|
<br />5. Cause of Floods.- Floods during the spring and summer of
<br />1951 in the Omaha District were at a minimum along the Missouri
<br />River, and, with the exception of four isolated conditions, were
<br />less than normal on its tributaries. At no point in the District
<br />on the Missouri River were the mean daily discharges in excess of
<br />150,000 cfs.
<br />
<br />6. In the latter part of March moderately heavy snow fell
<br />over the basins of the Big Sioux, Rock, Little Sioux, and Floyd
<br />Rivers, and over the upper portion of the Elkhorn River. On
<br />2,6 March 1951 temperatures rose to above 70~. in all these basins.
<br />This rise in temperature was accompanied by light1:,?:,moderate
<br />precipitation which, with the coinoident snowmelt, ca.Used)'.lQod-
<br />ing along the above streams. .
<br />
<br />7. During the spring and summer of 19S1, the,precipitation
<br />for all .months was heavy. However, due to the favorable " distribution
<br />of precipitation with time, losses were. high and runoff .~as relatively
<br />low. As a result only local flooding occurred.
<br />
<br />8. An intense storm occurred in the western part of the Omaha
<br />District on 2-3 August 1951. The runoff from this. storm caused
<br />severe floods in the Denver Area. 1sohyetal maps of the two main
<br />storm areas are appended hereto as Plates 7 and 8. A report on the
<br />storm is made in the following paragraphs.
<br />
<br />9. On 2 August 1951, a cold front, along the leading edge of
<br />a mass of continental polar air, moved into Colorado to the south-
<br />eastern part of the state. The flow aloft was southerly with.s
<br />trsjeQtory from the Gulf of Mexico, bringing in an ample supply of
<br />moisture at high levels. Surface dew points remained high, indicating
<br />a. plentiful moisture supply in the lower atmospMre..
<br />
<br />10. About noon, on 2 August 1951, cyclogenesis occurred in
<br />southeastern. Colorado, resulting in the formation of e. closed low
<br />in. that area. Northeast.winds on the north side of the low forced
<br />the air 'upslope over the foothills. and the front range, releasing
<br />the conditional instability of the warm moist air and resulting in
<br />a period of heavy rainfall over the area between Cheyenne, Wyoming,
<br />a.nd Trinidad, Colorado, and from the Continental Divide eastward
<br />some 50 to 70 miles. This situation oontinued through 3 August
<br />.1951, with the low center remaining in southeast Colorado, south-
<br />west ,Kansas, and the Oklahoma 'panhandle.
<br />
<br />11... .10 general, two storm centers resulted from the weather
<br />situation described above. The first occurred late on the 2nd and
<br />early on the 3rdsoutheast of Denver, with a 7-inch center near
<br />Kiowa, Colorado, and caused floods on West Bijou, ltiddle Bijou, and
<br />Bijou Creeks~ The second occurred on the evening of 3 August 1951,
<br />with a center..of over 12'inches, 6 miles southwest. of Bellevue,
<br />Colorado, arid caused severe flooding on Buckhorn Creek, Big Thompson
<br />River, Dry Creek, and the' Cache La Poudre River.
<br />
<br />2
<br />
|