Using Multi-Objective Management to Reduce Flood Losses in Your

storage basin. After a flood peaks, water is released or pumped out at a rate that
can be handled downstream. Reservoirs are most efficient in deep valleys with
more room to store water, or on smaller rivers where there is less water to store.
A diversion is a new channel, overflow weir, or tunnel that sends flood
waters to a different location, thereby reducing flooding along a watercourse.
During normal flows, the water stays in the old channel. During flood flows, the
stream spills over to the diversion channel or tunnel, which carries the excess
water to a lake or another river.
Reservoirs and diversions should be implemented after a thorough
watershed analysis that identifies the most effective and efficient location for one
or more structures and to ensure that they will not increase flooding somewhere
else. Because they involve more than one community and are so expensive, they
are typically implemented with the help of state or federal agencies, such as the
U.S. Army Corps of Engineers or the Natural Resources Conservation Service.
To Find Out More > > The U.S. Army Corps of Engineers, the Natural
Resources Conservation Service, and state natural or water resources agencies can
provide information on construction criteria and funding assistance. In western
states, the Bureau of Reclamation can help.
Channel and drainage modifications
When the conveyance of a channel, drainage ditch, or storm sewer is increased,
more water can be carried away. However, care must be taken to not increase a
flooding problem downstream.
Channel modifications include making a channel wider, deeper,
smoother, or straighter. Some smaller channels can be lined with concrete or even
enclosed in underground pipes.
Dredging is one form of channel modification. It is often too expensive to
be practical because the dredged material must be disposed of somewhere and the
stream will usually fill back up with sediment in a few years. Dredging is usually
undertaken only on larger rivers to maintain a navigation channel.
Drainage modifications include human-made ditches and storm sewers
that help drain areas where the surface drainage system is inadequate or where
underground drainageways are safer or more attractive than above-ground ones.
Drainage and storm sewer projects usually are designed to carry the runoff from
smaller, more frequent storms. They are particularly appropriate for depressions
and low spots that will not drain naturally.
Storm sewer improvements can increase the sewer’s capacity or prevent
overloading from flooding in certain areas. These measures include installing new
sewers, enlarging pipes, modifying storm sewer inlets, and preventing back flow.
Street modifications may help because streets in many developments are
used as part of the drainage system to convey runoff to a receiving sewer, ditch,
or stream. Streets can also be designed to store water from larger, less frequent
storms. Allowing water to stand in the streets and then draining them slowly can
be more effective and less expensive than building bigger sewers and ditches.
To Find Out More > > The U.S. Army Corps of Engineers and the Natural
Resources Conservation Service can provide information on projects for larger
channels. Public works departments and engineers are the best sources of
information on local drainage and sewer projects.
24