Promoting Wise Management of Natural Resources in Greene County, New York Since 1961

Living and Building by Streams

Floods

Floodplain1The Schoharie Creek overtopped its banks and flowed into the floodplain during the October 1, 2010 storm eventFloods 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?

floodplain2Schematic of a floodplainFloodplains 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

  • img3Typical flood damage along Catskill streams. Inadequate attention to NFIP regulations results in non-compliant structures threatened by stream erosion & floodingThe 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

FloodplainLossHistorically, 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:

LexingtonFloodOct2010_3Building in an active floodplain can put property at risk for flood damage during storm eventsAttempt 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.

Additional Resources

Flood Preparedness Information

National Flood Insurance Program

Post-Flood Emergency Stream Intervention Manual (4 Mb pdf)

Association of State Floodplain Managers

DEC Floodplain Management Information

DEC Floodplain Development and Floodway Guidance

Beyond Floodplain: LID Techniques for Upland Management of Floodplains

Building Activites in the NYC Watershed that Require a Permit

FEMA Model Flood Damage Prevention Ordinance

Floodplain Management Guide

Greene County Department of Emergency Services

FEMA

2008 NYS DEC Flood Summit Presentations

Risk & Liability Presentations

Flood Risk: A National Perspective, Looking towards 2050, Larry Larson (539 Kb)

No Adverse Impact Approach to Decreasing Risk and Liability, Ed Thomas; Slides 1-35 (1.2 Mb); Slides 36-80 (1 Mb)

Streams, Stormwater, and Watersheds Presentations

Appropriate Stream Management Techniques for Flood Reduction and Environmental Management, Vince McDermott; Slides1-5 (1.2 Mb); Slides 6-15 (1.2 Mb); Slides 16-22 (1 Mb); Slides 23-24 (1 Mb); Slides 25-26 (1 Mb); Slides 27-28 (1 Mb); Slides 29-35 (1.1 Mb)

What Can We Do? Presentations

An Integrated Approach to Flood Loss Reduction, Jon Kusler; Slides 1-28 (790 Kb); Slides 29-51 (1 Mb)

Traditional Flood Protection Approaches, Mike Stankiewicz; Slides 1-13 (1.1 Mb); Slides 14-32 (770 Kb)

Floodplain Management, Bill Nechamen (770 Kb)

Mitigation Planning and Projects, Rick Lord (560 Kb)