An Evaluation of BIOECOLOGICAL Drainage System (BIOECODS) as an Application of Urban Storm Water Management Manual in Malaysia
Rapid development has changed the land use and this will lead to an increase in the surface runoff caused by the increase of the impervious surface area. Impervious surface area will transform most of the rainfall directly as surface runoff. Hence a given rainfall now produces significantly more runoff volume then before.
Stormwater management in urban areas has changed from rapid conveyance approach to control at source that states the post development and pre-development peak flow should be the same. Department of Irrigation and Drainage has introduced Urban Stormwater Management Manual (MSMA) and directed all the new development should follow this new regulation. This regulation seeks that the quantity and quality of the surface run-off should be similar for the post and pre-development.
A numbers of Best Management Practices (BMPs) have been developed to control the quantity and quality of the surface run-off. Examples of the BMPs are wet pond, dry pond, swale, wetland and infiltration system.
The drainage system in Engineering Campus Universiti Sains Malaysia that used the control at source approach was chosen as the research site. Bioecological Drainage System (BIOECODS) is a pilot project that applied the control at source approach as described in MSMA. This research aims to evaluate the BIOECODS as one of Storm Water Management applications in Malaysia.
The implementation of the research requires a comprehensive data collection such as rainfall depth, velocity and discharge in the surface and sub-surface swale. The analysis of the data shows that BIOECODS has functioned as designed. Emptying time of ecological swale less than 24 hours is recorded in the surface and sub-surface swale after a rainfall event. Peak flow and volume attenuation also occur at surface and sub-surface swale. However the percentage of the attenuation depends on the ARI. The study of the dry pond indicates that emptying time of the dry pond also depends on the ARI. From the study the dry pond has emptying time less than 24 hours when the rainfall event is less than 2 year ARI.
Hydraulic simulation of BIOECODS using Storm Water Management(SWMM) computer model showed that peak hydrograph could be attenuated to the pre-development hydrograph. Calibration process result shows that SWMM model can simulate well in term of peak hydrograph rather than volume.
From the quality aspect, grab sampling results show that water quality at outlet type C achieves Class II A standard. The value of pH ranges between 6.5 – 7.7, Dissolved Oxygen between 5.74 - 6.4 and BOD between 3-6 mg/l is within the range of Class IIA. The existence of heavy metal is too little and the value of phosphate and total phosphate between 0.02 - 0.03.