Many storm water best management practice (BMP) devices function primarily by capturing particulate matter to take advantage of the well‐documented association between storm water particles and pollutants. The hydrodynamic separation or settling methods used by most BMP devices are most effective at capturing medium to large particles; however, these may not be the most predominant particles associated with urban runoff. The present study examined particle size distribution in storm water runoff from an urban watershed in southern California and investigated the pollutant–particle associations of metals (Cu, Pb, Ni, and Zn) and bacteria (enterococci and Escherichia coli ). During small storm events (≤0.7 cm rain), the highest concentration of pollutants were associated with a <6‐µm filter fraction, which accounted for 70% of the per storm contaminant mass but made up more than 20% of the total particle mass. The pollutant–particle association changed with storm size. Most pollutant mass was associated with >35 µm size particles during a 5‐cm rain event. These results suggest that much of the contaminant load in storm water runoff will not be captured by the most commonly used BMP devices, because most of these devices (e.g., hydrodynamic separators) are unable to capture particles smaller than 75 µm. Environ. Toxicol. Chem. 2013;32:320–328. © 2012 SETAC

Understanding the size distribution of stormwater particulates and the pollutants associated with each size fraction is becoming an increasingly important aspect of stormwater management. This paper evaluates the accuracy of the Laser In Situ Scattering and Transmissometry (LISST 100x) particle analyzer and describes the adaptation of the instrument for use in urban stormwater assessment. The accuracy of the instrument was evaluated with known particle size standards of 5, 20, and 100 mu m. While the mode of the size distribution corresponded with the average particle size indicated by the manufacturer, the weighted mean was 131%-141% of the average particle size of the standards. Measured concentrations of screened natural sediment (< 63 mu m) ranged from 71 to 120% of the nominal value, with a variation in replicate measurements of 3% (coefficient of variation). The pumping regime used to transport stream water to the instrument gave results that compared well with those obtained using a depth-integrated grab sampler. Bubbles in the pumped samples, which could be interpreted by the instrument as particles, were reduced using a modified filter device. Transmission of the laser through the samples was greatly improved using a reduced-volume flow-through cell. Field results using the adapted technique compared well with those obtained with a laboratory Coulter Counter, with a median relative percent difference between the two techniques of 8% for the silt and clay fraction and 20% for very fine and fine sands. With application of protocols outlined in this study, the LISST provides a new tool for continuous in situ analysis of stormwater particulates. DOI: 10.1061/(ASCE)EE.1943-7870.0000516. (C) 2012 American Society of Civil Engineers.

The mission of the Green visions Plan for 21st Century Southern California is to offer a guide to habitat conservation, watershed health and recreational open space for the Los Angeles metropolitan region. The Plan will also provide decision support tools to nurture a living green matrix for southern California. our goals are to protect and restore natural areas, restore natural hydrological function, promote equitable access to open space, and maximize support via multiple-use facilities. The Plan is a joint venture between the

Sediments in urbanized estuaries often have elevated levels of pollutants and are the subject of cleanup or management actions. Understanding particle dynamics in an estuary can provide insight into possible sediment sources and can inform management decisions. This study deployed a laser scatterometer (LISST-100X, Sequoia Scientific, Inc., Bellevue, WA) in the Ballona Creek Estuary (BCE), in southern California, throughout the summer of 2008 to investigate particle dynamics. The LISST100X sampled total suspended material (TSM) in the near-sediment water column analyzed particle size frequency in 32 log-spaced diameters between 2.73 and 462 μm once every 6 minutes. Tidal elevation was measured at the site to estimate the tidal prism throughout the deployment. The bio-fouling observed between instrument servicing was approximated by logistic equation and removed from the raw data. The detrended data matrix on particle size distribution was transformed using Principal Component Analysis (PCA) multivariate statistics. The three leading PCA modes (>92% of total variability) were attributed to different particle size classes: mid-size (71%), small-size (14%), and largesize (7%). Domination of mid-size TSM was associated with high phytoplankton biomass in the coastal waters. This conclusion was based on correlation between the first PCA mode and remotely-sensed satellite (MODIS-Aqua) observations of surface chlorophyll a (CHL) concentrations in Santa Monica Bay. In addition, first PCA mode variability was mostly diurnal rather than semidiurnal (i.e., associated with phytoplankton growth rather than tidal transport). Smalland large-size sediments (second and third PCA modes) were dominated by semi-diurnal variability, indicating the role of tidal circulation in forcing horizontal transport and resuspension. The relationship between tides and smalland large-particle TSM was non-linear, indicating high spatial heterogeneity of these particles. The extremes of both small and large-particle TSM were observed during spring ebb tides when low concentrations of smallsize particles and high concentrations of large-size particles were transported down-estuary. The results from this monitoring indicate that greatest pollutant level reductions in the BCE would come from minimizing the pollutant concentrations on sediment input into the system rather than efforts to clean up sediments in situ.

Accurate quantification of stormwater pollutant levels is essential for estimating overall contaminant discharge to receiving waters. Numerous sampling approaches exist that attempt to balance accuracy against the costs associated with the sampling method. This study employs a novel and practical approach of evaluating the accuracy of different stormwater monitoring methodologies using stormflows and constituent concentrations produced by a fully validated continuous simulation watershed model. A major advantage of using a watershed model to simulate pollutant concentrations is that a large number of storms representing a broad range of conditions can be applied in testing the various sampling approaches. Seventy-eight distinct methodologies were evaluated by "virtual samplings" of 166 simulated storms of varying size, intensity and duration, representing 14 years of storms in Ballona Creek near Los Angeles, California. The 78 methods can be grouped into four general strategies: volume-paced compositing, time-paced compositing, pollutograph sampling, and microsampling. The performances of each sampling strategy was evaluated by comparing the (1) median relative error between the virtually sampled and the true modeled event mean concentration (EMC) of each storm (accuracy), (2) median absolute deviation about the median or "MAD" of the relative error or (precision), and (3) the percentage of storms where sampling methods were within 10% of the true EMC (combined measures of accuracy and precision). Finally, costs associated with site setup, sampling, and laboratory analysis were estimated for each method. Pollutograph sampling consistently outperformed the other three methods both in terms of accuracy and precision, but was the most costly method evaluated. Time-paced sampling consistently underestimated while volume-paced sampling over estimated the storm EMCs. Microsampling performance approached that of pollutograph sampling at a substantial cost savings. The most efficient method for routine stormwater monitoring in terms of a balance between performance and cost was volume-paced microsampling, with variable sample pacing to ensure that the entirety of the storm was captured. Pollutograph sampling is recommended if the data are to be used for detailed analysis of runoff dynamics.

The mission of the Green Visions Plan for 21st Century Southern California is to offer a guide to habitat conservation, watershed health and recreational open space for the Los Angeles metropolitan region. The Plan will also provide decision support tools to nurture a living green matrix for southern California. Our goals are to protect and restore natural areas, restore natural hydrological function, promote equitable access to open space, and maximize support via multiple-use facilities. The Plan is a joint venture between the university of Southern California and the San Gabriel and The " Green Visions Plan for Twenty-first Century Southern California " project's watershed health assessment seeks to support and inform region-wide planning efforts that promote habitat conservation, water quality protection, and the creation of new recreational opportunities. In this report, hy-drologic models of the Green Vision Plan watersheds were developed for use as a tool for watershed planning, resource assessment, and ultimately, water quality management purposes. The modeling package selected for this application is the Danish Hydrology Institute's (DHI) MIKE BASIN. MIKE BASIN is a watershed model of hydrology and water quality, which includes modeling of both land surface and subsurface hydrologic and water quality processes. It was used to evaluate the current baseline hydrologic conditions and water quality and pollutant loadings in the GVP's five 8-digit HUC watersheds, namely, the Los Angeles River, meteorological data were used to develop the model seg-mentation and input, and detailed streamflow data were selected to conduct model calibration and validation over a nine year period (10/1996—09/2005). Both quantitative and qualitative comparisons were developed to support the model performance evaluation effort. The calibration and validation results, based on the graphic comparison and error analyses described herein, demonstrate a fair to good representation of the observed flow data. Statistical comparisons and model performance evaluation were performed at three stream locations throughout the watershed, for annual runoff, daily and monthly streamflow, water balance components, and annul water quality. These comparisons demonstrate conclusively that the model is a good representation of the water balance and hydrology of the Topanga Canyon and Malibu Creek subwatersheds. The model has demonstrated consistently fair to good simulations of total water volume and high winter and spring flow conditions, but poor modeling of summer low flows for the minimally developed subwatersheds draining into Santa Monica Bay. The water quality simulations did not match the mean concentrations and temporal variations in concentrations …

The mission of the Green visions Plan for 21st Century Southern California is to offer a guide to habitat conservation, watershed health and recreational open space for the Los Angeles metropolitan region. The Plan will also provide decision support tools to nurture a living green matrix for southern California. our goals are to protect and restore natural areas, restore natural hydrological function, promote equitable access to open space, and maximize support via multiple-use facilities. The Plan is a joint venture between the The purpose of the Green Visions Plan project watershed health assessments is to support and inform region-wide planning efforts from the perspective of habitat conservation, water protection, and recreational opportunities in southern California. In this report, hydrologic models of the Green Vision's Plan watersheds were developed for use as a tool for watershed planning, resource assessment, and ultimately, water quality management purposes. The modeling package selected for this application is the Danish Hydrology Institute's MIKE BASIN, which includes modeling of both land surface and subsurface hydrologic and water quality processes. It was used to evaluate the current baseline hydrologic conditions and water quality and pollutant loadings in the GVP's five 8-digit HUC watersheds, namely, the Los and meteorological data were used to develop the model segmentation and input, and detailed streamflow data were selected to conduct model calibration and validation over a nine year period (10/1996 – 9/2005). Both quantitative and qualitative comparisons were developed to support the model performance evaluation effort. The calibration and validation were performed at 14 stream locations throughout the watershed, for annual runoff, daily and monthly stream flow, water balance components, and annul water quality. The results, based on the graphic comparison and error analyses described herein, demonstrated a fair to good representation of the observed flow data. As shown in Figures A-5 through A-11, the model simulated the total water volumes fairly well for the 10 validation sites. Very good validation results were achieved for simulating the 90th percentile high flows while the 10th percentile low flows were poorly simulated with over-predictions at all sites. The water quality simulations were not as satisfactory as the flow simulations in reproducing the observed sample concentrations. Many predictions of constituent concentrations fell outside the range of acceptable values that was used for the water quality assessment. Graphically, some sample concentrations were captured while others were missed in the pollutographs and it did not always predict …

Impervious cover is a commonly used metric to help explain or predict anthropogenic impacts on aquatic resources; often it is used as a surrogate for intensity of human impacts when evaluating effects on aquatic resources. The most common way to estimate imperviousness is based on relationships with land use. Few studies have evaluated how the relationship between impervious surface and land use varies among geographies with different levels of development and between types of imagery used to assign land use type. In this study, we assess variability in estimates of imperviousness based on two locally available land use datasets: one based on aerial imagery (2-m resolution) and another based on satellite imagery (30-m resolution). The ranges and variability in imperviousness within land use categories were assessed at several spatial scales, including within counties, between counties, and between watersheds. Results indicate that there was considerable variability for all developed land use types. Estimated impervious cover often. varied over a range of 20-40% points within a land use category. Furthermore, there were clear spatial patterns both between and within counties, with impervious cover for a given land use type being higher near the urban centers and lower at the margins of development. Estimates of imperviousness for 12 study watersheds indicated that variability increased with increasing watershed development, making it difficult to confidently set management or regulatory targets based on impervious cover. This study suggests that locally derived, high resolution satellite or aerial imagery should be used to estimate imperviousness when a high level of accuracy and precision is required for regulatory or management decisions. Furthermore, the error associated with impervious land use relationships should be accounted for when using impervious cover in runoff or water quality models, or when making management decisions regarding stream health.

Structural best management practices (BMPs) have become a tool for stormwater managers to achieve water quality improvement and regulatory compliance. Existing empirical evaluation of BMP performance is valuable, but has limited applicability to predict BMP performance over extended durations under a variety of storm types. This study applies a dynamic model to simulate BMP performance over a 10-year period. The BMP model used hourly output from a calibrated and validated land-use model to evaluate two BMP types: a retention facility and a flow-through swale. The model evaluated each BMP alone and in series targeting volume, total suspend solids, and total copper. Effectiveness was based on load reduction, event mean concentrations, and frequency of exceedence of relevant water quality standards. The model predicted over 60% removal of solids and copper over most conditions; however, effectiveness was reduced during large storms and wet years. Although performance was similar based on load reduction and water quality standard exceedence, the latter was most sensitive to storm size. This study demonstrates that BMP modeling can help managers understand expected BMP performance over a range of storms, time periods, and design parameters, and, perhaps more significantly, evaluate BMPs in series.

To examine the spatial and temporal effect of low-volume land-based runoff on beach contamination, discrete batches of dye were released at the shoreline at three beaches in Santa Monica Bay in 2000 (Malibu Creek, Santa Monica Canyon and Pico–Kenter drain). Dye concentration was measured at the shoreline 25, 50 and 100m alongshore from the dye release point for up to 40min after dye release. The shoreline concentration time series are characterized either by approximately exponential decay in concentration after passage of the dye patch maximum concentration or by persistent low concentration up to 30min after passage of the initial dye patch front. In the absence of detailed measurements of physical conditions, several simple advection–diffusion models are used to simulate shoreline concentration time series for an idealized surf zone in order to probe the roles of alongshore current shear and rip currents in producing the observed characteristics in dye concentration time series. Favorable qualitative and quantitative comparison of measured and simulated time series suggest alongshore current shear and rip currents play key roles in generating the observed characteristics of nearshore dye patch dispersion. The models demonstrate the potential effects of these flow features on the extent and duration of beach contamination owing to a continuous contamination source.

Dry weather runoff in arid, urban watersheds may consist entirely of treated wastewater effluent and/or urban nonpoint source runoff, which can be a source of bacteria, nutrients, and metals to receiving waters. Most studies of urban runoff focus on stormwater, and few have evaluated the relative contribution and sources of dry weather pollutant loading for a range of constituents across multiple watersheds. This study assessed dry weather loading of nutrients, metals, and bacteria in six urban watersheds in the Los Angeles region of southern California to estimate relative sources of each constituent class and the proportion of total annual load that can be attributed to dry weather discharge. In each watershed, flow and water quality were sampled from storm drain and treated wastewater inputs, as well as from in-stream locations during at least two time periods. Data were used to calculate mean concentrations and loads for various sources. Dry weather loads were compared with modeled wet weather loads under a range of annual rainfall volumes to estimate the relative contribution of dry weather load. Mean storm drain flows were comparable between all watersheds, and in all cases, approximately 20% of the flowing storm drains accounted for 80% of the daily volume. Wastewater reclamation plants (WRP) were the main source of nutrients, storm drains accounted for almost all the bacteria, and metals sources varied by constituent. In-stream concentrations reflected major sources, for example nutrient concentrations were highest downstream of WRP discharges, while in-stream metals concentrations were highest downstream of the storm drains with high metals loads. Comparison of wet vs. dry weather loading indicates that dry weather loading can be a significant source of metals, ranging from less than 20% during wet years to greater than 50% during dry years.

Many waterbodies in the Los Angeles region suffer from impaired water quality. As a result, there are a number of total maximum daily loads (TMDLs) being adopted for urbanized watersheds. These TMDLs establish regulatory requirements to achieve water quality standards. Ultimately, TMDLs stipulate that all wet weather discharges should meet water quality standards regardless of storm size including large, but infrequent events that can result in large-scale flooding. The objectives of this study were to: 1) identify the water quality consequences of managing for different sized storms; and 2) investigate stormwater runoff management strategies to determine their potential effectiveness in achieving water quality targets, and the associated cost, to storms of differing sizes. The objectives were addressed by examining two different conceptual approaches: 1) identifying target runoff volumes or pollutant loads for treatment based solely on rainfall:water quality relationships; and 2) identifying target runoff volumes or pollutant loads for treatment based on effectiveness and cost of treatment technologies. The first conceptual approach was addressed using Hydrologic Simulation Program-Fortran (HSPF), a watershed-based runoff model. The model was calibrated and validated for Ballona Creek, a highly urbanized watershed at low elevation in the Los Angeles Region. Model results indicated that, for this entire watershed, capturing storms of approximately one-inch precipitation volume would treat 80% of the runoff volume and 80% of the total copper load over a 30-year simulation. Capturing a minimally larger fraction of runoff volume or load would have required capturing significantly larger storm events. The second conceptual approach was addressed using a modified version of Storm Water Management Model 4.4h (SWMM), a model that simulates long-term hydraulics and pollutant removal for structural best management practices (BMPs). The SWMM was applied to a typical 10-acre high-density residential land use catchment of 42% imperviousness. Three different BMP designs were evaluated using this approach: a swale; a swale with a flow-control basin; and a bioretention basin. At a design storm of 0.75-in rainfall volume or 0.25-in/hr intensity, and assuming a consistent, median level of BMP effectiveness, any of the three BMPs could effectively reduce the average annual frequency of storms that exceeded the dissolved copper water quality standard to less than 5%. Rough cost estimates were applied to each of the three generic BMPs. The bioretention BMP was the most costly for reducing the frequency of exceeding the dissolved copper water quality standard, but was the most cost effective for reducing dissolved copper loads. The two conceptual approaches examined in this study demonstrated that integrating costeffective strategies into design standards for determining TMDL implementation policies is possible. However, several technical challenges still exist before design standards for water quality can be incorporated into a regulatory framework including extrapolating to other locations or water quality constituents, further model validation, and assessing confidence in the model to achieve targets. Additionally, policy discussions should include an evaluation of potential implementation strategies such as those for new development/redevelopment versus retrofit applications.

Modeling Metals In Stormwater Runoff At Multiple Time And Spatial ScalesWatershed models are widely used to describe runoff dynamics and associated pollutant loadings, but are rarely tested for accuracy quantitatively. Here we evaluated the accuracy of the Hydrological Simulation Program – FORTRAN (HSPF) model for predicting concentrations and loads of total suspended solids, copper, and fecal bacteria in Ballona Creek (near Los Angeles, California), an arid,...Author(s)Drew AckermanStephen B. WeisbergSourceProceedings of the Water Environment FederationSubjectSession 71: Modeling: Greater Than the Sum of Its PartsDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2007ISSN1938-6478SICI1938-6478(20070101)2007:12L.5777;1-DOI10.2175/193864707787969982Volume / Issue2007 / 12Content sourceWEFTECFirst / last page(s)5777 - 5778Copyright2007Word count122

ABSTRACT: The Hydrologic Simulation Program-FORTRAN (HSPF) is a powerful time variable hydrologic model that has rarely been applied in arid environments. Here, the performance of HSPF in southern California was assessed, testing its ability to predict annual volume, daily average flow, and hourly flow. The model was parameterized with eight land use categories and physical watershed characteristics. It was calibrated using rainfall and measured flow over a five-year period in a predominantly undeveloped watershed and it was validated using a subsequent 4-year period. The process was repeated in a separate, predominantly urbanized watershed over the same time span. Annual volume predictions correlated well with measured flow in both the undeveloped and developed watersheds. Daily flow predictions correlated well with measured flow following rain events, but predictions were poor during extended dry weather periods in the developed watershed. This modeling difficulty during dry-weather periods reflects the large influence of, and the poor accounting in the model for, artificially introduced water from human activities, such as landscape overwatering, that can be important sources of water in urbanized arid environments. Hourly flow predictions mistimed peak flows, reflecting spatial and temporal heterogeneity of rainfall within the watershed. Model correlation increased considerably when predictions were averaged over longer time periods, reaching an asymptote after an 11-hour averaging window.

Understanding the factors that influence the incidence and dispersal patterns of freshwater runoff plumes in southern California is important for management of coastal water quality. Significant river discharge is associated with episodic winter rainstorms, leading to turbid pollutant and pathogen-laden stormwater plumes that are clearly visible nearshore in the Southern California Bight. We analyzed 1.1-km spatial resolution sea-spectral reflectance data acquired in 1997–2003 by the Sea-viewing Wide Field-of-view Sensor (SeaWiFS), focusing on four regions with distinctive adjacent watershed properties: Ventura, Santa Monica Bay, San Pedro Shelf, and Orange County/San Diego. The area of each plume was detected by the backscattering characteristics of surface waters, i.e., normalized water-leaving radiation of green–yellow wavelength 555 nm (nLw555). Plume area size was correlated with the rainstorm magnitude, which was estimated from atmospheric precipitation averaged over the total area of the watersheds connected to the seashore. The time lag between rainstorm and maximum plume was one day in San Pedro Shelf and two days in other three regions. Assessing maximum correlation between precipitated rainwater and the plume size, we estimated the optimal nLw555 values best characterizing the plume boundaries in each of the four study regions. Another quantitative characteristic derived from maximum correlation between rainwater and plume size was the “coefficient of persistence”, related to the speed of freshwater discharge and the time of plume water dissipation; it was also different in different watersheds. The primary factors regulating the relationship between rainstorm and plume were watershed land-use characteristics, size, and elevation.

Dry-season flow in the San Gabriel River system is comprised mostly of discharges from water reclamation plants (WRPs), imported water, and storm drains. Although the magnitude of dry-season discharge is generally known, the water quality associated with most of these “introduced” discharges has not been characterized, nor has the associated in-stream response, particularly near storm drain discharges. The goal of this study was to characterize the pattern and magnitude of storm drain and WRP inputs to the San Gabriel River system and the associated in-stream response. To accomplish this, two synoptic dry-weather surveys were conducted, one in 2002 and the other in 2003 during which flow, metals, bacteria, and nutrient concentrations were measured from the WRPs, storm drains, and in-stream locations at a single point in time. For bacteria and most metals, storm drains accounted for the majority of mass emissions to the river. In contrast, WRPs were the primary source for nutrients. In-stream water quality concentrations generally reflected the main sources. For example, in-stream ammonia concentrations were highest downstream of WRP discharges. In-stream bacteria concentrations were consistently high and showed no apparent spatial pattern, suggesting that storm drains or other in-stream sources are present throughout the watershed.

City of Los Angeles, Stormwater Management Division, 650 South Spring Street, 7th Floor, Los Angeles, CA 90014 ABSTRACT The Los Angeles River is one of the most highly modified water systems in the world. Dramatic engineering modifications to control the river have successfully reduced flooding and property damage, but little of this design has incorporated water quality improvements. The goal of this study was to identify sources of potential pollutants and characterize water quality along the river’s seven reaches during dry weather. The three primary sources of potential pollutants included water reclamation plants (WRPs), major tributaries, and storm drain outfalls. The three WRPs discharged the majority (72%) of the volume flowing in the Los Angeles River during this study. Likewise, the three WRPs discharged the highest concentrations and greatest mass emissions of nutrients including nitrate, nitrite, ammonia, and total phosphate. In contrast, 66 flowing storm drains and 6 flowing tributaries had the highest concentrations and mass emissions of bacteria including total coliform, E. coli, and Enterococcus. Water quality in the Los Angeles River responded to inputs of these pollutants. Levels of nutrients were generally low upstream and downstream of the WRPs (<0.1 mg/L ammonia), but were greatest in the immediate vicinity of the WRPs (approximately 6 mg/L ammonia). Concentrations of bacteria were generally high upstream and downstream of the WRPs (ca. 104 MPN/100 mL E. coli), but were lowest in the immediate vicinity of the WRPs (ca. 102 MPN/100 mL E. coli).

Storm water runoff is perceived as a major source of pollutants that results in adverse environmental effects, but large-scale assessments are rarely conducted. The problem is particularly pronounced in southern California where 17 million people have rapidly developed coastal watersheds. The goal of this study was to make regionwide estimates of mass emissions, assess the relative contribution from urbanized watersheds, and compare pollutant flux from different land uses. A geographic information system-based storm water runoff model was used to estimate pollutant mass emissions based on land use, rainfall, runoff volume, and local water-quality information. Local monitoring data were used to derive runoff coefficients; over 1,700 storm water sampling events were used to calibrate and validate annual loadings. An average rainfall year produced 1,073 X 10(9) L of runoff, 118,000 metric tons (MT) of suspended solids, 1,940 MT of nitrate-N, 108 MT of zinc, and 15 kg of diazinon. The majority of mass emissions were from urbanized watersheds except for suspended solids, total DDT, and chlorpyrifos. Agricultural areas had the greatest fluxes for pesticides, including total DDT and chlorpyrifos while open areas typically had the smallest.