Watershed Management in Singapore's Western Catchment

The ABC Waters ProgramThe ABC Waters Program is about achieving Active, Beautiful and Clean Waters for all in the 32 rivers or canals and 14 reservoirs throughout Singapore. The Public Utilities Board's water resources strategy is "Water for All: Conserve, Value, Enjoy". The first part of the strategy – "Water for All" is being met by ensuring a diversified and sustainable supply of water from local catchment water, imported water, NEWater and desalinated water. Local catchment water takes on an increasing significance as Singapore, a smaller intensively urbanized island, captures water from one half of its catchment area, increasing to two thirds in the near future.The second part of the strategy "Conserve, Value, Enjoy" is the foundation for the ABC Waters Program. Firstly it focuses on engaging the People-Private-Public (3P sectors) to conserve water and take ownership of our water resources. Bringing the people close to water and helping them to understand and enjoy it is an important part of the strategy. Secondly, the ABC Waters Program represents the physical manifestation of "Value" and "Enjoy". The ABC Waters Program ties together all the initiatives.The ABC Waters Program goes beyond the functional use of reservoirs and waterways as resources for water collection, storage and drainage and involves the People-Public-Private (3P) sectors in partnership with the PUB, to:• develop these water bodies into vibrant, clean and aesthetically pleasing lifestyle attractions with recreational and bonding activities for the public to participate in and enjoy;• tap ideas, expertise and resources to develop and manage our catchments and water bodies as new community spaces, while protecting the quality of our waters and public safety;• be an umbrella program for integrating and holistically managing all initiatives involving the catchments and water bodies; and•get the community closer to water so that in the process they will learn to treasure it more.Watershed ManagerThe PUB has engaged watershed managers for the three regional water catchments – Eastern, Central and Western. The role of watershed manager is to prepare a masterplan for the catchment – the subject of the current masterplan report and to implement selected projects over a three year period, as the initial stage of the ABC Waters Program. Black & Veatch is the watershed manager for the Western Catchment, and that catchment will be the focus of this presentation.Water Quality in the Waterbodies and WaterwaysWater quality measurements are taken monthly by PUB in all of the reservoirs and some of the waterways. Parameters measured are aesthetic (turbidity and color), dissolved oxygen, microbial criteria and nutrients. Water quality is generally good or very good in the more remote western reservoirs and in Pandan Reservoir; relatively good in Kranji Reservoir and Jurong Lake; and relatively good in major waterways such as Sg Pang Sua, Sg Jurong and Sg Lanchar.Sustainable Urban DrainageSustainable approaches to urban development have gained increasing acceptance, namely low impact development (LID in USA), sustainable urban drainage systems (SUDS in UK), and water sensitive urban design (WSUD, in Australia). SUDS are a concept that fully utilizes all aspects of an urban drainage system for both hydraulic considerations and environmental protection. It is an extension of the WSUD concept, but looks at all aspects of the drainage system for maximum utilization of all drainage assets and peak environmental performance.There are a number of important considerations in assessing the applicability of SUDS in Singapore:• Tropical rainfall intensities are severe;• Limited land areas and high population densities have forced traditional flood plains to be encroached, and concrete channels rather than natural waterways to be used, so that resulting quantities of runoff are significant;• The degree of development combined with encroached riparian reserves means that there is little potential for attenuating the peak storm flows using traditional methods such as detention storage ponds.• To account for the lack of attenuation, the historic development of Singapore's stormwater drainage system has assumed a high level of development and has used conservative methods to size its drainage channels (i.e. using Rational Method to estimate design flood flows); and• The existing channels generally have capacity to convey the high design flows safely and, since most of the channels are concreted lined, the risk of stream bank erosion is reduced.The focus on the improvements in the watershed was to reduce the amount of pollution introduced into the waters of the Western Catchment by improving the use of Best Management Practices (BMPs). The improvements must be made without interfering with the existing stormwater controls that the waterways currently provide.