Have you ever visited Sungei Buloh and seen the two brackish water ponds in front of the Main Hide filled with water? And at other times found that one pond has exposed mudflats while the other is completely filled with water and vice versa regardless of the tide (below)? What is the rationale for this water level regime?
The idea of managing the water levels in a wetland began with the desire to increase the number of migratory shorebirds that make use of Sungei Buloh. You see, historically and currently, Sungei Buloh acts as both a high tide roost site and a feeding ground for shorebirds but mainly as a high tide roost (top). When the tides are low across the northern coast of Singapore, these birds fly out from Sungei Buloh and forage on the tidal mudflats for polychaetes and mollusc. A few hours later when the water rolls in and submerge these mudflats at high tide, the birds need to find a roost to wait out the tides. Sungei Buloh serves to provide them this roost site within the ponds that have low water levels. And this is possible in Sungei Buloh, a forested mangrove area because of the network of existing bunds that have created ponds whose water levels can be regulated through the use of sluice channels and sluice gates (below).
Water levels in three brackish water ponds within the wetland are currently managed as a system on a fortnightly cycle generally between the shorebird migratory months of July and April. Outside of the migratory months, the water levels are generally not regulated and natural tidal influences are maintained. At no point in time are any of the three ponds mudflats submerged for more than four days (or left exposed to dry out for also more than four days). For perspective, there are five other brackish water ponds in the wetland whose water levels are not regulated at all and are subject only to natural tidal influence.
What might happen with respect to shorebirds should the water levels in all the ponds be left to natural tidal influences? The first effect would be the loss of valuable exposed mudflats for shorebirds to roost (and to a lesser degree, feed) on during high tide. These birds will have to find other areas to roost since the northern coastal flats of Singapore as well as Sungei Buloh would be submerged under water. And this will directly affect the number of shorebirds that are present (and can be observed) at Sungei Buloh during the high tide period. Should the shorebirds be unable to find alternative high tide roosts within close proximity to their feeding grounds, there is a possibility that the entire high tide roost cum feeding ground system (that is Sungei Buloh – Singapore north coast mudflats) may be abandoned for more suitable alternative systems in the region.
Tha above account and images are from the April 2007 issue of Wetlands, courtesy of the National Parks Board, Sungei Buloh Wetland Reserve.