Protection of downstream channels and reduction in flooding can potentially be improved by evaluating alternative site stormwater management (SWM) strategies at a watershed scale and selecting the optimal strategy for a subject watershed. Tailoring a management strategy for a specific watershed may be worthwhile to minimize development costs and maximize downstream benefit. A hydrologic/hydraulic model for a watershed in Blacksburg, Virginia, is used to evaluate downstream results based on implementation of several alternative SWM strategies currently practiced within the United States. Results show none of the strategies meet the goal of maintaining the baseline goal at the watershed POI for the full range of design storms. Modification to the strategy that performs best at the watershed scale did meet the watershed goal for all design storms except the 1-year. For smaller storm events, it appears that increasing the volume of an initial capture and the drawdown time to release that volume does not increase performance downstream. This is potentially significant as extra dollars spent on site would not provide extra benefit downstream. When post-development peak runoff rates are detained to the predevelopment rate for larger storm events, whether based on a site or watershed focused strategy, the watershed goal can be met. A volume reduction strategy performs well, but implementation is hindered by soils with poor infiltration and the presence of karst. Other insight to watershed based management strategies, the role of regional facilities and predevelopment condition assumptions at the site scale to maintain a baseline condition downstream are discussed. / Master of Science

The responsibility for mitigation of the ecological effects of urban stormwater runoff has been delegated to local government authorities through the Clean Water Act's National Pollutant Discharge Elimination Systems' Stormwater (NPDES SW), and Total Maximum Daily Load (TMDL) programs. These programs require that regulated entities reduce the discharge of pollutants from their storm drain systems to the "maximum extent practicable" (MEP), using a combination of structural and non-structural stormwater treatment — known as stormwater control measures (SCMs). The MEP regulatory paradigm acknowledges that there is empirical uncertainty regarding SCM pollutant reduction capacity, but that by monitoring, evaluation, and learning, this uncertainty can be reduced with time. The objective of this dissertation is to demonstrate the existing sources and magnitude of variability and uncertainty associated with the use of structural and non-structural SCMs towards the MEP goal, and to examine the extent to which the MEP paradigm of iterative implementation, monitoring, and learning is manifest in the current outcomes of the paradigm in Virginia. To do this, three research objectives were fulfilled. First, the non-structural SCMs employed in Virginia in response to the second phase of the NPDES SW program were catalogued, and the variability in what is considered a "compliant" stormwater program was evaluated. Next, the uncertainty of several commonly used stormwater flow measurement devices were quantified in the laboratory and field, and the importance of this uncertainty for regulatory compliance was discussed. Finally, the third research objective quantified the uncertainty associated with structural SCMs, as a result of measurement error and environmental stochasticity. The impacts of this uncertainty are discussed in the context of the large number of structural SCMs prescribed in TMDL Implementation Plans. The outcomes of this dissertation emphasize the challenge that empirical uncertainty creates for cost-effective spending of local resources on flood control and water quality improvements, while successfully complying with regulatory requirements. The MEP paradigm acknowledged this challenge, and while the findings of this dissertation confirm the flexibility of the MEP paradigm, they suggest that the resulting magnitude of SCM implementation has outpaced the ability to measure and functionally define SCM pollutant removal performance. This gap between implementation, monitoring, and improvement is discussed, and several potential paths forward are suggested. / Ph. D. / Responsibility for mitigation of the ecological effects of urban stormwater runoff has largely been delegated to local government authorities through several Clean Water Act programs, which require that regulated entities reduce the discharge of pollutants from their storm drain systems to the “maximum extent practicable” (MEP). The existing definition of MEP requires a combination of structural and non-structural stormwater treatment – known as stormwater control measures (SCMs). The regulations acknowledge that there is uncertainty regarding the ability of SCMs to reduce pollution, but suggest that this uncertainty can be reduced over time, by monitoring and evaluation of SCMs. The objective of this dissertation is to demonstrate the existing sources and magnitude of variability and uncertainty associated with the use of structural and non-structural SCMs towards the MEP goal, and to examine the extent to which the MEP paradigm of implementation, monitoring, and learning appears in the current outcomes of the paradigm in Virginia. To do this, three research objectives were fulfilled. First, the non-structural SCMs employed in Virginia were catalogued, and the variability in what is considered a “compliant” stormwater program was evaluated. Next, the uncertainty of several commonly used stormwater flow measurement devices were quantified in the laboratory and field, and the importance of this uncertainty for regulatory compliance was discussed. Finally, the third research objective quantified the uncertainty associated with structural SCMs, as a result of measurement error and environmental variability. The impacts of this uncertainty are discussed in the context of the large number of structural SCMs prescribed by Clean Water Act programs. The outcomes of this dissertation emphasize the challenge that uncertainty creates for cost-effective spending of local resources on flood control and water quality improvements, while successfully complying with regulatory requirements. The MEP paradigm acknowledged this challenge, and while the findings of this dissertation confirm the flexibility of the MEP paradigm, they suggest that the resulting magnitude of SCM implementation has outpaced the ability to measure and functionally define SCM pollutant removal performance. This gap between implementation, monitoring, and improvement is discussed, and several potential paths forward are suggested.

Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: In the context of rapidly expanding cities, it is imperative that urban planning in South Africa has sufficient guidance regarding stormwater and river corridor management, in order to provide solutions that address issues of flood risk and the environmental health of river systems. Attenuation of stormwater runoff, the focus of this study, is one of the most important structural mechanisms used for the mitigation of many of the negative impacts caused by uncontrolled urban runoff. Typically, it involves the use of attenuation ponds or wetlands, which temporarily store runoff during a storm and release flow downstream at a reduced rate so as to mimic natural flow patterns. The focus of urban stormwater management and flood control has historically been on the protection of human life and property. However, in recent decades, through growing environmental awareness and the advancement of the concept of sustainable development, urban stormwater management has become a growing field of research worldwide, with a broader focus which considers not only flood control, but also water quality, aquatic biodiversity and the amenity value of urban drainage systems. Flood attenuation controls are becoming more widely used within South African urban areas, primarily due to policies or legislation brought into effect by local authorities. However, there is often little understanding regarding the positive and perhaps negative effects that these attenuation controls are having on receiving watercourses downstream. Three case studies were assessed by means of stormwater modelling simulations to evaluate various flood attenuation practices which are currently in use in South Africa. Two of the study areas, the Mosselbank River Catchment and the Bayside Canal Catchment, were selected in areas of Cape Town where future development has been proposed by spatial planners. The third study area, the Upper Kuils River Catchment, was evaluated in terms of the performance of existing attenuation facilities in an area which is already almost completely developed. The study found that attenuation facilities constructed with a single culvert-type outlet structure, designed to reduce flows during large storm events, do not mitigate the impact of post-development runoff occurring during lower recurrence interval storm events. Attenuation facilities with multi-stage outlet structures were found to be much more effective at mimicking pre-development flow during a range of storm events. It was also found that because attenuation does not reduce post-development runoff volumes to pre-development levels, but merely reduces peak flow rates, the cumulative runoff from multiple attenuation controls across a large (>30 km2) urban catchment resulted in higher runoff peaks in downstream watercourses. The study concluded that more widespread use of stormwater Best Management Practices (BMPs) and Sustainable Drainage System (SuDS) controls allows a greater portion of runoff to infiltrate, resulting in less runoff volume and therefore reduced peak flows downstream, especially during low recurrence interval storm events. In addition, the study recommended the use of detailed catchment-wide stormwater modelling to understand specific catchment dynamics holistically, thus increasing the potential for designing effective attenuation controls in urban stormwater systems. / AFRIKAANSE OPSOMMING: In die konteks van die vinnige tempo van stedelike uitbreiding, is dit noodsaaklik dat stedelike beplanning in Suid-Afrika plaasvind met in aggenome van voldoende riglyne vir die bestuur van stormwater en rivierkorridors, ten einde oplossings te vind vir die kwessies van vloedrisiko en die omgewingsgesondheid van rivierstelsels. Vloedvertraging, wat die fokus van hierdie studie is, is een van die belangrikste strukturele meganismes wat gebruik word vir die verligting van talle negatiewe impakte wat veroorsaak word deur onbeheerde stormwaterafloop in stedelike gebiede. Tipies behels dit die gebruik van vloedvertragingsdamme of vleilande, wat afloop vertraag tydens 'n storm en dus vloei stroom-af teen 'n verlaagde tempo uitlaat met die doel om natuurlike vloeipatrone na te boots. Die fokus van stedelike stormwaterbestuur en vloedbeheer was in die verlede hoofsaaklik op die beskerming van lewe en eiendom gefokus, maar het egter die afgelope dekades verskuif na water gehalte, die biodiversiteit van waterekosisteme en die geriefswaarde van stedelike dreineringstelsels. Hierdie verskuiwing van fokus is weens die groeiende omgewingsbewustheid en die bevordering van die konsep van volhoubare ontwikkeling wat wêreldwyd 'n groter navorsingsgebied geraak het. Vloedvertraging beheermeganismes word al hoe meer algemeen gebruik in Suid-Afrikaanse stedelike gebiede, hoofsaaklik as gevolg van die beleide of wetgewing wat deur plaaslike owerhede in werking gestel is. Daar is egter dikwels min begrip vir die positiewe en moontlike negatiewe gevolge wat hierdie vertragingsmeganismes op stroom-af sisteme het. Drie gevallestudies is geëvalueer deur middel van numeriese modelstudies wat verskeie benaderings van vloed beheer, wat tans in Suid-Afrika gebruik is, in ag neem. Twee van die studie areas, naamlik die Mosselbank en die Bayside-kanaal opvanggebiede in die Kaapse metropool, is gekies in areas waar toekomstige ontwikkeling in die vooruitsig gestel is deur stadsbeplanners. Die derde studie area, die opvangsgebied van die bolope van die Kuilsrivier, is in terme van die prestasie van bestaande stormwater infrastruktuur in 'n gebied wat reeds byna heeltemal ontwikkel is, geëvalueer. Die studie het bevind dat vloedvertragingsfasiliteite met 'n enkele duiker uitlaatstruktuur, wat ontwerp is met die doel om die vloeispitse tydens groot storms te demp, nie die impak van die na-ontwikkeling afloop, wat gedurende storms met laer herhalingsinterval voorkom, verminder nie. In terme van vloedvertragingsfasiliteite met 'n veelvuldige uitlaatstruktuur, is dit bevind dat voorontwikkelingsafloop tydens 'n reeks van groot en kleiner storms veel meer effektief nageboots word. Daar is egter ook bevind dat die demping van die vloedspitse nie die naontwikkeling afloopvolumes verminder tot voorontwikkelingsvlakke nie, maar slegs tot die vermindering van maksimum snelhede lei. Die gevolg is dat die totale afloop van ‘n kombinasie van ‘n aantal vertragingsdamme oor 'n groot (> 30 km2) stedelike opvanggebied ‘n hoër spitsvloei in die stroom-af riviere tot gevolg het. Die studie het bevind dat die wydverspreide gebruik van bestebestuurspraktyke (BMPs) en volhoubare stedelike dreineringstelsels (SuDS) tot die infiltrasie van ‘n groter gedeelte van die afloop lei, wat laer afloopvolume en dus verminderde spitsvloei stroomaf tot gevolg het, veral gedurende storms met ‘n lae herhalingsinterval. Daarbenewens word die aanwending van gedetailleerde modellering van stormwatersisteme binne die groter opvangsgebied aanbeveel ten einde ‘n meer holistiese begrip van spesifieke aspekte van die opvangegebied dinamika, om sodoende die potensiaal vir die ontwerp van effektiewe vloedvertragingskontroles in stedelike stormwaterstelsels te verbeter.

Extended detention basins are not used for stormwater quality management in many areas of the US because they generally do not achieve the 80% removal of total suspended solids required by many regulatory agencies. The objective of this research was modification of the outlet controls of an existing basin to provide batch treatment of the urban stormwater runoff through efficient control of the hydraulic residence time. A solar powered automated valve and controller were developed and placed on the outlet of an extended detention basin in Austin, Texas to increase the detention time beyond the times achievable using an orifice. This system retained the diverted runoff in the basin for a variable preset period of time. The quality of the influent and effluent of the basin was monitored for concentrations of suspended solids, nutrients, chemical oxygen demand. and total and dissolved metals. The suspended solids concentrations in the basin were controlled by adjusting the residence time of the runoff in the basin to meet the required pollutant reduction. The automated valve can also be used to regulate flow into the receiving waters to control peak flow.

Thesis (M. S.)--Architecture, Georgia Institute of Technology, 2009. / Committee Chair: Dagenhart, Richard; Committee Member: Elliott, Michael; Committee Member: Green, David

The change in the hydrological cycle due to climate change entails more frequent and intense rainfall. As a result, urban water systems will be disproportionately affected by the climate change, especially in such urban areas as Las Vegas, which concentrates its population, infrastructure, and economic activity. Understanding the proper management of urban stormwater in the changing climate is becoming a critical concern to the water resources managers. Proper design and management of stormwater facilities are needed to attenuate the severe effects of extreme rainfall events. In an effort to develop better management techniques and understanding the probable future scenario, this study used the high-resolution climate model data conjunction with advanced statistical methods and computer simulation. Las Vegas Valley which has unique climatic condition and is surrounded by the mountains in every direction was chosen for the study. The North American Regional Climate Change Assessment Program is developing multiple high-resolution projected-climate data from different combinations of regional climate models and global climate models. First, the future design depths was calculated using generalized extreme value method with the aid of L-moment regionalization technique. The projected climate change was incorporated into the model at the 100 year return period with 6h duration depths. Calculation showed that, the projection from different sets of climate model combinations varied substantially. Gridded reanalysis data were used to assess the performance of the climate models. This study used an existing Hydrologic Engineering Center’s Hydrological Modeling System (HEC-HMS) model and Storm Water Management Model (SWMM) developed by the Environmental Protection Agency (EPA) were implemented in the hydrological simulation. Hydrological simulation using HEC-HMS showed exceedances of existing stormwater facilities that were designed under the assumption of stationarity design depth. Low Impact Developments such as permeable pavement and green roof were found to be effective in the attenuation of climate change induced excess surface runoff. The primary purpose of this study is understanding of proper designing, planning and management of the urban stormwater system in the predicted climate scenarios.

Purpose: Climate change and increased proportion of hard surfaces due to urbanization is causing problems with flooding. Although it has been known for a long time that traditional stormwater management needs to be complemented, progress towards Sustainable Drainage Systems, SuDS, is slow. Techniques to locally handle storm water are available for most situations, but there is a lack of knowledge and experience. The aim of this thesis is to present a proposal on how implementation of SuDS can be promoted in urban development projects in Jönköping municipality. Method: Using literature review, interviews, document analysis and observation a qualitative study was conducted in two urban development projects; Ekostaden Augustenborg in Malmö and Munksjöstaden in Jönköping. Findings: The majority of the stormwater management techniques available in Augustenborg have also been discussed in Munksjöstaden by Jönköping municipality. Only one third of the techniques which has been discussed will be realized. Jönköping municipality lacks clear goals and a vision that is integrated into the planning process, which can explain this. During the interviews the site conditions were presented as arguments to why SuDS is difficult to implement. However the analysis showed that it is the other conditions that are decisive, something that also the scientific studies indicated. In order to promote the implementation of SuDS general and project-specific actions were elaborated. Implications: The local plan is the municipality’s sharpest tool for control of the physical development and demands must be submitted in the local plan in order to promote SuDS. The municipality needs to reprocess a practice level and equate SuDS with traditional stormwater management in order to make relevant demands on developers. To promote the implementation of SuDS, the authors suggests that Jönköping municipality carry out a pilot project focusing on sustainable stormwater management in an upcoming urban development project. Limitations: Since the thesis only includes two projects, there is a limitation of the conditions treated. Since the other conditions and the recommended actions are based on the factors identified in a national survey, the applicability is considered to be good. Although the project-specific actions are based on Jönköping municipality, it is possible for other municipalities to apply the PDSA-wheel to the extent that is suitable for the municipality. / Syfte: Klimatförändring och urbanisering med ökad andel hårdgjorda ytor orsakar problem med översvämningar. Trots att det sedan länge är känt att den traditionella dagvattenhanteringen behöver kompletteras går utvecklingen mot Sustainable Drainage Systems, SuDS, långsamt. Tekniker för att ta hand om dagvattnet lokalt finns för de flesta situationer men det saknas kunskap och erfarenhet. Målet med arbetet är därför att presentera ett förslag på hur implementering av SuDS kan främjas i stadsbyggnads-projekt i Jönköpings kommun. Metod: Med hjälp av litteraturstudie, intervjuer, dokumentanalys och observation har en kvalitativ studie genomförts på två stadsbyggnadsprojekt; Ekostaden Augustenborg i Malmö och Munksjöstaden i Jönköping. Resultat: Majoriteten av de tekniker för dagvattenhantering som finns i Augustenborg har diskuterats även i Munksjöstaden från Jönköpings kommuns sida. Det visade sig dock att endast en tredjedel av det som diskuterats kommer att förverkligas. Detta kan bland annat förklaras av att Jönköpings kommun saknar tydliga mål och en vision som är integrerad i planeringsprocessen. Vid intervjuerna lyftes platsen förutsättningar fram som argument till varför SuDS är svårt att tillämpa. Analysen visade dock att det är de övriga förutsättningarna som är avgörande, något som även de vetenskapliga studierna pekat på. För att främja implementeringen av SuDS har därför generella och projektspecifika åtgärder riktade mot de övriga förutsättningarna utarbetats. Konsekvenser: Detaljplanen är kommunens skarpaste verktyg för att styra den fysiska bebyggelsen och för att främja SuDS är det därför viktigt att det finns krav i detaljplanen. Kommunen behöver upparbeta en praxisnivå och likställa SuDS med traditionell dagvattenhantering för att kunna ställa relevanta krav på exploatörer. För att främja implementeringen är författarnas förslag att Jönköpings kommun genomför ett pilotprojekt med fokus på hållbara dagvattenlösningar i ett kommande stadsbyggnadsprojekt. Begränsningar: Eftersom arbetet endast innefattar två projekt finns det en begränsning i vilka förutsättningar som behandlats. Eftersom de övriga förutsättningarna och de rekommenderade åtgärderna utgår från faktorer som identifierats i en nationell enkät-undersökning bedöms ändå tillämpligheten vara god. Även om de projektspecifika åtgärderna utgår från Jönköpings kommun, är det möjligt för andra kommuner att tillämpa PGSA-hjulet i den omfattning som passar den aktuella kommunen.

Stormwater runoff from existing impervious surfaces needs to be managed to protect downstream waterbodies from hydrologic and water quality impacts associated with development. As urban expansion continues at a rapid pace, increasing impervious cover, and climate change yields more frequent extreme precipitation events, increasing the need for improved stormwater management. Although green infrastructure such as bioretention has been implemented in urban areas for stormwater quality improvements and volume reductions, these systems are seldom monitored to validate their performance. Herein, we evaluate flow attenuation, stormwater quality performance, and nutrient cycling from eight roadside bioretention cells in their third and fourth years of implementation in Burlington, Vermont. Bioretention cells received varying treatments: (1) vegetation with high-diversity (7 species) and low-diversity plant mixes (2 species); (2) proprietary SorbtiveMediaTM (SM) containing iron and aluminum oxide granules to enhance sorption capacity for phosphorus; and (3) enhanced rainfall and runoff (RR) to certain cells (including one with SM treatment) at three levels (15%, 20%, 60% more than their control counterparts), mimicking anticipated precipitation increases from climate change. Bioretention water quality parameters monitored include total suspended solids (TSS), nitrate/nitrite-nitrogen (NOx), ortho-phosphorus (Ortho-P), total nitrogen (TN) and total phosphorus (TP), which were compared among bioretention cells’ inflows and outflows across 121 storms. Simultaneous measurements of flow rates and volumes allowed for evaluation of the cells’ hydraulic performances and estimation of pollutant load and event mean concentration (EMC) removal. We also monitored soil CO2 and N2O fluxes, as they represent a potential nutrient loss pathway from the bioretention cells. We determined C and N stocks in the soil media and vegetation, which are critical design elements of any bioretention, to determine the overall C and N balances in these systems. Significant average reductions in effluent stormwater volumes and peak flows were reported, with 31% of the storms events completely captured. Influent TSS loads and EMCs were well retained by all cells irrespective of treatments, storm characteristics, or seasonality. Nutrient removal was treatment-dependent, where the SM treatments consistently removed P loads and EMCs, and sometimes N as well. The vegetation and RR treatments mostly exported nutrients to the effluent. We attribute observed nutrient exports to the presence of excess compost in the soil filter media. Rainfall depth and peak inflow rate undermined bioretention performance, likely by increasing pollutant mobilization through the filter media. While the bioretention cells were a source of CO2, they varied between being a sink and source of N2O. CO2 fluxes were orders of magnitude higher than N2O fluxes. However, soil C and N, and plant C and N in biomass was seen to largely offset respiratory CO2-C and biochemical N2O-N losses from bioretention soil. The use of compost in bioretention soil media should be reduced or eliminated. If necessary, compost with low P content and high C: N ratio should be considered to minimize nutrients losses via leaching or gas fluxes. In order to understand trade-offs stemming from compost amendments, we conducted a laboratory pot study utilizing switchgrass and various organic soil amendments (e.g., different compost types and coir fiber) to a sandy loam soil contaminated with heavy metals and studied potential nutrient leaching and pollutant uptake. Addition of organic amendments significantly reduced metal bioavailability, and improved switchgrass growth and metal uptake potential. While no differences in soil or plant metal uptake were observed among the amendments, significant differences in nutrient leaching were observed.

<p>The presence of human pathogens in water indicates the sanitary risk associated with different types of water utilization. This study surveyed the sources of human pathogens in urban waters. In order to evaluate the microbiological water quality of urban water, the enumeration of various indicator bacteria (total coliform, fecal coliform, E.coli and enterococci) is usually used.</p><p>The abundance of indicator bacteria in urban water indicates the level of fecal contamination and the presence of other human pathogens such as protozoan pathogens (Giardia lamblia & Cryptosporidium parvum).</p><p>Fecal pollution of urban waters can be from human and animal origin. Point sources of fecal contamination in an urbanized area are the effluents of urban wastewater treatment plants. While non-point sources are usually originated from diffuse sources such as (runoff from roads, parking lots, pets, leaks, failing septic systems and illegal sewer connections to storm drains). urban stormwater is considered as a major carrier for delivering human pathogens from diffuse sources to receiving waters. Increases in urban stormwater volumes have resulted from increasing urbanization and growth of impervious surfaces.</p><p>In order to reduce high amounts of human pathogens in urban waters, different methods are used nowadays to develop urban wastewater treatment plants technologies and urban stormwater management practices.</p>

The presence of human pathogens in water indicates the sanitary risk associated with different types of water utilization. This study surveyed the sources of human pathogens in urban waters. In order to evaluate the microbiological water quality of urban water, the enumeration of various indicator bacteria (total coliform, fecal coliform, E.coli and enterococci) is usually used. The abundance of indicator bacteria in urban water indicates the level of fecal contamination and the presence of other human pathogens such as protozoan pathogens (Giardia lamblia & Cryptosporidium parvum). Fecal pollution of urban waters can be from human and animal origin. Point sources of fecal contamination in an urbanized area are the effluents of urban wastewater treatment plants. While non-point sources are usually originated from diffuse sources such as (runoff from roads, parking lots, pets, leaks, failing septic systems and illegal sewer connections to storm drains). urban stormwater is considered as a major carrier for delivering human pathogens from diffuse sources to receiving waters. Increases in urban stormwater volumes have resulted from increasing urbanization and growth of impervious surfaces. In order to reduce high amounts of human pathogens in urban waters, different methods are used nowadays to develop urban wastewater treatment plants technologies and urban stormwater management practices.