WSP12086

• File Number: 8449.800.A
• Description: Metro Study SB 96-74
• State: CO
• Basin: South Platte
• Date: 4/1/1998
• Author: CWCB
• Title: Denver Basin and South Platte River Basin Technical Study, Technical Addendum 1 and 2, Senate Bill 96-074
• Water Supply Pro - Doc Type: Publication

Chapter 1: South Platte Basin Inventory

March 21,1998
Page 1-6

Hydrosphere Resource Consullants, 1002 Walnut Sulle 200, Boulder, CO 80302

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1,1.2,4 South Platte at Henderson

For this gage location we estimated natural flows based on Denver's natural flow
estimates, but with an adjustment for Clear Creek, To develop natural flow estimates
for this location, Denver used the following general equation:

South Platte at Henderson natural flow =
South Platte at South Platte natural flow +
Plum Creek at Louviers historical gage flow +
Bear Creek at Morrison historical gage flow +
Cherry Creek Below Cherry Creek Lake gage flow +
Clear Creek At Mouth Near Derby +
(natural stream gains between South Platte at South Platte gage
and South Platte at Henderson gage)

Denver quantified the natural stream gains between the South Platte and
Henderson gages via mass balance analysis using daily data for stream flows,
diversions, wastewater and power plant discharges, changes in reservoir storage and
reservoir evaporation within this reach.

We believe that Denver's use of historical gage data for Clear Creek At Mouth
results in a significant under-estimation of natural flow at Henderson. The Clear Creek
At Mouth gage reflects diversions by several major agricultural, municipal and industrial
users. A better choice would be the Clear Creek Near Golden gage, which has only
very minor diversions occurring above it. The average annual flow at Clear Creek Near
Golden is approximately 100,000 acre-feet greater than that at Clear Creek At Mouth,
We therefore adjusted Denver's natural flow estimate for the Henderson gage by
subtracting Clear Creek At Mouth and adding Clear Creek Near Golden. The historical
period of record for the Clear Creek Near Golden gage covers only from 1909 to 1974.
We extended this period of record through 1980 via correlation with natural flow
estimates for Boulder Creek at 75lt1 Street (see below). We believe that the resulting
estimates for this location are the best available data and are satisfactory for the
purposes of this study. Natural flows estimates for the South Platte at Henderson gage
location are presented in Table 1-4 and Figure 1-4.

1.1.2.5 South Platte at Kersey

To develop natural flow estimates for this location, we used the following
equation:

South Platte at Kersey natural flow =
South Platte at Henderson natural flow +
Boulder Creek at 75U1 Street natural flow +