FLOOD03848

• County: Denver
• County: Jefferson
• Community: Denver County
• Stream Name: South Platte River
• Basin: South Platte
• Title: Stream Stability Investigation South Platte River
• Date: 11/1/1983
• Prepared For: UDFCD Denver
• Prepared By: Michael Stevens
• Floodplain - Doc Type: Floodplain Report/Masterplan

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soupstreamfromthestreamgagingstationatHenderson. The Tocatfonsof
these gages are shown on the street index map in Appendix 1.
Diversions. The Missouri Basin Inter-Agency Committee (1971) has
reported that the South Platte River drainage was, in 1969, a highly used
surface~water system whlch has attained almost ~ximum development. More
than 90 percent of the river depletion is used for irrigation farming.
Return flow from irrigation is reused by irrigators downstream. Municipal
and1ndustrfalusersdlvertoutlessthan5percent. In the per10d between
1949 and 1970, the total depletion from the South Platte Basin upstream from
Weldona (approximately 100 miles downstream from Denver) was 44,300 acre.
feet per year. In comparison, the 10ng4erm average annual streamflow in
the South Platte River at Denver is 222,000 ilcre.feet.
The Denver and Aurora water supply systems diverted water from the
South Platte River at a rate of approximately 96,000 acre.feet per year in
1975.

streamflow in the Cache la POudre was approximately 22 percent greater than
from 1925 to 1980.

The record of annual streamflow in the South Platte River at Denver
has been divided into two parts. The measured streamflow prior to 1925 was
398 cubic feet per second. Thereafter,therneanwasoll1y308cubicfeet
per second. That is a 23 percent decrease. The deviations shown in Fig.
4 are computed using the high mean prior to 1925 and the lower one after.
The main characteristic of the streamflow record is the long
sequences of less than average streamflow, interrupted by short bursts of
higher than nonnal streamflow. There are 31 higher than nonnal years and
55 lower than normal years. The persistence table for the annual stream-
flows is given below.

Persistence Table
Annual Streamflow at Denver
(Units are ~ of years)

The return flows from the native water diverted from the South
Platte River and the imported water were approximately 143,000 acre-feet
per year at the 1975 level of development. Thus, return flows were larger
than the diversions of native water.

FollowingYearfs

W,t

O'y

At Denver and Henderson, current annual streamflow may not be much
different than the unregulated native streamflow. At Denver only a portion
of the return flow occurs upstream of the gage. At Henderson, most of thc
return flow from native and imported water is back in the river, but diver-
sions from the South Platte River into the Burlington, Fulton, and Brantner
Ditches between the Denver and Henderson gages reduces the streamflow, can~
celling out a part of the effect of importing water.

Wet

,

27

Antecedent
year is

27

37

Dcy

Annual Streamflow

If the streamflow sequence were entirely random, we would expect wet
years to follow wet 25 percent of the time. Similarly, wet years would
follow dry years 25 percent of the time and so on. At Denver, there is a
persistence of dry years to follow dry and a deficiency in the number of times
wet years follow wet. Thus, there isa strong persistence inthfs hyclro-
logic record.

Denver. Annual streamflow measurements have been made at the U.S.
Geological Survey's streamgaging station on the South Platte River in
Denver ever since 1895. The gage is located approxir.mtely 0.4 miles down-
stream from Cherry Creek. The natural catchment upstream is 3,804 square
miles. These annual flows are plotted in Figure 4 along with the deviations
from the average. The average for the 86.year period of recorcl is 339 cubic
feet per second. The largest annual streamflow was in 1942 when the average
for the year was 1107 cubic feet per second. The lowest was 1902 with only
81.1 cubic feet per secolld.
A careful study of the sequence of annual flows at Denver indicates
that prior to 1925 the streamflow was on the average greater. Vevdjevich
{1961} found the same for the virgin flows of the Colorado River at Lee' s
Ferry but the change there came in 1930. Virgin flows are those which would
have occurred if there had been no diversions and w~n.induced consumptive
use upstream. The Cache la Poudre exhibits the same phenomenon (Tudor
Engineering Company, 1983). In the period from 1884 to 1924, the virgin

In the record from 1925 to 1980, there is even a stronger persistence
with dry years following dry 43 percent of the time. From 1925 to 1942, and
again from 1950 to 1969, streamflow was consistently low. In the latter
sequence, there were seven extremely dry years in a row.
The average annual measured streamflow of 30B cubic feet per second
since 1924 is equivalent to an annual volume of 223,000 acre.feet.

Henderson. The Henderson strealT19age on the South Platte River is
located approximately one-quarter mile upstream from the bridge on State
Iilghway22. The two major tributaries between this gage and the Denver gage
are Clear Creek and Sand Creek. The total catchment area is 4,713 square
miles.