Comparison of green roof performance in stormwater mitigation

Paper no. 81365The impervious surfaces in urban areas often increase overland flow and river discharge leading to flooding issues. Green roof, being one low impact development technique, can potentially facilitate stormwater management and advert flooding problems. Although there are a number of studies examining the hydrologic behaviour of green roof, they are often limited to the monitoring periods which may not involve extreme rainfall events. They are also specific to the rainfall conditions of the study areas, making it difficult to transfer the knowledge to other countries. This study uses numerical models to quantify the hydrological behaviour of green roof and to examine the effectiveness of green roof in stormwater management. In particularly, it compares its performance in extreme rainfall events of different countries. A one-dimensional variably-saturated flow model is used. The calibrated model is subjected to the rainfall conditions of a few cities (i.e., Hong Kong, Singapore, Nagoya and London) of two-year return period. The reduction and the delay of the peak discharge, and the fraction of water retained are compared. The green roof performances (e.g., peak reduction, rainfall retained) vary due to the differences in rainfall characteristics (e.g., temporal pattern, total rainfall volume). The modeling results from different countries allow a consistent comparison, generating insights that might facilitate the transfer of results across countries. Overall, this study improves our understanding of hydrological behaviour of green roofs for stormwater management, in particularly benefiting the interpretation of green roof hydrological studies performed at rainfall conditions different from the area of interests.published_or_final_versio

Restoring groundwater surface-water interactions at urban drains

Conference Theme: Emerging Patterns, Breakthroughs and ChallengesOral Communication - Amphi H sessionImpervious areas from urbanization minimizes infiltration in a catchment, resulting in an increase of peak flows during storms. To efficiently divert stormwater away from developed areas, Singapore has built a network of waterways consisting of 7,000 km of concrete lined canals and drains, and has successfully alleviated flooding in many flood-prone areas. Unfortunately, it has also tremendously degraded many riverine habitats and removed the natural groundwater-surface water interactions and the riparian zones. River restoration is multi-disciplinary and multi-faceted. This study particularly examines the possibility of rehabilitating the urban drains in Singapore by restoring the groundwater-surface water interactions without significantly comprising their conveyance capabilities. It first compares and contrasts the groundwater-surface water ...postprin

Optimizing bio-retention system locations for stormwater management using genetic algorithm

As part of stormwater best management practices, bio-retention systems have been applied in a number of developed countries to minimize the change of hydrological regime due to urbanization. Optimization techniques have also been applied to determine the locations that give the most hydrological benefits. However, optimization tools are commonly built in together with specific hydrological models, usually restricting the choices and components of hydrological models. Furthermore, it is redundant to build another hydrological model that has a built-in optimization tool if a hydrological model, and possibly more comprehensive one, has already been developed for the study area. The objective of this study is to develop a genetic algorithm (GA) that is independent from and can therefore be coupled with any existing integrated distributed hydrological model to optimize the locations of bio-retention systems. The GA is written in Visual Basic considering factors such as topography, distance from a river and groundwater table depth. The alternative combinations of bio-retention locations suggested by the GA are used as inputs of an integrated distributed hydrological model. The combination that gives the lowest outlet discharge is then regarded as the best solution. We demonstrate the approach by taking Marina catchment in Singapore as a case study and feeding the GA with results from MIKESHE. Overall, the GA developed is not only transferable to other study area but also can also be coupled with any hydrological model that is the most suitable for that particular case study.postprin

Managing stormwater with low impact development in highly urbanized areas

2014 is the 25th Anniverssary of the Drainage Services Department (DSD) of the HKSAR GovernmentPaper A2-2Low impact development (LID) implements small-scale hydrologic controls throughout a catchment to replicate the pre-development hydrologic regimes or in other terms control stormwater as close to the source as possible. Examples of such controls include green roofs, bioretention swales, rain gardens, porous pavements. This project evaluates the effectiveness of large-scale LID implementation in Singapore and Hong Kong. We examine the hydrologic impacts, namely peak discharge mitigation and baseflow restoration, under different land uses, rainfall conditions and LID strategies. For further comparison, we adopt an integrated distributed hydrological model for Singapore and a lumped hydraulic model for Hong Kong. Studies of both Singapore and Hong Kong suggest that LID is effective if there is substantial level of infrastructures (e.g., covering 5 to 10% of catchment area). LID is more efficient in reducing/delaying peak discharge and restoring baseflow on an average long term basis. However, its performance, particularly in peak discharge mitigation, diminishes during design storms (e.g., ARI of 5 years). In terms of modeling techniques, integrated distributed hydrologic models require extensive parameterization but can accurately simulate some important processes (e.g., increase of infiltration and restoration of baseflow) that are simplified in lumped hydraulic models. Overall, large-scale LID potentially provides more sustainable stormwater management but its success depends on factors such as design objectives, existing land uses and drainage networks. We should therefore further research to increase the feasibility of large-scale LID in highly urbanized areas such as Singapore and Hong Kong.postprin

Predicting stream baseflow using genetic programing

Developing reliable methods to estimate stream baseflow has been a subject of research over the past decades due to its importance in catchment response and sustainable watershed management (e.g. ground water recharge vs. extraction). Limitations and complexities of existing methods have been addressed by a number of researchers. For instance, physically based numerical models are complex, requiring substantial computational time and data which may not be always available. Artificial Intelligence (AI) tools such as Genetic Programming (GP) have been used widely to reduce the challenges associated with complex hydrological systems without losing the physical meanings. However, up to date, in the absence of complex numerical models, baseflow is frequently estimated using statistically derived empirical equations without significant physical insights. This study investigates the capability of GP in estimating baseflow for a small monitored semi-urban catchment (0.021 km2) located in Singapore. A Recursive Digital Filter (RDF) is first adopted to separate the baseflow from observed streamflow. GP is then used to derive an empirical equation to relate the filtered baseflow time series particularly with groundwater table fluctuations which are relatively easy to be measured and are physically related to baseflow generation. The equation is then validated with a longer time series of baseflow data from a groundwater numerical model. These results indicate that GP is an effective tool in determining baseflow.postprin

Bioavailability in soils

The consumption of locally-produced vegetables by humans may be an important exposure pathway for soil contaminants in many urban settings and for agricultural land use. Hence, prediction of metal and metalloid uptake by vegetables from contaminated soils is an important part of the Human Health Risk Assessment procedure. The behaviour of metals (cadmium, chromium, cobalt, copper, mercury, molybdenum, nickel, lead and zinc) and metalloids (arsenic, boron and selenium) in contaminated soils depends to a large extent on the intrinsic charge, valence and speciation of the contaminant ion, and soil properties such as pH, redox status and contents of clay and/or organic matter. However, chemistry and behaviour of the contaminant in soil alone cannot predict soil-to-plant transfer. Root uptake, root selectivity, ion interactions, rhizosphere processes, leaf uptake from the atmosphere, and plant partitioning are important processes that ultimately govern the accumulation ofmetals and metalloids in edible vegetable tissues. Mechanistic models to accurately describe all these processes have not yet been developed, let alone validated under field conditions. Hence, to estimate risks by vegetable consumption, empirical models have been used to correlate concentrations of metals and metalloids in contaminated soils, soil physico-chemical characteristics, and concentrations of elements in vegetable tissues. These models should only be used within the bounds of their calibration, and often need to be re-calibrated or validated using local soil and environmental conditions on a regional or site-specific basis.Mike J. McLaughlin, Erik Smolders, Fien Degryse, and Rene Rietr

Measurements of the Propagation of EM Waves through the Vacuum Chamber of the PEP-II Low Energy Ring for Beam Diagnostics

We present the results of our measurements of the electron cloud density in the PEP-II low energy ring (LER) by propagating a TE wave into the beam pipe. By connecting a signal generator to a beam position monitor button we can excite a signal above the vacuum chamber cut-off frequency and measure its propagation through the beam pipe with a spectrum analyzer connected to another button about 50 meters away. The measurement can be performed with different beam conditions and also at different settings of the solenoids used to reduce the build up of electrons. The presence of a modulation in the TE wave transmission, synchronous with the beam revolution frequency, which appear to increase in depth when the solenoids are switched off, seem to be directly correlated to the electron cloud density in the region between the two BPM's. In this paper we present and discuss the measurements taken in the Interaction Region 12 straight of the LER during 2006 and the first part of 2007