Entity

Time filter

Source Type

United States

Askarizadeh A.,University of California at Irvine | Rippy M.A.,University of California at Irvine | Fletcher T.D.,University of Melbourne | Feldman D.L.,University of California at Irvine | And 12 more authors.
Environmental Science and Technology | Year: 2015

Catchment urbanization perturbs the water and sediment budgets of streams, degrades stream health and function, and causes a constellation of flow, water quality, and ecological symptoms collectively known as the urban stream syndrome. Low-impact development (LID) technologies address the hydrologic symptoms of the urban stream syndrome by mimicking natural flow paths and restoring a natural water balance. Over annual time scales, the volumes of stormwater that should be infiltrated and harvested can be estimated from a catchment-scale water-balance given local climate conditions and preurban land cover. For all but the wettest regions of the world, a much larger volume of stormwater runoff should be harvested than infiltrated to maintain stream hydrology in a preurban state. Efforts to prevent or reverse hydrologic symptoms associated with the urban stream syndrome will therefore require: (1) selecting the right mix of LID technologies that provide regionally tailored ratios of stormwater harvesting and infiltration; (2) integrating these LID technologies into next-generation drainage systems; (3) maximizing potential cobenefits including water supply augmentation, flood protection, improved water quality, and urban amenities; and (4) long-term hydrologic monitoring to evaluate the efficacy of LID interventions. © 2015 American Chemical Society. Source


Wu W.,University of Mississippi | Altinakar M.S.,University of Mississippi | Song C.R.,University of Ottawa | Al-Riffai M.,Building and Infrastructure Testing Laboratory Ltd | And 39 more authors.
Journal of Hydraulic Engineering | Year: 2011

Embankment breaching processes are very complex and involve mixed-regime free-surface flow with overfalls and hydraulic jumps, pressurized pipe flow, strong vertical and lateral erosion, discrete mass failure, and headcut migration. The failure mode and mechanism are affected by upstream and downstream water conditions, embankment configurations, and soil properties and state. Great progress has been made to investigate embankment breaching processes through laboratory and field experiments and real-world case studies. However, most laboratory experiments were for smallscale homogeneous embankments, only a few outdoor experiments were conducted at large scales (up to several meters in height) and/or were of composite construction, and only limited data sets for historical embankment failures were sufficiently documented. A number of parametric, simplified physically-based, and detailed multidimensional physically-based embankment breach models have been established in the past decades, but prediction with these models involves significant uncertainties. The biggest limitation of the existing breach models is quantifying erosion rates or erodibility of cohesive soils and sediment entrainment under embankment break/breaching flows. It is important to conduct more large-scale laboratory experiments and field case studies to improve existing embankment breach models or develop new ones. These models should also be enhanced by incorporating better physical insights, by using more efficient computational technologies, and integrating them into more robust flood forecasting and risk assessment systems with comprehensive relevant databases © ASCE. Source


Viswanathan S.,University of San Diego | Voss K.A.,Duke University | Pohlman A.,RBF Consulting | Gibson D.,San Diego Regional Water Quality Control Board | Purohit J.,EcoLayers Inc.
Journal of Environmental Engineering | Year: 2010

In this study, bioassessment data collected between 1998 and 2005 were synthesized and analyzed for streams and rivers throughout the San Diego Hydrologic Region to provide a spatial and temporal context for the results of several monitoring projects conducted between 1998 and 2005 and to ascertain the applicability of the Southern California benthic macroinvertebrate index of biological integrity (SoCal B-IBI) to the region's streams. The water quality of the sites studied in the region, as reflected by temporal and spatial analyses of SoCal B-IBI scores, was found to be quite poor. When streams were analyzed individually most showed stable scores over the time frame of the study with some showing better scores in the fall. Spatially, scores were found to be better farther away from the coast in the upstream reaches of the watersheds. This study further explored the applicability of the SoCal B-IBI to a focused geographic region by demonstrating the necessity of each component metric to the assignment of biological condition. Although all component metric scores were deemed to be necessary, the percent intolerant individuals score had a more significant effect in driving impairment. The analysis of the component metrics of the SoCal B-IBI provides useful insights to the changes in scores among and between the sampled sites in the region's watersheds. Based on this study, natural resource management agencies responsible for managing water quality should incorporate regular measures of biological integrity into their water quality programs to ascertain regional and temporal trends. © 2010 ASCE. Source


Taylor S.M.,RBF Consulting | Cazenas P.A.,U.S. Federal Highway Administration
Green Streets and Highways 2010: An Interactive Conference on the State of the Art and How to Achieve Sustainable Outcomes - Proceedings of the Green Streets and Highways 2010 Conference | Year: 2010

The Domestic Scan Program was developed to highlight innovative practices of high-performing transportation agencies that could be beneficially adopted by other interested agencies. The Scan Program provides the opportunity for technology transfer on a relatively economical basis with significant benefits on a national scale. The Clean Water Act (CWA) places requirements on Departments of Transportation (DOTs) for the discharge of stormwater from their systems through the National Pollutant Discharge Elimination System (NPDES). Non-compliance with NPDES permits can impact project design, engineering and construction schedules and increase construction time and costs. Successful compliance with NPDES permits requires the appropriate transfer of information and accountability through multiple phases of project delivery. State DOTs that are under NPDES Municipal Separate Storm Sewer System (MS4) Phase I or Phase II permit coverage are anticipating implementation of the total maximum daily load (TMDL) process which poses potential stormwater permitting concerns based upon the method of implementation chosen and the types of receiving water impairments addressed. This paper summarizes a Domestic Scan for stormwater that occurred in July, 2009. Four primary topics were selected as the subject of this Scan. Benefits of this Scan include better insight into stormwater requirements during the project delivery process, improved compliance with NPDES permits, and reducing project delays associated with NPDES violations and noncompliance. The Scan provided an excellent opportunity to document lessons learned and share experiences to assist individual DOTs in negotiating, developing, implementing and tracking TMDL programs as part of NPDES MS4 compliance. © 2010 ASCE. Source


Petersen C.M.,Camp Dresser and McKee Inc. | Rifai H.S.,University of Houston | Villarreal G.C.,RBF Consulting | Stein R.,Texas Commission on Environmental Quality
Journal of Environmental Engineering | Year: 2011

Bacterial levels in Buffalo Bayou in Houston commonly exceed contact recreation standards. Potential sources of bacteria include wastewater treatment plants, sanitary sewer overflows, septic systems, wet and dry nonpoint-source discharges via direct runoff and pipes, direct deposition, and sediment. A water-quality model in the Hydrologic Simulation Program-FORTRAN (HSPF) was calibrated and validated for hydrology, sediment, and Escherichia coli and subsequently used to evaluate the impacts of the bacterial sources in the watershed. In addition, simple estimates of bacterial loads were calculated along with source evaluations from load duration curves. Load reductions based upon the simple estimates indicated that water-quality standards were met by reducing dry-weather indicator bacterial loads by 69% and wet-weather loads by 98%. When these load reductions were implemented in the HSPF model, however, standards were not met under dry-weather conditions. Residual nonpoint-source loading was found to cause the discrepancy between simple load estimate calculations and the developed water-quality model. This paper demonstrates that runoff can play a significant role in maintaining high levels of bacteria under all flow conditions and that understanding the temporal variations in bacterial source loading is critical to ensure that load reductions will achieve water-quality standards. © 2011 American Society of Civil Engineers. Source

Discover hidden collaborations