Breakwater monitoring and maintenance

Published: 18 August 2015
Last edited: 17 June 2021

A monitoring system is used to measure sediment accretion, and to monitor the condition of the T-fences. In addition, natural regeneration of mangroves is monitored. During the first year after construction, functionality of the T-fences should be ensured through monthly visual inspections and maintenance where necessary. After one year, visual inspections and maintenance should be carried out at least after the end of every storm season. In addition, seasonal GPS surveys of the shore line at low tide can be used to see whether the T-fences have impacts on the shape of the coastline nearby. The natural regeneration of mangroves is documented by recording species, size and density or through fixed-point photos. The latter can also be used as a simple alternative for GPS shore line surveys.

Classifications

Category
Evaluation, effectiveness measures and learning
Scale of implementation
Local
Phase of solution
Monitoring

Enabling factors

  • Know-how and manpower for regular surveys (data collection for monitoring) and routine visual construction inspections. 
  • Benchmark poles for recording vertical accretion at several transects. 
  • Fixed point photos are an easy to use tool to monitor mangrove regeneration and shoreline changes. 
  • Measurements of sediment consolidation (mud-density).
  • GPS survey equipment and know-how for long-term surveillance.

Lessons learned

A standardized monitoring system for the condition of breakwaters, accretion of sediments and natural regeneration of mangroves is crucial for measuring the long-term success of T-fences. The need for maintenance and repair works may vary considerably between sites. Long-term surveillance based on GPS surveys must include neighbouring areas to discover possible negative side effects of T-fences (down drift erosion). It is important to realize that once floodplains are restored and an appropriate mangrove cover is in place, mangrove protection measures must be implemented to ensure sustainability of coastal protection. Once the mangrove forest is fully established, the breakwater construction is no longer needed. This process may take several years.

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