Room for the River: What Happens When a Floodplain Comes Back?

Inga

4 minutes ago

4 min read

For much of modern history, we treated rivers like pipes. We straightened them, lined them with levees and sent floodwater downstream as fast as possible. But a healthy river is more than its channel. It spills onto the land beside it, storing water, feeding soils, filtering pollution and creating habitat. Give a river its floodplain back, and it can start behaving like a river again, often with real benefits for nearby communities and wildlife.

*The Coorong Wetlands. The Coorong is a national park and lagoon ecosystem in South Australia - Credit Flickr, Rene Kisselbach*

The river we forgot

A floodplain is the low, gently sloping land beside a river that is covered by water from time to time. It isn’t wasted land waiting for development. It is part of the river’s natural plumbing. In high flows, water spreads across the plain, slows down, drops its sediment and soaks into the ground. As the river falls, the floodplain releases moisture slowly, supporting plants, wetlands and groundwater.

Many rivers have lost this connection. Levees, drains, towns, farms and flood-control works squeeze them into narrow corridors. Water moves faster, erosion increases, habitat shrinks and flood risk can be passed on to communities downstream.

Restoration doesn’t mean letting rivers flood wherever they like. It means redesigning the landscape so water can reach suitable places, such as wetlands, side channels, old river bends and flood-storage areas, while homes and critical infrastructure stay protected.

Water comes first

The first change is usually to the water itself. When floodwater reaches a floodplain, the land acts like a sponge, holding water temporarily and slowing the flood peak. Flood damage depends heavily on how fast water arrives and how high it rises, so even a modest delay can help. How much it helps depends on the site, how much floodplain is restored and what is happening across the wider catchment.

Restored floodplains can also help in dry times. Water that soaks into soils and wetlands recharges groundwater and keeps the landscape moist after the rain ends. In a study of restored wetlands along Victoria’s Loddon River, RMIT University (Australia) researchers found soil moisture was 55 per cent higher, even after the wetlands themselves had dried out.

*River Rhine/Germany - Credit Pixabay, Peter Wasser*

Despite restoration efforts elsewhere in Germany, large stretches of the Rhine remain heavily engineered for shipping, flood control, hydropower, and water extraction, so it has not been returned to a fully natural, free-flowing state.

Cleaner water, healthier soil

As water slows among reeds and wetland plants, sediment settles out and nutrients such as nitrogen can be taken up or held in the soil. That means less pollution reaching rivers and coasts. Excess nutrients fuel algal blooms and strip water of oxygen, harming aquatic life. In the same RMIT study, restored wetlands held 45 per cent more nitrogen in their soil. (It was a small study, comparing three restored wetlands with three degraded ones.)

Floods also deliver silt and organic matter that refresh soils and support floodplain plants.

A home for wildlife

A single straight channel offers limited habitat. A reconnected floodplain offers a mosaic of shallow water, deep pools, mudflats, reeds, sedges and native trees. Fish feed, spawn and shelter their young there. Waterbirds nest and feed. Frogs, turtles, insects, bats and woodland birds all benefit. In Australia, environmental flows that reconnect rivers with wetlands can trigger native fish movement and breeding and provide nesting habitat for waterbirds.

The results can be encouraging. A 2026 global review in the Journal of Applied Ecology found that for levee setbacks, floodplain lowering and side-channel excavation, more than 90 per cent of studies reported positive biodiversity outcomes. Most of that research comes from temperate regions, especially Europe, so results on Australian rivers may differ.

A bonus for the climate

Wetland soils and plants build up organic carbon over time. At one Victorian/Australia floodplain wetland, surface organic carbon stocks were 53 per cent higher six years after water flows were restored. That is a single site, and restoration is no complete climate solution, but it adds to the case for repairing these landscapes.

What restoration looks like

Restoration takes many forms, depending on the river, the landscape and the community:

Removing levees or setting them back so water can spread into designated areas
Reconnecting side channels and billabongs cut off from the river
Replanting banks and floodplains with native species
Rebuilding wetlands and restoring natural wet-and-dry cycles
Removing barriers such as unnecessary weirs and culverts
Delivering environmental flows at the right time, depth and duration

In Victoria’s Murray floodplain, the state’s restoration project is using regulators, channels and pumps to put water onto wetlands and hold it there longer. The aim is to revive old waterbird breeding sites and help native vegetation regenerate.

Not a simple fix

Floodplains are often working landscapes. Farms, towns, roads, cultural sites and private property may sit within them, so projects must balance ecological gains with land use, water rights, safety and community priorities. Even the methods are debated: some conservation groups argue that heavy engineering is no substitute for returning water to the river itself.

Wetland area - Green Point Park, Cape Town/South Africa - Credit Flickr, SA Venus.com — *Wetland area - Green Point Park, Cape Town/South Africa - Credit Flickr, SA* *Venus.com*

There is also a risk of overselling. Restoration can reduce or delay flood peaks, but it cannot eliminate flood risk, particularly in extreme events or where only a small part of a catchment has been restored. The best projects pair restoration with good planning, emergency management and honest communication. They also keep monitoring water levels, plants, fish, birds and water quality long after the earthworks finish.