PROJ00462

• Contract/PO #: FS0036X
• Contractor Name: Idaho Springs, City of
• Contract Type: Loan
• Water District: 0
• County: Clear Creek
• Loan Projects - Doc Type: Feasibility Study

I

On Figures 8, 9, and 10 the density decreases with depth, indicating
a bulking and/or saturation of the embankment material. In this same zone,
the drill holes were in saturated core material. Figure 11 (soils report)
picks up the trickling flow observed in field inspection at station 6 + 37. The
first water layer occurs about 8 feet and again at 14 feet below the dam crest.
At 28 foot depth, the log picks up a zone of washed out material or voided
compaction area. The void area could also be a fracture in the foundation
material, not uncovered and grouted during construction.

The amount of seepage flow was not measured during this investigation.
An indication of volume of seepage is made by flow net analysis and compared
to visual observation of seepage. The flow net is drawn as shown on Sheet 2.
From this the flow is computed for each incremental section of the dam using
the Darcy equation:

F
Q = khN

Q

3
flow in ft /hr

,I. ~1.s 4

/
:1..-'-' /

k - permeability in ft/year (range 0.2 - 0.7 l/yr)

.- '" /\ .C:u r tC~":::.
c>D'J"'- -.... _(
-1 (,vA! ~c --{:D

F - flow paths

N number of increments

h - hydraulic head

6 3
Q = 0.5 I/yr. 23 x IS = 4.6 ft Iyr.
3 c>.ooooG~ 7
= 0.000525 ft /hr; 0.22 !}pm

Applying this to the total Iength.Skthe dam, one can expect a totaI
seepage in this type material of about 138 gpm. Observation of the flow down-
stream of the embankment indicates this is a reasonable estimate. On the
other hand, the two (2) high rate locations probably create 20 gpm each.

The phreatic line was drawn for most of the sections to determine the
location of "piping" action and its comparison to the electrical resistivity
analyses. The phreatic line on the sections at centerline of the dam occurs
from 8 - 12 feet below the crest at reservoir level equal to spillway elevations.

III-8