FLOOD CONTROL
by Reason
McLucus
The following was written during the major flooding in the
nineties. I am posting it now without attempting to modify
it or review what I wrote then. I cannot quarantee that I still
agree with all of the proposals, but it's not an issue I'm interested
in dealing with right now. I am posting it now because the recent
flooding may cause an increased willingness of politicians
to develop better flood control measures.
The recent flooding along the Mississippi River and some its
tributaries demonstrates the need to change the flood control system
both upstream and downstream. Government cannot
prevent all flooding, but local, state, and federal governments can
adopt changes capable of reducing the amount of flood water and
controlling floods more effectively so that they don't
significantly damage property.
Flood experts explain concepts like 50-year floods or 100-year floods
in terms of the probability of heavy rain falling. However, runoff
rather than just the amount of rain determines the
degree of flooding.
Land use changes such as urban development and elimination of upstream
wet lands have gradually increased the portion of rainfall running off
the land into the Mississippi and its
tributaries. A 50-year rain today will produce more runoff than a
similar rain would have produced 50 years ago. Recent rains would have
produced some flooding this year without land
use changes, but the changes increased the level of flood waters.
Upstream flood control systems emphasize moving potential flood water
from the area quickly. This approach works well for the short term
flooding that results from one or two heavy
rains in a small area, but exacerbates downstream flooding during the
type of weather pattern that caused the flooding in the upper
Mississippi River basin. Rains falling on high waters
rushing from upstream can quickly raise the water above flood level in
downstream areas.
Upstream changes in the flood control system should emphasize
preventing any increase in storm runoffs entering the river system and
where possible reducing or controlling existing storm
runoffs so that the water doesn't create a threat of downstream
flooding. Downstream changes should emphasize controlling flood waters
by diverting them from developed property or
by increasing the area rivers can use to carry excess water, such as by
moving levees farther away from river beds.
The federal government should adopt a policy that prohibits development
or other changes in upstream wetlands that would reduce their ability
to hold water after rains. Repeated rains
can limit the value of wetlands, but any elimination of wetlands
increases storm runoff. Increasing the size of wetlands, other than by
eliminating artificial drainage systems, wouldn't be a
cost effective way to reduce flooding because wetlands often don't hold
enough water and because wetlands normally contain water except during
very dry periods.
Local governments should require developers to design their
developments to significantly reduce or control potential storm runoffs
that their developments would cause, especially runoffs
related to large parking lots. Control measures would at least need to
temporarily hold runoffs during periods of heavy rains and release the
water only after stream levels have dropped to
near normal levels. Developers will complain about increased costs, but
they should assume such costs rather than force residents downstream to
assume a higher risk of flood damage.
Commercial developers could reduce runoff from buildings and large
parking lots by constructing underground catch basins that could be
pumped out when the threat of flooding had
eased. Residential developers could dig a hole on each lot, fill it
with rocks, cover it with soil, and slope the land so that much of the
runoff would flow to the area of the hole. This
approach might increase the threat of water getting into basements in
the development, but why should they have dry basements at the expense
of causing someone downstream to have a
wet basement.
Development regulations could take the form of requiring that new
developments not create any increased risk of flooding of other
developed areas, including those far downstream. Such
regulations might take a form similar to that used by some cities to
prevent new buildings taken as a group from reducing the amount of open
space. For example, some cities have
regulations that limit the height of new buildings to 20 stories, but
allow a developer wanting to construct a 30-story building to purchase
the rights to the extra 10 stories from someone
who only wants to construct a 10-story building.
Flood control regulations could allow a developer to compensate for new
storm runoff by reducing existing runoff from some other source. For
example, a developer might pay to contour
area farms to cause any runoff to flow into a pond constructed by the
developer. Farmers would be able to use pond water later to irrigate
their crops during dry periods.
In rapidly developing areas, developers might combine their funds to
pay for widening the stream or river that drains the area of their
developments. Widening a river, by moving its banks
away from the normal water line, allows it to carry more runoff without
raising the level of the water higher than it would otherwise have
risen. A community wishing to encourage new
developments might widen the river in advance.
Periodically dredging smaller upstream rivers in urban areas,
especially those that only carry large amounts of water during periods
of heavy rains, would allow them to carry more water
reducing the risk of both local and downstream floods. Water flows down
hill with a velocity that depends on the change in elevation from one
point to another. Storm runoff carries dirt
and debris into rivers where it can raise the level of the river bed.
As sand and dirt build up in a river the elevation of its bed increases
causing flood water to flow downstream at a higher
velocity.
Reducing the elevation of the river bed would allow the river to hold
more water during dry periods, for possible recreational use, and carry
more water during wet periods. The increased
difference in elevation between the river bottom and city streets would
allow faster drainage of storm runoff. The reduced relative difference
in elevation between upstream and
downstream areas would reduce the threat of downstream flooding because
water would flow downstream at a lower velocity.
State and federal governments should establish a "flood lease" program
for farm land that would compensate farmers for allowing temporary use
of their land to store flood waters. The
government would construct some type of levee around farm buildings if
necessary to protect them from flood waters. This program could also
apply to "wetland" areas that are
sometimes dry enough to be used for agriculture.
Compensation would include paying farmers for crops they have planted
as well as crops they would be unable to plant because of the water.
Government would absorb any costs
needed to return the land to usable condition and design the system to
divert flood water onto farmland in a way that minimized damage to the
land.
Developers could choose to pay a tax(during periods of flooding) into
the flood lease program to cover the costs associated with the need to
allow flood water to cover more land. In this
situation, government might use dams, pumps, or other means to divert
river water to flood leased farm land.
In the short run floods prevent farmers from planting or harvesting
crops. However, in the long run floods can benefit farms by depositing
top soil. Floods have been responsible for the
richness of the soil in "river bottom land". Small dams used in the
flood lease could also be used to maintain higher water levels in
rivers to provide water for irrigation during dry periods.
The federal government should consider establishing a system of
diversion canals in upstream areas to divert water from river basins
with flood problems to drier basins. These canals
would generally connect streams that are close to each other, but which
feed different rivers. The system should be able to shift water from
stream to stream through several different river
basins possibly shifting water as far as from North Dakota to Texas.
This system wouldn't simply shift flood waters. The system would also
shift upstream water away from overflowing reservoirs to reduce the
need to release water into areas with flood
problems. The need to release excess water from flood control dams
played a major role in the flooding in northeastern Kansas as well as
increasing the flood problem along the Missouri
River.
Construction of a system of pipelines connecting major rivers and
reservoirs between the Rockies and Appalachians would also allow
shifting water away from flood areas. Pipelines
could move water over, or through, hills between nearby rivers.
Such a system of canals and pipelines in eastern Kansas and western
Missouri could have transferred some of the flood water from west of
Kansas City to the Arkansas River basin
which empties into the Mississippi in southern Arkansas. A similar
system in Illinois could have diverted flood water from the upper
Mississippi into the Ohio River basin or into one of the
tributaries to the Great Lakes.
The federal government should construct new flood control dams,
preferably in hilly areas that are poorly suited for development or
agricultural use to avoid the need to take people's
homes or farms. Hilly areas have much higher runoff rates than flat
areas and thus contribute more to flooding. New dams wouldn't have to
be large or hold water for long periods. Water
could be let out slowly as soon as water levels downstream had fallen
to normal levels.
Government could use canals and dams to divert and store water in areas
where it would be most likely to eventually replenish underground
aquifers. One of the primary faults of current
flood control philosophies is the failure to recognize that what is
considered excess water during periods of heavy rain could be stored to
offset the impact of a subsequent drought.
Rain seldom falls at the same rate it is needed. We either get too much
or too little. Designing the flood control system to retain "flood"
water for later use or moving such water to areas of
drought would reduce the potential for water shortages. Manual
desalinization of ocean water is very expensive. The planetary weather
system performs this process for free.
The most important change downstream would involve giving Old Man River
more room to "keep rolling along". Where possible government should
move levees farther back from the
river, possibly moving them as much as half a mile or more. The land
between the levee and the river could be set aside for recreation or
used for agriculture during drier periods. Levees
might be constructed to protect only developed areas and divert flood
water onto land covered by the flood lease program.
Rebuilding levees at their current locations, except in heavily
developed areas, would be a waste of money because we already know
levees at these locations can fail. New levees should
be built high enough and far enough away from the river so the volume
of water associated with recent floods would have only risen halfway up
the levee. Good engineers always attempt
to allow for a margin of error in new construction. Moving levees
farther from the river would provide a better margin of error for
dealing with future high water periods.
Government should condemn damaged buildings and land that would be
inside the new levees and pay owners what their property was worth
prior to the flooding. Owners of property in
areas where the levees held but required sand bags to keep the river
inside might also be willing to sell under such terms. The recent
flooding will reduce the market value of property near
rivers until people forget this year's flood.
Government should construct canals or pipelines to divert flood water
around heavily developed areas where moving levees would be impractical.
Local governments should prohibit new development near levees to allow
using bulldozers to widen levees when heavy flooding is possible.
Engineers need to develop a sturdier design
for levees possibly using thick layers of non-biodegradable plastic
within the levees to reduce passage of water through them.
Moving entire towns should only be done as a last resort. The cost of
moving a town includes reestablishing its economy as well as moving its
buildings and replacing streets, utilities, and
sewage treatment plants. In some cases a town's economy may be so
strongly associated with its location that attempting to move the town
would destroy its economy.
None of the above measures would totally prevent future floods by
themselves. However, together they would reduce the potential for
flooding and facilitate control of any flooding that
did occur. Even upstream measures that only reduced runoff by a few
thousand cubic feet apiece would significantly reduce downstream
flooding if used by enough different communities.
Floods differ from the other major Midwestern calamity, tornadoes. The
latter hit at random and seldom strike the same location twice. Floods
occur at irregular intervals, but they always
strike the same areas. Our technology can do nothing to prevent
tornadoes, but we can do something to control flooding and reduce the
damages it can cause.
Flood control measures can be expensive, but replacing flood losses can
also be expensive. The economic benefits of using flood water would
offset costs associated with some of the
above measures such as diversion canals and pipelines.
Since this was written there has been concern about declining water
levels in the Great Lakes. Diverting water from the Mississippi River
Basin northeast of St. Louis to streams emptying
into the Great Lakes could reverse this trend. Part of this diversion
would directly involve flood waters. Shifting water when areas to the
west are having excessive rain would also help
relieve flooding on the Mississippi even though the streams on the
northeast would only carry normal levels of water.
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