Defining a Flood
A flood is a natural reoccurring event that poses inherent flood risks to people and property along waterways and their adjacent floodplains.
Causes of a Flood
- Rapid snow melt.
- Debris and ice jams blocking or reducing channel flow.
- Over-development.
- Deforestation, and loss of wetlands.
- Global climate change.
- Dam or levee failures.
Stopping a Flood
No manmade project can stop a flood from happening. Flood risk reduction methods can minimize flood impacts for communities but cannot eliminate the residual risk that remains after the methods are implemented. Various methods include non-structural and/or structural strategies, that are site specific and are based on balancing the benefits of the methods to their costs and environmental impacts.
Flood Risk Management Methods
Non-structural
Some of the most important and cost effective strategies for safeguarding life before a flood occurs involve improving flood emergency preparedness and weather and flood predictions. These strategies along with floodplain management and floodplain regulation are considered non-structural methods.
Structural
Structural methods, are considered when the floodway and floodplain can no longer safely pass the floodwaters through a community. The features of a structural flood risk reduction project can include: channel improvements, closures, drainage structures, levees, floodwalls, ice control structures, ponding areas, and pumping stations. Each feature is briefly described below.
- Stream channel improvements - may require the channel to be re-aligned, widened or moved altogether to reduce the risk of flooding in a protected area.
- A closure - is a wall-like structure used to bridge a gap in a levee or floodwall at a road or railway crossing. They are usually constructed with aluminum stop logs that are inserted into slots in anticipation of a high water event to form a continuous line of protection with the levee or floodwall.
- Drainage Structures - are conduits with riverside flap gates that allow water to flow from the landside to the waterside of a levee during non-high water periods, then automatically close during high water stages.
- Levees - are earthen embankments designed to specific standards and constructed to keep high water from flowing into a protected area.
- Floodwalls - are concrete walls with a similar function as levees. The walls are constructed to keep high water from flowing into protected areas.
- Ice Control Structures - there are several designs for ice control structures. One design consists of a series of concrete pillars anchored into bedrock across a watercourse to prevent ice buildup further downstream in the vicinity of a protected area. The pillars act to stop the ice flow while the rising water is then redirected to a diversion channel to carry the water to a point further down the watercourse.
- Collection ponds - or ponding areas are constructed on the protected side of a project, usually near the landside of a levee. These ponds are often necessary to store interior drainage that cannot flow to the river during high river stages.
- Pumping Stations - are used to pump interior stormwater that has collected behind the landside of a levee or floodwall to the riverside, thereby preventing water from building up on the landside when the drainage structure gates are closed, such as during a high water event. Pumping stations are necessary when ponding capacity is not large enough to store all interior drainage.
Given below are two other additional types of structural flood risk management projects.
- Clearing and Snagging Project - this is a project that includes the removal of sediment and/or tree debris from a waterway to clear a blockage in order to allow adequate flow capacity during a high water event.
- Streambank Stabilization and Shoreline Protection Project - reinforcers streambanks and shorelines to prevent erosion or collapse during a high water event usually requiring use of large sized stones (riprap).
DEC's Flood Risk Management Projects
DEC operates and maintains over 100 United States Army Corps of Engineers built Flood Risk Management (FRM) Projects within New York State. Each FRM Project is uniquely engineered to work within the community hardscape and waterway, and built to the flood of record at the time of construction. Most of the existing FRM Projects are now beyond their project life, and are undergoing major rehabilitation and upgrades to keep them functioning in an everchanging flood risk environment.
DEC's flood team includes managers, engineers, and operational staff who not only work to repair, operate & maintain the FRM projects, they also monitor the projects and river gages during flood events. As an aid to help educate and train flood emergency first responders, DEC has created a handy pocket-sized Flood Patrol Manual (PDF) reference booklet.
Another way DEC preserves the integrity of New York's Flood Control Projects is though the use of Flood Control Land Use Permits (PDF). Additional legal details of this permit can be found in 6 NYCRR Part 501: Use of Flood Control Lands.