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A lack of capacity in drainage systems and a slow groundwater absorption rate are major causes of rain flooding, especially in urbanized areas. The amount of impervious surface coverage greatly contributes to this issue as it collects large volumes of stormwater and channels to specific drainage systems, increasing in velocity and picking up debris and pollutants along the way. The volume and velocity of the stormwater can damage infrastructure, erode riverbanks, and create dangerous conditions for traveling such as hydroplaning and moving water on the road. This type of flooding typically contributes to the conditions for riverine flooding.

Riverine Flooding

Flooding along rivers and streams may occur seasonally or during/after heavy rainfall. Also related to a lack of capacity, riverine flooding occurs when the river capacity is full and fills the floodplains. This type of flooding can impact multiple parts of a watershed besides the immediate area, specifically downstream where flooding can occur several days later and can be just as impactful as the original storm event. The damming of Goose Creek reduces the risk of riverine flooding downstream from the spillway; however, this increases the risk of flooding for properties along the reservoir.

Flash floods can occur due to heavy rainfall that causes a rapid surge in water levels in streams and rivers. Long periods of rain over large areas of land, such as during a hurricane or tropical storm, can cause steady but intense riverine flooding that can potentially last for several days. Common stormwater management practices, such as restoring riparian buffers, reducing the amount of impervious surfaces, and having proper building guidelines and setbacks from commonly flooded areas can help mitigate damage that riverine flooding can cause to properties and infrastructure.

Coastal Flooding

Coastal flooding occurs mainly due to abnormally large high tides and/or heavy rainfall in coastal communities. While this type of flooding does not impact as many people or as large of an area as the other types of flooding, coastal flooding has become increasingly more common due to rising sea levels.

Potential Impacts

Damage from flooding goes beyond the monetary value of the built environment but/and can have serious impacts on the natural environment, such as water pollution, erosion of streambanks, destruction of habitats and the displacement of wildlife. Many would believe that damage to a forest or a streambank is better than building or property damage, and while that is correct from an economic standpoint, the restoration of these environmental buffers is important for mitigating future flood events. The following are different environmental impacts that can be affected by flooding.

• Water Pollution and Water Quality

The quality of the surface and groundwater can be negatively affected by flood waters transporting pollutants such as debris, minerals, oils, trash, excess nutrients, industrial chemicals, etc. into streams, rivers, reservoirs, lakes, and aquifers.

• Debris

Large fast-moving volumes of water are able to pick up and transport larger, heavier, debris such as trash, rubber from tires, nails and other metals, lawn clippings or dead leaves, animal waste, and plastics, depositing them in streams and rivers and introducing foreign and possibly harmful objects into the natural ecosystem.

• Erosion