1997-06-13_REVISION - M1981302 ‎(61)‎

• Permit No: M1981302
• IBM Index Class Name: Revision
• Doc Date: 6/13/1997
• Doc Name: CITY OF BOULDER EXHIBIT L
• Type & Sequence: AM2
• Media Type: D
• Archive: No

Wetland Hydrology owners considered before draining wedands, flood
The Minois study found that wetlands can affect flood protection and drainage provided by federal proj-
ects had the largest impact.This incentive to farm
heights in two ways: by intercepting and storing the floodplain was not taken into consideration in
water and by slowing the rate at wfuch water reaches making the decision to build a flood control project "
the stream. Although the hydrologic response may
vary, there is one basic truth: streams adjacent to a
wedand will have very different flow characteristics Nonstructural Alternatives
from streams denuded of riparian vegetation.° Like Soldiers Grove, several communities in differ-
Other researchers have found that peak flows ent parts of die country have used nonstructural al-
increase substantially after adjacent wetlands are ternatives to control flooding.These projects gener-
drained. One researcher studying the effect of wet- ally involve returning the floodplain to its natural
lands losses on streamflows in Wisconsin found that state, and in some cases restoring the associated wet-
flood peaks might be as much as 80 percent lower in lands. A project similar to Soldiers Grove used the
basins with significant lake and wetland area.' Oth- natural flood control functions of 8,500 acres of wet-
ers have come to similar conclusions, finding that lands along the upper Charles River in Massachu-
the hydrologic detention function of wedands re- setts.The cost of buying full tide or easements to
duces the size of flood pulses.8 the wedands was S10 million, far less than the $100
Although wetlands types ear3,, the most com- million needed to build upstream clams and levees.
mon wetlands in the Midwest are depressions that The wetlands store more than 50,000 acre-feet of
temporarily detain water, known as shallow basins water, as much as a medium-sized reser oir. A U.S.
or prairie potholes. Losing these wedands has greadv Army Corps final report on the project found that
increased the rate at which water moves off the land- "nature has already provided the least-cost solution
scape and into the floodplain.' to future flooding in the form of extensive wetlands
that moderate extreme highs and lows in stream
The Effect of Levees flow. Rather than attempt to improve on this natu-
ral protection mechanism, it is both prudent and
By confining the water to the channel and prevent- economical to leave the hydrologic regime estab-
ing it from spreading over the floodplain, levees in- lished over the millennia undisturbed.""
crease flood heights.1°A study of the 1973 flood on The ciw of Littleton, Colorado, established a
the Mississippi attributed higher flood stages to a 625-acre floodplain park and natural area along 2.5
combination of levees and navigation projects. Com- miles of the South Plate River, where water can be
paring the 1973 flood with the 1908 flood, the study absorbed and temporarily stored during big floods.
found that while the two floods had nearly the same Officials in Boulder, Colorado, created a five-mile
volume of water, the 1973 flood crest was eight feet recreational greemvav and bike path along Boulder
higher." A study by the U.S. Army Corps indicates Creek. In Boulder, wedands have been created or
that the record 1844 flood would now crest about restored to temporarily absorb and snore stormwater.
ten feet higher at Boonville, Missouri, and 12 feet Meanwhile, the trout'fishery has been restored and
higher at Hermann, Dlissoun. the park has become a central meeting point for the
Before channelization, the Mississippi eroded its community. In a siniihr project, the city of Tulsa,
bottom and banks during flood peaks, making room Oklahoma, after a series of floods,developed a green-
for floodwaters by increasing the storage capacity,of way plan for Mingo Creek that links parks and trails
the channel and by using the floodplain as a natural with multipurpose flood control structures.
reservoir." By the time the Great Flood of 1993 ar-
rived, the river channel had lost about one-third of The Future of Flood Control
its volume to channelization, sedimentation, and
other effects of development, and the floodplain The current groundswell of support for relocation
had been replaced by farms and cut off from the and wedands restoration has not gone unnoticed. In
river by a canyon of sand and gravel. August, the Clinton Administration instructed the
In addition to the damage associated with the Corps and other relevant federal agencies to consider
levees themselves, federal flood control projects "nonstructural alternatives and design modifications
have encouraged landowners to drain wetlands. that could provide greater local benefits of flood
Two economists have found that nearly one-third control, reduction of future potential flood damages
of the wedands lost in the Mississippi Valley were to the applicant and adjacent upstream and down-
lost because of private decisions induced by federal stream localities, lower long-term costs to the fed-
flood control projects. Construction of flood con- eral government, and natural resource protection.""
trol and drainage projects led to a higher rate of The administration has created several task
wedands conversion than would have occurred, as forces, including one specifically focused on the I
these projects allowed farming in areas not pre- levee rebuilding issue. However, the guidance the
viously suitable. In fact, of all the factors that land- administration has issued does not go far enough to
26 Urban Land • il-larrb 1994