Manual Saliran Mesra Alam (MSMA)

1 Manual Saliran Mesra Alam ( msma ). Pusat Penyelidikan Kejuruteraan Sungai dan Saliran Bandar (REDAC). Kampus Kejuruteraan, Universiti Sains Malaysia Seri Ampangan, 14300 Nibong Tebal, Pulau Pinang. Tel: 04-5941035 Fax: 04-5941036. ii Concept and Design Requirement of msma . Design Standard Urban Stormwater Management Manual for Malaysia ( Manual Saliran Mesra Alam Malaysia, msma ). General Urbanization results in the growth and spread of impervious areas and a diversification of urban landuse practice with respects to the hydrologic and environmental terms. Landuse changes from rural to urban industrial areas cause local runoff impacts on receiving water flow, quality, and ecology.

2 Apart from erosion and sedimentation problems associated with development, it has become increasingly apparent that stormwater runoff contributes to receiving waters a significant part of total loads of such pollutants as nutrients (including phosphorus and nitrogen), heavy metals, oil and grease, bacteria, etc. New, comprehensive, and integrated SWM strategies are now needed to be in line with the government's drive to archive a sustainable developed nation status in the early 21st century. Such new strategies will incorporate interalia, runoff source control, management and delayed disposal on a catchment wide, proactive, and multi-functional basis.

3 This should result in flood reduction, water quality improvement, and ecological enhancement in downstream receiving waters. To some extent, it should also contribute to improved urban amenity through the application of wetlands, landscape for recreation, potential beneficial reuse of stormwater (especially as a non-potable supply source), and recharge of depleted urban groundwater aquifers to enhance stream base flow during dry seasons. Stormwater management has development to the point where there are now two fundamental different approaches to controlling the quality, and to some extant, the quality of stormwater runoff.

4 In addition to the traditional conveyance-oriented approach, a potential effective and preferable approach to stormwater management is the storage-oriented approach. The function of this approach is to provide for the temporary storage of stormwater runoff at or near its point of origin with subsequent slow release to the downstream stormwater system or receiving water ( detention ), or infiltration into the surrounding soil (retention). detention and retention facilities can reduce the peak and volume of runoff from a given catchment (Figure ), which can reduce the frequency and extent of downstream flooding.

5 detention /retention facilities have been used to reduce the costs of large stormwater drainage system by reducing the size required for such systems in downstream areas. The reduced post-development runoff hydrograph is typically designed so that the peak flow is equal to or less than the pre-development peak flow rate. Additionally, in some instances, the volume of the post-development runoff hydrograph is required to be reduced to the same volume as the pre-development runoff hydrograph. This latter requirement will necessitate the use of retention facilities to retain the differences in volume between the post and pre-development hydrograph.

6 Post Development Uncontrolled Runoff Pre-Development Uncontrolled Runoff Discharge Post-Development Controlled Runoff by detention Time Figure Hydrograph Schematic Urban Stormwater Management Short Course 1. Concept and Design Requirement of msma . ON-SITE detention . Principles of Quantity Control Stormwater quantity control facilities can be classified by function as: (i) detention , or (ii) retention facilities. The detention concept is most often employed in urban stormwater drainage systems to limit the peak outflow rate. The primary function of detention facilities is to reduce peak discharge by the temporary storage and gradual release of stormwater runoff by way of an outlet control structure or other release mechanism.

7 Retention facilities are commonly sized to provide only a reduction in the volume of stormwater runoff generated from an urban area. However, peak flow reduction can also be achieved in minor storm events if the storage volume is large enough to capture the peak flow before the storage is filled, the time to fill the basin is longer than the time to peak of the inflow hydrograph. detention and retention storages may be classified on the basis of their location and size as follows (Figure ): (i) on-site storage : small storages constructed on individual residential, commercial, and industrial lots (ii) community storage : storage facilities constructed in public open space areas, or in conjunction with public recreation and sporting facilities (iii) regional storage : large community storage facilities constructed at the lower end of catchments prior to discharge to receiving waters Facilities can also be categorised as: (i) on-line storage.

8 A facility that intercepts flow directly within a conveyance system. (ii) off-line storage : the diversion of flow from a conveyance system into a separate storage facility. (iii) conveyance storage : This is an often-neglected form of storage, because it is dynamic and requires channel storage routing analysis to identify. detention Facilities The most common type of storage facilities used for controlling peak flow are dry facilities', which release all the runoff temporarily detained during a storm. Other facilities which are becoming more commonly used are detention ponds', which incorporate a permanent pool of water for water quality control as well as provision for the temporary storage and release of runoff for flood control.

9 On-Site detention On-site detention (OSD) may be provided as above-ground storages, below-ground storages, or a combination of both. The common types of above and below-ground storages used are illustrated in Figure (a) Above-ground Storages The main advantages of above-ground storages are they can generally be easily incorporated into the site by slight regrading or modification to the design of surface features and are relatively inexpensive compared to below-ground storages. The above-ground storages include: (i) Landscaped areas (such as lawns and garden beds). (ii) Impervious areas (such as ar parks, driveways, paved storage yards).

10 (iii) Flat Roofs (iv) Surface Tanks (b) Below-ground Storages The main advantages of below-ground storages are they are out of sight, occupy less physical space, and will not cause any inconvenience with ponding of water that could result using above-ground storage. The examples of below-ground storage are: (i) Underground Tanks (ii) Pipe Packages Urban Stormwater Management Short Course 2. Concept and Design Requirement of msma . Infiltration Trench Car Park detention (CIRIA, 1996). Park Pond LEVELS. On-site Community Regional Infiltration Basin Storage Reservoir Artificial Recharge (Hall, et al.)