Flooding

What can Residents do today?

Residents are reminded that protecting themselves from flooding requires simple action, including: storing important documents in a safe, dry area, adhering to local evacuation plans and purchasing flood insurance to protect their financial investment. FEMA also offers the following tips to prepare for flooding:

Before a Flood

• Have a safety kit with drinking water, a first-aid kit, canned food, a radio, flashlight and blankets.
• Know safe routes from home, work and school that are on higher ground.
• Protect your property. Most homeowners insurance does not cover flooding.
• Make sure that your flood insurance policy is up to date.

During a Flood

• If flooding occurs, go to higher ground. Get out of areas subject to flooding. This includes dips, low spots, canyons, washes, etc.
• Avoid areas already flooded, especially if the water is flowing fast. Do not attempt to cross-flowing streams.
• Roadbeds may be washed out under floodwaters. NEVER drive through flooded roadways. If your vehicle is suddenly caught in rising water, leave it immediately and seek higher ground.

After a Flood

• Do not turn the electricity back on in your home if you detect gas or if the electrical system has been flooded.
• Wear gloves and boots to clean and disinfect everything that was touched by floodwaters or mudflows and throw out any such foodstuffs.
• Follow directions from local officials regarding the safety of drinking water.

Flood insurance is available through approximately 90 insurance companies in more than 20,500 participating communities nationwide. Visit http://www.fema.gov/fema/csb.shtm to check if your community participates in the National Flood Insurance Program (NFIP). The average flood insurance policy costs around $500 a year. Everyone can purchase flood insurance - renters, business owners and homeowners. Last year a quarter of all claims paid by the NFIP were for policies in low-to moderate risk areas. In low-to-moderate risk areas, lower-cost Preferred Risk Policies start as low as $119 a year. Individuals can learn more about their flood risk and how to protect their property by visiting www.FloodSmart.gov or by dialing 1-800-427-2419.

Most flooding occurs when the volume of water in a river or stream exceeds the capacity of the channel. Flooding has also taken place along lakes and Long Island Sound, when higher than normal water levels inundate low-lying areas.  Numerous factors affect the rate at which a stream flows as the water tries to move towards Long Island Sound, and therefore the potential for flooding. Most important are the amount and type of precipitation, the nature and condition of the drainage basin, and the antecedent (past) rainfall, which affects soil conditions.

All rivers are subject to fluctuations in flow. During a rainstorm, the amount, intensity, duration, area of storm, and path of the storm, all influence the runoff reaching the stream. The amount, intensity, and duration of storms affect the ability of the land to absorb the precipitation and therefore affect the rate of runoff. How the area and path of a storm relate to the area and shape of the basin receiving rainfall will in turn produce greater or lesser amounts of flooding. The cross-section area of the stream, the runoff rate, and the rate of flow will determine the volume of water that will pass a given point downstream.  The shape, size, soil type, and topography of the drainage basin are other factors affecting the quantity of water reaching the stream. These factors are usually constant. However, the absorptive or shedding properties of the soil vary with vegetation cover, season, and previous (antecedent) rainfall.  In the case of heavy forestation and vegetation, the rate at which surface water flows to the main channel may be slowed, and hence the runoff is spread over a longer period. In addition, the passage of water tends to be retarded in basins with many natural storage areas, such as lakes, swamps and wetlands, and even those with artificially created storage such as from dams and levees. Consequently, smaller peak flows are produced in such rivers than would be the case in basins without these modifying influences. The best North American example of a basin with large natural storage is that of the St. Lawrence River, which has the Great Lakes in its headwaters.  Climate has an important influence on the relationship between precipitation and runoff. Ground frost makes most soil impenetrable if the soil contains moisture. In northern latitudes, the winter season, during which a large part of the year's precipitation is stored in the form of snow, is often followed by sudden melting, with much of the runoff flowing quickly over frozen ground to reach streams. Also, the heavy ice formation on rivers influences flooding, particularly on rivers in northern latitudes. Several climate factors (e.g. temperatures below 32 F for long periods of time) control the thickness of an ice cover in winter. Its eventual manner of breakup is controlled by opposing factors such as warming temperatures and the amount of rainfall / runoff which enters the ice-laden rivers. These factors combine to govern the severity of ice jamming.

Snowmelt Runoff

During the winter months, most of the precipitation is simply stored as snow or ice on the ground. During the spring freshet, huge quantities of water are released, which explains our heavy spring runoff and flooding.  Floods resulting from snowmelt runoff combined with heavy rains are the most common type of flooding along the Connecticut River and other larger rivers in our state. These floods generally occur in the spring but will also occur during sudden winter thaws. Heavy runoff can result from the rapid melting of the snow under the combined effect of sunlight, winds, warmer temperatures and even the level of humidity in the air. When the ground is frozen, the water produced by the melting snow is unable to penetrate and runs off over the ground surface into streams and lakes. The amount of surface runoff is usually within the capacity of the channel to drain off without flooding. However, if there is an above-average snow depth, a sudden thaw, heavy rainfall, or a combination of these factors, then the potential for high volumes of runoff and subsequent flooding increases. The later the thaw, the more likely that warm temperatures will lead to a sudden release of runoff. Since the climatic factors influencing the rate of snowmelt are often widespread, snowmelt runoff flooding conditions can exist over vast areas.

Flash Floods

Flash floods can be extremely dangerous. Unanticipated, they usually happen on small watersheds as a result of a torrential downpour, often caused by heavy thunderstorm activity.  A flash flood is characterized by the occurrence of the peak of the flood within six hours of the onset of rainfall. The flood conditions develop rapidly because the rainfall is so heavy and the ground is incapable of absorbing the water quickly enough, resulting in a very high runoff rate. Flooding of this type is generally localized, very intense and damage is usually restricted to a limited area. Large rivers typically remain below flood stage, while smaller streams can overtop their banks, even in a drought year.

Coastal

Many residents living along the shores of major lakes, such as the Great Lakes, or along Connecticut’s shoreline have experienced flooding and property damage as a result of high wind and wave action resulting from a coastal storm such as a hurricane or nor’easter. The term most commonly used for this type of flooding is “storm surge”.  These storm surges are caused by sudden drops in atmospheric pressure, sustained high winds from either a North/North East or South direction and by the duration of these winds and pressure drops, which accompany moving storm systems. Storm systems are significant because of their high frequency here in New England and potential for causing abnormal water levels at coastlines.  In many coastal regions (including Connecticut), the maximum potential for storm surges are from major tropical hurricanes.  Determination of water elevations during storms is a complex problem involving interaction between wind and water, differences in atmospheric pressure and even the shape of the coastline. Winds are responsible for the largest changes in water level due to surge. A wind blowing over a body of water exerts a horizontal force on the water surface and induces a surface current in the general direction of the wind. These currents are impeded in shallow water areas, causing the water level to rise downwind while at the windward side of the basin the water level falls. The term "storm surge" is used to indicate departure from normal water level due to the action of storms. The term "wind surge" is often used to indicate rises in lakes, reservoirs, and smaller bodies of water.  Along the coasts of Connecticut, major hurricanes can cause rare surges of up to 16-20 feet, but in some areas of the world, notably Bangladesh, severe storms can produce surges in excess of 32 feet. Typically most surges from storms in Connecticut are less than 5 feet and generally, surges in lakes and reservoirs are less. Among the most extreme lake surge observed in the world are those on Lake Erie, amounting to 8 feet at the eastern end of the lake. These rises in water levels can also provide a base on which high waves can attack the upper part of a beach and penetrate farther inland.  Wind-induced surge, accompanied by wave action, accounts for most of the damage to coastal structures and beach areas.  Flooding can also result from the failure of dams or other hydraulic structures, when a veritable wall of water can go hurtling down the river channel. As might be expected, the suddenness and magnitude of such an event, which is almost always the result of human failure in design, construction or operation, has disastrous results.

Connecticut River Facts

The Connecticut River is the largest river in New England. It flows 410 miles from its source at Fourth Connecticut Lake, a tiny beaver pond 300 yards from the Canadian border, to Long Island Sound. New Hampshire and Vermont share some two thirds of the river's length, or 275 miles. The river's depth varies from a few inches to 130' deep just below the French King Bridge in Gill, Massachusetts. The depth of the river in most places is constantly changing as the river transports and rearranges its load of sediment.  The Connecticut River drains 7.2 million acres, or 11,250 square miles, of New England and also a very small part of Quebec, in the Hall Stream basin.  The Connecticut River begins its journey a few hundred yards south of the Canadian border at Fourth Connecticut Lake, at an elevation of 2,670 feet above sea level. It drops half of that elevation before it ever leaves the town of Pittsburg. By the time the river reaches the Massachusetts line, it has fallen to approximately 190 feet above sea level. In the Connecticut River, flows vary widely according to location, time of year, snowmelt, precipitation, and management of dams. For more information, and links to US Geological Survey gages that give real time flow data, go to www.crjc.org. There are 13 existing dams on the main stem of the upper Connecticut River, and two more that the river has breached.  There are hundreds of smaller dams on tributaries throughout the watershed. Congress created the Silvio O. Conte National Fish & Wildlife Refuge in 1991, encompassing the entire four-state watershed, with the Connecticut River as its centerpiece. The following year, NH General Court designated the Connecticut River into the New Hampshire Rivers Management and Protection Program. In 1998, the White House designated the Connecticut as an American Heritage River.

The Housatonic River

The Housatonic River flows 149 miles from its four sources in western Massachusetts. Following a south to southeasterly direction, the river passes through western portions of Massachusetts and Connecticut before reaching its destination at Long Island Sound at Milford Point. The Housatonic River has a total fall of 1430 feet (959 feet from the confluence of the East and West Branches). Its major tributaries are the Williams, Green and Konkapot Rivers in Massachusetts, the Tenmile River in New York, and the Shepaug, Pomperaug, Naugatuck and Still Rivers in Connecticut.  The Housatonic River and its tributaries drain an area of 1,948 square miles. The river's name comes from the Mohican phrase "usi-a-di-en-uk", translated as "beyond the mountain place". The Mohican family of the Algonkin Indians, who came from New York west over the Taconic mountains, were the first valley settlers. The river was sometimes known as "Potatuck", or the "Great River", until the 18th century. Waterpower played a prominent role in 19th century industrial development, and remnants of dams, mill races and iron ore furnaces can still be seen today. Northeast Utilities operates five hydroelectric facilities on the river today.  Dams at three of these facilities - the Shepaug, Stevenson and Derby - form a chain of lakes, Candlewood Lake, Lake Lillinonah, Lake Zoar and Lake Housatonic, from New Milford south to Shelton.  This stretch is also a tidal estuary, which supports a number of critical habitats for rare plants and animals and is a significant contributor to Connecticut's shellfish population. The Housatonic estuary is the most consistent producer of seed oysters in the northeast as a public oyster bed, and generates over one-third of all oyster seed available to the state shellfish industry. The United State Navy also named a ship for the Housatonic River. The USS Housatonic had the unfortunate distinction of being the first ship in history to be sunk by a submarine, the confederate vessel CSS H.L. Hunley.