Stormwater management is always a problem in Hong Kong since its development from a fishing village. Contributed by abundant precipitation, hilly topography, and dense urban development, flooding has been causing enormous economic losses to Hong Kong and is a main focus of local stormwater management. With the construction of many conventional hardcore engineering stormwater management structures in recent decades, such as underground detention tanks and stormwater tunnels, the flooding problem in Hong Kong has been well alleviated. It is now the time to move forward and incorporate more sustainable stormwater management principles and techniques, namely the strategy of low-impact development (LID), into the local practices in Hong Kong. Stormwater should be viewed not only as a problem, but also as a valuable resource. This research aims at a feasibility study on the possible applications and hydrologic benefits of bioretention and permeable pavements under the local conditions of Hong Kong. The buildability of infiltration devices in Hong Kong is examined by constructing pilot-scale physical models of both bioretention and permeable pavements in this study. Hydrologic monitoring of these physical models under Hong Kong rainfall events is carried out for at least one wet season. The monitoring data are analyzed to evaluate the hydrologic performance of bioretention and permeable pavements, as indicated by peak flow reduction and volume retention of stormwater runoff. The long-term hydrologic performance is also evaluated by the numerical model SWMM (Stormwater Management Model). After model calibration and validation using field data on the physical model, SWMM isused to simulate bioretention performance for the past ten year precipitation records of Hong Kong under systematic variations of two relevant parameters, namely the exfiltration rate and the area ratio of bioretention to catchment. Results show that both bioretention and permeable pavements are feasible to be applied in Hong Kong. The hydrologic performance of bioretention is influenced by the precipitation patterns, the size of bioretention, the stormwater storage, and the properties of soil. As in common practice, the available storage of bioretention is much smaller than design rainfalls in Hong Kong. Therefore, peak flow reduction shall not be the target of incorporating bioretention in local storm drain designs. The influence on long-term water balance in the urban area may be considered as the main benefits from bioretention, using the annual retention ratio as a performance indicator. The hydrologic performance of permeable pavements is influenced by the storage depth provided by the gravel layer and the properties of in-situ soil. Considerably good peak flow reduction and volume retention are obtained in the experimental permeable pavements subjected to the local extreme precipitation events. In actually applications, the storage of permeable pavement may be designed to capture the total depth of design storms in Hong Kong, after which peak flow reduction may be obtained. It is anticipated that this research can provide reference information on both the design and hydrologic benefit estimation of bioretention and permeable pavements practices for applications in Hong Kong. / published_or_final_version / Civil Engineering / Master / Master of Philosophy

Thesis (M.S.)--University of Hawaii at Manoa, 2006. / Includes bibliographical references (leaves 98-105). / viii, 105 leaves, bound ill. 29 cm

Superelevation transition is often used to help balance the centrifugal forces on vehicles through curved roadway sections. Such transitions have regions with near-zero cross-slope as the pavement cross-section rotates from a negative to positive grade. For drainage of roadway surfaces, regions with near-zero slope constitute 'irregular topography'. This condition promotes extended stormwater runoff drainage path lengths and may result in excessive splash from vehicles and hydroplaning. A critical concern is the effect of longitudinal slope on stormwater drainage through superelevation transition. The overall goal of this study is to provide design guidance on longitudinal slope at superelevation transitions through application of a numerical simulation model of highway drainage. Sheet flow on urban pavement surfaces is very shallow, typically measuring a depth less than one centimeter. For modeling of such flow conditions, any small discontinuity or over-simplification of the surface geometry may result in failure in the flow computation. The kinematic wave approximation to the full Saint-Venant equations is often used in many surface and subsurface water models due to its simplicity in application. However, this model fails when backwater effects, ponding, or flow on reverse slope occurs in the local scale. Furthermore, due to the complexity in the surface geometry and the existence of drainage systems, the kinematic wave model is not sufficient for modeling urban stormwater runoff. On the other hand, the full dynamic wave (DW) model usually requires more computational effort. The long computation time of DW model often compromises the accuracy of the model, making the model practically inefficient. In this study, an algorithm was developed to properly represent the irregularly shaped roadway surfaces near superelevation transition areas with unevenly spaced curvilinear grids based on the geometry profile provided by a roadway design software package such as MicroStation CAD. With this accurately defined geometric representation, a nonlinear hydrodynamic diffusion wave model for hydraulic analysis developed in this research estimates the flow depth and runoff volume on the pavement surfaces. The model computes the flow responses for rising hydrographs using a preconditioned general Conjugate Gradient method. Kinematic boundary conditions developed for the open boundaries at the upstream and downstream boundaries compute the boundary values explicitly at each time step. The result of a numerical experiment shows that the spread and concentration of sheet flow is closely related to the transition in cross slope, longitudinal slope, rainfall intensity, and the width of the road. The characteristics of the sheet flow on superelevation transition areas are analyzed to find the optimal longitudinal slope. It is found that the longitudinal slope in the range of 0.3%-0.4% is the optimal slope at superelevation transition areas which minimizes the depth of stormwater runoff. An example application of the model on a rural highway in Texas is also presented. It is found that a significant amount of stormwater may exist on traffic lanes at the superelevation transitions tested. The predicted ponding depth exceeds the minimum value for potential hydroplaning, and the pattern of the flow concentration may cause differential drag forces on traffic vehicles. / text

Despite the technology advancement, degradation of water quality due to stormwater continues to be a significant threat to the water and ecosystems due to the exponential growth of industries and agricultural enterprises that discharge stormwater. These anthropogenic activities are the sources of high nitrogen and phosphorus quantities in stormwater, which is responsible for eutrophication phenomena and deterioration of public health. Floating Treatment Wetlands (FTWs) are a potential solution to this problem. Both microcosm and mesocosm level studies were conducted for the effective removal of nutrients in stormwater wet detention ponds with different sorption media under varying nutrient concentrations and weather conditions. Water depth, percent area coverage of the FTWs and littoral zone emergent plants were varied in order to determine nutrient removal efficiency before implementing in an actual pond. Focus has also been placed on the observations of macrophyte-epiphyte-phytoplankton interactions in order to understand temporal characteristics of ecological phenomena. Water quality parameters included Total Nitrogen, Total Phosphorus, Orthophosphate, Nitrate-Nitrogen, and Ammonia-Nitrogen in addition to in-situ parameters such as pH, Dissolved Oxygen, Temperature and Chlorophyll-a. Results clearly indicate that an FTW filled with sorption media of 80% expanded clay and 20% tire crumb can significantly promote the biomass growth. Different levels of nutrient concentrations did affect the plants’ growth and cold temperature in late winter was detrimental to growth. To make the system more viable irrespective of the seasonal weather conditions, the adoption of mixed vegetation is highly recommended in the FTWs implementation. It is also recommended that, the positioning of the floating wetlands should not be in the vicinity of the outlet of the pond as assimilated nutrient under the mat might increase the nutrient concentration in the discharged water. Finally, One-way ANOVA test is performed to check whether or not iv these grouped microcosms and mesocosms with differing experimental setup can be deemed statistically significant

A project report submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in partial fulfillment of the requirements for the degree of Master of Science in Engineering. Johannesburg, 1997 / Detention storage IS a well tested, and generally accepted, method of attenuating flood hydrographs, but relatively littlo data is available from the monitoring of full scale instc'lations An onstrearn pond was constructed at Sunninqhill Park and details of 15 inflow and outflow hydro [Abbreviated Abstract. Open document to view full version] / MT2016

In the United States, an aging and overburdened urban infrastructure has become a substantial challenge for civil engineers. Among these challenges, systems for stormwater management are of significant concern, considering their direct impact on environmental quality, local ecosystems, and the hydrologic cycle. Given the high costs for rehabilitation of traditional stormwater infrastructure in urban settings, low impact, or "green" development strategies have become critical components in plans for meeting future stormwater management goals. In particular, New York City (NYC) has pledged $1.5 billion over the next 20 years to improve environmental quality through the mitigation of urban runoff, where utilization of green infrastructure is a primary goal. Cost effective implementation of this, and similar plans around the world, requires comprehensive understanding of green infrastructure functionality. In response, this dissertation investigates the stormwater management potential of full-scale green roofs in NYC through lenses of observation, modeling, and design. Exploration of this topic has resulted in new findings which quantify the: influence of dominant environmental and physical properties on green roof hydrologic performance, envelope of potential green roof rainfall capture in NYC, and predictive efficiency of contemporary hydrologic models for green roof assessment. This work has also lead to new methods for the: extension of green roof observations to account for the influence of rainfall distribution, parameterization of green roof hydrologic processes, and prediction of full-scale green roof rainfall capture in advance of construction. Going forward, these findings and methods are useful for informing green roof policy, planning, and design; where, in particular, this information supports the development of green roof policies that correlate to specific stormwater management goals. In summation, the characterization of green roof stormwater management in NYC, as presented in this dissertation, has contributed to the understanding of, among other topics, green roof design, urban stormwater management, hydrologic modeling, and the broad interdisciplinary field of urban ecological systems.

Green Stormwater Infrastructure (GSI) has become a popular method for flood mitigation as it can prevent runoff from entering streams during heavy precipitation. In this study, a recently developed neighborhood in Gresham, Oregon hosts a comparison of various GSI projects on runoff dynamics. The study site includes dispersed GSI (rain gardens, retention chambers, green streets) and centralized GSI (bioswales, detention ponds, detention pipes). For the 2017-2018 water year, hourly rainfall and observed discharge data is used to calibrate the EPA's Stormwater Management Model to simulate rainfall-runoff dynamics, achieving a Nash-Sutcliffe efficiency of 0.75 and Probability Bias statistic of 3.3%. A synthetic scenario analysis quantifies the impact of the study site GSI and compares dispersed and centralized arrangements. Each test was performed under four precipitation scenarios (of differing intensity and duration) for four metrics: runoff ratio, peak discharge, lag time, and flashiness. Design structure has significant impacts, reducing runoff ratio 10 to 20%, reducing peak discharge 26 to 68%, and reducing flashiness index 56 to 70%. There was a reverse impact on lag time, increasing it to 50 to 80%. Distributed GSI outperform centralized structures for all metrics, reducing runoff ratio 22 to 32%, reducing peak discharge 67 to 69%, increasing lag time 133 to 500%, and reducing flashiness index between 32 and 62%. This research serves as a basis for researchers and stormwater managers to understand potential impact of GSI on reducing runoff and downstream flooding in small urban watersheds with frequent rain.

Stormwater treatment is commonly performed with a combination of approaches including the utilization of natural systems and engineered devices. Before using a proprietary treatment instrument it is required to verify its performance and efficiency in reducing different pollution components including the TSS. Different states have developed strategies and regulations for accepting new instruments. In this thesis the stormwater management plan of the City of Portland, Oregon(2008), is analyzed in order to improve the current regulations. These rules apply to new technologies which are proposed by vendors to be used in Portland's stormwater treatment plans. Each requirement which should be met by the applying vendors is thoroughly analyzed followed by a comparison with the Stormwater management plan(2008)regulations of the state of Washington the so called Technology Assessment Plan-Ecology TAPE (Howie, 2011). Because of the similarities in the climate and land use between these two testing frameworks in order to evaluate the potential applicability of data submitted by vendors who had devices approved by Washington, to be utilized by Portland. The treatment of total suspended solids (TSS) is the focus of this thesis since it is central to the testing process and since most of the other pollutions are attached to TSS and will get treated if TSS is treated. The overall analysis shows that Portland adopts more restrictive requirements on the characterization of stormwater event samples to be treated by a technological instrument while Washington's restriction are more stringent on the efficiency of total suspended solid removal, in which it demands higher standards on the treatment of TSS compared to Portland's efficiency requirements. In order to study practical context in which regulations are administrated by Portland, rainfall data from 66 gauges covering the period of 1980-2011 was studied and the impacts of seasonality, land use, land form, periods of no rain before and after an event and Portland's Modified Performance line on the number of accepted rain events were analyzed. The results which were accepted by state of Washington were also compared with the results accepted by the city of Portland on Portland's Standard Performance line. Our seasonality study suggests that Portland's requirements are unnecessarily restrictive which results in the disqualification of many otherwise useful stormwater events, sometimes allowing no natural events to be available for testing in dry years. The analysis of land use showed that land use has no statistically significant impact on the concentration levels of TSS, thereby indicating that land use restrictions in the testing rules could be usefully relaxed. Decreasing the interevent no-rain period significantly increases the total number of events providing sufficient data to assess the performance of treatment facilities. We also showed that many more events become suitable for performance testing if events separated by one hours or less are considered a single, longer event. Finally we identified a statistical relationship between number of forecasted accepted stormwater events and the total average daily precipitation in a given year.

Modern cities are often perceived as the antithesis of nature; the built environment is understood as the transformation of raw and untamed nature into a rationalized human landscape. However, a variety of scholars since the nineteenth century have noted the persistence of nature in cities, not only in providing essential services but also resisting human control. Most recently, urban geographers and environmental historians have argued that processes of urbanization do not entail the replacement of natural with artificial environments, but are more accurately understood as a reconfiguration of human/nature relations. In this dissertation, I employ this relational perspective to study a specific form of urban nature: stormwater flows. Urban drainage or stormwater management activities in US cities are a vivid example of the tensions between nature, society, and technology. In this study, I present a comparative case study of two US cities--Austin, Texas and Seattle, Washington--where stormwater issues have been a central focus of public debate over the last four decades. Using textual analysis, in-depth interviews, and experiential research methods, I argue that stormwater management practices involve not only the rational management of technological networks but also implicate a wide range of seemingly unrelated issues, such as local governance, environmental protection, land use decisionmaking, community development, aesthetics, and social equity. To describe the relational implications of urban nature, I present a framework of ecological politics to characterize drainage activities as rational, populist, or civic. I argue that the latter form of politics has the greatest potential to relieve the tensions between urban residents and their material surroundings by embracing a systems perspective of human/nonhuman relations and engaging local residents in the hands-on management of environmental flows. It is through the development of deliberative and grounded forms of civic politics that urban residents can forge new relationships between technology and nature, and in the process, understand their place in the world. / text

[Truncated abstract]This thesis investigates aspects of urban stormwater modeling and uses a small urban catchment (NE38) located in the suburb of Nedlands in Perth, Western Australia to do so. The MUSIC (Model for Urban Stormwater Improvement Conceptualisation) model was used to calibrate catchment NE38 using measured stormwater flows and rainfall data from within the catchment. MUSIC is a conceptual model designed to model stormwater flows within urban environments and uses a rainfall-runoff model adapted to generate results at six minute time steps. Various catchment scenarios, including the use of porous asphalt as an alternative road surface, were applied to the calibrated model to identify effective working stormwater disposal systems that differ from the current system. Calibrating catchment NE38 using the MUSIC model was attempted and this involved matching modeled stormwater flows to stormwater flows measured at the catchment drainage point. This was achieved by measuring runoff contributing areas (roads) together with rainfall data measured from within the catchment and altering the seepage constant parameter for all roadside infiltration sumps. ... The MUSIC model generated future scenario outcomes for alternative stormwater disposal systems that displayed similar or improved levels of performance with respect to the current system. The following scenarios listed in increasing order of effectiveness outline future stormwater disposal systems that may be considered in future urban design. 1. 35% porous asphalt application with no sumps in 2036 2. 35% porous asphalt application with no sumps in 2064 3. 68% porous asphalt application with no sumps in 2036 4. 68% porous asphalt application with no sumps in 2064. Future scenarios using the current stormwater disposal system (with roadside infiltration sumps) with porous asphalt were also run. These scenarios reduced stormwater runoff and contaminant loading on the catchment drainage point however the inclusion of a roadside infiltration sump system may not appeal to urban designers due to the costs involved with this scenario. Climate change will affect the design of future stormwater disposal systems and thus, the design of these systems must consider a rainfall reducing future. Based on the findings of this thesis, current stormwater runoff volumes entering catchment drainage points can be reduced together with contaminant loads in urban environments that incorporate porous asphalt with a stormwater disposal design system that is exclusive of roadside infiltration sumps.