FLOOD03719

• County: Adams
• Community: Thornton
• Stream Name: Big Dry Creek
• Basin: South Platte
• Title: Floodplain Information Report
• Date: 4/15/1988
• Prepared For: Thornton
• Prepared By: McLaughlin Water Engineers, Ltd.
• Contract/PO #: &&
• Floodplain - Doc Type: Floodplain Report/Masterplan

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features could occur. In addition, if channel banks are left unprotected, low flows
would cut into the banks and encroach, thus damaging fairways and tees over time.

Using two riprap SIZIng methods, the extent of protection in the high velocity zones
was determ ined. Drawing No. 8 shows the protection zones and typical sections.
Protection is also described at local overflow routes identified in the golf course
Utilities Report (McLaughlin Water Engineers, Apr. 1988). It should be noted that the
2-year event has similar velocity characteristics.

Calculations show that extensive bank protection is not needed downstream of the 10th
green site. Therefore, buried Type VL toe protection (d50 = 6 inches) should be used
along most reaches, with buried Type M used on the outside of bends. Higher velocity
zones, such as at the 10th green and 11th green sites, should have more extensive
protection as shown on Drawing No.8.

In general, toe protection is used to stabilize stream banks and to prevent stream
horizontal migration over time. The protection would be buried and would not be
visible, except possibly at the low flow water line. Some optional Type VL treatment is
shown on Drawing No.8. These zones are where stream migration may be allowed to
occur without causing significant damage. The proposed protection will not prevent
some damage during severe events, but the extent of damage will be greater if no
protection is used.

The capital cost of streambank protection is approximately $312,270, with an additional
$12,100 if the optional treatment zones are installed. Calculations are shown in
Appendix A. If streambanks are left unprotected and unstabilized, the City would be
leaving itself open to incurring substantial ongoing operating and maintenance expenses.

Four stream crossings are also shown on the attached drawings. Each of the bridges
were sized with a 20-foot span to minimize costs. The exact construction of the
bridges will be determined in final design, but could be either cast-in-place concrete,
pre-cast concrete boxes, pre-cast three-sided boxes or Cor- Ten steel prefabricated
structures. The basic hydraulic configuration for these structures is the same.

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