|
<br />E20 FLQQDS OF 1965 IN THE' 'lL'ITTED STATES
<br />
<br />FLOODS OF MARCH-MAY IN: 'IHE UPPER MISSISSIPPI RIVER BASIN
<br />
<br />Flaads af Ma~ch-M:ay in the upper Mississippi River basin were
<br />th~ ma~t. devasting in the histaryaf the area. Five States-Minnesata.
<br />Wlscansm, Iaw~, ~lli;>a~, ~d Missauri~were affected (fig, 10). Peak
<br />sta;ges an the MISSISSlppI RIver were higher than previaus maximums
<br />af recard thraughaut the 680-mile reach .fram Fart Ripley, Minn.,
<br />. to Saverton, Mo.., and were fram 3 to. 4 feet higher than previaus maxi-
<br />mums ~ram the mauth af the~innesataRiver at St, Paul, Minn., to.
<br />~uscatlUe, ,Iawa: Recard-breaking floods occurred an the Minnesata
<br />RI ver ~d .It~ tr:bu~aries ~am Mankata to. the mauth and Qn many
<br />ather MISSISSIPPI River tnbutaries in Minnesata and Wisconsin
<br />A silp'~fic.ant, fe~ture af the flood was the great valume af r';"aff.
<br />The MI",!IS~IppI ~Iver remained abave f1aod stage far almost a manth.
<br />I~ the MiSSISSIppI RIver fram Rayalton, Minn, (25 miles south af Fort
<br />R;pley), to. the mouth of the Missauri River and in the Minnesota
<br />RIver fram Mankato to the mauth, the volume af runoff was mare than
<br />25 percent greater than that af any previausly recorded f1aod.
<br />, Floading occi1rre~ in mast of the upper Mississippi River basin dur-
<br />. ;ng two. separate perIOds almast a month apart. During the first period,
<br />1U early March, f1aods occurred in sautheastern Minnesota, northeast-
<br />
<br />SU~RY QF FLQQDS
<br />
<br />E21-
<br />
<br />103'
<br />
<br />".
<br />
<br />".
<br />
<br />".
<br />
<br />'"
<br />
<br />ern Iawa, and sauthwestern Wiscansin. Warm temperatures in late
<br />February and early March melted the winter accumulatian of snow.
<br />The runoff fram snowmelt and fram rainfall, which exceeded 2 inches
<br />in the first 3 days af March" caused severe f1aading in the Zumbro. and
<br />Root River basins in Minnesata and in the Cedar River basin in Min-
<br />nesota and Iowa.
<br />During the secand f1aod periad, fram early April and into May,
<br />f1aods occurred in the entire upper Mississippi River basin. They were
<br />caused by the rapid melting of the winter accumulatian af snaw in
<br />narthern Minnesata and Wiscansin and af the March accumulation of
<br />snow in narthern Iowa, southern Minnesata, and Wiscansin. The water
<br />equivalent af snaw ranged up to 11 inches, Warm temperatures moved
<br />narthward into Minnesota during the last days in March, and nighttime
<br />temperatures remained abave freezing. Up to 3 inches af rainfall in
<br />early April accelerated the snawmelt .and increased runaff. A severely
<br />cald winter had cauSed deep frast penetration, and consequently much
<br />af the rain and snawmelt ran aff. Many af the streams in the secand
<br />f1aod periad were the same as were invalved in the first f1aad period.
<br />Fifteen lives were lost, and aver 700 persans were injured fram the
<br />f1aads and associated events, Property damage was estimated at $160
<br />millian,
<br />These floods are described in detail by Andersan and Burmeister
<br />(1970). The repart summarizes peak stages and discharges at 333 sites
<br />and presents the previaus maximum at sites when such data are avall-
<br />..ble. Recurrence intervals are tabulated far many sites, Flood damages
<br />are discussed, and damage figures are tabulated.
<br />
<br />49'r-
<br />
<br />
<br />NE8RASI(
<br />
<br />----
<br />
<br />".
<br />
<br />~ 100 0
<br />Flood Area I I I
<br />
<br />'~,
<br />'\
<br />L___u___ ')../
<br />
<br />FLOODS OF. APRIL IN THE LITTLE SIOUX RIVER BASIN, IOWA
<br />
<br />After :HABI..A.N H. SCHWOB (1966)
<br />
<br />A cambination of snawmelt and rain in northwestern Iawa in early
<br />April caused severe flaading in the Little Sioux River basin (fig, 11).
<br />This flood was the greatest of record along the lower part af the
<br />Little Sioux River.
<br />Canditians leading to. the severity af the flood were heavy snawfall,
<br />deep frost penetratian, and a sudden rise af temperature accompanied
<br />by rain. A snaw survey during March 26-29 showed a water equiva-
<br />lent of 6-8 inches at Spirit Lake, 2-3 inches in the area fram Spencer
<br />to Cherokee, and less than 1 inch in the southern part af the basin.
<br />Warmer temperatures and rainfall af about 2 inches in the basin abave
<br />Cherokee during April 3-6 accelerated the melting. The frazen ground
<br />prevented infi]tratian, and the resulting runaff praduced maximum
<br />discharge af recard in the Little Sioux River dawnstream fram Gillett
<br />Grove.
<br />
<br />1
<br />"''''0 ;-..
<br />..---_h ~l
<br />.\~
<br />~
<br />.'"
<br />, .~
<br />f------- ---._-- '\ -
<br />i
<br />! K NSAS
<br />
<br />". ..-0------- _______u
<br />
<br />i
<br />i
<br />t---
<br />i
<br />41'1.
<br />
<br />100 200 300 400 MilES
<br />I 1 j
<br />
<br />FIGURE lO.-Flood area, Mareh-May in the Upper Mississippi River basin.
<br />
|