FLOOD04316

• Designation Number: 507
• County: Arapahoe
• Community: Aurora
• Basin: South Platte
• Title: Flood Insurance Study - Aurora, Adams, Douglas and Arapahoe Counties
• Date: 9/1/1998
• Designation Date: 11/1/1999
• Floodplain - Doc Type: Floodplain Report/Masterplan

to the confluence of Unnamed Creek. Upstream from the
confluence, the channel slope increases to 39 feet per mile.

The average sLope of East Toll Gate Greek is 22 feet per mile.
The channel averages about six Ieet in depth and 30 to 40 feet
in width.

West Toll Gate Creek Tributary has an average channel slope of
60 feet per mile.

Unnamed Creek, a tributary of West Toll Gate Creek, has an
average channel slope of 25 feet per mile. The channel is
irregular in size and shape, ranging from very shallow depths
to depths of approximately 6 feet; widths are from 20 to 30
feet.

Westerly Creek, Sable Ditch, and Cranby D1tch have almost
fully developed basins which result in more frequent flooding
d......ges. In many places, these drainageways have been filled
in or severely encroached upon, leaving little flood
conveyance capacity.

2.3 Principal Flood Problems

The main causes of floods in Aurora are cloudbursts vbich
normally occur during the months of May through August.

There bave been approximately eleven floods in the Sand and
Toll Cate Creek basins since 1896. These floods occurred in
1896, 1912, 1917, 1921, 1933, 1938, 1948, 1957, 1963, 1965,
and 1973. The following frequencies bave been assigned to
historic floods: 1) 1948 flood on Sand Creek-1S-year flood;
2) 1957 flood on Toll Gate Creek--35-year flood; 3) 1965 flood
on Toll Gate Creek--70-year flood; and 4) 1965 flood on Sand
Creek--40-year flood. The following is a documentation of tbe
major recorded floods:

"On May 30, 1948, a localized thunderstorm dropped 8 inches of
rain and hail in four hours on the lower basin of Sand and
Toll Cate Creeks. Flooding resulted downstream of Colfax
Avenue. Estimated discharges on Sand Creek of 7,720 cubic
feet per second (cfs) and 10,500 cfs, respectively, at Collax
Avenue and at the mouth caused overbank stages from 4 to 8
feet deep. Tourist cabins near Colfax Avenue and an oil
refinery near the mouth were d......ged, but farms and livestock
feed lots in the flood plain suffered the most. On
Hay 8 and 9, 1957, intense rains occurred over Toll Cate Creek
and the middle of Sand Creek Basin. The rains began about
11:00 p.m. on May 8 and Toll Cate Creek crested at 3:30 a.m.
on Hay 9 at Colfax Avenue. The estimated peak discharge on
Toll Gate Creek was 10,500 cfs at 6th Avenue, while 25,500 cfs
was estimated for Sand Creek at Yosemite Street."

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