PERMFILE41307

• Permit No: M1977526
• IBM Index Class Name: Permit File
• Doc Date: 11/4/1977
• Doc Name: DESCRIPTION OF WATER RESORCES
• Media Type: D
• Archive: No

b}' the USAGE and the United States Gelogical Survey (USGS)
from gaging station measurements and calculations of flow
over Henderson Road to be approximately 30,000 cfs. A
special report on the flood was prepared by the USAGE
in July, 1974, titled "Post Flood Re^ort, Platte River and
Tributaries, Nebraska, Wyoming, and Colorado, Floods of
May-June, 1973". The ~>:tent of the flooded area was outlined
on aerial photographs taken during the flood. The flooded
area also is reproduced on Plates I, LI, anti III. Examination
of the plates indicates that the t:ay 1973 flood was more
extensive t~.an the FIA-UDFCU flood plain south of Henderson
Road and less extensive north of the road. Levees were
overtopped in several locations indicating interaction
between le_`t overbank and channel flows. The flooded areas
f.,r the May 6, 1973 flood r~present a better approximation
of tl~e 100-year flood plain be~.use it is based on documen-
tation of actual floodin~* which approximates the 100-year
event. The flood event ~•:as used to identify the ]00-year
flood plain on the mining site. The west edge of the floodway
was estimated by identifying the areas of apparent signifi-
cant flow on aerial photographs of the flood of May 6, 1973
(Plates I, II, and lII). A summary of all of the flood
hazard area delineations is contained in Table E.
In each of the flood studies, flood waters are shown
to back up behind Henderson Road. In the 1963 USAGE study,
the back-up occurcd behind a road which is now replaced by
Henderson Road. This creates an area of wider, deeper aid
slower moving caater south of _.~derson Road. It is estimated
that depths of flooding south of Henderson Road range between
2 anr' 4 feet, and that velocities average 1 to 3 feet per
second. Flood depths n~rCh of Henderson Read are expected to be
1 t:; 3 fee* and velocitic 2 to 4 fe,~t per second.
Computations of peak discharges over Henderson Road
for the Hood of May 6, 1973 indicate that the overbank
flood was approximatel}• 10,000-20,000 cfs in magnitude. This
is approximately 1/3-Z/3 of the estimated 27,000-33,000 cfs
total flow. These computations are basr~l on the JDFCD detailed
topographic mappi:..3; a flood elevation established by the
USGS; and limits of flew est~hlished by the USlCE 1974
study. 15,000 cfs is con~ider~~ an appropriate plan„ing
estimate for tkic overbank 100-year flood.
Site Drainage
The Land between the Brantner Ditch, the South Platte
River, Eenderson Road, and the southern boundary of the
property is land which has historically been irrigated
by the Brantner Ditch. Ditch laterals from the Brantner
Ditch control internal drainage. Storm runoff from the
property has historically flowed towards the laterals and
of: the property into B__~nt::er Gulch. The first ditch
lateral at the .intcrscction of the Brantner Ditch and the
n-operty's sou*_herr boundary. The secon!i lateral is approx-
ima~ely 2,900 feet to the north. The laterals divert water
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