C153379 Feasibility Study

• Contract/PO #: C153379
• Contractor Name: Brook Forest Water District
• Contract Type: Loan
• Water District: 9
• County: Jefferson
• Bill Number: SB 80-67
• Loan Projects - Doc Type: Feasibility Study

III-6

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and Broadway (Table III-I). Remnants of the Slocum terrace are srar~c,

generally occuring as small buried channels covered by younger allu~ium

and aeolian sand and silt. A possible exposure of Slocum Alluvium occurs

on the north-facing hillside between the Empire and Bijou Canals, 1.75

miles west of the proposed Hardin Dam axis. This exposure, located 45 ft

above the present South Platte River, contains calcium carbonate-cemented,

sandy cobble gravel adjacent to Fox Hills Sandstone and covered by aeolian

sand. A thickness could not be measured due to thick talus below the vertical

exposure. Further east in the Fort Morgan area, the Slocum consists primarily

of 45 ft of iron-stained coarse sand with scattered cobbles (Gardner, 1967).

The Nussbaum, Rocky Flats, Verdos ,and Slocum occur in such small and

scattered exposures that they are important only in defining the surficial

stratigraphy of the Hardin area. The Louviers Alluvium, however, not only

occurs over large areas, but is the thickest surficial unit in the area

(Gardner, 1967). This extent is not evident at the surface because the

Louviers is buried by younger alluvium and aeolian sand in most areas. This

alluvium has, however, been traced in a deeply buried, Pleistocene channel of

the South Platte from Denver to Fort Morgan, and probably extends to its

confluence with the North Platte River (Gardner, 1967). This deep channel,

which was cut into the Pierre Shale to a depth of 160 ft at the proposed

Hardin axis (Woodward-Clyde-Sherard, 1964) formed during the low stand of the

oceans.

During the late Pleistocene (Wisconsin), so much of the earth' s water

was "locked up" in glaciers that the "base level" (sea level) to which

rivers were eroding was as much as 300 ft lower than the present sea level.

Examples of this low sea level, besides the buried South Platte channel,

include the "drowned coastline" of Chesapeake Bay, the deep fiords of Alaska

and Norway, and the below sea-level channel of the Hudson River.

A cross-section showing this channel (Figure III-2) indicates that the
Louviers at the proposed dam site is approximately 140 ft thick. This
corresponds to the estimate by Gardner (1967) that the original thickness of