Peak Flow Attenuation using Dry Pond for Existing Housing Schemes 


Stormwater management in Malaysia has been largely based on 1975 DID Urban Drainage Design Manual that covers essentially the planning, basis of design, flood discharge, hydraulic design of open channels, structures, storm drainage for urban streets, detention storage, erosion and sediment control and information to be submitted with design. Rapid disposal approach adopted in the first manual has led to higher occurrence of flash floods as a result of the increase in surface runoff, peak discharges, shorter flow duration and others.

Department of Irrigation and Drainage (DID) Malaysia is taking a proactive step by introducing new urban drainage manual known as Storm Water Management Manual for Malaysia (Manual Saliran Mesra Alam or MSMA). Effective from 1st January 2001 all new development in Malaysia must comply with the new guideline, which requires the application of Best Management Practices (BMPs) to control stormwater from the aspect of quantity and quality runoff to achieve zero development impact contribution. It is hope that this new strategy will be a sustainable solution to mitigate the existing flood problems but also to prevent the occurrence of such problem in the new developed area. 

The present study embarked on using the stormwater management BMPs for an individual house in Kota Bharu, Kelantan. The objectives of the present study on the application of MSMA for an individual house were to seek the attenuation effect of biological swales - dry pond system and the suitability of applying the Stormwater Management Model (SWMM) in simulating rainfall-runoff for the biological swales - dry pond system. The house is actually an old government quarters occupying a land area of about 1556 m2. The house was retrofitted to accommodate biological swales and a dry pond with biological subsurface infiltration modular tanks in 2001. The open channel flow was then monitored using ultrasonic water level sensor and an automatic rainfall recorder was also established on site. Data collection was started in 2002 until 2003. Nineteen events were observed especially in the months of October, November and December during the two-year study period. 

The flow volume in the swale and dry pond was reduced from 2.94% to 100% while the reduction in peak flow ranges from 11.69% to 100%. For low depth rainfall events the percentages of volume captured and peak reduction are found to be totally absorbed but for higher depths there will be an outflow which is consistent within the designed limits for the system that is the system should be able to cater for a flow of 10-year ARI before development. Application of SWMM model shows that it is able to simulate the rainfall-runoff of the events for the biological swales - dry pond system used in the present study. The simulations show that the system is capable of attenuations peak flow and volume for events up to 10-year ARI.