Metro Manila, others need landscape reengineering to forestall future Ondoy-type floodings
by Virgilio M Gaje
Baler, Aurora (15 May) -- With typhoon Ondoy-induced flooding and devastation still lingering in the memories of Metro Manilans and other affected populations, a global expert has proposed landscape reengineering to harvest rainwater and ease the pressure off existing drainage networks.
Ming Jiang, regional director of China Environmental and Ecological Planning, offered this advice in a technical presentation entitled "Alternative Sources - Landscape Design for Rainwater Harvesting" at the ongoing Water Conference on the Wise Adaptation of Technologies for Clean H2O (Water WATCH) scheduled 14-16 May at the Bay's Inn Conference Tenthouse here, under the auspices of the Congressional Commission on Science and Technology and Engineering (COMSTE).
Ming, who also works as consultant for AECOM, a top Fortune 500 company, talked about common problems from urban stormwater runoff, value of landscape design for rainwater harvesting, selections of landscape design for rainwater harvesting, and model projects in Singapore and other countries dealing with negative impacts of urbanization.
He debunked misconceptions about rainwater harvesting technologies as being suited only to high rainfall areas, requiring wet and lush landscape features, as being difficult to justify additional expenses, as being unable to satisfy drainage requirements, and being difficult to maintain.
He said modern landscape systems designed for rainwater harvesting employ best planning practices and specific planning approaches to achieve broad-based objectives of holistic water balance, water conservation, water quality, environmental objectives, and social objectives.
Bioretention planters are slowly becoming popular in reengineered urban centers as vital elements of a holistic rainwater harvesting landscape. (COMSTE/AECOM)
Ming explained that properly planned rainwater harvesting networks promote water conservation and quality objectives to minimize import and use of public water, reuse stormwater, minimize irrigation demand, minimize sediment and nutrient loading, minimize pollutant export to surface and groundwater, protect and enhance riparian vegetation, and minimize impact of wastewater pollution.
Urban rainwater harvest design, according to Ming, goes under various names, such as WSUD (water-sensitive urban design), LID (low-impact development), SUDS, BMP (best management practices), and sustainable design. Whatever the name, Ming said that "water sensitive development involves simple design and management practices that take advantage of natural site features and minimise impacts on the water cycle. It is part of the contemporary trend towards more sustainable solutions that protect the environment."
"It is an approach to urban planning and design that incorporates water resources and related environmental management into the planning process at various scales and time horizons, that relies on decentralized water management systems, integrates land use planning with water supply, wastewater management and stormwater planning," argues Ming.
According to Ming, the large volume and fast flows of stormwater runoff cause pollution and nutrient loads deposited in receiving waters resulting in poor water quality, which in turn cause algal blooms, weed infestation, water deoxygenation, and fish kills.
Stormwater also carries pollutants like heavy metals, salinity from road salting, and pesticides, leading to contamination of potable water supplies, poor visual amenity, erosion and associated damage to vegetation and infrastructures such as pipes.
Ming argues that green infrastructures such as rainwater-harvesting landscapes are intended to provide key benefits like: providing visual improvement and recreation venue, reduction of peak runoff flow rate and volume, relieving the load off drainage infrastructures, improvement of runoff water quality, habitat creation and movement corridors, and provision of shade and minimizing "heat islands".
Riparian zones, as component of green infrastructures, can remove significant amounts of nitrogen from groundwater because vegetation intercepts sediments and associated pollutants from surface water flows, he said.
Ming cited research showing that vegetation in small streams can trap 60% of particulates. He said shade by vegetation maintains cooler water temperature (as much as 10 degrees in small streams) and reduces the variability of temperature, decreases light and prevents excessive growth of nuisance plants such as algae and weeds, and provides cool areas for recreation.
Selections of landscape design for rainwater harvesting were presented by Ming, including eco-roofs, cisterns, downspout disconnection, rain gardens, bioretention planters, constructed wetlands, urban forest, and permeable paving.
Ming gave examples of rainwater harvesting technology projects in Docklands, Melbourne, Victoria in Australia; Singapore's urban stormwater harvesting at Marina Bay Reservoir; and the water detention basin in Yi Zhuang, China.
Singapore's urban stormwater harvesting project at Marina Bay Reservoir designed by AECOM.
Ming's presentation is downloadable from the COMSTE website download section. (PIA) [top]