Ecosystem-based coastal protection through floodplain restoration

Cong Ly, GE Wind
Published: 18 August 2015
Last edited: 17 June 2021
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Summary

The solution provides protection of the muddy coasts and the people living near the coast from floods, storm surges and erosion. This is achieved by restoring eroded floodplains as precondition for natural regeneration or rehabilitation of mangrove forests as elements of an ecosystem-based approach to area coastal protection. T-shaped, permeable bamboo fences filled with soft brushwood bundles are effective at restoring eroded flood plains. This solution only works within a specific set of boundary conditions and must be site-specific and appropriate. Developed for the Lower Mekong Delta’s muddy coast in Vietnam, it provides security for people living directly behind dykes.

Classifications

Region
Southeast Asia
Scale of implementation
Local
Subnational
Ecosystem
Mangrove
Marine and coastal ecosystems
Theme
Adaptation
Cities and infrastructure
Geodiversity and Geoconservation
Other theme
Ecosystem restoration
Challenges
Floods
Storm surges
Tropical cyclones / Typhoons
Tsunami/tidal wave
Erosion
Ecosystem loss
Aichi targets
Target 14: Ecosystem services
Target 15: Ecosystem restoration and resilience
Sendai Framework
Target 1: Reduce global disaster mortality by 2030
Target 2: Reduce the number of affected people globally by 2030
Target 3: Reduce direct disaster economic loss in relation to GDP by 2030

Location

Soc Trang Province, Vietnam | Soc Trang, Bac Lieu, and Ca Mau Provinces, Lower Mekong Delta, Vietnam

Challenges

Along the mangrove mud-coasts of the Mekong Delta, erosion, flooding and storms are affecting the livelihood and life of thousands, often poor farmers and fishers. Once the mangroves, which protect the coast, are degraded or destroyed, waves will erode the floodplains and then waves will start eroding the earth dyke. This will lead to dyke overtopping and eventually destruction of the dyke. Solutions such as strengthening the dyke with sandbags or gabions are only temporary measures which don’t address the root cause – a low floodplain due to erosion. Therefore, a solution is required which address the root cause.

Beneficiaries

The people living behind sea-dykes and in flood-prone areas, fishermen and aquaculture farmers.

How do the building blocks interact?

The building blocks build on each other to achieve a sound solution to sustainably restore floodplains, and rehabilitate mangrove belts and their ecosystem services. The ‘Numeric modelling of hydro- and sediment-dynamics’ (building block 1) provides the sound basis to fully understand local dynamics at the area as well as providing important boundary conditions for the design and construction of the breakwaters. It is the necessary prerequisite for building block 2, the ‘Planning, design and construction of appropriate breakwaters’, which includes selection of suitable sites for construction of T-fences. The two first building blocks thus contribute to sediment accretion where desired and natural mangrove regeneration. Building block 3 ‘Breakwater monitoring and maintenance’ ensures proper functioning of the infrastructure component itself, and building block 4 ‘Mangrove protection and planting’ completes the solution by protecting natural mangrove regeneration and, if necessary, supplementary planting of appropriate species. The creation of awareness and ownership by involving all stakeholders is not only crucial for the success of each building block but also for the long-term sustainability of the solution.

Impacts

Technically, the solution is effective for flood, storm surge and erosion protection, and increasing biodiversity and availability of ecosystem services through floodplain restoration as a precondition for mangrove rehabilitation in sites where the floodplains have been eroded. Mangroves provide nursery, food and shelter for many aquatic species. They are highly productive and up to 80% of near-shore fishery catches globally are directly or indirectly dependent on mangroves. The values of mangroves have been estimated to be between US$ 2,000 - US$ 9,990 per hectare per year and thus rank among the most economically valuable of all ecosystems. Mangroves sequester up to 5 times more carbon than tropical rain forests. Financially, direct costs for dyke maintenance and repair were drastically reduced. Socio-economic impacts are security for people living directly behind the dyke, securing livelihoods by improving small-scale fishery and aquaculture.

Story

Mrs. Sà Vọng has lived near Nopol at the coast of Soc Trang Province as long as she can remember. Her family had a good life collecting fire wood, catching fish, collecting clams and cockles in the mangrove forest and on mudflats to supplement the income from her small fish pond. Many people used the road next to her house to access the mangrove forest just beyond the earth dyke which was built after a big storm 20 years ago. Over time the small path that was thus created through the mangroves to access the mudflats with their abundance of aquatic resources such as goby fry, cockles and juvenile crabs grew wider and could be used by small fishing boats. This development led to erosion. Over time it destroyed a 100 m long stretch of mangrove forest in front of the dyke. As a result Mrs. Sà Vọng saw that during the stormy season and high tides waves often overtopped the dyke and salt water flooded her small vegetable garden and her house. When the dyke threatened to break, local authorities spent much money to raise its height and to re-enforce its front with gabions and Melaleuca poles. After most spring high tides the dyke had to be repaired again as shown in the picture from Vinh Tan (near Nopol). The GIZ project,  Management of Natural Resources in the Coastal Zone of Soc Trang Province, was asked to assist local authorities to find better solutions. To ensure the long-term viability, the project applied an ecosystem-based approach to restore eroded floodplains through T-shaped bamboo fences as a precondition for the subsequent natural regeneration of mangroves. In May 2012 the construction of T-fences started. Already during the construction work Mrs. Sà Vọng told project staff that she is very happy as waves no longer reach the dyke, and her house is no longer subject to floods or strong wind. Only one year after construction a lot of sediments had accumulated behind the T-fences and started to consolidate to allow for mangroves to reappear. At a nearby T-fence site Avicennia seedlings occurred and grew well only 9 months after completion of the T-fences. This is a clear indication that the T-fences have re-created conditions suitable for the growth of mangroves.

Contributed by

Klaus Schmitt Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH

Other contributors

Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH
Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH