This component supports priority rehabilitation and improvement of flood and drainage management infrastructure identified as a priority by the inter-agency Flood Mitigation Task Force chaired by the Sri Lanka Land Development Corporation (SLLDC). The investment packages under this component are essential and critical to reduce the impact of future floods in the catchment of the Colombo Water Basin. Most of the structural investments will be aimed at improving the system of primary and secondary canals, retention areas, and drainage of the Colombo Water Basin. The development of an integrated flood management system and interventions to enhance the economic value and aesthetic qualities of the water bodies will also be supported. The component comprises the following four subcomponents:
Floods in Colombo are caused by heavy rainfall and a macro-drainage system with insufficient storage, conveyance, and outflow capacity. In the last decade the storage capacity in the Basin has reduced by about 30 percent, due to uncontrolled landfill and flood plain encroachments by illegal settlements. The conveyance capacities are restricted by solid waste, floating debris, and bottlenecks in the canals. The outflow capacity of the system is too small, particularly in the north through Mutwal Tunnel and the North Lock and South Lock in the St. Sebastian canal. During the monsoon season, the outflow is further limited as heavy rainfall coincides with high levels at Kelani Ganga, reducing the outflow through the North Lock to nil. Discharges at the Beira Lake are further enlarged by the pumped outflow from St. Sebastian Canal. Unauthorized sewerage discharges into canals have also led to low quality water and related diseases in inundated areas. All these impacts are likely to worsen in the future due to the effects of climate change; rainfall trends indicate larger loads on the system and sea level rise impedes gravity drainage.
Based on the above constraints to effective flood management, the following flood mitigation measures have been devised under this subcomponent:
Investments under this subcomponent will aim at improving the capacity and performance of the micro-drainage system in 15 selected flood-prone areas under the jurisdiction of the CMC. The CMC has identified 45 flood prone areas where flooding occurs regularly. The main problems causing recurrent flooding include (i) unauthorized constructions on and along drainages, (ii) dumping of waste in the drainages that obstructs/blocks free flow, (iii) drainage being impeded by backwater from the main canals system during major floods, and (iv) lack of regular maintenance and cleaning of the drainage system. Short duration rainfall amounts have also increased in the past decade.
Out of the 45 localized flood-prone areas, the following 15 sub-projects have been identified for implementation by the CMC:
This subcomponent will aim at improving the overall drainage system management for the Greater Colombo Water Basin to ensure the sustainability of project investments. It will comprise (i) investments for selected landscaping along canals and supporting a pilot water-based transport system to demonstrate the viability of using the main canals for public transport, (ii) purchase of canal maintenance machinery, and (iii) development of an integrated flood management system for the Colombo Water Basin. The integrated flood management system will include monitoring and management of the retention/wetland areas, operation and maintenance systems for wetlands, canals and drainage systems, monitoring and enforcement of land-use planning to safeguard the capacity of the basin to cope with floods, and interagency coordination protocols and mechanisms.
This subcomponent will aim at improving the public fruition of the east and southwest Beira Lake through the development of a continuous promenade (linear park) and green areas (nodal parks) along its shores, and establishing a natural park on a wetland branch of the Parliament Lake. The following two key sub-projects will be implemented:
The objective is to complement the flood-reduction measures under Component 1 by providing opportunities for urban regeneration along the east and west Beira Lake waterfronts. Currently, the Lake is not accessible to the public due to inadequate bank protection and multiple uses along the shoreline. A phased approach will be adopted to address these issues. In the first phase, protection walls will be constructed along 2.5 km of shoreline on the west and east Beira Lakes and steps will be taken to restore the McCallum Lock Gates, which have historic value. In the second phase, a 4-kilometer pedestrian path/promenade, with an average width of 6 meters, will be constructed on top of the protection walls. This will provide a natural connection between the east and west Beira Lake waterfronts and the walkways connected to the southwest Beira lake waterfront. Ultimately, a contiguous recreation space within the core area of the city, which has potential for development by the private sector, will be created.
The objective is to ensure the protection of the Beddagana Wetland Sanctuary and Kotte Ramparts from future encroachments and enable it to function as a flood-retention area for the city. The target area is a 32-hectare marshland and wetland habitat in the SJ-KMC and a part of the Parliament Lake. In a context of rapid urbanization, this area provides locals and visitors a rare glimpse of a wetland habitat that is home to several species of flora and fauna. Interventions will include (i) enhancing the hydrology of the wetland area by cleaning existing canals, (ii) reforestation of areas that have been deforested to enhance bird habitats, (iii) provision of bird-watching hides, towers, board walks, nature trails, and orientation centre to create awareness about the sanctuary to visitors, (iv) provision of play areas at the boundary of the wetland sanctuary and a 2.2 km jogging track for recreational use, and (v) minimal interventions to improve the existing bund road. Interventions will have minimal impact and will use resources that are environmentally friendly. Overall, the outcomes of these interventions are expected to improve livability for local people, facilitate protection of a historic area, and increase ecotourism opportunities.