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<p>Low Impact Development (LID) practices have been increasingly used to mitigate the adverse impacts of urbanization. Reliable methods are in need to provide hydrologic performance assessment of different types of LID practices. The purpose of this thesis is to develop a set of analytical models which can be used to assist the planning and design of commonly used structural LID practices such as green roofs, rain gardens, bioretention and permeable pavement systems.</p> <p>The analytical LID models are derived on the basis of exponential probability density functions (PDF) of local rainfall characteristics and mathematical representations of the hydraulic and hydrologic processes occurring in association with the operation of LID practices. Exponential PDFs are found to provide good fits to the histograms of rainfall characteristics of five cities located in different climatic zones. The mathematical representations are all physically based and most of the input parameters used in these representations are the same as those required in commonly used numerical models.</p> <p>The overall reliability of the analytical LID models are tested by comparing the results from these analytical models with results determined from long-term continuous simulations, in addition to that the accuracy of the analytical model for green roofs is also verified against observations from a real case study. The long-term rainfall data from the five cities and a variety of LID practice design configurations are used in the comparisons. The relative differences between the results calculated using the analytical LID models and the results determined from corresponding SWMM simulations are all less than 10%.</p> <p>The Howard’s conservative assumption is adopted in the development of the analytical models for rain gardens and permeable pavement systems. This assumption results in conservative estimations of the stormwater management performances of these LID practices. Instead of adopting the Howard’s conservative assumption, an approximate expected value of the surface depression water content of a bioretention system at the end of a random rainfall event [denoted as ] is derived and used in the development of the analytical model for bioretention systems. The use of is proven to be advantageous over the use of the Howard’s conservative assumption.</p> <p>The analytical LID models are comprised of closed-form mathematical expressions. The application of them can be easy and efficient as illustrated in the application examples. For a specific location of interest, with a goodness-of-fit examination of the exponential PDFs to local rainfall data and verification of the accuracy of the analytical LID models, these models can be used as a convenient planning, design, and management tool for LID practices.</p> / Doctor of Philosophy (PhD)

The Ministry of Environment and Climate Change establishes design criteria for the sizing of Low Impact Development (LID) practices in the province of Ontario. The current sizing standards are based on the concept of the 90th percentile storm and require LIDs to provide enough storage capacity to store catchment runoff from a 25 mm rainfall event. The notion of 90th percentile storm means that 90% of all rainfall events have event volumes below a 25 mm rainfall event. This research examines the performance and cost of infiltration trenches and bioretention cells sized for alternative sizing standards ranging from 5–50 mm. Analytical probabilistic equations are used to determine the runoff reduction rates of infiltration trenches and bioretention cells, while the Sustainable Technologies Evaluation Program (STEP)’s LID Practices Costing Tool is used to estimate the overall cost of each LID. The costs are used to create a ratio denoted the fraction of maximum cost by dividing each cost by the cost of the 50 mm sized LID to receive a unitless ratio. This ratio is compared with the runoff reduction rates of both LIDs. Four different catchment sizes and various soil types are included to broaden the scope of the analysis and make the conclusions more dependable. Results indicate that the current sizing standard of 25 mm is probably too high and not cost-effective. In fact, depending on the type of soil and LID, little increase in performance occurs while there is a large increase in cost. A new methodology is proposed for setting sizing criteria for infiltration trenches and bioretention cells which focuses on achieving a desired capture efficiency instead of a required volume of rainfall. The method proposes using the capture efficiency, fraction of maximum cost and sizing criteria to determine what value is an economically more justifiable sizing standard based on individual catchment size and soil type. Use of the analytical probabilistic approach allows for the capture efficiency to be easily calculated and provides better sizing targets on a case by case basis. Recommending a specific capture efficiency can be more uniformly applied LID design in any soil conditions or any catchment size. This can reduce government spending when building LIDs and greatly reduce the possibility of over-design. / Thesis / Master of Applied Science (MASc)

The goal of Low Impact Development (LID) is to mimic the pre-development hydrologic regime of a catchment through infiltration, filtration, storage, evaporation, and detention of post-development runoff using small-scale hydrologic controls close to the source. A LID facility located in Northern Virginia was examined for pollutant removal and hydrologic performance. The treatment train included four in-line grass swales followed by a bioretention cell with a gravel base. The facility retained 85% of the rainfall. Influent and effluent pollutant loads were calculated using three common substitution methods for datasets censored by values below the analytical detection limit. The Summation of Loads (SOL) method was used to facilitate understanding of how data censoring affected performance results when substitution methods were used. The SOL analysis showed positive removal performance for most nutrient species, sediment, oxygen demanding substances, selected trace metals and total petroleum hydrocarbons. Negative performance was observed for oxidized nitrogen, total dissolved solids and oil & grease. LID facility influent and effluent loads were also compared using the Effluent Probability Method (EPM). The EPM analysis showed statistically significant (p d 0.05) pollutant load removal performance over the entire range of sampled events for total suspended solids, total phosphorus, total nitrogen, total Kjeldahl nitrogen, ammonia nitrogen, chemical oxygen demand, copper, zinc and alkalinity. EPM analysis did not show significant removals of oxidized nitrogen, total dissolved solids, orthophosphate phosphorus and hardness. / Master of Science

Low impact development (LID) is an innovative stormwater management technique that was introduced in early 1990s. However, the transition to use of this more sustainable method has been slow due to technical, institutional, and regulatory barriers to LID adoption. The research questions for this study are: What constitutes LID adoption? Why do localities adopt LID? What are the major factors that influenced the level of LID adoption by local governments? Specifically, this study focused on motivations and key determinants of LID adoption by local governments. By answering these questions, we will have better knowledge about how to approach the adoption process of environmental innovations. The findings of the study will benefit any potential localities considering LID adoption. The theory of diffusion of innovations is applied as it is very flexible to investigate complex topics like environmental innovation involving multiple factors and environments. To explore the role of local governments in LID adoption, sub-theories like organizational innovation and policy adoption are reviewed. Based on these theoretical foundations, four constructs of variables which include innovation, organizations, motivations, and surrounding organizational context are investigated. The case study method is used for eight counties (Amherst, Bedford, Chesterfield, Fairfax, Isle of Wight, Roanoke, Stafford, and Spotsylvania) and two cities (City of Charlottesville, City of Roanoke) in Virginia. Key informants from each locality were selected for in-depth interviews and additional document reviews for each case are used to support multiple case studies. LID adoption consists of various forms such as regulations, practices, and plans. A combination of all forms of LID activities and programs was used to measure LID adoption level. Based on nine criteria (i.e., adoption mode, use of the term "LID" in local codes, code details, LID manuals, demonstration projects, number of LID projects after LID code adoption, education programs, task force, and incentives), localities with three levels of LID adoption have been determined. Influencing factors of innovation adoption varied depending on level of LID adoption (high, moderate, and low). Therefore, strategies to promote environmental innovation should be developed in relation to the level of innovation adoption. The research findings revealed two major determinants that influenced the level of LID adoption. One is strong champions, and the other is regulatory mandates. A champion-driven LID adoption model is found in high level LID adoption localities. Usually, individuals from local governments, NGOs, and development communities have played a critical role in LID adoption process. The local government organizations in this group are usually self-motivated for innovation adoption. Especially, the presence of strong champions was identified as a key factor to the higher level of innovation adoption. On the other hand, a regulation-driven LID adoption model is found in moderate to low level LID adoption localities. These localities are strongly influenced by state regulatory mandates. In these cases, external forces motivate local governments to adopt innovations. / Ph. D.

Biofiltration systems like rain gardens and bioswales are an important tool for capturing andinfiltrating polluted runoff, but little data exists on their efficiencies within Mediterraneanclimates. A two-year study initiated in 2015 investigated water retention and pollutant loadingand retention in the Ballona Creek Rain Garden (BCRG). This 300 by 3 m biofiltration systemwas constructed by The Bay Foundation in 2011 along Ballona Creek in Culver City, Los AngelesCounty, California. The purpose of the garden was to capture and infiltrate runoff from lightindustrial and commercial operations bordering the Creek, thus reducing pollutants enteringthis waterway and flowing into Santa Monica Bay 9 km downstream. During storm events,runoff enters the garden via five inlets, and when filled, flows into the creek via two outlets.The goal of this study was to sample flows and pollutant concentrations in runoff entering andleaving the garden and then integrate these to calculate mass loading estimates. Flows weremeasured at all inlets and outlets using 90° V-notch weirs outfitted with Hobo water levelsensors to produce hydrographs. The following pollutants were measured at all flowing inletsand outlets two to three times per storm depending on its duration and intensity: fecalindicator bacteria (E. coli and enterococci), total suspended solids, metals (copper, zinc, andlead), and semivolatile hydrocarbons (polyaromatic hydrocarbons, diesel hydrocarbons, andmotor oil hydrocarbons). The summation of load method was used to calculate the mass ofcontaminants entering and leaving the garden for each storm event, and their percent capturewithin the garden. The BCRG was very effective at infiltrating runoff and sequesteringpollutants. The garden’s infiltration rates ranged from 73% to 100% (with 100% for many of thesmaller storms percent retentions were in the 80-90% range for all pollutants, with an average of 90% for allnine pollutants sampled. This suggests rain gardens and other Low Impact Development (LID)systems can be used successfully in urban Mediterranean climates like Los Angeles to promoteinfiltration, capture pollutants, and prevent polluted stormwater from reaching impaired waterbodies.

abstract: The rate of urbanization has been impacted by global economic growth. A strong economy results in more people moving to already crowded urban centers to take advantage of increased employment opportunities often resulting in sprawling of the urban area. More natural land resources are being exploited to accommodate these anthropogenic activities. Subsequently, numerous natural land resources such as green areas or porous soil, which are less flood-prone and more permeable are being converted into buildings, parking lots, roads and underground utilities that are less permeable to stormwater runoff from rain events. With the diminishing of the natural landscape that can drain stormwater during a rainfall event, urban underground drainage systems are being designed and built to tackle the excess runoff resulting from urbanization. However, the construction of a drainage system is expensive and usually involves massive land excavations and tremendous environmental disturbances. The option for constructing an underground drainage system is even more difficult in dense urban environments due to the complicated underground environments, creating a need for low footprint solutions. This need has led to emerging opportunities for low impact development (LID) methods or green infrastructures, which are viewed as an environmentally friendly alternative for dealing with stormwater runoff. LID mimics the pre-development environment to retain the stormwater runoff through infiltration, retention, detention and evaporation. Despite a significant amount of prior research having been conducted to analyze the performance of runoff volume reduction and peak flow decrement of various green infrastructures, little is known about the economic benefits of using LID practices. This dissertation fills the gap in the knowledge regarding the life-cycle-cost effectiveness of green infrastructure in current urban developments. This study’s two research objectives are: (1) Develop a life cycle cost calculation template to analyze the cost benefits of using LID compared to the traditional drainage system (2) Quantify the cost benefits based on the real-world construction projects A thorough literature review led to the data collection of the hydrological benefits of using LIDs in conjunction with overviewing three real-world construction projects to quantify the cost benefits of LIDs. / Dissertation/Thesis / Doctoral Dissertation Civil, Environmental and Sustainable Engineering 2019

In coastal urban regions, underground stormwater treatment units are suitable infrastructure options because they take less space where premium land is expensive. Even then, they should be accessible and ideally small enough to fit into existing stormwater networks. Since 2003, the City of Tampa and Florida’s Department of Transportation (FDOT) have installed 47 baffle boxes into the city’s stormwater pipe networks. Baffle boxes are underground stormwater treatment structures designed to capture sediments and floating debris. Since their deployment, many challenges regarding their practical sediment capturing performance was raised by the city. The objective of this research was to evaluate the effects of rainfall, land use, and maintenance on the sediment trapping efficiency of the baffle boxes and identify solutions to enhance their performance. This was addressed through site visits, sediment accumulation measurements and analysis of historical and field data. The results of these measurements and analysis were then compared to rainfall intensity, catchment characteristics, size and type of the units. During the preliminary site visits and sediment measurements it was observed that most of the units located in the south of Tampa were inundated by backflows from Tampa Bay. Survey information collected from inspection crew members also showed that resuspension of trapped sediments frequently occurs in these units. Concerning operation and maintenance (O&M), it was indicated that units mounted with screens are costly and difficult to clean-out. Additionally, it was found that 80% of the units have very small trap inlets and lack the baffle structures needed to slow down and settle sediments. Historical sediment measurements and O&M practices were analyzed to calculate the overall performance of the units. The analysis of the data determined the sediments captured, the resuspension rate, and yearly cost of maintenance for different types of baffle boxes. Rainfall intensity and land use and land cover (LULC) data for each catchment of the units was correlated to the performance of the units. The LULC data used impervious fraction and tree canopy area of the catchments to project sediment and leaf matter accumulation within the units. This research study found that total daily rainfall intensity is a good predictor of sediment accumulation. Cleanout crews can use this relationship to conduct their work efficiently and to promptly react to occurring rainfall events. Thus, the prediction of sediments accumulated from rainfall events and the coordination of clean-out trucks can optimize O&M practices. It was also determined that large-sized (24-40 in) units and those with three chambers (baffles) perform better at trapping sediments. Thus, installing baffles in units within the large-sized ones can enhance their performance. The study also found that baffle boxes mounted with screens can individually take up to eight hours to cleanup which makes them costly and difficult. This can be detrimental for municipalities to follow up on their O&M practices effectively. Therefore, to alleviate the clean out complexity and reduce maintenance expenditures complementary practices such as bag filters need to be explored and implemented for trials

Vegetated roof technologies are increasingly being adopted as treatment measures to mitigate the effects of urban stormwater. A mass balance approach was used to assess the wet weather performance of a vegetated roof on the top of city hall in Waterloo, Ontario. Vegetated and control roof sections were instrumented to measure precipitation inputs, storage and outflow for 18 storm events from June to October, 2006. Concentrations of suspended solids (SS), total phosphorus (TP), soluble reactive phosphorus (SRP), copper (Cu), zinc (Zn), chromium (Cr) and cadmium (Cd) in precipitation and roof (vegetated and control) runoff were measured. A total of 155.6 mm of rain fell during the study period. The vegetated roof retained 64.5 mm (41.5%) of the total rainfall while the control roof retained ~ 5.1 mm (3.3 %). For individual rain events, the vegetated roof retained an average of 3.5 mm (47.6 %) while the control roof retained ~ 0.3 mm (4.7 %). Water retention varied with storm size, season and was influenced by wetting history. The vegetated roof retained 80.6 % of precipitation for light storm events (≤ 3.5 mm) and 34.9 % for large storm events (> 3.5 mm). The control roof retained 7.6 % light storm events and 3.7 % for large storm events. Water quality from the vegetated roof did not show significant improvement as only Zn concentrations in runoff from the vegetated roof were significantly lower than that measured in runoff from the control roof. Concentrations of SS, Cu, Cr and Cd in vegetated roof runoff were relative to concentrations in rainfall and control roof runoff and TP and SRP concentrations were significantly higher than that in rainfall or control roof runoff. Results gained from this study may assist people in planning and stormwater management by providing insight into the monitoring, development and application of new stormwater controls.

Vegetated roof technologies are increasingly being adopted as treatment measures to mitigate the effects of urban stormwater. A mass balance approach was used to assess the wet weather performance of a vegetated roof on the top of city hall in Waterloo, Ontario. Vegetated and control roof sections were instrumented to measure precipitation inputs, storage and outflow for 18 storm events from June to October, 2006. Concentrations of suspended solids (SS), total phosphorus (TP), soluble reactive phosphorus (SRP), copper (Cu), zinc (Zn), chromium (Cr) and cadmium (Cd) in precipitation and roof (vegetated and control) runoff were measured. A total of 155.6 mm of rain fell during the study period. The vegetated roof retained 64.5 mm (41.5%) of the total rainfall while the control roof retained ~ 5.1 mm (3.3 %). For individual rain events, the vegetated roof retained an average of 3.5 mm (47.6 %) while the control roof retained ~ 0.3 mm (4.7 %). Water retention varied with storm size, season and was influenced by wetting history. The vegetated roof retained 80.6 % of precipitation for light storm events (≤ 3.5 mm) and 34.9 % for large storm events (> 3.5 mm). The control roof retained 7.6 % light storm events and 3.7 % for large storm events. Water quality from the vegetated roof did not show significant improvement as only Zn concentrations in runoff from the vegetated roof were significantly lower than that measured in runoff from the control roof. Concentrations of SS, Cu, Cr and Cd in vegetated roof runoff were relative to concentrations in rainfall and control roof runoff and TP and SRP concentrations were significantly higher than that in rainfall or control roof runoff. Results gained from this study may assist people in planning and stormwater management by providing insight into the monitoring, development and application of new stormwater controls.