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    1. Erosion Control

    Delta scientists report four ways to save deltas from sea level rise

    May 19, 2022
    A team of Ultrecht University researchers identified sediment-based strategies to raise delta lands amid rising sea levels.
    Photo 2300035 / High © John Wollwerth | Dreamstime.com
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    A team of scientists from Utrecht University have published a series of sedimentation enhancing strategies to keep deltas dry in the face of rising sea levels.

    To keep up with sea-level rise, delta land needs to be raised with sand and mud from rivers — but sand and mud supply from rivers is decreasing globally. These supplies often no longer reach delta, which causes flooding and land loss.

    Utrecht University’s team of specialists investigated and reviewed existing and planned projects that raise delta land. They identified four key ways to keep deltas dry.

    Their research is published in Global and Planetary Change.

    Four Ways to Keep Deltas Dry

    Four strategies were discovered which could be used to save deltas from drowning, ranging from a specific type of sluice gate construction to mangrove restoration.

    Fig 2

     “All four of these strategies trap sand and mud onto delta lands and raise it above sea level,” said Jana Cox, river-delta researcher and lead author, in a press release. “They are effective and can offset even extreme sea-level rise conditions. Different projects are available at a variety of different scales for deltas of different sizes. Projects can last from ten to a hundred years, depending on what the desired outcome is.”

    These processes are:

    • River diversions: diverting some water and sediment from the main channel of a river into adjacent floodplains.
    • Tidal flooding: breaching existing dikes and allowing water and sediment to be delivered by the tides to adjacent floodplains.
    • Sedimentation structures: placing structures (e.g. willow dams) in river channels to trap the existing sediment in the water.
    • Vegetation planting: planting additional vegetation which traps sediment in its roots.

    The team also assessed the positive and negative environmental impacts and the land-use change that would be required for these strategies.

    Fig 3
    “We found that the strategies generally have many positive environmental and ecosystem impacts: creating new habitats, aquaculture opportunities and create new flood storage spaces, which means the flood risk decreases,” explained Cox. “However, this comes at the expense of urban or agricultural land in many cases. Available land for implementing strategies is a key aspect in determining possibilities for each individual delta.”

    Long-Term Solutions

    The review indicates that low-cost strategies only last 10-15 years and cover only small portions of the delta area. Meanwhile, projects that last for 100+ years are very expensive but can cover a large amount of the delta area. The combination of several smaller scale projects will also be crucial in deltas where available land is low, like Europe and southeast Asia.

    However, all projects take several years to plan and implement and require several successful political and legal decision making processes, along with stakeholder engagement to enhance success. So, to offset rapidly rising sea level, decision makers in deltas need to begin testing, planning, and pursuing these projects as soon as possible.

    “However, all projects combined only encompass 0.1 percent of delta land” explains Jaap Nienhuis, a delta researcher and principal investigator of the project. “Strategies are effective in the small areas where they are implemented, but they need to be expanded. Time is running out.”