|
<br />~
<br />
<br />!
<br />,
<br />I I -
<br />I .
<br />i ~
<br />
<br />, !
<br />i
<br />i
<br />I
<br />
<br />~
<br />r
<br />.
<br />
<br />I
<br />.
<br />
<br />!
<br />,
<br />t
<br />f
<br />"
<br />
<br />I
<br />I
<br />t
<br />I
<br />i
<br />I
<br />,
<br />i
<br />I
<br />,
<br />,
<br />I
<br />i .
<br />
<br />,
<br />, .
<br />
<br />~
<br />f
<br />
<br />Plum Creek near Castle Rock, Plate 47 shows a comparison of the computed PMF hydrograph
<br />peak with the historic flood peak for this site.
<br />
<br />
<br />A similar PMF analysis was performed for the 154,000 ft3/s measured at Louviers. The PMP values
<br />were adjusted for the larger 308-mi' basin The resulting PMF peak was 549,000 ft3/S, The historic
<br />peak is 28 percent of this estimate. Plate 48 shows a comparison of the computed PMF hydrograph
<br />peak with the historic flood peak for the 1965 event.
<br />
<br />40, Otter Creek and Tributary to Kinneman Creek, Central North Dakota
<br />
<br />A severe thunderstorm accompanied by much hail swept through southwest-central North Dakota
<br />on the afternoon of June 24, 1966. Rainfall of up to 13 in caused floods hi9her than any previously
<br />recorded in the area. The storm traveled in a northeasterly direction, with most of the rain occurring
<br />in approximately 2 h in anyone location, The severity of the storm was first computed by comparing
<br />the rainfall with charts in the US. Weather Bureau Technical Paper No. 40, which shows the
<br />100-yr 2-h precipitation to be about 3 in over the storm area. The areas of heaviest rainfall also
<br />accrued the most hail in this storm. At the town of Stanton, a reported one-third of the windows
<br />were shattered and many buildings were severely damaged. Large areas of crops were completely
<br />destroyed and many trees were defoliated.
<br />
<br />The flood area included parts of the Knife River, Square Butte Creek, Heart River Basins, and some
<br />unnamed small tributaries to the Missouri River. As far as could be determined, a flood of this
<br />magnitude had never occurred in this area. The maximum unit discharge determined was that of
<br />a Kinneman Creek tributary, with 3,040 ft3/s per mi' from a 2.45-mi' basin, On Otter Creek near
<br />Hanover, a peak discharge of 45,300 ft3/s was reported for a 42.9-mi' basin, This is more than
<br />1,000 ft3/s per mi2, the most intense runoff for this size basin ever recorded in the area, No loss
<br />of human life was reported during these events, although little warning was available in the mostly
<br />rural area [64].
<br />
<br />The PMP for this comparison study was derived using HMR 51-52 [3, 4] procedures, Because
<br />both the Kinneman Creek and Otter Creek drainage basins are within 10 mi of each other, only
<br />one set of readings from the HMR 51 maps was made. However, different adjustments for area
<br />size were made for these basins, Table 38 lists the adjusted PMP derived for these basins for
<br />different durations.
<br />
<br />The values in table 38 compare favorably with the maximum reported 2-h point rainfall value of
<br />approximately 13 in,
<br />
<br />Lag times were computed based on basin factors measured on USGS topographic maps combined
<br />with assumed C values of 1,5 for Otter Creek and 1.2 for the tributary to Kinneman Creek, These
<br />C values were chosen on the basis of the agricultural nature of the basins and the relatively flat
<br />stream slopes involved (S = 19 ft/mi on Otter Creek), The computed lag times for Otter Creek
<br />and the tributary are 4,39 and 1,08 h, respectively, Loss rates for both basins were assumed to
<br />be 0,25 in (initial) and 0,20 in/h (constant) These were judged to be appropriate for the relatively
<br />flat agricultural areas, No information on antecedent conditions in the immediate area of these
<br />
<br />87
<br />
|