ESCI409 Floods

Flood

A geologic hazard that occurs when the river stage is too high and exceeds the bankfull stage, causing water to spill out of the channel and onto the floodplain.

River stage

Also known as gauge height, it refers to how high the water is at a specific location along the river.

Bankfull stage

The height that the water needs to reach in order to fill the river to its banks.

Floodplain

The area adjacent to a river channel that is prone to flooding when the river stage exceeds the bankfull stage.

Bankfull discharge

The amount of water discharge required to fill a river to its banks.

Flood stage categories

Below flood (normal levels), action, minor, moderate, and major, which categorize the severity of a flood event.

River flooding factors

Excessive rainfall, snowmelt, severe storms, and hazardous blocking of the stream channel by trees or rock avalanches.

Magnitude of extreme events

The intensity of extreme events, such as floods, which is inversely proportional to how often they occur.

Flood recurrence interval

The time period between flood events, calculated using the formula R=(N+1)/M, where N is the number of years and M is the ranking.

Human impacts on flooding

Climate change, watershed development, and river corridor development, which can alter floodplains and increase the severity of floods.

Flood control: levees

Raised banks along a stream channel that can worsen floods by increasing flow downstream.

Flood control: dams

Structures that store river water, delaying its arrival downstream and potentially causing scour downstream.

Flood control: retention ponds

Ponds that trap surface water and sediments before they reach the water, delaying the arrival of water and allowing for infiltration and evaporation.

Netherlands "Room for the River" project

A project initiated in 2007 to mitigate severe river flood damage by creating more space for rivers to accommodate floodwaters.

Weeks Act

A legislation passed in 1911 that allows the federal government to purchase private land to protect the headlands of rivers in the eastern US.