What is the history of flooding in Schoharie County? Do you know how your property is affected by flooding? What does “100-year Floodplain” really mean? Are streams the only thing that cause flooding? The information on this page will help you identify your risk, and understand what it all means.
THE 100 YEAR FLOOD – WHAT DOES THAT MEAN??
- There is a 1% Chance of Flood Occurring in Any Given Year
- There is a 26% Chance of Flood Happening in the life of a 30 Year Mortgage
- Also known as Base Flood
- Also known as Special Flood Hazard Area (SFHA)
- Charateritics of a Floodplain
Is your home in a special flood hazard area? FEMA’s Map Service Center (MSC) can help you determine if it is. The FEMA Flood Map Service Center is the official public source for flood hazard information produced in support of the National Flood Insurance Program (NFIP). Use the MSC to find your official flood map, access a range of other flood hazard products, and take advantage of tools for better understanding flood risk.
WHAT CAUSES FLOODING?
Floods are the most common natural disaster in the United States. You don’t need to live on the coast to be at risk. Flash floods, inland flooding, and seasonal storms affect every region of the country, severely damaging homes and businesses.
Dams provide many functions for a community, including recreation, flood control, irrigation, water supply and hydroelectric power. Dams range from massive concrete structures to smaller earthen structures, such as those near a farm’s pond.
But dams also can increase the risk for floding. Intense storms can raise water levels and produce a flood within a few hours or even minutes. Dam failure may occur within hours of the first signs of breaching or overtopping. Other factors, such as debris jams or an accumulation of melting snow, can cause breaches days or weeks after the first sign of trouble. Flooding can occur downsteram when excess water is released in an effort to avoid overtopping or a breach at the dam.
Gilboa Dam (Schoharie Reservoir)
Owned by NYC DEP, the Schoharie Reservoir was created by impounding Schoharie Creek. Portions of it lie in the towns of Conesville and Gilboa in Schoharie County, Roxbury in Delaware County, and Prattsville in Greene County.
Constructed in 1919-1927 and placed into operation in 1927, the Dam has been in service for almost 90 years. The average storage capacity of 17.6 billion gallons provides approximately 16 percent of the total water supply for NYC. Water travels through the Shandaken Tunnel about 15 miles to the Esopus Creek.
Gilboa Dam is a classic NYCDEP gravity dam design, consisting of a 160 foot high by 1,326 foot long spillway, constructed of mass cyclopean concrete with a 3-5 foot thick Ashlar masonry facade of mortared quarried stone on the entire downstream face. The Dam is abutted on the west by a 160 foot high by 700 foot long Earthfill embankment section consisting of homogenous rolled earthfill with a concrete corewall. A stair-stepped overflow structure, also constructed of cyclopean concrete with stone veneer facing, cascades water from the spillway into the side channel. The stepped spillway is intended to dissipate energy as water overflows the spillway.
In December 2005, remedial measures began to ensure that the Gilboa Dam satisfied NYSDEC dam safety criteria for the stability fo the gravity section. The primary emergency structural improvement to the dam was installation of post-tensioned anchors in the spillway and its foundation.
There are no flood control devices on the structure, so once the reservoir exceeds 1,130 feet elevation, water will flow over the spillway into the side channel.
NYPA Dam (Blenheim-Gilboa Reservoir)
Owned by the NY Power Authority, the Blenheim-Gilboa Pumped Storage Power Project generates more than one million kilowatts of electricity in peak demand periods by drawing water from the Schoharie Creek and recycling it between two huge reservoirs.
Nestled beneath 2,000 foot tall Brown Mountain, B-G serves two vital functions. It saves money for NY consumers by providing low cost electricity when they need it the most, and it stores water for emergency power production. If needed, the project can be up and running within two minutes and can take over if another plant or line suddenly goes out of service.
Each of the reservoirs – one atop Brown Mountain, the other at its foot – holds five billion gallons of water. When generating power, the water cascades down a concrete shaft that’s five times taller than Niagara Falls. When storing water, ususally at night or over the weekend, the process is reversed and water is pumped back up the shaft for storage.
The B-G Project is regulated by the Federal Energy Regulatory Commission (FERC), and are required to release the same amount of water that comes into the reservoir. For example, if 1,000 cfs of water flows into the reservoir, NYPA is required to allow 1,000 cfs of water to flow out of the tainter gates into the spillway. However, in emergency situations, with FERC permission, NYPA is allowed to “step” the release to protect downstream. This means that if they can safely hold some water temporarily until stream levels go down, they will do so. This is not always possible – the safety of the dam/power station must be taken into consideration.
Development Development Flood risk isn’t just based on history; it can change due to building and land development. Just because you haven’t experienced a flood in the past doesn’t mean you won’t in the future.
Construction and development can change the natural drainage paths and create brand-new flood risks. That’s because new buildings, parking lots, and roads mean less land to absorb excess precipitation, which can leave an area more susceptible to flooding during a hurricane, tropical storm or heavy rain.
Development is defined as any man-made change to improved or unimproved real estate, including but not limited to buildings or other structures, mining, dredging, filling, grading, paving, excavation or drilling operations or storage of equipment or materials.
A Floodplain Permit is REQUIRED for all Development – regardless of who owns the property. Farms are NOT exempt from this regulation. NYS DEC or ACOE Permits are NOT Floodplain Permits. You must speak to your local Building Code Enforcement Official.
Heavy rains can happen throughout the year, putting property at risk. Cresting rivers, backed-up storm drains, and saturated ground all contribute to significant flooding when there is an excessive amount of rainfall.
A Flash Flood is a rapid flooding of low-lying areas in less than 6 hours. Flash floods are known to contain excessive force as water travels fast – they are known to roll boulders, tear out trees, and destroy buildings and bridges.
Mudflows are rivers of liquid and flowing mud on the surface of normally dry land, often caused by a combination of brush loss and subsequent heavy rains. Mudflows can develop when water saturates the ground, such as from rapid snowmelt or heavy or long periods of rainfall, causing a thick, liquid, downhill flow of earth. Mudflows, covered by flood insurance, are different from other earth movements where there is not a flowing characteristic – such as landslides or slope failures – that are not covered by flood insurance.
Levees/Berms are designed to protect against a certain level of flooding. A levee/berm is a structure created parallel to the course of a river to prevent inundation. However, levees can and do decay over time. Levees can also be overtopped or breached during large floods. Farms are the largest user of levee/berm’s in our area.
Tropical storms and hurricanes can pack a powerful punch with soaking rain, high winds, and storm surge. Atlantic hurricanes typically occur from June to November. In addition to causing extensive damage in coastal areas, the storms often bring heavy rain hundreds of miles inland, posing a threat to millions of people who don’t live near a shoreline.
Tropical storms and hurricanes have the potential to unload heavy and sustained rainfall that can overwhelm drainage systems and result in flooding.
Storm Surge is the water that is pushed toward the shore by strong storm winds. These wind-driven waves can cause severe flooding in coastal areas. Storm surge combined with high tides can be extremely dangerous and destructive.
Every region in the United States is at risk for winter flooding. Many people are focused primarily on ice and snow this time of year, but it is important to also consider winter flood risks.
Long cold spells can cause the surface of rivers to freeze, leading to ice jams. When a rise in the water level or a thaw breaks the ice into large chunks, these chunks can become jammed at man-made and natural obstructions, resulting in severe flooding.
A mid-winter thaw can produce large amounts of runoff in a short period of time. Because the ground is hard and frozen, water cannot be reabsorbed. The water then runs off the surface and flows into lakes, streams, and rivers, causing excess water to spill over their banks.
During the spring, frozen land prevents melting snow or rainfall from seeping into the ground. Each cubic foot of compacted snow contains gallons of water and once the snow melts, it can result in overflow of streams, rivers and lakes. Add spring storms to that and the result is often serious, spring flooding.