Using Multi-Objective Management to Reduce Flood Losses in Your

water is running off the land into Small Creek and human development helps it get
there even faster.
The amount of water that used to come downstream once every 20 or 30
years now comes down about every 10 years. Because of the buildings, roads, and
small bridge openings, there is less room in the floodplain to carry the extra
water. Flood waters rise higher, cover a larger area, and flood farmlands, roads,
utilities, buildings, and other development that had never been flooded before.
In addition, the channel banks are exposed to faster-moving waters and
have become more susceptible to erosion. Higher flood waters running across bare
construction sites and tilled farm lands cause more erosion and carry sediment into
the streams and lakes.
Pollutants from lawn fertilizers, pesticides, farm chemicals, street surfaces,
and industrial areas are also delivered to the rivers and lakes. Many beneficial
plants and animals are harmed or exterminated by these pollutants and sediments.
The original species are being replaced by different ones that may not be desirable
or beneficial to the rivers, lakes, or environment.
It can be seen that there is a close relationship between natural flooding,
development in the floodplain, and what happens in the rest of the watershed. As
a general rule, the smaller the watershed, the more quickly it reacts to changes.
As one experienced floodplain manager has put it, “You don’t solve flood
problems by working at the bottom of the hill.” You must look at the whole
picture−where the water comes from and where it goes.
Coastal Flooding
Areas along the seashore or lakeshores are prone to coastal flooding and erosion.
Coastal flooding happens during storms that drive water onto adjacent land. These
can be hurricanes, “nor’easters,” or tropical storms, but even a severe winter
storm or thunderstorm can cause flooding.
Flooding
Coastal flooding or storm surge is caused by high water from wind and the air
pressure differences that accompany a storm. A storm surge is not a tidal wave or
sudden rush of water; it is more of a gradual increase in water level. While this
may sound harmless, a surge can be as high as 20 feet above normal water levels,
flooding normally dry areas far inland. Most of the damage and deaths caused by
a hurricane are the result of flooding, not high winds.
Like communities with riverine flooding, most coastal communities
have a Flood Insurance Rate Map that shows their base floodplains. The maps
also show the parts of the floodplain subject to high damage potential from waves,
known as velocity zones.
Another form of coastal flooding may or may not be shown on the
map. A tsunami is a wave that is caused by an earthquake under the ocean.
Tsunamis are not tidal waves nor are they related to storms, because they can
happen on a clear day as a result of seismic activity hundreds of miles away. They
can produce flood levels far above the mapped base floodplain. In this country,
they are most common on the Pacific coast, especially in Alaska, Hawaii, and the
Northwest.
8