FLOOD09107

• County: Statewide
• Basin: Statewide
• Title: Protecting Floodplain Resources
• Date: 6/1/1996
• Prepared For: US
• Prepared By: FEMA
• Floodplain - Doc Type: Floodplain Report/Masterplan

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II Understanding Floodplain Resources

What Are Floodplain Natural Resources?

The term "natural resources" often brings to mind products, such as timber or fossil
fuels that may be extracted from their natural environments and sold as commodities
for profit. But the natural values of floodplains are different; their value lies not in their
removal and sale, but in the functions that they perform within the floodplain environ-
ment. Floodplain natural resources include the soils, nutrients. water quality and quan-
tity, and diverse species of plants and animals that exist in the areas between the \vater's
edge and the higher ground adjoining flood-prone areas. These can be considered as
natural "infrastructure." But what is it about these resources that make a naturally
functioning floodplain so valuable? \Ve will begin the discussion with some basic
information about hO\v l100dplains are formed.

Rivers Slzape tlze Landscape. The formation of a !loodplain is intimately tied to the
adjacent river or stream, \vhich over long periods of time carves out the surface geology
of the landscape and deposits sand, silt. and other material (these deposits are referred to
as alluvium) that form rich soils. A typical river corridor has several features that result
from the geological and hydrological processes that form these landscapes (Figure 4).
The river channel meanders through the landscape, carving through the terrain and
depositing sediment as it goes. Sediment deposits and depressions around the water's
edge may result in the formation of wetlands, areas that are always or periodically
inundated with water.

The level areas bordering river channels are known as floodplains. These portions of
river valleys are frequently defined in terms of the likelihood of flooding in a given
year. Hence, the" I OO-year" flood is the flood having a 1 % chance of occurring during
any given year. (Similar definitions can be made for the 25- or 50-year !loods.) As the
river cuts downward it may leave terraces. formed from a time \vhen the river flowed
at higher elevations. These landforms are a part of the larger river corridor. and are
extremely important to the functioning of the floodplain ecosystem.

ll'ater.5heds - \Vhile the floodplain and its resources are the ccntcrpiece of discussion
for this guidebook, watersheds are central to the understanding and management of
resources in floodplains. A watershed includes the area of land that is drained by a
river and its tributaries. Different watersheds are separated from each other by ridges

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