Increasing River Floodplain
Type of Development
Restoration, Reconnection
Topography
Valley, Baylands
Longevity
Long Term
Environment
Urban, Natural
Maintenance
Low
Cost
The residential economy increases dramatically when water features are nearby. Costs gradually increase in denser populated areas because of concrete and infrastructure removal.
Overview
Increasing riverine floodplains refers to restructuring river banks to their more natural form in order to mitigate flooding. Industrialization has lead to the tightening and straightening of riverbeds as well as increased hardscape levees to prevent flooding. This leads to faster moving water with less room to flood and evolve naturally. Floodplain restoration is essential for flood management and will lead to health benefits like lowering urban heat and sequestering carbon. With freer flowing water, sediment and nutrients will move naturally through ecosystems. Water flows will slow down, reducing erosion and flooding. Increasing floodplains or restoring them to their natural state is the most effective action to mitigate flooding and increase water health. Every other Nature Based Solution will be more efficient with an increased flood plain.
Function
Increasing river floodplain mitigates flooding by creating wider rivers, increasing storage capacity, and creating stronger banks. An increased floodplain creates habitats and opportunities for tree canopies.
Benefit
Increasing floodplains of creeks will massively reduce urban flooding and provide habitat for native animals and plants. Banks with larger widths have increased water capacity during heavy rains. When sloped banks are filled with native plants, they become sturdy enough to avoid erosion. Additionally, increasing the floodplain with curves not only slows water speeds but also creates more surface area for rivers to flow, creating less potential for overflow. Increasing the floodplain and daylighting covered sections of creeks are essential in reducing flooding and connecting the watershed.
Dependency
Space
Development Considerations
Floodplain management should be done as far upstream as possible, to avoid flooding at the bottom of the watershed. Reintroducing oxbow lakes (detention ponds adjacent to rivers), or creating them will add additional support in heavy flooding events. The opening of channels that have been cut off with levees, like the Coyote Canal will help reconnect the water systems.
Environmental Considerations
Native plants along sloped river banks will avoid erosion and create sturdy sides during flood events.
Maintenance Consideration
Maintenance and monitoring of floodplains is necessary considering that rivers naturally change and move over time. Newly increased floodplains should be monitored regularly within the first two years. Problems can arise from obstructions, debris, and storms which can cause erosion, sediment pile ups, and destruction of habitat.
Cost Considerations
The residential economy increases dramatically when water features are nearby. Costs gradually increase in denser populated areas because of concrete and infrastructure removal.
Case Studies
Napa River Flood Protection
The Napa River had a history of catastrophic flooding events, impacting downtown Napa, tourism, and agricultural assets. After a long history of utilizing engineered solutions, a multi-faceted collaboration with stakeholders, the Army Corps of Engineers, businesses, and others worked together to develop an approach to let the river run free - a "Living River" concept that was then and is still groundbreaking. The Napa Flood Protection project is an early and lasting example of using natural systems to manage flooding while protecting important assets in an affordable, durable, and effective way.