1405565096-Chapter 6
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Proposed Residential Development on Lot 1021, Lot 1297, Lot 2273, Lot 25 and PT 23730 (New Lot 20506), Mukim Semenyih, District of Hulu Langat, Selangor Darul Ehsan for Sime Darby Properties (Selangor) Sdn. Bhd. IDENTIFICATION OF ENVIRONMENTAL CHAPTER IMPACTS AND RECOMMENDED 6 MITIGATION MEASURES DURING OPERATIONAL PHASE 6.1 Introduction The environmental impacts during the full operational phase such as wastewater contamination of the rivers, air and noise pollution generated by increased traffic, solid waste disposal, biological and sociological impacts are identified in this section where the mitigation measures are recommended for each impact. However, a few significant impacts that cannot be fully mitigated will remain as residual impacts. 6.2 Stormwater Management Impact Preservation of water quality and surface runoff detention are important objectives of drainage planning and stormwater management as the landuse constituent of the Project Site will have gone through a major alteration. Preservation of water quality and surface runoff retention are important objectives of drainage planning and stormwater management as land use constituent of the project site will have gone through an alteration. Within the project site, the surface runoff will increase resulting from the reduction in rainfall infiltration capacity of the soil and thus a sufficient drainage system must be established in order to fully accommodate the increased flow of Sg.Saringgit and Sg.Semenyih. The consulting engineer, Jurutera Perunding Zaaba Sdn. Bhd. in their ‘Design Report for Drainage and Stormwater Facilities’ has evaluates the stormwater management requirements of the proposed new development site. The report quantifies stormwater runoff on the project site for existing and post development conditions. The internal drainage network within the Project Site is planned to take into account the respective flood return year periods and are usually permanent structures. The design rainfalls for different average recurrence intervals (ARI) were determined for minor and major drainage system. The design ARIs considered for the project are 5yrs and 10yrs for minor system and 100yrs for major EUROPASIA ENGINEERING SERVICES SDN. BHD. 6-1 Proposed Residential Development on Lot 1021, Lot 1297, Lot 2273, Lot 25 and PT 23730 (New Lot 20506), Mukim Semenyih, District of Hulu Langat, Selangor Darul Ehsan for Sime Darby Properties (Selangor) Sdn. Bhd. system. The quality control ARI considered is 3 months ARI for all types of development. Implementation of the proposed Project requires the installation of various stormwater management practices to retard the abrupt flow of the runoff as enunciated by Jabatan Pengairan and Saliran’s “storm discharge” concept and will meet or exceed the requirements set in the Urban Stormwater Management Manual of Malaysia 2000 regarding post-development stormwater quantity. Mitigation Measures Preservation of water quality and surface runoff detention are important objectives of drainage planning and stormwater management as land use constituent of the Project Site will have gone through an alteration. Within the Project Site, the surface runoff will increase resulting from the reduction in rainfall infiltration capacity of the soil and thus a sufficient drainage system must be established in order to fully accommodate the increased flow. Generally drainage works involved all the required excavation, filling, compaction, grading and other related works within the limits of the site boundary for the construction of concrete monsoon drains, concrete block drain with brickwork, building parameter drain, road side drains, cascading drain, reinforced concrete pipe crossings (culvert) and brick or concrete sumps. All drains will be designed and constructed to give the best hydraulic features and in normal condition there will be no flooding, ponding, silting-up either during construction or after completion of the works. The design of drainage system generally to meet the stormwater management requirements:- • Prevent untreated discharges to receiving waters • Preserve hydrologic conditions that closely resemble pre-development conditions • Reduce or prevent flooding by managing the peak discharge and volume of runoff • Minimize erosion and sedimentation • Reduce suspended solids and other pollutants to improve water quality • Provide increased protection of sensitive natural resources • Shall be designed for easy and adequate access for maintenance and the continuation of maintenance requirement EUROPASIA ENGINEERING SERVICES SDN. BHD. 6-2 Proposed Residential Development on Lot 1021, Lot 1297, Lot 2273, Lot 25 and PT 23730 (New Lot 20506), Mukim Semenyih, District of Hulu Langat, Selangor Darul Ehsan for Sime Darby Properties (Selangor) Sdn. Bhd. 6.2.1 Existing Drainage Condition The existing topography of the proposed Project Site shows this area is drained by natural streams and depressions. There is one (1) seasonal stream from the Project Site flow northwesterly into Sg. Semenyih while another two (2) seasonal streams which originate from the Project Site drain the eastern portion of the Project Site prior to flowing into Sg. Saringgit in the south of the Project Site which drains into Sg. Semenyih in the western region. The surface runoff from Lot 25 flows into the road side drains in the eastern boundary of the lot which will eventually drain into Sg. Saringgit in the southern region and then to Sg. Semenyih. 6.2.2 Detention Pond The Urban Stormwater Management Manual for Malaysia recommends that in case where Retention Facilities could not be provided, detention facilities or a combination of detention and detention facilities could be provided for control of Stormwater Quality for Urban Stormwater. Detention pond is provided to reduce peak discharges in storms up to 100 year ARI. In this proposed development, the site is proposed to be from RL55.00m to RL80.00m for the whole development area and, main drains reserve and the detention ponds system are proposed for the development area. The percentage of detention pond for the development area is 3.87% of the total development area. Three separated detention ponds (Pond A, B, C) is located at the proposed site to create an aesthetic and green environment. All discharges will be flowing to Sg.Saringgit and Sg.Semenyih which is located at the west of the project site. See Table 6.1 for the summary of Detention Pond Design for the proposed site. The runoff quantity control criterion for new development is to reduce post development peak flows to less than or equal to the pre-development values. The majority of the proposed development upstream of the pond will be medium density housing lot. The minor and major design strorms for primary outlet are 5 and 50 year ARI, while the secondary outlet is 100 year ARI. EUROPASIA ENGINEERING SERVICES SDN. BHD. 6-3 Proposed Residential Development on Lot 1021, Lot 1297, Lot 2273, Lot 25 and PT 23730 (New Lot 20506), Mukim Semenyih, District of Hulu Langat, Selangor Darul Ehsan for Sime Darby Properties (Selangor) Sdn. Bhd. Table 6.1: Summary of Detention Pond Design Description Detention Detention Detention Pond A Pond B Pond C Pond area allocated (ac) 1.24 4.43 10.81 Catchment Area (ha) 12.181 27.845 42.46 3 Q5 pre (m /s) 1.9 3.2 4.9 3 Q5 post (m /s) 1.52 2. 199 4.46 3 Q50 pre (m /s) 3.6 2 5.9 9.1 3 Q50 post (m /s) 3.48 5.468 8.793 3 Q100 pre (m /s) 4.0 6.6 10.2 3 Q100 post (m /s) 5.03 6.832 10.312 Water depth (m) 2.0 3.0 3.0 Nett Pond Area (m 2) 2,475 4,25 6 11,801 Storage Volume (m 3) 4,194 7,463 28,069 Pond Vol ume (m 3) 3,751 8,961 20,217 Source: Jurutera Perunding Zaaba Sdn. Bhd., 2014 The Detention ponds design calculations with the respective pond sections are as shown in Appendix 13. The ponds are designed with assumptions that all rain water and compound drainage will be diverted into the detention pond via the last drainage manholes that will be fixed with Gross Pollutant trap (GPT) to filter out trash before entering the ponds. 6.2.3 On Site Detention Pond (OSD) The increase in the imperviousness as a result of urbanization will results the increase in the surface runoff, which if unregulated may cause existing channel to exceed their hydraulic capacities (design capacity) eventually causing flood. One way of mitigating this problem is by the construction of On Site Detention (OSD). OSDs are basically designed to deal with storm water runoff from the proposed development. For this project, there will be proposed roadside drains at Lot 25 before discharging into the proposed two (2) numbers of On-site Detention Ponds. The provision of on-site stormwater detention tanks is to facilitate the control of surface before being discharged into the existing roadside drain. The engineer proposed two numbers of 30m x 20m x 2m OSDs at the open area at Lot 25. Refer to Figure 6.1 for the proposed location of the drainage systems and OSDs at the developed area. EUROPASIA ENGINEERING SERVICES SDN. BHD. 6-4 Proposed Residential Development on Lot 1021, Lot 1297, Lot 2273, Lot 25 and PT 23730 (New Lot 20506), Mukim Semenyih, District of Hulu Langat, Selangor Darul Ehsan for Sime Darby Properties (Selangor) Sdn. Bhd. EUROPASIA ENGINEERING SERVICES SDN. BHD. 6-5 Proposed Residential Development on Lot 1021, Lot 1297, Lot 2273, Lot 25 and PT 23730 (New Lot 20506), Mukim Semenyih, District of Hulu Langat, Selangor Darul Ehsan for Sime Darby Properties (Selangor) Sdn. Bhd. 6.2.4 Main Drain Drainage reserves shall be provided for stormwater conveyances purposes. A 10m and 5m main drain reserves are provided at the northern boundary of the project site, initially the tributary of Sg.Semenyih and from part of the northeast catchment respectively, where it drains to Sg.Semenyih at the northwest boundary of the project site.