Stephen Carter’s research while affiliated with Tetra Tech and other places
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Various Total Maximum Daily Loads (TMDLs) developed for Los Angeles County watersheds require comprehensive implementation plans to strategize specific best management practices (BMPs) to meet required pollutant load reductions during storm events. Ongoing efforts for assessment of BMPs in Los Angeles County have repeatedly indicated a need to identify a water quality design storm for both regulatory and BMP design purposes. The Los Angeles County Flood Control District's Watershed Management Modeling System (WMMS) has served as the enhanced platform for the design storm development approach. The analysis is dependent on three key factors: (1) storm sizes and associated treatment volume, (2) BMP costs, and (3) achievement of water quality standards. Finally, this paper proposes threshold storm sizes that can be treated for best pollutant reduction benefits while considering economic impact. The results are also presented as BMP sizing recommendations for TMDL attainment purpose. Ultimate analyses of costs and benefits can potentially lead to identification of the maximum extent practicable (MEP) target with which BMPs can be implemented to achieve water quality standards within receiving waters.
Several Total Maximum Daily Loads (TMDL) have been developed for multiple river segments for pollutants (including nutrients, metals, and bacteria) within the Los Angeles County regional watershed area, with urban runoff and stormwater as the primary source. Managing stormwater quality is complex because it involves many aspects that must be considered collectively to make informed decisions that are cost-effective and meaningful. To address these challenges, the Los Angeles County Flood Control District through a joint effort with United States Environmental Protection Agency has developed the Watershed management Modeling System (WMMS) that identifies cost effective water quality improvement projects through an integrated, watershed based approach. The WMMS encompasses the Los Angeles County's coastal watersheds of approximately 3,100 square miles, which is composed of more than 80 incorporated cities and unincorporated County areas. Traditional TMDL developments typically rely on iterative trial-and-error modeling approaches for testing compliance. Considering the tremendous implementation costs within this highly urbanized context, a key objective of the WMMS was to develop TMDL implementation options that are both environmentally compliant and financially efficient. As a result, the model development included mapping climate and land cover variability, BMP treatment opportunities, and a range of viable options at a high degree of spatial resolution (2,655 subwatersheds), with water quality targets at 166 unique TMDL compliance points within the instream network. Because simulation-optimization problems at this scale have been an unsolvable problem for decades, this study applied a new algorithm named Nonlinearity-Interval Mapping Scheme (NIMS) developed during this study, which was used to optimize management under various risk tolerance levels for achieving TMDL compliance with minimum BMP implementation cost. The results of this study show a promising trend for future watershed scale optimal TMDL development and implementation plan formulation.
Applications using simulation-optimization approaches are often limited in practice because of the high computational cost associated with executing the simulation-optimization analysis. This research proposes a nonlinearity interval mapping scheme (NIMS) to overcome the computational barrier of applying the simulation-optimization approach for a waste load allocation analysis. Unlike the traditional response surface methods that use response surface functions to approximate the functional form of the original simulation model, the NIMS approach involves mapping the nonlinear input-output response relationship of a simulation model into an interval matrix, thereby converting the original simulation-optimization model into an interval linear programming model. By using the risk explicit interval linear programming algorithm and an inverse mapping scheme to implicitly resolve nonlinearity in the interval linear programming model, the NIMS approach efficiently obtained near-optimal solutions of the original simulation-optimization problem. The NIMS approach was applied to a case study on Wissahickon Creek in Pennsylvania, with the objective of finding optimal carbonaceous biological oxygen demand and ammonia (NH4) point source waste load allocations, subject to daily average and minimum dissolved oxygen compliance constraints at multiple points along the stream. First, a simulation-optimization model was formulated for this case study. Next, a genetic algorithm was used to solve the problem to produce reference optimal solutions. Finally, the simulation-optimization model was solved using the proposed NIMS, and the obtained solutions were compared with the reference solutions to demonstrate the superior computational efficiency and solution quality of the NIMS.
The Los Angeles County Flood Control District through a joint effort with United States Environmental Protection Agency has been developing the Watershed management Modeling System (WMMS) that would identify cost-effective water quality improvement projects through an integrated, watershed based approach. In WMMS, watershed model closely estimates collective impact of a variety of point and non-point pollutant sources. The results are incorporated into detailed BMP simulation models and combined with locally derived Best Management Practice (BMP) installation and maintenance costs. The WMMS has been applied to a small pilot watershed to demonstrate the watershed modeling and BMP selection methodologies and to improve accuracy prior to a regional application. The best solutions identified by the WMMS for the pilot watershed are composed of centralized BMP sizes, distributed BMP types and sizes, and percent of area treated for each land use within the delineated eight subarea groups. The WMMS made it possible to quantify the BMP implementation details at various watershed conditions to achieve specific management goals such as TMDLs.
The Los Angeles County Flood Control District (LACFCD) is currently developing a decision support system to evaluate the most cost-effective combination of distributed and entralized BMPs to support water quality improvement planning of the County's watersheds, including the evaluation of the benefits of decentralized BMPs and potential savings in terms of alternative stormwater infrastructure improvements. Building on an extensive body of relevant studies in the Los Angeles region, including monitoring, model development, and regional model parameterization efforts, this study is designed to develop and apply a comprehensive modeling framework for the evaluation of alternative stormwater BMPs and Low Impact Development (LID) methods. This decision support system allows managers to evaluate the ability of various BMP scenarios to provide necessary flow volume and pollutant load reductions and optimizes the scenarios based on benefits and costs. In addition to overall stormwater quality management, results of this study will support numerous initiatives including TMDL implementation planning, investigation of a water quality design storm to assist in BMP design, development of BMP/LID design/sizing criteria, and financial assessment of capital projects. This study has resulted from a collaboration of LACFCD and the U.S. Environmental Protection Agency, Region 9, with a focus on developing an approach to water quality improvement planning and TMDL implementation that considers practicable application of BMPs that considers costs and effectiveness. Once completed, the decision support system will be available to the public to support their individual planning needs involving water quality improvement.
Protecting environmental quality requires a comprehensive approach that heavily relies on our ability to confidently predict or forecast impacts, evaluate the ability of natural systems to absorb impacts, and determine the combination of options that will provide an acceptable level of protection and/or restoration. These forecasts, when accepted, can help stakeholders to understand the potential cost or implications of restoration options and guide the development of effective protection strategies that can mitigate and prevent adverse impacts. Forecasts, which are typically based on combinations of modeling and analysis, must be designed to be sensitive to changes in the watershed and to in-stream responses. The difficulty with forecasts is that they are just predictions based on what we know now and what we believe might happen in the future. That is why environmental protection studies emphasize rigorous science-based approaches that can build confidence in forecasts. Building on an extensive body of relevant studies in the Los Angeles region, including monitoring, model development, and regional model parameterization efforts, this study is designed to develop and apply a Best Management Practice Decision Support System (BMPDSS) for the evaluation of alternative storm water best management practices (BMPs) and Low Impact Development (LID) methods. The system allows managers to evaluate the ability of various BMP scenarios to provide necessary flow volume and pollutant load reductions for Total Maximum Daily Load (TMDL) implementation and optimizes the scenarios based on benefits and costs. The approach is designed to provide guidance for a public incentive plan for implementing onsite BMP/LID techniques. The framework developed in this study provides a technically defensible and repeatable basis for evaluating quantitative measures associated with alternative BMP implementation plans. The BMPDSS represents an advanced method for simulating BMP processes and analyzing benefits (e.g., load reductions). Results of this study provide an interesting glimpse into the most relevant and economical BMPs for typical land uses in the Los Angeles watershed.
This paper presents a hydrodynamic and water quality modeling system for Wissahickon Creek, Pa. Past data show that high nutrient levels in Wissahickon Creek were linked to large diurnal fluctuations in oxygen concentration, which combining with the deoxygenation effect of carbonaceous biological oxygen demand (CBOD) causes violations of dissolved oxygen (DO) standards. To obtain quantitative knowledge about the cause of the DO impairment, an integrated modeling system was developed based on a linked environmental fluid dynamics code (EFDC) and water quality Simulation program for eutrophication (WASP/EUTRO5) modeling framework. The EFDC was used to Simulate hydrodynamic and temperature ill the stream, and the resulting flow information were incorporated into the WASP/EUTRO5 to simulate the fate and transport of nutrients, CBOD, algae, and DO. The standard WASP/EUTRO5 model was enhanced to include a periphyton dynamics module and a diurnal DO simulation module to better represent the prototype. The integrated modeling framework was applied to Simulate the creek for a low flow period when monitoring data are available, and the results indicate that the model is a reasonable numerical representation of the prototype.
Wissahickon Creek drains an urbanized watershed in southeast Montgomery County and northeast Philadelphia, Pennsylvania, and is currently included (with tributaries) on the State's 303(d) list of impaired waters due to elevated levels of nutrients, organic enrichment, low dissolved oxygen levels, habitat modification, extreme flow variability, and noticeable problems resulting from siltation. The Wissahickon is designated for trout stocking, and therefore is subject to seasonal dissolved oxygen standards as set by the Pennsylvania Department of Environmental Protection (PA DEP). From analysis of continuous sensor data and diurnal data collected in 1998, high nutrient levels in the creek were linked (due to eutrophication and excess periphyton growth) to relatively large diurnal fluctuations in oxygen concentration causing violations of standards. In addition, due to rapid development associated with urbanization, high storm flows have resulted in much streambank erosion and siltation of the streambed. This form of habitat modification compounds the impact on aquatic life resulting from nutrient loading.
Increased development of the Wissahickon watershed has resulted in an increase in point source discharge, and a rise in the magnitude of storm flows resulting from runoff from impervious areas. From an analysis of streamflows and water quality data, higher nutrient levels show a positive correlation to low flows, suggesting levels are dominated by point source contributions. To address impacts of urbanization, modeling analysis focused on both dry and wet conditions to analyze impacts of pollutants associated with each respective period. For dry weather, point sources were the dominant contributor to streamflow, resulting in reduced assimilative capacity of the stream, higher nutrient levels, and greater impacts on aquatic life. A modified, low-flow, steady-state WASP model was used to determine the nutrient TMDL and develop wasteload allocations to point sources on the Wissahickon and tributaries. This modified version of WASP included an added sub-routine that simulated processes associated with attached algae. For wet weather, a modified version of the GWLF watershed model was used for determination of the siltation TMDL and wasteload allocations. This modified version included a streambank erosion routine to estimate the siltation loads resulting from higher peak flows associated with increased urbanization.
For development of nutrient and siltation wasteload allocations, considerations were made regarding capabilities of stakeholders to reduce loads to meet TMDLs, regulatory measures through discharge permitting (including stormwater MS4 permits), and watershed management options through best management practices. To ensure that all such considerations were complete, stakeholder involvement was a key component in the success of the TMDL and provided assurance that resulting wasteload allocations were reasonable and attainable through proper implementation and watershed management. Public meetings with the United States Environmental Protection Agency, PA DEP, dischargers, environmental groups, municipalities, and concerned citizens were critical to ensure that such considerations were included throughout the process of TMDL development.
Citations (5)
... In 2010, the U.S. EPA MS4 Permit Improvement Guide adopted guidance that recommends the use of surrogate parameters, such as volumetric stormwater flows, for evaluating TMDLs rather than specific pollutant Volume Reduction in the Urban Highway Environment 15 discharge limits. This practice has already been implemented in U.S. EPA Regions 1 and 3, where flow has been used to track sediment loading and has been used in TMDLs as a proxy for pollutant loading (U.S. EPA, 2003). ...
... In some countries, a major challenge faced by stormwater managers is ensuring compliance with stormwater quality regulations while achieving a cost-effective design (e.g. Sim et al., 2010). Surface water flooding can have a negative impact on receiving water quality -foul water contamination can occur, particularly with combined sewers and where other pollutants (such as sediments, oils, fuels and toxic metals) can be washed from urban surfaces into receiving waters (Gordon-Walker et al., 2007). ...
... (2) The NIMS could obtain not only improved designs, as expected for the response-surface based approach but also true near-optimal solutions comparable to those obtained by a well-established global optimization algorithm GA. This method has been used for waste load allocation analysis (Sim et al. 2011;Zou, et al. 2010a), implementing optimal load reduction management schemes (Liu et al. 2011b), nutrient reduction-optimization (Liu et al. 2011a;Yang, et al. 2014), environmental economic optimization (Zhang et al. 2013), and planning of vehicle recycling (Simic and Dimitrijevic 2013). However, the REILP model cannot discriminate between different pollution sources, when it is used for equitable waste load allocation. ...
... These studies generally use trial-and-error based approaches to meet the relevant water quality standards; however, it is not practical to obtain solutions for multiple pollutant sources (Boose, 2002). Recently, most WLA studies have only been carried out to determine the quantity of reducing pollution levels at the sources by simulationoptimization model until obtaining satisfactory water quality and maximum discharge load considering the economic efficiency of production facilities (Burn and Yulianti, 2001;Cho et al., 2004;Jia and Culver, 2006;Deng et al., 2010;Zou et al., 2010, Han et al., 2011Afshar and Masaumi, 2016;Afshar et al., 2018;Saadatpour et al., 2019;Su et al., 2019). Thus, many studies involving simulation-optimization models can be found in the scientific literature. ...
... EFDC (Zou et al. 2006;Li et al. 2011), a general purpose and open-source three-dimensional numerical model, was applied in the Minjiang River Estuary, including hydrodynamics, water ages, and water quality. The process and equation of DO is shown as follows: ...