PROJ00538

• Contract/PO #: C153581
• Contractor Name: Minnesota Canal and Reservoir Company
• Water District: 0
• County: Gunnison
• Bill Number: XB 99-999
• Loan Projects - Doc Type: Feasibility Study

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TABLE 6.4
LOeAL STORM INeREMENTAL PMP
Duration (hrs) 1 2 3 4 5 6
Incremental PMP (in) 0.2 0.5 6.9 1.1 0.4 0.1

6.3.4 Evaporation

Average annual free water surface evaporation for the project site is approximately 40 inches,
of which nearly 78 percent occurs between the months of May through October. Evaporation
data for the project site is summarized in Table 6.5.

TABLE 6.S
EVAPORATION
Evaporation elass Depth (Inches)
Free Water Surface May-Oct. 31
Annual 40
elass A Pan May-Oct. 41
Reference: (NOAA, 1982)

6.4 Geology

The project site lies in a geologic transition zone known as the Grand Hogback. South of the
eolorado River, the Grand Hogback separates the Piceance Basin from the Elk and Sawatch
mountain ranges. The Grand Hogback was formed due to the intrusion and uplift of the Elk and
Sawatch mountain ranges; as a result, sedimentary formations were deformed and exposed to
create Hogback ridges and mesa landforms which characterize the region. A geologic map of
the project area is provided in Figure 6.4.

The surficial geology of the New Minnesota Dam project site is primarily characterized by
Quaternary surficial deposits. Within the stream channel floodplain, deposits are comprised of
alluvial and colluvial deposits (Qc). Elevations generally above 7,600 ft to 7,700 ft are capped
by a thin veneer of unconsolidated Pleistocene deposits (Quwe) derived primarily from rocks of
the Sawatch Formation, and to some extent intrusive rocks of the West Elk Mountains. These
unconsolidated deposits are heterogeneous to moderately well sorted, and may be unstratified
to well stratified. The heterogeneous and unstratified components of these deposits are most
susceptible to erosion and mass movements (Qls). Based upon exploration drill logs supplied

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