Natural & Beneficial Functions

Jefferson County Floodplains header

Floodplains in Jefferson County are the lower areas adjacent to rivers, lakes, and creeks that are periodically flooded at intervals of varying frequency. Floodplains are important components of their respective watersheds. Floodplains are hydrologically important, environmentally sensitive and ecologically productive areas within a watershed that perform many natural functions.

Floodplains contain a wealth of cultural and natural resources that are of enormous value to society. Riverine floodplains, such as the floodplains found in Jefferson County, vary in steepness, width, stream flow, sediment deposition and erosive characteristics. The natural functions that are associated with a particular floodplain depend in part on its location within this system. The frequency, duration and extent of flood events will also vary among different types of floodplains, dependent upon their hydrology, geology, and amount of floodplain development.

Floodplains are formed and modified by the dynamics of stream and river migration and periodic flooding. Although many riverine floodplains usually flood during the spring storms, they can also experience multiple flood events within the same year with duration varying from hours to days. Periodic flooding of riverine systems and the related processes of erosion and deposition determine, to a considerable extent, the shape of the floodplain; the depth and composition of soils; the type and density of vegetation; presence and extent of wetlands; richness and diversity of wildlife habitats; and depth to the groundwater.

The major flood conveyance component of the floodplain is the floodway. The National Flood Insurance Program defines the floodway as that area of the watercourse and adjacent floodplain necessary to carry the base flood without increasing the water surface elevation more than a designated amount (generally one foot). The base flood is the flood that has a one percent chance of being equaled or exceeded in a given year. Communities are required to prohibit development within the floodway that would cause an increase in flood heights. This requirement has the effect of limiting development in floodways that in turn helps to maintain some of the floodplain’s most important natural resources and functions.

There are a number of walking paths and bike paths throughout many of the floodplains in Jefferson County. These paths provide an opportunity for out citizens to enjoy the vegetation and wildlife that thrives in our floodplains.