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What does it mean to have a connected and healthy floodplain?
First, let’s start with what floodplain even means. It’s the relatively flat land adjacent to a river or stream that is inundated with water during high flow events, which most of us simply call floods. As a result of this flooding, the land is generally highly fertile and biodiverse, and marks a transition zone between the river and the upland systems.
If a floodplain that has been disconnected is often characterized by steep, high, or concrete banks that cause the water to move through more quickly. This can add pressures to manmade water control systems, such as dams or levees and reduces water quality benefits.
A connected and healthy floodplain, on the other hand provides riverine systems more room as they rise, and improve water quality. As the water overtops the banks of the river, floodplains allow sediment and nutrients to settle out, and provide an opportunity for additional water to seep into underground aquifers, which is a primary water and irrigation source for many communities around the world. In addition, connected and healthy floodplains provide habitat for a variety of plant and animals species.
But that’s not all: floodplains also provide fertile grounds for agriculture, due to centuries of nutrient deposits. Depending on the current course of the river system, these nutrient rich areas may or may not be within 100-year or 500-year floodplains, and this is something landowners may want to consider as they consider development options, crops, and systems to alleviate the pressure of periodic flooding.
There are, of course, more benefits to connected and healthy floodplains, which is part of why river restoration often includes examining floodplain connectivity and working to improve or restore floodplain connectivity as part of the restoration plan. Depending on the needs of the community, this restoration work can take many forms, including:
- Breaching or removing levees to allow floodwaters to reach the floodplains;
- Installing flood bypasses that allow for controlled flooding (such as weirs or floodgates);
- Excavating a floodplain terrace, which helps offset the vertical difference between the flow levels and the floodplain;
- Setback levees, which allows more water to reach floodplains while still providing flood protection to areas behind the cities;
- Adding sinuosity back into channelized streams and culverts;
- Countour and keyline ploughing to direct higher flows into floodplains; and
- Addressing flow regulation to restore minimum floodplain activating flows.
Restoring floodplain connectivity benefits humans as well as plants and animals, and the fact that floodplain restoration has become an integral part of many river restoration projects is a reason for hope about how the impacts of flooding may look different in the future.
Great Ecology has worked on floodplain restoration projects in several states, across dozens of projects.