St. Johns River Water Management District St. Johns River Water Management District St. Johns River Water Management District St. Johns River Water Management District St. Johns River Water Management District St. Johns River Water Management District
St. Johns River Water Management District -

Water bodies, watersheds and storm water

Flooding and stormwater tools and terms to know

Flood-prone area

A flood-prone area is any land area susceptible to inundation by water from any source. The following are examples.

  • Floodplains are low-lying areas that are considered more susceptible to flooding than areas at higher elevations. Local, federal and state agencies draw floodplain boundaries based on past activities in the areas.
  • The 100-year floodplain designates a scope of flood that has a 1 percent chance of occurring in any given year. There is a 63.5 percent chance of a 100-year flood occurring over the course of 100 years.
  • The 50-year floodplain refers to sizeable areas that have a 2 percent chance of flooding in any given year.
  • Floodways are permanent channels composed of streams or other waterways, plus any adjacent floodplain areas. They must be kept clear in order to discharge a 100-year flood.

Stormwater treatment areas

Stormwater pond with aeration fountain and overflow intake

Stormwater pond with aeration fountain and overflow intake.

Stormwater treatment areas are either man-made or natural depressions that naturally enhance or improve water quality and control flooding. During heavy storms, up to and including 25-year storms, these areas hold rainwater long enough to protect downstream areas from flooding.

Water control structure

A water control structure is a man-made structure or work designed to control the flow of water. To prevent over-reliance on man-made processes, the district combines natural processes, like wetland restoration, with water control structures to protect property while preserving the natural health of an area.

Other water control methods

Aerial image of a spillway that controls levels between adjacent bodies of water

Spillways control levels between adjacent bodies of water.

  • Canals are artificial waterways or artificially improved rivers used for travel, shipping, drainage or irrigation. They can alleviate flooding effects by diverting floodwater from its natural path.
  • Dams are barriers constructed across waterways to control the flow or raise the level of water. Many dams work in conjunction with water control structures to regulate discharges.
  • Levees are generally lengthy, earthen embankments in place to prevent a water body from overflowing.
  • Pump stations are mechanical systems, diesel or electronically driven, used for the removal or lowering of waters from tracts of land on one side of a levee, discharging it into a water body on the other side of the levee. Pump stations are generally constructed on levees or elevated roads.
  • Spillways are gated structures that are operated to control water by carrying it through water control structures.
  • Weirs, sometimes built across streams, raise water levels or divert, measure or regulate flows.


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St. Johns River Water Management District
4049 Reid Street, Palatka, FL 32177
(800) 725-5922