, land use, and stormwater drainage infrastructure in a GIS. The methodology developed and results generated will help stormwater planners visualise localised runoff and potentially adapt existing drainage networks to accommodate runoff, prevent flooding and erosion, and improve the stormwater quality entering nearby surfacewater bodies.