WSP05705

• File Number: 8407
• Description: Platte River Basin - River Basin General Publications
• State: CO
• Basin: Statewide
• Date: 3/11/1964
• Author: CWCB
• Title: Engineering and Geologic Investigation and Analysis of Alternate Proposed Dam Sites on the South Platte River - Morgan and Weld Counties-Colorado
• Water Supply Pro - Doc Type: Report/Study

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,;1 determining the correct location of the axis for this dam, thL'se

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consultants were instructed to confine their study to the relative

engineering geologic conditions and earth embankment design cri-

ttria at the sites involved or to those things on which geologic

or soil factors might have some degree of influence.

It was

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pointed out that studies performed by the U. S. Bureau of

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Reclamation and others had indicated that each site area had cer-

tain advantages over the other and as a result, the geologic and

soil conditions might eventually be the deciding factor in the

final site selection.

A summary of our basic conclusions is given below.

SUMMARY

(1) Seepage analysis of the proposed lower Weld County site in-
dicates an expected loss of 31 cubic, feet per second with no
cutoff beneath the dam as compared to 40 cubic feet per sec-
ond at the Narrows site with a 5,000-foot upstream blanket.
The upper Weld County site offers the possibility of an es-
sentially complete cutoff of reservoir seepage and of the
South Platte underflow, if desired. Such an opportunity docs
not exist at the Narrows site.

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(2) Impervious materials are available within 7 miles for the
lower Weld County site, and within 1 mile at the Narrows site.
The cost of overhaul for the Weld site will depend on the de-
sign volume of the impervious section and could be minimized
by constructing a thin ,impervious core.

(3)

Comparative estimates of construction costs for Narrows as
compared to Weld County should be made, using the data ob-
tained in these investigations.

\ (4)

It is our general opinion, from the engineering and geologic
viewpoint, that the Weld site is superior to the Narrows site.

INVESTIGATION DATA

The following data from prior investigations was made avail-

able to the writers by the U. S. Bureau of Reclamation, The

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Riverside Irrigation District, and others.

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U. S. G. S. topographic quadrangle sheets with all