|
<br />record (1939-present) is 9,170 fl3/s occurred in 1945, The flood of record of 39,900 fl3/s
<br />for Cherry Creek near Melvin (06712500) occurred on June 16, 1965; the maximum
<br />paleoflood is about 74,000 fl3/s (fig. 4) in at least several thousand years, The June 16 peak
<br />of 59,000 fl3/s entering Cherry Creek Reservoir reflected the Melvin peak at 1830 hrs and
<br />runoff from the ungaged area (27 mi2) between the Melvin gage and the Reservoir, primarily
<br />Piney Creek (14,100 fl3/s) at 1500 hrs (Matthai, 1969),
<br />
<br />3, The largest flood for Cherry Creek near Franktown (06712500) resulted from the failure
<br />of Castlewood Canyon Dam during a rainstorm on August 3, 1933 (Matthai, 1969), A
<br />rainstorm produced 3 to 9 inches of rain in about 9 hours in upper Cherry Creek basin (U,S,
<br />Army Corps of Engineers, 1976), Good to excellent paleoflood evidence (top of coarse bouldery
<br />flood-deposited sediments) for the 1933 flood is preserved at many sites in upper Cherry
<br />Creek basin (e,g" figs, 2 and 3), The maximum paleoflood upstream from Castlewood Dam is
<br />about 30,000 fl3/s. The maximum paleoflood downstream from Castlewood Dam is about
<br />44,000 fl3/s (rainstorm flood exacerbated by the dam-failure flood) at the gage (06712000)
<br />near Franktown, Because Cherry Creek is constrained by bedrock on the bed and walls, the
<br />1933 paleoflood deposits represent the largest flood in more than 10,000 years at the
<br />Franktown gage and upstream from Castlewood Canyon Dam,
<br />
<br />4. No streamflow-gaging stations have been operated on Box Elder Creek, Historical reports
<br />indicate upper Box Elder Creek (Running Creek) has not had significant flooding since at least
<br />the early 1880s (Follansbee and Sawyer, 1948; Matthai, 1969; Water Resources Consultants,
<br />1979; CH2MHILL, 1995), A flood of 4,700 fl3/S for Box Elder Creek downstream from 1-70
<br />near Wiggins on May 30,1948 was estimated by the U,S, Geological Survey using the slope-
<br />area method (McKee and Doesken, 1997), The flood of record is about 6,000 fl3/s in lower
<br />Box Elder Creek in May 1969, which was estimated from records since the early 1900s at
<br />Bootleg Reservoir (fig, 1) in Adams County (CH2MHILL, 1995). The largest flood in Running
<br />Creek at Elizabeth (upper Box Elder Creek) occurred in May 1935; flood damages were limited
<br />to a small wooden bridge that washed out, and erosion of part of the railroad embankment located
<br />low in the floodplain (Water Resources Consultants, 1979),
<br />
<br />The maximum paleoflood near Elizabeth is about 9,000 fl3/s in at least several hundred years
<br />to several thousand years. The maximum paleoflood in Adams County just downstream from 1_
<br />70 is about 8,700 fl3/s during the past 100 to 500 years, There may be slightly higher and
<br />substantially PSis corresponding to a paleoflood, Additional fieldwork is needed to better define
<br />this larger paleoflood, The maximum paleoflood is about 4,700 fl3/s for Coyote Run near its
<br />confluence with Box Elder Creek just north of 1-70.
<br />
<br />The headwaters of Running Creek (upper Box Elder Creek basin) have substantial exposed
<br />bedrock and shallow soils, which exacerbate runoff potential. However, Running Creek near
<br />County Road 86 (drainage area about 5,5 mi2) has a maximum paleoflood of about 1,600 fl3/S
<br />in at least several hundreds of years (based on a thick soil-profile development). Maximum
<br />paleofloods near the headwaters are relatively small (table 1), which can be used to infer that
<br />maximum rainfall amounts are smaller than in nearby basins closer to the crest of the Palmer
<br />Divide, Deep well-drained soils in downstream contributing areas to Running and Box Elder
<br />Creeks (Water Resources Consultants, 1979; CH2MHILL, 1995) and thick sand-bed channels
<br />(high infiltration) also contribute to relatively small peak flows, The average width of
<br />
<br />8
<br />
|