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Ganl. Bull. Singapore 70 (Suppl. 1) 2018 
stream network for short periods (typically less than a day). This artificial flooding 
occurs in response to weather conditions when water is exchanged between reservoirs, 
to maximise storage, relative to use, rainfall, and evaporative loss. Model results 
provide estimates of the magnitude of these flows: the reservoir contribution to total 
modelled catchment outflow was about 55% higher than that of natural stream flow in 
the lower part of the catchment (Liong Shui-Yui, personal communication). 
Despite this hydrological resilience, we found evidence that substantial erosion 
has taken place within the stream network. Our analysis of the 1.95 m sediment core 
and the corresponding sedimentation rates, together with the observations of Murphy 
(1997), suggest that stream channel erosion has been significant in the past. In the 
sediment core we examined, dates derived from 14 C analysis (on pollen) corresponded 
to 1950 CE and 5500 BCE at depths of 50 cm and 51 cm, respectively (also discussed 
below). This large, abrupt age gap is best explained by the erosion of sediment layers 
that had accumulated over about 7000 years. 
Murphy (1997) indicated incision of the stream by as much as 1 to 2 m may have 
resulted from runoff and accelerated erosion related to construction and maintenance 
of a water pipeline that bisects the catchment. During our recent surveys, disturbance 
by the pipeline, roads, and trails on the stream channel are apparent, but their 
geomorphological impacts are now less severe than indicated by Murphy (1997). The 
greatest disruption to the stream system is trampling during military training activities, 
by unauthorised personnel during hikes, as well as unauthorised mountain biking on 
sloping trails and stream crossings. 
Soil erosion and denudation 
By measuring the radionuclides 10 Be, 137 Cs, and 210 Pb and major elements in rocks and 
soils, we are able to assess the following: (a) element accumulation/loss related to 
physical and chemical weathering processes; and (b) catchment short- and long-term 
erosion and sedimentation rates (in accordance with human influenced and natural 
processes). Several elements, including Ca, K, Mg, Ba, Na, Mn, Ti, Co, Sr, Ni, Zn, 
Cr, Fe, and V, are depleted throughout the soil catena, relative to stable Zr. Loss in 
concentrations of elements of low mobility (e.g. K, Ti, Cr, and V) suggests intense 
weathering has occurred in the catchment. However, element depletion/enrichment 
is variable within soil profiles in the catchment. Alternating zones of enrichment 
and depletion of selected elements along catenas are not associated with commonly 
reported micro- or macro-environmental forcing variables (gradient, organic matter, 
soil texture, infiltration) but may be a result of pulses of surface erosion and deposition 
along the slopes. 
Total denudation rate, determined from the cosmogenic nuclide 10 Be in Nee 
Soon stream sand (recalculated using the correction for quartz enrichment) is -9 + 0.8 
m Ma _1 , or about 23.4 + 2.08 Mg km 2 yr 1 (assuming a rock density of 2.6g cm 3 ). The 
estimated physical erosion rate (5.6 + 0.5 Mg km 2 yr 1 ) and the chemical weathering 
rate (17.8 + 1.58 Mg knr 2 yr 1 ) for soil are calculated from the total denudation rate 
