1. Metro Colombo Urban Development Project
Total Page：16
File Type：pdf, Size：1020Kb
1. Metro Colombo Urban Development Project Public Disclosure Authorized Public Disclosure Authorized Environmental Screening Report for Public Disclosure Authorized 1. Improvements to Mutwal Outfall (box drain, tunnel inlet and outlet) 2. Reconstruction of Aluth Mawatha culvert 3. Embankment protection along selected locations of the Main Drain Final Report December 2011 Public Disclosure Authorized Uni‐Consultancy Services University of Moratuwa 1 Table of Contents 1. Project Identification 3 2. Project Location 3 3. Project Justification 5 4. Project Description 8 5. Description of the Existing Environment 11 6. Public Consultation 19 7. Environmental Effects and Mitigation Measures 7a. Screening for Potential Environmental Impacts 21 7b. Environmental Management Plan 29 8. Conclusion and Screening Decision 51 9. Screening Decision Recommendation 65 10. EMP implementation responsibilities and costs 66 11. Details of Persons Responsible for the Environmental Screening 69 Annexes 1. Photographs of some of the important locations along project roads 2. Detailed drawings of project components 2 URBAN UPGRADING WORK Metro Colombo Urban Development Project Environmental Screening Report 1. Project Identification Project title 1. Improvements to Mutwal Outfall (box drain, tunnel inlet and outlet) 2. Reconstruction of Aluth Mawatha culvert 3. Embankment protection along selected locations of the Main Drain Project Sri Lanka Land Reclamation and Development Corporation Proponent 2. Project Location Location Location of the project is depicted in the Fig. 1. Definition of The project area is the (i) culvert across Aluth Mawatha, (ii) the canal banks of Project Area the Main Drain from St. Sebastian North Canal through Prince of Wales Avenue and to Port Access Road up to the culvert at Aluth Mawatha, (iii) Mutwal tunnel and the outfall (The geographical extent of the The geographical extent is shown in Fig. 1. project & areas affected during construction) Adjacent land See “Other features” in Section 5. and features 3 Figure 1. Location map showing the Main Drain and the Mutwal Tunnel Outlet 4 3. Project Justification Need for the project The Colombo Drainage System comprises a network of large open drainage canals, smaller tributary canals and low-lying marshes functioning as natural retention basins. It functions to serve the drainage needs of the Greater Colombo area and reduces incidence (What problem is the of flooding and thereby protects the urban community, particularly project going to solve) the urban poor who inhabit low-lying regions of Colombo. The system could be broadly divided into two, with canals to the north of Sri Jayawardenepura Mawatha as Colombo North system and that to the south as the Colombo South system (see Figure 1. The system has four outlets and three of which Dehiwala and Wellawatte Outfalls and Mutwal Tunnel directly discharging in to the sea, while the North Lock discharges in to the Kelani River. There is a fifth outlet for the spill waters of the Beira Lake, via a circular weir near the old Parliament; the canal system is no longer connected to the lake to prevent highly polluted canal waters entering the lake. When the Kelani River level is high, the gate at the North Lock outlet to Kelani River is closed, so that reverse flow (from the river into the system) cannot take place. This operation is now carried out by the Department of Irrigation. Mutwal Tunnel of diameter 1.8 meters, functions as the outlet of the Main Drain. The head of the canal system could be considered as Parliament Lake, to the East of Kotte Lake. Under dry weather conditions the North Lock, Wellawatte and Dehiwala outfalls are the major outflow points. In a flood situation, with the North Lock closed due to high water level in the Kelani River, the system has to rely mainly Wellawatte and Dehiwala sea outlets. Also the Mutwal Tunnel helps ease the drainage problems of North Colombo to a great deal at times when the North Lock is closed. Aluth Mawatha Canal, Mutwal Tunnel and Outfall The Main Drain takes off the flow from St. Sebastian North Canal through a culvert crossing Prince of Wales Avenue and it runs mostly parallel to the Port Access Road and crosses the canal at two locations. 5 Then the canal changes its direction to the North and enters Aluth Mawatha area by crossing the Railway Track to the Colombo Port. At Aluth Mawatha the Main Drain connects to the Mutwal Tunnel through Aluth Mawatha Culvert (of which the existing capacity is not adequate) followed by a box drain (3 m x 3 m; L = 82 m). There is an urgent need to increase the capacity of this culvert. Mutwal Tunnel is approximately 1.8 m diameter horse shoe type tunnel of which the length is 570 m. The Mutwal Tunnel outlet is the only outlet that discharges storm water from the Colombo North area canal system directly into the sea. The inlet to the tunnel is at a dilapidated state at the moment that needs urgent rehabilitation. Thus the enhancement of the conveyance capacity of the Mutwal Outfall is essential and accordingly rehabilitation & upgrading of the system is required. Purpose of the project The purpose of the project is to: - Increase the capacity of the culvert across Aluth Mawatha (what is going to be achieved by carrying out the - Accommodate improvements to Mutwal Outfall (box drain, project) tunnel inlet and outlet) - Embankment protection along selected locations of the Main Drain The purpose of the project is to derive the following benefits and the beneficiaries are listed below: Benefits ∗ Enhancement of flood control. ∗ Reduction in allocations for flood relief for the Government. ∗ Increased in land values in adjacent areas. ∗ Improved health conditions & reduction in health expenditure. ∗ Reduction in annual operation & maintenance cost to the central government. ∗ Increased use of the canal system for recreational purposes & waterfront development. 6 Beneficiaries ∗ People residing close to the Main Drain and with the combined effect, the entire Colombo Metropolitan area. ∗ The Government and the agencies managing the storm water drainage. Alternatives considered No other alternative is considered for the project as it is envisaged that there are no any technically feasible and economically viable (different ways to meet the engineering interventions that could be accommodated in place of project need and achieve the proposed option. the project purpose) 7 4. Project Description Proposed start The tender documents are expected to be ready by December 2011. Awarding of date the tender will take place only after the 16th of March 2011. Construction period is estimated to be one year. Proposed It will take minimum 12 – 15 months to finish the project from the date of opening completion date bid documents. Estimated total Estimate: 3.34 US$ million cost Present land Entire project lies in areas belonging to SLLRDC. ownership Description of The detailed drawings of the project are given in Annex 2. the project (with supporting List of Proposed Activities material such as 1. * Rehabilitation of Main Drain Bank Protection maps, drawings New Gabion walls - 1450 m etc attached as New sheet pile walls - 57 m required) Rehabilitation of gabion walls - 778 m {Total length of Main Drain = 1650 m} ∗ Reinstatement of storm water drainage connections (hume pipe) to Main Drain through gabion walls and introducing catch-pits wherever required. 2. Aluth Mawatha Culvert Improvement ∗ Demolish and reconstruct 3.0 x 3.5 x 12 m reinforced concrete box culvert ∗ Connection of box culvert to existing 3.0 x 3.0 mm box drain leading to Mutwal Tunnel. ∗ Reinstatement of Aluth Mawatha at culvert locations ∗ Temporary shifting & relocation of service lines (electricity, water, telecom, sewer) 3. Renovation of existing box drain (covers of the openings - 6 Nos.) connecting Aluth Mawatha culvert & Mutwal Tunnel and anticipated catch-pits carrying storm water. 8 4. Replacement of covers of Mutwal Tunnel manholes (03 Nos.) a). Stream lining of inlet area to suit the transition ∗ Introducing a trash screen ∗ Formation of 2 Nos. new storm water manholes at Mutwal inlet and connection of the above two to inlet areas. ∗ Construction of boundary fence around the inlet areas a (with a gate) as a safety measures. 5. Stream lining the Mutwal Outfall In addition to the above, operation and maintenance of the drainage system is needed. The main drain, Mutwal box drain, & tunnel are under the custody of SLLRDC. Hence it will be maintained by Colombo North Regional Office; Drainage Division of SLLRDC. Following are the activities done under regular maintenance. a). Regular observations b). Surface clearing c). Canal dredging d). De-silting of box drain, tunnel & catch-pits. Project Agency: Management Team The agency responsible for design and implementation is the SLLRDC and the organization structure for the project is given in Figure 2 Contact person: Ms. A.H. Thushari Assistant General Manager (Special Projects) Sri Lanka Land Reclamation & Development Corporation Nature of the consultation and input received: Meeting and consultation at design office and site were done. Design drawings, master plans and other relevant information were too gathered. 9 Figure 2. Implementation arrangements for MCUDP under SLLRDC PROJECT MANAGER DEPUTY PROJECT MANAGER Environmen Social Consultant Planning Design Accountant Consultant (Land Project Project talist Planner Engineer Engineer Engineer Acquiring) Engineer Engineer (Contracts (A) (B) & Claims) Land Officer AO/Clerk Draughtsmen Quantity Computer Project Project Project Project Surveyors Operators super‐ super‐ super‐ super‐ Office Driver visor visor visor visor Aide 10 5. Description of the existing environment 5.1 Physical features – Ecosystem components Topography and terrain The topography of Sri Lanka is marked by great diversity caused by long years of faulting and erosion of the landscape. The central mountainous region with the highest elevations covered by virgin forests and grasslands rises up to about 2,500 m above mean sea level. The surrounding plains, which rise to about 50 to 100 m above sea level, are largely used for agriculture and homesteads, but still have virgin scrubland where the population distribution is lower.