Applying PCSWMM for Stormwater Management in the Wat Phnom Sub Catchment, Phnom Penh, Cambodia

Aims: Wat Phnom sub catchment in Phnom Penh, Cambodia, is highly susceptible to flash flooding during rain events. The objective of this study is to determine where wastewater and stormwater in the Wat Phnom area are discharged and to determine the hydrological and hydraulic functionality of the drainage system in the area. This specific subcatchment has not been included in previous drainage system modelling of Phnom Penh.

Place and Duration of Study: Phnom Penh, Cambodia, 2014.

Methodology: In this study, PCSWMM was selected to do the model simulation. Rainfall events for May 23rd, 2014 and 3 design storms of rainfall (2 year, 5 year, and 10 year return periods) were developed to drive the model. The Sensitivity-based Radio Tuning Calibration (SRTC) tool was used for model calibration with the depth of water at junction WL16 for the May 23rd, 2014 event. SRTC provides fast calibration for any model size or model complexity and calibrates to multiple objective or response functions simultaneously by filters to find matches for specific calibration locations. Consequently, PCSWMM can be employed as a useful tool to examine the hydrological and hydraulic performance of the drainage system with different rainfall design storms to provide information for stormwater management.

Results: This study confirmed that the Wat Phnom sub catchment is a part of the area which transfers water to the Boeng Cheng Ek wetland. There are two sub catchments within Wat Phnom (Sub catchment No. 1 and No. 5) which had particularly high runoff, and four specific nodes were particularly sensitive to flash flooding.

Conclusion: The drainage system is not sufficient to handle rainfall exceeding a 2 year return period, where surface flooding could occur for duration of up to 2 hours.