FLOOD03704

• County: Clear Creek
• Community: Georgetown
• Stream Name: Clear Creek
• Basin: South Platte
• Title: Flood Hazard Evaluation 6th to 7th Streets
• Date: 10/6/1977
• Prepared For: Georgetown
• Prepared By: Georgetown
• Floodplain - Doc Type: Floodplain Report/Masterplan

A summary of the estimates made is attached, showing, on
sheet 1, the cross sections and their respective flow elevations;
and on sheet 2, a profile of the creek's water surfaces from above
6th Street to 7th Street; that affect the floodel~ations pertinent
to the particular area.

Conditions examined for the estimates

The extent of the flooding threat to the area is significantly
affected by the creek's up-stream physical conditions that limit and
restrict the amount of the creek's flow capacities and any subsequent
excess flows onto adjoining areas.

From the conditions examined and evaluated, three levels
of flow were distinctive with regard to existing "in bank" capacities
and "over flows" out-of-bank onto adjoining areas. These are given
as: 1. flows occurring more frequently up to 500 cfs with no over
flowing out of the exi~ting creek, 2. flows occurring less frequently
of 600 to 1200 cfs, whose excesses are greater than 500 cfs over-
flow adjoining areas; and 3. flows occurring infrequently of 2500 cfs
whose excesses from in-bank capacities significantly affect depth
and velocities of overflows onto adjoining areas

A. For the more frequent flow conditions, the most
restrictive in-bank creek cond:il:ion, whose effects are
significant to overflows down 6th Street is the limited
opening provided by the 6th Street bridge crossing.

As affected by the physical arrangement of the
openings limited dimensions of 4 to 4.5 feet deep,
creek flows up to ,500 cfs will be contained "in-bank"
with its depth at the opening restricted to about 5.2 ft.;
and downstream thru the timber-walled reach to a depth
of about 2.3 feet. These are shown by the cross section
1 and the profile for a 500 cfs flow.

B. As the in-bank flows increase up to an overflow
spilling onto 6th street at the bridge opening to a
depth of 6.5 ft., a "back-up" condition occurs in a
recently constructed concrete open ditch from Argentine
Street. This condition allows creek flows in excess
of 500 cfs up to the "spill-over" flows that backs
water up the concrete ditch, inundating 6th Street
from the bridge north to Rose Street, with overflows
spilling to the north of about 50 cfs, at a maximum
depth on 6th Street of about 0.2 feet.

An analysis of the cross sections to 7th Street
indicate these overflows restricted to the openings
between the existing buildings are shallow flows as
they flow down to Clear Creek at 7th Street.

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