Success! Nature Seychelles proves that wetlands help prevent flooding
Recent heavy rains have proved that Nature Seychelles improvements to the Sanctuary at Roche Caiman wetland are working. The NGO manages the artificial wetland, which is in close proximity to Victoria, the capital of Seychelles.
Flood protection, flow maintenance and water purification are some of the important functions that wetlands provide, and during the past couple of weeks it was noted that unlike in previous years, the road leading to the offices of Nature Seychelles as well as the main road and surrounding areas were not flooded by the heavy rains that fell on the Seychelles island of Mahe.
"It's incredible what a well maintained wetland can do. The wetland did not overflow, our road and its surroundings was not flooded, and we were able to go in and out of our premises. This was not the case before. In the past, we have even once or twice had to tell members and staff to stay away because our road was inaccessible," said Dr. Nirmal Shah, Nature Seychelles Chief Executive.
The reasons behind the superb functioning of the wetland are the recent works undertaken at the Sanctuary under a mangroves enhancement
project funded by the Mangroves for the Future (MFF) initiative and carried out with the generous support of Sun Excavations of Mahe.
Wetlands hold excess water runoff after a storm, and then release it slowly. Most wetlands have the capacity to do this depending on size, shape, location, and soil type, which determine the capacity to reduce local and downstream flooding.
In the case of the Sanctuary, the recent profiling of the wetland has deepened pools that hold water during the rains, while also allowing the design of outlets that slowly release the water.
Robin Hanson, the wetland manager explains.
"If I can give you an analogy using a bathtub, what we had was a shallow bathtub that quickly overflows when it rains. Additionally, the drainage system was not allowing water to flow properly. What we have now done is make sections of the bathtub deeper, with proper drainage, that allow for proper water movement," he says.
The mangroves and reed beds also had a role to play in trapping sediment and retaining excess nutrients and other pollutants.
Robin also says that the wetland has the potential to increase the amount of storm water it can handle. "We have seen that we could divert storm water from the over burdened drainage ditch close to the highway into the reserve, reducing the risk of flooding to the highway. The option is there, but we can't do it on our own. Nature Seychelles are calling for community minded corporate organisation to support this initiative," he says.
Apart from these functions, wetlands are diverse habitats that are extremely important for biodiversity.
The enhancement of the Sanctuary at Roche Caiman has not only improved the site for ecological services, but it has also increased the area under mangroves, themselves a useful and key coastal ecosystem, and has also increased the number and diversity of flora and fauna.