Larry A. Roesner

Physical Effects of Wet Weather Flows on Aquatic Habitats: Present Knowledge and Research Needs

This study explores the current state of knowledge with respect to the effects of wet weather flows from urban areas on the physical character of aquatic habitat. It identifies knowledge gaps with respect to our ability to define the cause-effect relationships, examines the comprehensiveness of the data used in support of the published literature in the subject area, and makes a qualitative determination of the usefulness of those data for further analysis to increase our knowledge in the subject area. Finally, it recommends further research studies that will increase our knowledge in the subject area, with emphasis on pilot-scale projects that can be used to develop practical protocols for preventing or mitigating the effects. Major findings and conclusions are: 1) we lack a solid conceptual framework for predicting the impact of large-scale watershed modifications and wet weather flows on ecological processes that influence stream communities; 2) there is a need for longer-term monitoring; 3) there is no widely accepted system for quantifying geomorphic instability and degradation of physical habitat; 4) there is a need for process-based stream classification; 5) specific links between urbanization characteristics and stream degradation are lacking; 6) there is a need for urban best management practice (BMP) assessment standards; and 7) developing a multi-scale understanding of habitat potential in human-dominated watersheds is needed. The report recommends a research program that first and foremost, includes comprehensive, long-term monitoring augmented with mathematical modeling of the linkages between development style/drainage system design, flow regime, and multi-scale changes in physical habitat and biotic response. Improved diagnosis and predictive understanding of future change require multifaceted, multiscale, and multidisciplinary studies based on a firm understanding of the history and processes operating in a drainage basin. Detailed long-term analyses of the influence of hydrologic regime and channel morphology on differences between communities in recruitment, immigration/emigration, mortality, and age structure are also needed. Finally, future research should directly examine tradeoffs between: 1) flood mitigation versus channel roughness, habitat heterogeneity, debris inputs, and riparian protection; 2) chemical water quality improvement through extended detention versus geomorphically-based flow regime controls; and, 3) rehabilitation of aquatic habitat using static features versus allowing the potential for dynamic adjustments in channel form and habitat structure. It is extremely important that the research be pragmatic, and focus on developing pilot/demonstration studies that will lead to design guidance that municipalities can use to design new systems, or improve existing systems, that will protect not only the safety and welfare of the citizenry that it serves, but also the aquatic ecosystems in the streams that receive the wet weather discharges from these urbanized sites. This title belongs to WERF Research Report Series ISBN: 9781843396482 (Print) ISBN: 9781780403243 (eBook)

Evaluation of pollutant loads from stormwater BMPs to receiving water using load frequency curves with uncertainty analysis.

This study examined pollutant loads released to receiving water from a typical urban watershed in the Los Angeles (LA) Basin of California by applying a best management practice (BMP) performance model that includes uncertainty. This BMP performance model uses the k-C model and incorporates uncertainty analysis and the first-order second-moment (FOSM) method to assess the effectiveness of BMPs for removing stormwater pollutants. Uncertainties were considered for the influent event mean concentration (EMC) and the aerial removal rate constant of the k-C model. The storage treatment overflow and runoff model (STORM) was used to simulate the flow volume from watershed, the bypass flow volume and the flow volume that passes through the BMP. Detention basins and total suspended solids (TSS) were chosen as representatives of stormwater BMP and pollutant, respectively. This paper applies load frequency curves (LFCs), which replace the exceedance percentage with an exceedance frequency as an alternative to load duration curves (LDCs), to evaluate the effectiveness of BMPs. An evaluation method based on uncertainty analysis is suggested because it applies a water quality standard exceedance based on frequency and magnitude. As a result, the incorporation of uncertainty in the estimates of pollutant loads can assist stormwater managers in determining the degree of total daily maximum load (TMDL) compliance that could be expected from a given BMP in a watershed.

Effect of the Seasonal Rainfall Distribution on Storm-Water Quality Capture Volume Estimation

Thewater quality capturevolume (WQCV) is a design parameter that is used for sizing urban storm-water treatment facilities. The storage, treatment, overflow, and runoff model (STORM) in NetSTORM was used to translate historical hourly rainfall records into storm event runoff data and to compute the WQCV (set at the 85th percentile capture of the annual runoff volume) of eight cities located in various climatological areas of South Korea. For each city, one-parameter and two-parameter exponential distributions were fitted to the set of storm event runoff volumes that were computed by STORM, and the 85th percentile runoff volume that was determined from the STORM was compared to the 85th percentile runoff volumes that were obtained from the two exponential distributions. The results demonstrate that the more easily applied distribution approach is adequate in South Korea for determining the WQCV. In Seoul, which is a city located in the northwestern part of South Korea, the two-parameter exponential distribution yielded the best estimate of the WQCV computed by STORM. For Chuncheon, Wonju, and Daejeon, which are cities located in the north-central and central parts of South Korea, the WQCVs were accurately estimated using both the one-parameter and two-parameter exponential distributions. Finally, in the cities of Gangneung, Gwangju, Daegu, and Busan, which are located in the northeastern and southern parts of South Korea, the WQCVs were best estimated using the one- parameter exponential distribution. It was found that seasonal variations in rainfall and rainfall event depth are important factors in assessing the WQCV. This study also found that the one-parameter exponential distribution approach, which is the most common approach used in the United States, may not be adequate for WQCVestimation if the standard deviation for average monthly rainfall is significant. DOI: 10.1061/ (ASCE)WR.1943-5452.0000204.

Performance Modeling of Storm Water Best Management Practices with Uncertainty Analysis

The performance of storm water best management practices (BMPs) contains many uncertainties that make predicting BMP performance difficult. The objective of this study is to build a BMP performance model that incorporates uncertainty analysis and to evaluate this model using observed total suspended solids (TSS) from detention basin data sets in the International Stormwater BMP Database. The representative storage-treatment performance model, the k-C* model, was chosen to represent BMP performance. Its input parameters, influent event mean concentration (EMC) (Cin), and the areal removal rate constant (k) are considered with the uncertainty analysis. To estimate the variance associated with k, the prediction interval method is applied to the linear regression equation relating hydraulic loading rate (q) to k. To estimate the variance of Cin, observed Cin data in the BMP database are used. This study assumes that both Cin and k can be represented by lognormal distributions. The probability density function...

The Effect of Stormwater Controls on Sediment Transport in Urban Streams

Urbanization of a watershed increases impervious area, and consequently increases stormwater runoff. When left uncontrolled, these increases in stormwater runoff cause downstream flooding, accelerate channel erosion, and impair aquatic habitat. Increases in the magnitude and duration of stormwater runoff that accompany uncontrolled development allow a stream to carry more sediment than it could prior to watershed development. When a watershed cannot supply the stream with the volume of sediment it has the capacity to carry, channel degradation may occur in the form of incision, lateral migration or, or a combination of both. This study evaluates the potential impact of watershed development on sediment transport in a prototype headwater stream subjected to typical residential development. Event based and continuous simulations, using 50 years of hourly rainfall records were performed with two climatically different locales. The first in the semiarid climate of Fort Collins, Colorado and the other in a typical southeastern climate, Atlanta, Georgia. Five conditions were evaluated for the study watershed, including: current (undeveloped) conditions, fully developed conditions, without stormwater controls, and fully developed conditions with stormwater controlled using (a) the City of Fort Collins flood control standard, (b) the City of Fort Collins flood control standard and water quality capture volume (WQCV) criteria, and, (c) using common standards of practice in the United States: control of the 100- and 2-year storms to historic peak discharge rates and control of the WQCV. For each scenario examined, sediment transport potential is evaluated for two noncohesive soil types: medium gravel and medium sand.

Effect of Detention and BMPs on Flow Frequency of Runoff

Urban stormwater controls for peak flow attenuation are currently being used throughout the world. Standard practice typically dictates bringing postdevelopment peak flows down to the predevelopment levels. In most cases the flow controls target low frequency events, while the smaller, higher frequency events are not affected. This study examines the effects of the state-of-practice in flow control on the peak flow frequency curve, and how well the postdevelopment flows are controlled to predevelopment levels. Continuous simulation, using 50 years of hourly rainfall record, was performed on two climactically diverse locales. Detention ponds with a variety of flow control orifices were examined singularly and in conjunction with extended detention best management practices (BMPs). Conclusions are drawn regarding the efficiency of current practice, and recommendations are made regarding the future of urban stormwater control.

Estimation of Graywater Constituent Removal Rates in Outdoor Free-Water-Surface Wetland in Temperate Climate

AbstractAlthough constructed wetlands have become an accepted technology for the treatment of graywater for nonpotable reuse, little guidance is available on the design and sizing of wetlands specifically for graywater treatment. A common practice for sizing constructed wetlands is to apply the first order plug flow k-C* model. The objective of this work was to estimate k and C* parameters in a free-water-surface wetland processing graywater during summer, fall, and winter months for five-day biochemical oxygen demand (BOD5), total nitrogen (TN), and ammonia. Mass removal rates were consistently higher during summer months than winter months. Estimated values for k were higher in summer than winter for BOD5 (15.9  m year−1 compared to 2.5  m year−1) and TN (16.4  m year−1 compared to 5.5  m year−1). Additionally, estimates of k for BOD5 removal during all seasons was lower for graywater than typically observed for domestic and livestock wastewaters. The parameter (k and C*) estimates provided here can be ...

Improving estimates of oil pollution to the sea from land-based sources.

This paper presents improvements to calculation methods used in the National Research Councils (NRC) Oil in the Sea reports from 2003 and 1985 to estimate land-based contributions of petroleum hydrocarbons to the sea from North America. Using procedures similar to the 2003 report, but with more robust methods for handling non-detections, estimated land-based contributions for 1977 and 2000 were over 50% lower than the best 1996 estimate in the NRC report. The largest loads were from the northeastern United States and the Gulf of Mexico region for both the 2003 report and updated calculations. Calculations involved many sources of uncertainty, including lack of available data, variable methods of measuring and reporting data, and variable methods of reporting values below detection limits. This updated analysis of land-based loads of petroleum hydrocarbons to the sea highlights the continued need for more monitoring and research on inputs, fates and effects of these sources.

Long-Term Effects of Graywater Irrigation on Soil Quality in Arid Regions

As communities throughout the United States and abroad are becoming interested in innovative approaches to water resource sustainability, household graywater reuse for residential landscape irrigation is gaining popularity. However, the application of graywater for irrigation may result in increased levels of emerging contaminant and pathogens, negative impacts to soil quality, or potential groundwater contamination with chemical constituents present in graywater. A study is currently being conducted at Colorado State University to examine the long-term effects of graywater irrigation. The objective of this research project is to elucidate information on the fate and occurrence of graywater chemical constituents and pathogens and their long-term potential impacts on soil quality, as a result of its application for residential landscape irrigation. Sampling locations were selected to encompass a variety of soil types and climatic conditions. Soil samples were collected at four different households where graywater has been applied for irrigation for more than five years in Arizona, California, Colorado, and Texas. Soil cores were taken at depths of 0–15, 15–30, and 30–100 cm separately in both an area irrigated with graywater as well as a control area with analogous soil and landscaping that irrigated with fresh water in each site for quantification of soil physical and chemical properties, antimicrobials, surfactants, and pathogen indicator organisms. Soil samples were analyzed for pH, electrical conductivity, organic matter, total C, total N, extractable NH 4 -N, NO 3 -N, P, effectivecation exchange capacity, sodium adsorption ratio (SAR), surfactants, and antimicrobials. Widely used surfactants including linear alkyl benzene sulphonates, alcohol ethoxylates, and alcohol ether sulphates and two common antimicrobials in personal care products, triclosan and triclocarban have been quantified by liquid chromatography-mass spectrometery in soil samples. Soil samples also were analyzed for indictor organisms including total coliforms, E. coli, Enterococci, Clostridium perfringens. Results from this study will provide guidance to decision makers, water agencies, regulators, product manufactures and consumers so that safe graywater irrigation systems can be installed and operated for household landscape irrigation.

Development of Urban Storm Sewer Optimal Layout Design Model Considering Risk

Rapid expansion of urban area since 1970’s in Korea has caused the difficulties to discharge the flood in urban area watershed. Building the rational and optimal urban sewer network in urban area is very important to overcome the flood disaster. Sewer network installation needs two important requisites; the first is runoff analysis including design discharge and the second network layout design optimized economically. Many researches for runoff analysis as well as efforts to attenuate peak flows in urban watershed have been doing well. But layout design technology, relatively, has less devoted to develop network system or assessment methodology. What is interested in sewer layout design nowadays is not only how to discharge peak flow but also how to set up economic layout condition with results of simulated design discharge. This study aims at developing simulation model which might come up with the optimal condition of pipe capacity, slope, water depth and return cost in terms of least cost optimization in urban sewer layout design according to design discharge. In order to evaluate the risk at each state, first order second moment approximation was adopted to uncertainty analysis in the risk–reliability relationship, which would be able to calculate the risk cost of the element. And DDDP (Discrete Differential Dynamic Programming) which is application of DP (Dynamic Programming) is used as an optimization technique in the sewer layout design. Clanguage was used to code the model and analyzed node-link structure for manholesewer pipe. This model was applied to a newly developed resident area in Ulsan, Korea to assess the installed sewer network layout. As a result, the method in this study could suggest the more optimal condition to about 9% attenuation in terms of return cost considering risk.