Rehabilitation of concrete canals in urban catchments using low impact development techniques

- A Green Channel Cover (GCC) is decked on an existing concrete canal.
- Hydrologic performance of the GCC is simulated using a Singapore catchment.
- The GCC decreases and delays the peak flow of a large storm by 14%.
- GCC's performance is particularly encouraging given its small space requirement.

SummaryUrbanization generally increases surface runoff and pollutant loading and decreases infiltration and dry weather flow in canals. Efforts to handle the increased surface runoff, such as widening and deepening canals, further degrade the landscape and riverine habitats. To avert the negative effects of such changes, low-impact development (LID) has been adopted to restore natural flow processes and enhance nutrient removal from urban runoff in recent years. However, the installation of LID techniques often requires space, which can be very limited in intensely developing catchments. This study proposes to install a LID structure, referred to as the Green Channel Cover (GCC), in the space available on top of an open concrete canal to retain stormwater at the receiving end of the water body. The bioretention LID module of the Environmental Protection Agency's Storm Water Management Model 5 was used to simulate flow through the proposed GCC. The peak canal flow depth in a heavily urbanized, tropical catchment was reduced by up to 14% in the presence of the GCC, which occupied only 0.07% of the catchment area. The proposed GCC also retained up to 36 mm of the storm water runoff during peak flows, which resulted in peak flow reduction, especially during high intensity rainfall events with precipitation rates greater than 25 mm h−1. A sensitivity analysis showed that the hydraulic conductivity and depths of the soil and storage layers of the GCC did not influence the peak flow reduction as much as the percent impervious area of the catchment. A partial GCC, with an opening that allows direct sunlight and rainfall into canal, was also successfully tested for efficiency in reducing canal peak flows. Overall, the GCC was found to be a good augmentation to existing rehabilitation measures in urban catchments.