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FLOOD00533
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Last modified
11/23/2009 1:21:44 PM
Creation date
10/4/2006 9:20:45 PM
Metadata
Fields
Template:
Floodplain Documents
Designation Number
265
County
Boulder
Community
Unincorporated Boulder County
Stream Name
South Boulder Creek
Title
Flood Hazard Area Delineation - South Boulder Creek
Date
7/1/1986
Designation Date
11/1/1986
Floodplain - Doc Type
Floodplain Report/Masterplan
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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />J <br />I <br />I <br />I <br />I <br /> <br />The following section briefly describes some of the major storm events that have <br />caused flooding on South Boulder Creek (Reference 2). Due to the relatively <br />undevelop~d nature of the South Boulder Creek basin, information and observations <br />related to major flood events is somewhat lacking in comparison to the adjacent, <br />more heavily developed Boulder Creek floodplain. <br /> <br />crop losses were suffered on lands outside the floodplain which were dependent on <br />irrigation diversions from Boulder Creek. <br /> <br />31 August - 4 September, 1938 <br /> <br />FLOOD of 29 May - 2 June, 1894 <br /> <br />This storm produced general rains over all of eastern Colorado. The largest <br />amounts of precipitation occurred in the mountains where more than 6 inches was <br />reported west of Eldorado Springs. Eldorado Springs recorded 4.42 inches of <br />rainfall. Approximately 80 percent of the total precipitation falling in the <br />South Boulder Creek basin fell in the late afternoon and evening of September <br />2nd. The resulting flood, with a peak discharge of 7,390 cfs passed through <br />Eldorado Springs at 10:00 p.m. on September 2nd. The resort community of <br />Eldorado Springs suffered heavy damage and numerous buildings were destroyed when <br />flood waters eroded their foundations. The valley from Eldorado Springs to <br />Boulder Creek and down Boulder Creek to St. Vrain Creek was in shambles. This <br />flood is the highest recorded flood on South Boulder Creek. <br /> <br />Heavy ra i ns fe 11 over the mounta i ns extend i ng from the Co 1 orado-Wyomi ng border <br />southward into the Republican and Arkansas River basins. Rainfall over the <br />Boulder and South Boulder Creek basins was particularly heavy. Rainfall records <br />for a 96-hour period ending at 3 a.m. on 2 June, 1894 indicate that the mountain <br />drainage area received from 4.5 to 6.0 inches of precipitation. Rainfall amounts <br />over the high plains gradually decreased from west to east and varied from 5 <br />inches at Boulder to approximately 2.5 inches at the mouth of Boulder Creek. The <br />mountain rainfall combined with the snowmelt runoff produced the greatest flood <br />known at Boulder, inundating the valley during the night of 30 May, 1894. <br />Buildings, bridges, roads, and railroads were washed away. Computations made 18 <br />years later produced estimates of the peak discharge on Boulder Creek in Boulder <br />that ranged from 9,000 cubic feet per second to 13,600 cubic feet per second, <br />The Eldorado Springs stream gaging station was not functioning during this flood <br />event. <br /> <br />4-8 May 1969 <br /> <br />In Boulder, floodwaters covered the entire area between Water Street (Canyon <br />Boulevard) and University Hill to depths as great as ei9ht feet. Every bridge in <br />Boulder and a number of residences were swept away. Other types of damage <br />included commercial establishments, pUblic utilities, railroad property, roads <br />and streets, and irrigation structures. Many people were trapped in their homes <br />and had to be rescued. Only one life was lost; this was due, in part, to the <br />flood's slow onset. <br /> <br />Flooding in May of 1969 resulted from a long duration general storm. Runoff <br />resulted from a combination of rainfall and snowmelt, with the heaviest preci- <br />pitation reported in the mountains. Rainfall continued at a moderate rate for <br />nearly four days. Total precipitation for the storm amounted to 7.60 inches at <br />Boulder and 9.34 inches at the Boulder Hydroelectric Plant on Boulder Creek <br />located about 3 miles up the canyon from Boulder. Precipitation amounts totalled <br />8.11 inches at Eldorado Springs and 10.05 inches at Gross Reservoir on South <br />Boulder Creek. Peak flooding occurred on the 7th of May at Boulder and Eldorado <br />Springs. A peak discharge of 1,690 cfs occurred on South Boulder Creek at <br />Eldorado Springs. Large portions of the floodplain were inundated below the <br />confluence of South Boulder and Boulder Creeks. <br /> <br />In the valley, downstream from Boulder, the floodplain was reported to have been <br />inundated to an average width of approximately one mile for several days. <br />Agricultural damages included loss of livestock, crops, pastures, fences, roads <br />and deposition of sand and silt on floodplain lands. In addition, considerable <br /> <br />Analysis of gaging records show that floods the size of the May 1969 flood OCcur <br />on an average of about once every seven years on South Boulder Creek (Reference <br />2) . <br /> <br />5 <br />
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