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<br />at 5,000 cubic feet per second,
<br />
<br />Flood of 2-7 June 1921, Little is known of this flood except that it produced the highest peak discharge ever
<br />recorded at the Oradell gage, A discharge of 2,500 d,s, was recorded on 6 June, Rainfall totalE,d 3,36 inches
<br />at Boulder through a period of 2-7 June,
<br />
<br />Flood of 3-10 June 1923, This storm centered over the high plains east of the mountains. Rainfall at
<br />Boulder totaled 3,S4 inches through a period of 3,10 June with 2,39 inches of the total precipitation falling on
<br />9 June, Combined flows from Boulder, South Bouldel', and Bear Canyon Creeks produced flooding
<br />downstream of Valmont
<br />
<br />Flood of 4 Seotember 1938. A large storm produced general rains over all of Eastern Colorado, The
<br />largest amounts of precip~ation occurred in the mountains where over 6 inches was reported west of Eldorado
<br />Springs, Boulder reported 3.62 inches of precipitation from :31 August to 4 September with 2,3,! inches falling
<br />on 2 September. Eldorado Springs, located in the South Boulder Creek basin, had 4.42 inches of rainfall.
<br />Approximately SO percent of the total precipitation falling in tile South Boulder Creek basin fell in the late
<br />afternoon and evening of 2 September. The resulting flood on South Boulder Creek had an estimated peak
<br />discharge of 7,390 d,s, at the Eldorado Springs gaging station, The peak gradually subsided as the flood
<br />moved downstream, maximum discharge of 4,410 c.f,s, occurred near the mouth of Boulder Creek at noon
<br />on 3 Septem ber. Several buildings 'n Eldorado springs were destroyed as a result of erosion around their
<br />foundations, Numerous bridges were destroyed and the South Boulder Creek valley from Eldoraclo Springs
<br />to Boulder Creek and down Boulder Creek to the St Vrain Creek was described by local newspapers as being
<br />in shambles, This flood is the highest recorded flood on the South Boulder Creek,
<br />
<br />Flood of 6-S May 1969, This flood was also the result of long duration rainfall. Precipitation was heaviest
<br />in the mountains, part of which fell as snow. In the Boulder and South Boulder Creek basins the rainfall
<br />continued at a moderate rate for nearly 4 days, Total precipitation for the storm amounted to 7,60 inches at
<br />Boulder and 9.34 inches at the Boulder Hydroelectric Plant located about 3 miles up the canyon from Boulder,
<br />Precip~ation amounts totaled 8.11 inc~les at Eldorado Sprin!Js and 10,05 inches at Gross Reservoir on South
<br />Boulder Creek. Peak flooding occurred on the 7th of May on both Boulder and South Boulder Creeks, The
<br />gaging station at Orodell recorded a peak discharge of only 1,220 cubic feet per second, In Boulder, however,
<br />local inflow increased the Boulder Creek peak to an estimated 3,000 cubic feet per second, The peak
<br />discharge on South Boulder at Eldorado Springs was 1,690 cubic feet per second, Flooding below the
<br />confluence of these two streams extended over large portions of the flood plain,
<br />
<br />4,1.9 LEFT HAND CREEK
<br />
<br />Flood History, Left-Hand Creek floods are most frequently produced by intense rainfall during
<br />thunderstorms. Snowmelt runoff combined with runoff from spring rains of long duration also produce high
<br />streamflows, The former are characterized by a high peak clischarge of short duration. The latter usually have
<br />lesser peak discharges and are of longer duration, Because of the steep stream slopes, the flood peaks travel
<br />down the valley with such rapidity that little time is available to warm or evacuate residents, A general
<br />description of the last four major floods occurring on Left-Hand Creek is provided to illustrate the flood potential.
<br />Heavy damages were not recorded for these floods since the flood plain was rural in nature,
<br />
<br />Colorado Flood
<br />Hydrology Manual
<br />
<br />4.11
<br />
<br />DRAFT
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