FLOOD09998

• County: Statewide
• Basin: Statewide
• Title: Annual Report-1998 Tributary Reservoir Regulation Activities
• Date: 12/1/1998
• Prepared For: Missouri River Division
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Floodplain Report/Masterplan

advance, particularly in Day County. By mid-1998, the lakes posed a credible
threat to the town of Waubay and had already destroyed some homes along Blue
Dog Lake in the northern part of the town. An advanced measures levee was
constructed along the western edge of the town in July to protect it from Little
Rush Lake.

Lake elevation increases came quickly from storms in the spring of 1998.
Elevations rose from 1801.34 feet above mean sea level Ift-msll on April 14, 1998
to 1803.0 ft-msl by June 22, 1998. This followed a rise from 1799.98 ft-msl on
November 14, 1997 to the April reading of 1801.34 ft-msJ. A summary of spring
rainstorms and their impact on lake elevation are listed in Table 4 as follows:

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TABLE 4
RESPONSE OF WAUBAY LAKE, SO TO SPRING RAINFALL

Reported Waubay Lake
Date Rainfall Rise
26-Apr-98 2.95" 0.47'
1 2-May-98 3.80" 0.70'
12-Jun-98 1.50" 0.20'

b. Significant Weather Events, August 1997 through July 1998.

(1) Late Summer 1997.

In early August 1 997, a strong monsoonal flow continued to support flash
flooding near the Front Range of the Rockies. A persistent upper-level system over
the central Rockies acted as a conveyer belt to move tropical moisture northward
into the high plains, where daily heating and upslope winds combined to produce
powerful thunderstorms nearly every afternoon. The result was heavy rains and
hail on a daily basis, somewhere in the high plains or foothills.

High water also continued on the Missouri River in western North Dakota,
with gage heights at Williston about 3 feet above flood stage due to heavy rain in
July and high releases from Ft. Peck Dam, High releases from the other Missouri
Mainstem Dams also resulted in high within-bank stages on the Missouri River
during late summer. Reservoirs near Hot Springs, South Dakota, remained near
record pool elevations on August 1st following the 8.05 inches of rain recorded at
Hot Springs in the month of July.

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Flash flooding occurred on Box Elder Creek near Nemo, South Dakota, on
August 1 st, as a stationary thunderstorm dumped very heavy rain over parts of the
Black Hills. More flash flooding was reported in the Nebraska Panhandle and the

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