How do you make space for rivers without rendering land unusable?

I wrote previously about how making more space for rivers is part of an adaptive flood mitigation strategy. It comes at the cost of some land flooding during peak floods. But what if we could use this land in new ways to mitigate the negative impacts of temporary flooding and even bring further benefits?

Making the most of flooded land

Nature-based and room for the river approaches can help traditional dams, levees, and other riverine flood defences adapt and cope with increasing levels of precipitation. These approaches can include allowing seasonal flooding in new areas or in areas that previously flooded but have been embanked over time. 

One potential issue with this specific approach to flood protection is that land that was previously protected from flooding will now occasionally flood. However, most of the time this land or space is still usable, as long as new use cases are resilient to flooding or can be moved during wet seasons.

In developed countries, this often means that those areas are used for nature, recreation, and sometimes agriculture. One example are floodplains in the Netherlands that are protected by summer dykes (see figure below). In developing countries, many inhabitants heavily depend on land for their food production and income, so converting that land to a floodplain may not be feasible. 

What if there was a way to make use of flooded land to enrich agriculture, or create all new revenue streams that can benefit local communities? That’s exactly what flood-based aquaculture and flood-based agriculture aim to do. They offer win-win solutions so seasonally flooded land offers significant benefits that can vary from region to region.

Flood-based adaptations all around the world

Double dike systems support cattle grazing and provide new sites for nature and recreation

In developed countries flooded parts of double dike systems (see below) are used in dry seasons for grazing cattle, as nature and recreation spaces, or for other purposes. And in cases where an area is mainly used for flood storage, these spaces are also well suited for agroforestry, where trees and shrubs are planted on the same land as crops or cattle grazing spaces. 

These approaches can help create more diverse, multifunctional landscapes and:

• Reduce soil erosion
• Improve water infiltration
• Increase soil fertility
• Provide timber, fuelwood, fruits, and other resources

In many cases, extreme floods may only occur in a specific area once every 10-100 years, meaning that land can be put to use in other ways far more consistently.

Fishing and water-based agriculture opportunities

In regions like Asia, flooded land can offer great opportunities for fishing or water-based agriculture. For example, by using rice fields as fishing ponds during flood seasons, farmers can benefit from alternate revenue streams and improved crop yields, as the water can flush out harmful substances and supply new fertile soil. And they can also be used for growing crops that are adapted to wet conditions, such as floating rice, taro, and lotus. As a nice bonus, the new fertile soil and sediments help combat subsidence of deltas.

Similarly, wetlands created by new flood mitigation measures can be used to support agricultural production and contribute to local ecosystem services. For example, wetlands can contribute to water purification, flood regulation, and biodiversity conservation. And they’re excellent spawning grounds for fish, so they can support healthier ecosystems that lead to greater fishing yields in the future. Those are important measures for our natural systems, because fish populations in the Mekong for example have declined by about 90% in the last 20 years. Reintroducing flooding can benefit fisheries and potentially add to farmers’ incomes over time.

And in warmer climates with brackish to saline environments, mangroves can be integrated with aquaculture to support shrimp and crab fishing, as well as mollusc farming (see figure below). Mangroves offer further benefits, providing an ecosystem that:

• Controls erosion
• Sequesters carbon
• Protects coastlines
• Improves water quality

But how do these approaches look in the real world?

How do you engage communities to make flood-based agriculture and aquaculture possible?

The WWF worked with farmers to help develop new income streams that would adapt to flooding rather than work against it – all based on traditional knowledge. By using sediment from flood water as a natural fertiliser and transitioning to floating rice farming during the wet season, local farmers could maintain crop yield in wet seasons, all while contributing to reducing flood risk and improving biodiversity. After successful pilot projects, two communes in Vietnam found they could reduce costs for local farmers due to less need for fertiliser, while generating more income and improving water retention and sediment quality.

But outside of these specific project examples, the benefits can go even further. In a recent study, we demonstrated that two other nature-based solutions that work in concert with flood reduction can be financially feasible, while supporting livelihoods and providing many other climate resilience benefits.

Similar to how produce sold with the Fairtrade label can be seen as more desirable to socially-conscious shoppers, fish and crops sourced in a sustainable way could command more interest and higher prices – leading to even greater economic benefits for countries with strong export links.