The Ministry for Environment and Energy says the drainage master plan for La Digue was presented during a consultative meeting held on the island on the 6th of December 2013, few people attended the said meeting. This follows the Ministry’s announcement of five priority projects, which is part of the drainage master plan for La Digue. The five priority projects are expected to start within a month.
Following severe floodings which happened last year after Cyclone Felleng , a drainage task force comprising of engineers from the Ministry of Environment and Energy, Ministry of Land Use and Habitat and Seychelles Land Transport Agency, was set up to evaluate, coordinate and proposed long term solutions. Government also commissioned a study by WSP, a South African based company with a branch in Seychelles which collaborated with a local Diguois engineer, David Moustache.
The study was to find the best possible solutions for the island given its difficult topography. These were presented at a public meeting on Saturday 9th March 2013. Following the meeting where the few people who attended gave their inputs, the scope of work and term of reference for the consultants was developed, this included a plateau wide hydrology assessment, where detailed visits were conducted over a 3 months period, where public interviews were conducted and data were gathered.
At the end of the ground work, a paper was prepared the recommended drainage projects for flood alleviation on La Digue Plateau, this was endorsed by the cabinet of Ministers on the 27th of November 2013. The paper presented the background of the situation, the adopted methodology and protocol, the findings of the report, proposed solutions and recommendations. A detailed breakdown of the costing of the proposed projects was also submitted. Cabinet endorsed the budget of more than Rs 40 million which will be used for short term projects and recommended that residents of the island are sensitised on the master plan and they are given clear explanations of what projects will be implemented.
On the 6th of December 2013, the Ministry held a final consultative meeting with the people of La Digue, at the School Hall, where only nine Diguois attended, during the meeting chaired by the PS for the Ministry, Mr. Wills Agricole and attended by all members of the drainage task force, the following findings were presented:
• The Wetlands system was seen to be well maintained largely. There was seen have proper embankments, well cleaned periphery and overall was in very good state to accept additional run off if needed. A number of spill over and attenuation basins were also located.
• The Main Outlets, upon inspection was clearly seen that the La Passe Outlet allows the wetlands to fully drain at low tide resulting in reduced ecological water retention and increased saline intrusions. The L’Union Outlet also has a weir system in place, this will need to be re-sized to cater for the flow conditions it now needs to deal with.
• Roads, Road Side Drains and Culverts, remain largely a negative finding. Mostly there is no road side drainage and sinks show isolated drainage infrastructure built to deal with specific micro flooding issues and are largely insufficient and unconnected. Road cutting culverts do exist but are poorly sized. There is a need to develop a maintenance program for the upkeep and maintenance of these culverts.
• On Site Drainage was seen to be largely nonexistent with most dwellings not equipped with down pipes and guttering, poor site grading and land use for reduction in micro depressions along the plateau. This is indeed a big contributor to the localized flooding that happened.
The pertinent issues were also pointed out:
• Plateau Run off at present not being effectively directed to wetlands system.
• Plateau to be divided to catchments basins that run off to wetlands and partially to sea.
• A total of 22 cubic meters per second can be channelled to the wetlands as half of the plateau run off will be directed back to wetlands
• Surface mapping of wetland allows for 106,000 Square meter Area with possible 40 % deepening creating total storage capacity of 100,000 cubic meters.
• We need to exploit the storage and attenuation capacity of the wetland system thus allowing the outlets to be control gates for both ecological retention and safe storm water evacuation.
The main solutions being proposed are the installation of multiple collector feeder- drains that discharge to the wetlands from selected topography height and other that would connect into main outlet to sea. Given plateau flatness, the drains designed need to be modified and be concrete lined to increase flow velocities in a terrain with little gradient difference.
Creation of additional retention ponds is seen as a natural and cost effective means of dumping excess storm water to ecological sites which shall allow for greater attenuation and damming effect while also enhancing natural ground water recharge at reduced intervention costs. These have been explored and locations have been identified. The main works will involve the installation of collector drains in plateau areas, the installation of wetlands, smothering of bends in wetlands by rock armouring and gravel road re-profiling, upgrading Coastal Road and provision of drainage alongside.
Other long term solutions are also being proposed as it is to be noted that the drainage master plan for La Digue will be implemented over several year. During the meeting some suggestions were made by residents with regards to the construction of drains, and the Ministry have taken these into consideration. The Ministry of Environment and Energy says that the participation and input of members of the public in consultative meetings, are key in any environment related project with direct benefit to the community project.
No comments:
Post a Comment