Mangangka, Isri R. and Liu, An and Goonetilleke, Ashantha and Egodawatta, Prasanna
(2016)
Enhancing the Storm Water Treatment Performance of Constructed Wetlands and Bioretention Basins.
Springer, SPRINGER BRIEFS IN WATER SCIENCE AND TECHNOLOGY.
ISBN 978-981-10-1659-2
Abstract
Urbanisation leads to both quantitative and qualitative changes to storm water
runoff. While the quantity changes have received much attention in the past, now
the quality changes are beginning to receive significant attention. The quality
changes are primarily due to a range of anthropogenic activities common to urban
areas, which result in the generation of various types of pollutants. These pollutants
accumulate on urban catchment surfaces and are eventually washed off by storm
water runoff creating irreversible impacts on receiving water environments. In this
context, structural storm water treatment measures are introduced, promoting pollutant
removal through physical, chemical and biological processes. They also
detain, retain and regulate storm water runoff to improve water quantity and quality
characteristics.
Bioretention basins and constructed wetlands are among the most common
storm water treatment systems, and their treatment performance is closely dependent
on hydrologic and hydraulic characteristics. Consequently, the in-depth
understanding of the role of hydrologic and hydraulic factors in bioretention basin
and constructed wetland treatment performance is important for effective urban
storm water design strategies. This research monograph presents the outcomes of a
detailed investigation into the influence exerted by hydraulic and hydrologic factors
on the treatment performance of bioretention basins and constructed wetlands.
In relation to bioretention basins, the research outcomes confirmed that the
antecedent dry period is an important factor influencing pollutant removal efficiency.
A relatively long antecedent dry period will result in comparatively low
moisture content in the filter media, which can enhance the runoff retention capacity
and consequently improve treatment performance. This implies that planting of
vegetation with high evapotranspiration capacity would enhance treatment efficiency.
Additionally, it was found that pollutant leaching influences bioretention
basin treatment performance, particularly reducing the ability for nutrient removal.
This highlights the importance of the selection of appropriate filter media and its
timely replacement.
In the case of constructed wetlands, it was found that large and small rainfall
events are subjected to different treatment. The pollutant load reductions in the
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initial sector of the runoff hydrograph from large rainfall events were relatively low
due to the rapid mixing. This highlights the need to establish an inlet pond to
initially intercept the flow entering the constructed wetland so that the inflow is
stabilised. This is also supported by the fact that the initial sector of the runoff
hydrograph generally carries higher pollutant loads, namely the first flush effect.
Additionally, the provision of a bypass system is recommended to control the runoff
to the constructed wetland. This will protect the treatment system from erosion
damage resulting from high runoff rates.
This research monograph further showcases an innovative approach for using
conceptual models to analyse storm water treatment system performance. The
approach adopted has the capability to generate key hydraulic data for individual
rainfall events in relation to the treatment systems investigated. This is a significant
advancement from conventional approaches for the analysis of treatment system
performance, which is based on the use of lumped parameters. The knowledge
presented provides practical guidance and recommendations for improved urban
storm water management to assist researchers, design engineers, decision-makers,
urban planners and storm water quality model developers.
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