FLOOD05196

• County: Adams
• Community: Thornton & Westminster
• Stream Name: Big Dry Creek
• Basin: South Platte
• Title: LOMR - Affected Panel 080008 0001 B, 08001C 0030 G, 08001C 0036 G - Case No. 02-08-211P
• Date: 3/6/2002
• Prepared For: Thornton / Westminster
• Prepared By: FEMA
• Floodplain - Doc Type: Historic FEMA Regulatory Floodplain Information

~
~

2

Please forward your payment to one of the addresses listed below.

Using U.S. Postal Service:
Federal Emergency Management Agency
Fee-Charge System Administrator
P.O. Box 3173
Merrifield, VA 22116-3173

Using overnight service:
Fee-Charge System Administrator
c/o Dewberry & Davis, METS Division
840 I Arlington Boulevard
Fairfax, VA 22031

We have completed an inventory ofthe items that you submitted. The items identified below are
required before we can begin a detailed review of your request. Please submit two copies of any
additional data required.

I. This proposed revision extends downstream into the City of Thornton. Please submit a letter from
the Chief Executive Officer (CEO), or designee, of the City of Thornton, stating they have
reviewed the proposed project and are in concurrence with the proposed changes to the FIRM.

2. Please submit a copy of the public notice distributed by your community stating its intent to revise
the regulatory floodway, or a statement by your community that it has notified all affected
property owners and affected adjacent jurisdictions.

3. Please submit letters from your community and the City of Thornton stating the modified
regulatory floodway will be adopted and enforced.

4. Please submit a set of as-built drawings for the portion of the project in the vicinity of 1-25.

5. Please submit an annotated FIRM at the scale of the effective FIRM showing the revised 100- and
500-year floodplain and the floodway boundaries, and how they tie-in to those shown on the
effective FIRM downstream and upstream of the revisions.

6. Please submit a set ofworkmaps showing the items listed on MT-2 Form 5. In particular, the
items left-off of the workmaps submitted include: The location and alignment of the cross
sections downstream of Section 200 and upstream of Section 4500; current community
boundaries; the effective 100-year floodplain and floodway boundaries from the FIRM reduced or
enlarged to the scale of the workmap; tie-ins between the effective and revised 100-, 500-year and
floodway boundaries; community easements; the signed certification of a registered professional
engineer; the location and description of reference marks; and the vertical datum of the workmap.

7. The profiles submitted are confusing (there appears to be multiple 500- and I OO-year profiles, with
some of these profiles below the 10-year profile). Please submit profiles for the 10-, 50-, 100-,
and 500-year flood events, at the scale of the profiles shown in the effective Flood Insurance
Study (FIS), that include the information listed on MT-2 Form 4.

8. A computer disk containing full input and output listings of the hydraulic models. The post-
project HEC-RAS model submitted will be reviewed for use in this revision, and the input and
output files are required (as well as files for the duplicate, corrected, and pre-project models).
However, the post-project conditions HEC-2 model submitted is erroneous and unnecessary, and
will not be used in this revision unless it reflects the as-built channel conditions.

9. The downstream starting water surface elevations (WSELs) of the hydraulic models do not tie-in
to the effective information. Please revise and resubmit the analysis. If necessary refer to the
Adams County and Incorporated Areas FlS for the correct starting WSELs.

10. The HEC-RAS post-project floodway model has surcharges (the difference in WSEL between the
floodway profile and the 100-year floodplain profile) greater than 1.00 foot at cross sections 10,
540,3000, and 3800, and surcharges less than 0.00 at cross sections 605, 800, and 4100. Please

Updated 6-11-01

316-ACK.FRQ