2006-06-12_REVISION - M1982015 ‎(23)‎

• Permit No: M1982015
• IBM Index Class Name: Revision
• Doc Date: 6/12/2006
• Doc Name: CLOMR
• From: Carroll & Lange
• To: DMG
• Type & Sequence: AM1
• Media Type: D
• Archive: No

Carroll sc Lange ~
Professional Engineers & Land Surveyors \,
• Lakewood Loveland Winter Park
January 30, 2006
JN: 3075
Weld County Public Works
Attn: David Bauer, PE
1111 H Street
P.O. Box 758
Greeley, CO 80632-0758
Re: CLOMR for PZ-1078 St. Vrain Lakes PUD
Dear David:
We have reviewed your comments made in a letter dated January 12, 2006. For ease
of addressing the comments, we have included the comments and offered our
responses in bold.
1. St. Vrain Lakes PUD is planned for up to 5, 131 single family residential and
commercial building sites. The south edge of the proposed project borders the
100-year floodplain of the St. Vrain River.
• 2. Carma / St. Vrain Lakes PUD (applicant) has been submitted, to Weld County
and FEMA, a 12/12/05 CLOMR report requesting a revision of the 100-year
floodplain map. The report relies on an un-published 1977 U.S. Army Corps of
Engineers hydrology report for determination of the peak flow in the St. Vrain
River. The peak flow in the St. Vrain River is influenced by seasonal snowmelt in
addition to contributions from rainstorm runoff.
Response: See response with comment 3.
3. A substantial amount of change to the St. Vrain River drainage basin up-gradient
of the Carma/St. Vrain Lakes site due to new development has occurred since
1977. Those structural changes likely contribute a significant amount of runoff to
the river. On-going sand and gravel mining up-gradient of and adjacent to the
Carma/St. Vrain Lakes site also likely influence the flood response of the river.
The modeling approach presented in the CLOMR report is an acceptable
approach to evaluation the 100-year floodplain, however the hydrologic
assumptions need verification.
Response: The hydrologic data used in the CLOMR (Conditional Letter of
Map Revision) report is consistent with the peak discharge data from the
Longmont Flood Insurance Study published in 1987 by the Federal
Emergency Management Agency. A copy of the table from this FIS has
been attached for review.
• A report by Water Resources Consultants, Inc. {WRC), titled Floodplain
Information and Flood Control Plan for St. Vrain Creek at Longmont,
165 Soudt Union Blvd., 8ui[e 156 ~ Lakewood, Colorado 80228 ~ Wain [phone] • Fax [phone]
3985 Sou[h Lincoln Avenue, 8ui[e 250 • Loveland, Colorado 80537 • Main [phone] • Fax [phone] • Denver Dir. [phone]
47 Cooper Creek u'a}', Suite 328 • P.O.BOS 3395 • Winter Park Colorado 80482-3395 • :Main [phone] • Fax [phone] • Dem~er Dir. [phone]