Backyard Streams: Floodplains

What is a Floodplain and why are functional ones important?

A floodplain is the flat, low lying area of land next to a river or stream that periodically floods at different points in time. Floodplains are hydrologically important, environmentally sensitive and ecologically productive areas that perform many natural functions. Flooding occurs naturally along every river and in coastal areas. During seasonal floods, water spreads over the riverside floodplains and creates seasonal wetlands that provide critical habitat for fish and birds.

Many people think that floods are bad, but they are essential to the health of a river. Streams that can meander and access floodplains are part of a riparian system that can store water, sediment, nutrients, and woody debris and convey water during flood events.

During big floods, a healthy floodplain benefits communities by slowing down and spreading out dangerous flood waters that would otherwise flood streamside communities, harming people and property. Healthy floodplains are nature’s flood protection.

Developing in Floodplains

The importance of maintaining natural floodplains is not a difficult idea to understand. However, humans have always been attracted to floodplains and development and industrialization have taken a toll on the natural functions of the floodplains. Development in the floodplains causes decreases in water quality from polluted rainwater entering the system, loss of wildlife habitats, and an increase in severity and frequency of flood losses because storage during a flood event is removed. Understanding the importance of maintaining the natural functions of floodplains can lead to better floodplain management approaches that will better protect the natural and beneficial functions of floodplains. And by creating more healthy floodplains, communities do not have to pay the high cost to repair property damage from flooding and streambank erosion impacting utilities and infrastructure surrounding streams.

By filling floodplains, developing in floodplains and damming rivers, we have diminished the ability of the land to absorb large storms and we send our problems and pollution downstream for someone else to handle. A majority of our floodplains and wetlands have been lost to development and of those remaining, most are in poor condition which negatively impacts fish and wildlife populations.

Solutions for helping our Floodplains

The first step in helping out our floodplains is to stop developing in flood-prone areas. Regulations are in place nationally to prohibit development within varying distances of our streams/waterways, and this is managed by local communities through the National Flood Insurance Program with assistance from FEMA, the Federal Emergency Management Agency. The second step is to fix our past mistakes by repairing damaged floodplains.

Big picture strategies include buying out frequently flooded properties, setting back or removing levees to widen the river and floodplain and restoring floodplains to recreate critical ecological function. The challenge with these efforts is that they can be costly.

One of the easiest solutions is to give rivers room to move and to store floodwaters, but in an urban environment with buildings, utilities and infrastructure located close to a stream, this might not be possible. So here are a few things you can do to make your streamside property more functional.

• Do not fill in your floodplain
• Do not build a structure, even a shed, in a floodplain
• Do not dump anything in your floodplain, including yard waste, as the excess nutrients can harm wildlife
• Do not dredge the creek and change its natural hydrology
• Do not mow up to the edge of the stream, but give the stream a natural setback ( a riparian buffer). Plants along a stream add roughness, slow down water and the roots hold streambanks together helping to prevent erosion.
• If you have mowed to the edge of the stream, stop mowing the grass next to the stream to allow vegetation to grow, but be careful to watch that invasive species don’t take over the riparian area. Trees and shrubs shade and cool stream water which is beneficial for aquatic organisms.
• Where a stream has become incised and cannot access its floodplain, excavate out and reconnect the stream to its floodplain. This solution is more expensive and usually requires permits and engineering.

The Floodplain Administrator in Union County is the Union County Engineer.