FLOOD06925

• County: Larimer
• Community: Greeley
• Stream Name: Cache La Poudre River
• Basin: South Platte
• Title: Master Floodway Planning
• Date: 3/11/1983
• Prepared For: Greeley
• Prepared By: Simons Li & Associates Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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sections. This will allow trade-offs between the City and property OWners to

maximize the developable area.

During the floodway analysis, close coordination will be required. The

best way to establish a floodway acceptable to the City is to start with

Method 4 to establish an equal encroachment floodway that meets the FEMA cri-

teria. At this stage, the City can express its desires and sketch a practical

floodway to meet floodplain management and implementation goals. Other

methods will be used to establish a floodway that meets the FEMA criteria and

is as close to the desired floodway as possible. Again, a trial an error pro-

cess will be used in order to establish a floodway acceptable to the City.

The recommended floodway will be delineated on a set of administrative mylar

maps at a scale of 1" = 100'. The administrative maps will also label the

streets, roadways, and update other identifiable features.

All references to previous information, documentation of hydraulic

variables used, bridge calculations, HEC-2 output, and all other information

will be fully documented in a technical addendum to allow future reproduction

of the results.

E. Improvement Plan Formulation and EValuation

Alternative plans of improvement will be formulated to alleviate flooding

problems in the study area. Plans will be formulated such that economical,

yet effective, solutions can be made. Improvement plans to be considered will

include channelization, levees, increased capacities at road crossings,

nonstructural methods such as floodplain regulation, flood insurance, or adop-

tion of a floodway, and combinations of improvement measures.

As indicated in the RFP, the study reach has sedimentation problems. The

City has been required to dredge the channel about every other year. SLA has

proposed to perform a qualitative assessment of the stability of the existing

channel and collect bed and bank material samples for determining sediment

sample distributions during the field investigation. Based on the results of

the hydraulic analysis and the sediment distribution, SLA proposes to perform

a geomorphic analysis to determine the most stable channel cross section and

slope. At this time, channelization seems to be an attractive alternative

because (1) channelization will have a narrow floodway and possibly more deve-

lopable land, (2) narrow and deep cross sections will provide a higher flow