FloodCauses Flooding occurs most commonly from heavy rainfall when natural watercourses do not have the capacity to convey excess water. Floods are not always caused by heavy rainfall.

Tropical cyclone, a tsunami or a high tide coinciding with higher than normal river levels. Characteristics of a Flood A number of criteria determine the dangers of a flood. The University of Wisconsin have came up with the following criteria such as depth of water, duration,

velocity, rate of rise, frequency or occurrence, and seasonal. Velocity- high velocities of flow create erosive forces and can do things like destroy foundations. Depth of Water- floatation, failures on foundation, vegetation survival, etc.. Rate of Rise- is the rate at which the water level increases. Seasonal- the land during growing season, the effects on agriculture production and other things like that. Causes of Floods and Flood Damage Heavy

rain Spring snowmelt Dam failure Low absorption or no soil percolation Business and residential growth in flood areas Factors Contributing to Flooding Rainfall intensity

Rainfall duration Topography Soil conditions Ground cover Heavy rain Heavy rainfall exacerbates problems with: Runoff Absorption

Flood-control measures In rocky and heavily paved areas, lack of absorption can cause flash flooding Spring snowmelt Snowmelt is surface runoff produced from melting snow Rapid snowmelt can cause flooding.

If the snowmelt is then frozen, very dangerous conditions and accidents can occur, introducing the need for salt to melt the ice. Dam failure A dam is a barrier across flowing water that obstructs, directs or slows down the flow, often creating a reservoir, lake or impoundments. Causes of DAM Failure : Sub-standard construction

materials/techniques (Gleno Dam) Spillway design error (South Fork Dam, near failure of Glen Canyon Dam) Geological instability caused by changes to water levels during filling or poor surveying (Malpasset Dam). Sliding of a mountain into the reservoir (Vajont Dam not exactly a dam failure, but caused nearly the entire volume of said reservoir to be displaced and overtop the dam)

Poor maintenance, especially of outlet pipes (Lawn Lake Dam, Val di Stava dam collapse) Extreme inflow (Shakidor Dam) Human, computer or design error (Buffalo Creek Flood, Dale Dike Reservoir, Taum Sauk pumped storage plant) Internal erosion, especially in earthen dams (Teton Dam) Earthquake Low absorption or no soil percolation land is converted from fields or

woodlands to roads and parking lots, it loses its ability to absorb rainfall. Urbanization increases runoff 2-6 times over what would occur on natural terrain. In areas with rocky geology, rainfall or snowmelt cannot be absorbed. The result can be flash flooding with little or no warning. Business and residential growth Nature and frequency of flooding

The Nature of Flooding Intense rainfall, severe storms, monsoonal rain, tropical cyclones and storm tides. All of these factors contribute to the likelihood of flooding. There are three main types of flooding that affect the region 1) Flash flooding 2) River flooding 3) Storm tide flooding

Flash flooding Flash flooding is generally defined as flooding that occurs within six hours of intense rainfall occurring. Flash flooding can occur in one of two ways: localized flooding relating to difficulties in drainage creek flooding. Localised flooding Localised flooding occurs when part of the storm water drainage system is blocked or capacity is exceeded. Possible effects include water damage to property and home and contents, backyard/front yard flooding and localised road flooding.

Liability for damages may apply if building on, filling or not maintaining a property increases flooding impacts on a neighbouring property. Creek (portion of stream that is affected by the flow of ocean tides)flooding Creek flooding is the result of intense localised rainfall and can occur in both undulating coastal and hinterland regions. Often occurring with little warning time, creek flooding can pose a

significant risk to life and property, River flooding River flooding results from widespread and prolonged rainfall over a major river's catchment area. Predominantly affecting the coastal floodplains, floods may last a couple of days to several weeks and represent a major impact on life and property. The time a flood peak arrives and the duration of

flooding is defined by the area and slope of the river catchment as well as the length of the river. Council has prepared flood information maps that show areas possibly impacted by river flooding Storm tide flooding Storm tides are associated with tropical storms and cyclones. Storm tide flooding comes from the ocean and is a result of combined high tides and heavy seas. Storm tides often coincide with periods of intense and prolonged rainfall and can impact on existing swollen river systems

and low lying coastal areas. Storm tides can increase the severity, extent and length of any simultaneous river and creek flooding.. How Forcasters Predict Floods Predictions of a Flood

Deep Snow can melt into a lot of water. It usually floods because of rain or rapid warm temperatures. Frozen ground wont absorb as much water, the rain and/ or snow causes flooding on frozen ground. Full reservoirs- Reservoirs are very big and are man-made to hold water for drinking or

irrigation. It wont absorb anymore water f full and it causes it to overflow. High River or Stream Levelsmelting flows into a full river and overflows on banks. Effects on the Environment Sometimes its a good thing when a flood occurs. The environmental benefits of flooding are fisheries, wetlands, and irrigation. It also makes a mess of the environment. The soil becomes poor because the oxygen is limited due to so much water. The pH in soil decreases, rate

decomposition of organic matter in flooded soil tends only to be half that unflooded soil Trees are effected as well. It effects the height, age, vigor, roots, and species. During the growing season flooding is very harmful especially to woody plants compared a flood in a dormant season. Floods could carry chemicals from agricultural fields, sewage,etc. and cant handle large bodies of water. Crops die because they cant survive because of the conditions. Precautions to Take

To remain safe from floods you need to know when and how to deal with them. Lives could be saved by having more warnings of floods for places in threat. There are things used for antiflood protection and it makes your house, yard and much more, safe and protected when a flood arrives. They can be used over and over again.

Structural Responses to Flood Hazards Channelization Dams, retention ponds, and reservoirs Controlled release of flood water Levees, dikes, flood walls May worsen flooding upstream and downstream

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