Low-Flow Modification of Flood Control Channels in Cities
Many rivers and streams throughout the world have been severely af-fected by human activities in the past century including water abstraction, watershed land use changes, power generation, and dam and levee construction. In cities, engineering practices advocate straightening, enlarging, and converting the natural rivers and streams into concrete channels to maximize the efficiency of conveying the floodwaters away from populated areas. These engineering structures disrupt the natural equilibrium of fluvial systems and eliminate macro-invertebrates and aquatic and riparian species in watercourses. With a growing awareness of the value of the natural riverine ecosystems, a global movement of river management has shifted from manipulation and control to restoration and conservation in the past decade (Ham-mersmark and Mount, 2005; MTO, 1997; Bockelmann et al., 2002; Ness and Joy, 2002; Doll et al., 2003). The objective of this research is to de-velop a general stream restoration approach for providing low flow habitat in flood control channels in highly urbanized areas. The restora-tion goals are: (i) to provide a natural and self-sustainable river and geomorphic system; (ii) to establish appropriate pools and riffles and in-stream covers for extending and providing a better living conditions of the aquatic habitats; and (iii) to maintain flood control function. A concrete flood channel in Yuen Long, Hong Kong, that drains into a na-ture reserve, the Mai Po Nature Reserve in Deep Bay, will be used as a pilot site to demonstrate the design methodology and application of the flood channel restoration approach. Meanders, deflectors and instream covers will be applied to the low-flow channel for pools and riffles crea-tion in order to achieve the restoration goals.
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