Floodplain Management - Greene County Soil & Water Conservation District

Living and Building by Streams

Floods

Floodplain1 Floods are natural events that occur in response to heavy rains and snow melt. Under flood conditions, waters rise, often overflow stream banks, and spill onto adjoining low-lying land.

Historically, streamside landowners have responded to floods by making straighter, deeper stream channels to carry the water downstream as fast as possible. However, this approach actually can cause more damage in the long run, since it increases stream power and causes severe erosion and damage to nearby structures.

Rather than fighting against a stream, it is more practical to work with the natural landscape to avoid damages by reducing the speed and volume of flood waters.

What is a Floodplain?

floodplain2 Floodplains are low-lying lands next to rivers and streams. When left undisturbed in a natural state, floodplains store water and dissipate floods without adverse impacts on humans, buildings, roads and other infrastructure. Without floodplain access, which serves the essential purposes of slowing floodwaters and storing sediment, stream banks are subjected to the full power of flood flows, leading to extensive damage and erosion.

Functions of Healthy Floodplains

Flood waters can spread over a large area in floodplains that have not been encroached upon. This reduces flood velocities and provides flood storage to reduce peak flows downstream.
Water quality is improved in areas where natural floodplain cover acts as a filter to remove impurities from runoff and overbank flows.
Natural floodplains moderate water temperature, reducing the possibility of adverse impacts on aquatic plants and animals.
Floodplains can act as recharge areas for groundwater, and reduce the frequency and duration of low flows of surface water.
Floodplains provide habitat for diverse species of flora and fauna, some of which cannot live anywhere else. They are particularly important as mating and feeding areas.

Factors that Affect a Healthy Floodplain and Increase Flood Damage

The removal of stabilizing vegetation around stream banks and rivers.
Erecting structures that deflect or inhibit the flow of floodwaters. This modifies flow paths and can spread flooding problems and erosion.
Constructing bridges, culverts, buildings, and other structures that encroach on the floodplain. These developments reduce the storage area available for floodwaters.
Building drainage systems that feed stormwater quickly into the receiving body.
Straightening meandering watercourses to hasten drainage. This transfers flooding problems downstream and also alters habitat.
Filling and dumping in floodplains. Floodwaters can transport this debris, which may interfere with the movement of the floodwater causing increased flood elevations.

Encroachment & Loss of Floodplains

FloodplainLoss Historically, floodplains were the first lands developed. Whether for transportation, farming, power production, or simply for the use and enjoyment of living by a stream, streamside property is still highly desirable for developers. However, it is a fact of life that floods occur along streams and rivers; floods are a natural and unavoidable. On the other hand, loss of life, property, personal items, and our homes is an avoidable situation.

The Cost of Building on the Floodplain

Average annual flood losses in the United States are currently estimated at $6 billion. This is a four-fold increase over the past century, and is a doubling in terms of dollars of damage per capita. The general trend is for flood losses to increase every decade due to increasing development in the floodplain, open spaces, and wetlands. As a result, floods have become far larger and more frequent.

Local Example: Why to Avoid Building in the Floodplain

The downtown area of Phoenicia, NY (Ulster County) is built almost entirely in active floodplains of the Stony Clove and Esopus Creek.This fact, coupled with an undersized bridge on Main St. that spans the Stony Clove, causes intense, damaging flooding during rain events. The video below shows the flooding in Phoenicia during the December 1, 2010 event (a 10-year flood).

General Advice for Floodplain Management

DO:

…Remove blockages such as large trees or debris that are underneath or against a bridge or culvert.

…Work with your neighbors to find mutually supportive solutions that do not harm property upstream or downstream.

…Contact Greene County Soil & Water to assist with design work and restoration.

…Contact state or federal resource agency about obtaining the required permits to use machinery in a stream or along a stream bank.

DON’T:

…Attempt to bulldoze or dig out the stream. Dredging a stream speeds up flood waters and increases erosion up and downstream of the site. Dredging also can severely damage bridges and roads.

…Remove all large rocks and boulders from a stream. Gravel bars, rocks and boulders all help reduce flood power, keep a stream stable and provide valuable aquatic habitat.

…Place loose gravel and material on stream banks or build up artificial barriers, debris piles or levees. This will prevent the stream from spreading out on the floodplain and will increase water velocities and associated flooding downstream.

…Assume that any permit applies to flood response work in or near a stream. Call Greene County Soil & Water to learn the rules for permits.

…Allow unqualified contractors to work on your land. You may be held responsible for any permit violations or damage caused to neighboring properties.