Infrastructure development can alter the tidal flow that sustains mangroves well beyond its footprint. A Vietnam case study shows how to assess this and turn the findings into practical measures.
Most mangroves depend on tidal exchange, since regular flooding and drainage flush salt from the soil, deliver sediment and carry fish larvae into nursery creeks. As infrastructure development increases, this exchange can be disrupted even where forest clearance is limited. Roads or embankments that narrow tidal channels can trap saline water and cut sediment supply, causing dieback that may appear years later. In addition, bridge piers and land reclamation can alter current speeds without blocking channels, leading to scour or siltation. Less sediment also makes it harder for mangroves to keep pace with sea level rise.
Because these changes extend beyond construction sites and develop slowly, assessments based on species lists and habitat area alone may overlook them. Their assessment should therefore cover the wider hydrological network.
This presentation describes the approach used to assess these impacts for infrastructure development in the estuarine Can Gio Mangrove Biosphere Reserve, Vietnam. Aquatic surveys over two seasons, together with an ecosystem services assessment, showed that rivers and canals provide a key nursery function, particularly in the wet season. Hydrological alteration was then assessed as a separate impact pathway for each development activity. The findings informed measures in the Biodiversity Management Plan, from design recommendations on embankments and culvert sizing in tidal zones to limits on in-water works during fish spawning, restoration of tidal flow at temporary sites and monitoring of juvenile fish.
An Dong is an Environmental Consultant at RINA Consulting with over five years of biodiversity experience, from Mekong Delta wetland research to ESIA and Critical Habitat Assessment across Asia.