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Ganl. Bull. Singapore 70 (Suppl. 1) 2018 
Various characteristics were derived for each sub-catchment, such as, elevation, 
slope, rainfall, evapotranspiration, leaf area index, root depth, groundwater table, 
and surface water area extent. Groundwater table map and surface water depth map 
were also produced from the numerical model for the present hydrological condtion. 
Both maps show the spatial distribution of surface and groundwater of the present 
climate. These serve as references in assessing the hydrological vulnerability of the 
catchments towards climate change. In addition, an eco-hydrology model which links 
the hydrological conditions with the ecological recordings also helps to assess the 
climate change impact on local eco-hydrology. 
Twelve scenarios were introduced; they are combinations between various 
reservoir water operating levels and the projected future rainfall amounts resulting 
from a climate change study. Despite rainfall appearing to be the most influential factor 
affecting the overall catchment water, i.e., the spatial average over the catchment, it is 
interesting to observe the differing contributing factors of both rainfall and reservoir 
level at sub-catchment levels. The effects of the two inputs differ depending on the 
locations as it can be seen from hydrological maps (Sun et al., 2018). This spatial 
distribution information is of importance should eco-hydrological management be 
approached at sub-catchment level or spatially distributed. 
Several management strategies were suggested to mitigate severe drought and 
flood resulting from projected climate change impacts. These included the possibility 
of adding water during droughts, and retaining water during floods. 
Introducing additional water from the reservoirs to the upstream points of the 
catchment is a conceivable option for the severe drought scenario. Two systems were 
suggested for a point source management strategy. A pump and pipe system would be 
required to increase the water head if the point sources are located at higher elevations 
than the reservoir water levels. A pump system could provide broad coverage, but 
would incur higher cost in construction and management. A pipe system alone could 
be recommended if the point sources are located at lower elevations (i.e. lower than 
the operating reservoir water level) or near the stream. A pipe system would cover 
smaller areas, but would be more effective in conserving the swampy area at lower 
cost and with less water consumption. There would be severe issues to be considered. 
Amongst these are changes in water quality and the accidental introduction of alien 
vertebrates and invertebrates. There would also be questions over disturbance to 
soils and vegetation through the construction and maintenance of any such systems. 
Practicality could also be questioned if low water levels in the stream system were to 
coincide with water shortages in the reservoirs and in Singapore generally, as expected 
during a severe regional drought. In lieu of the water quality of the reservoirs waters, 
to protect the fauna in Nee Soon freshwater swamp forest the introduced reservoir 
water to the point sources might have to be first filtered. In addition, the importance 
and the highest priority of providing drinking water during drought is fully understood 
and acknowledged. The proposed irrigation of the swamp will only take place when 
reservoir water yield permits to do so. 
Retention ponds are a conceivable option for severe flood scenarios. Rentention 
ponds not only can reduce the affected flooding areas, but also promote habitat for 
