Characterizing natural surface water and groundwater interactions for stream restoration

Abstract

Surface water intrinsically interacts with groundwater and this interaction is hydrologically and ecologically important. However, the design of urban drainage often does not account for surface water and groundwater (SW-GW) interactions. This study evaluates the natural SW-GW interactions in a relatively undisturbed catchment within Bukit Timah Nature Reserve in Singapore, aiming to shed light on conserving or restoring the interactions in urbanized catchments. Three piezometers were installed across a stream transect: one on each side of the stream being 2 m and 9 m away from the stream while the third one on the streambed. Water table on both sides was close to the ground surface with a maximum depth of less than 1.0 m. The elevation difference in water table and stream surface suggest that in general groundwater recharged the stream on one side while the stream recharged the groundwater on the other side. During non-rainy days, the stream, being recharged by groundwater, flowed with a maximum stage of 0.6 m. During rainfall events, piezometers on two sides respectively recorded a maximum saturation excess overland flow of 1 cm and 7 cm. Stream and groundwater responded to rainfall differently depending on rainfall intensity and antecedent moisture conditions. For example, the response lasted from several hours for events larger than 25 mm/hr up to a few days for smaller events. Further research is being performed to critically evaluate the SW-GW interactions, particularly in identifying the zone of interaction using numerical modeling. The results from this research will facilitate the design of urbanized drainage systems, mainly to incorporate SW-GW interactions to sustain environmental flows for ecological benefits during non-rainy days. The interactions might also be beneficial to storm water management due to the additional subsurface storage for flood alleviation.