HomeMy WebLinkAboutReports - 10/21/2025
CACHE LA POUDRE RIVER
Fort Collins, Colorado
SERFER FLOODPLAIN MODELING
REPORT
PREPARED FOR:
Serfer Land Ventures LLC
6776 CR 74
Fort Collins, CO 80521
SUBMITTED TO:
City of Fort Collins
Floodplain Administration
970-416-2632
PREPARED BY:
Galloway & Company, LLC.
5235 Ronald Reagan Blvd., Suite 200
Johnstown, CO 80534
DATE:
October 21, 2025 ( Preliminary)
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Table of Contents
I. INTRODUCTION .................................................................................................................... 1
1.1 Background ...................................................................................................................................... 1
1.2 Previous Studies .............................................................................................................................. 3
1.3 Mapping ............................................................................................................................................ 3
1.3.1 Effective (EC) Topography ........................................................................................................... 3
1.3.2 Corrected Effective (CE) Topography........................................................................................... 3
1.3.3 Revised Condition (RC) Topography ............................................................................................ 3
1.3.4 Vertical Datum and Horizontal Coordinate System Considerations ............................................. 3
1.4 Purpose and Scope of Study .......................................................................................................... 4
II. HYDROLOGY .................................................................................................................. 5
IV. DUPLICATE EFFECTIVE CONDITION ........................................................................... 6
4.1 Definition of Hydraulic Plans .......................................................................................................... 6
4.2 Boundary Conditions, Tie-ins, Roughness Coefficients, and Encroachments ......................... 6
4.3 Duplicate Effective Analysis Results ............................................................................................. 6
V. CORRECTED EFFECTIVE CONDITION ......................................................................... 7
5.1 Definition of Hydraulic Plan ............................................................................................................ 7
5.2 Boundary Conditions, Tie-ins, and Roughness Coefficients ...................................................... 7
5.3 Corrected Effective Analysis Results ............................................................................................ 7
VI. REVISED CONDITION .................................................................................................... 8
6.1 Definition of Hydraulic Plans .......................................................................................................... 8
6.2 Boundary Conditions, Tie-ins, and Roughness Coefficients ...................................................... 8
6.3 Results .............................................................................................................................................. 8
6.4 Scour Analysis ................................................................................................................................. 8
VII. FLOODPLAIN MANAGEMENT AND COMPLIANCE ....................................................10
7.1 Local Floodplain Management ..................................................................................................... 10
7.1.1 City of Fort Collins ................................................................................................................. 10
7.1.2 Larimer County ...................................................................................................................... 10
7.3 State of Colorado Floodplain Management ................................................................................ 10
7.4 Federal Emergency Management Agency .................................................................................. 10
7.4.1 MT-2 Forms ........................................................................................................................... 10
7.5 Conclusions ................................................................................................................................... 11
VIII. REFERENCES ...............................................................................................................12
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APPENDICES
A. Background Information
A.1. FEMA Effective Information
A.1.1. FIRM Panels
A.1.2. FEMA FIS
A.2. Topography
A.2.1. Duplicate Effective Topography (DIGITAL ONLY)
A.2.2. Corrected Effective Topography (DIGITAL ONLY)
A.2.3. Certified Corrected Effective Topography
A.2.4. Revised Condition Topography (DIGITAL ONLY)
A.3. Design Plans (DRAFT Version, Excerpts Only)
A.4. Previous Studies
A.5. Manning’s Roughness Coefficients
B. Hydraulics
B.1. Duplicate Effective HEC-RAS v5.0.7 Model Outputs
B.2. Duplicate Effective HEC-RAS v6.6 Model Outputs
B.3. Corrected Effective HEC-RAS v6.6 Model Outputs
B.4. Revised Condition HEC-RAS v6.6 Model Outputs
B.5. Digital Hydraulic Models (DIGITAL ONLY)
C. Workmaps
C.1. Duplicate & Corrected Effective Comparative Workmap
C.2. Corrected Effective & Revised Condition Comparative Workmap
C.3. Effective & Revised Condition Comparative Workmap
C.4. GIS/CADD Files
D. Summary Tables
D.1. Base Flood Elevation Comparison Table
D.2. Corrected Effective Map-Model Agreement Table
D.3. Revised Condition Map-Model Agreement Table
D.4. Effective Model Verification
E. Floodplain Management
E.1. FEMA MT-2 Forms
Annotated FIRM
E.2. Public Notifications
E.2.1. List of Affected Property Owners
E.2.2. Public Notification Letter Template
E.3. ESA Compliance Report
E.4. Local Floodplain Permit
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I. INTRODUCTION
1.1 Background
The Cache la Poudre River (CLPR) is a FEMA -regulated tributary of the South Platte River that flows
through Fort Collins and Larimer County. In large storm events, the river overtops its right overbank
upstream of Interstate 25, creating the CLPR I -25 Divided Flow Path (CLPR I25 DFP), which conveys
overflow several miles before rejoining the main channel. A vicinity map showing the location of the project
site is displayed in Figure 1.1.
Figure 1.1: Location Map
Galloway and Company, LLC (Galloway) has been retained by Serfer Land Ventures, LLC (Serfer) to
complete hydraulic analyses and permitting in support of a Conditional Letter of Map Revision (CLOMR)
for the portion of the CLPR I25 DFP crossing the Serfer Property. The study evaluates proposed grading
to formalize overflow channels and emergency access crossing, in relation to effective or best available
FEMA floodplain mapping. A map of the project area is presented in Figure 1.2.
Commented [CP1]: This generic description of where the
overflows go could really be back up by showing the flow path
on figure 1.1. Lable a couple more streets on Figure 1.1
(kechter, Horsetooth, Strauss Cabin & LCR 5) would help with
the written descriptions.
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Figure 1.2: Project Site and Study Limits Map
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1.2 Previous Studies
In 2000, FEMA approved a CLOMR-F (based on fill) and subsequent LOMR-F (Case No.s 00-08-182C and
00-08-175A) for a parcel in the southeast corner of Harmony Road and Strauss Cabin Road. These cases
applied directly west of the current project area.
In 2014, Anderson Consulting Engineers (ACE) submitted a LOMR -BD (Case No. 14-08-0580P) to correct
a floodplain/floodway delineation error introduced during the conversion of floodplain workmaps to FIRM
panels. The correction extended from Harmony Road sou th to Kechter Road/Larimer County Road 36 (LCR
36).
Since 2016, FEMA and their consultant AECOM have been completing a comprehensive hydrologic,
hydraulic, and mapping restudy of the CLPR under the RiskMAP program. Preliminary data w as issued in
a preliminary FIS on January 26, 2021, and revised preliminary FIRMs were issued in December 2021. The
latest revised preliminary FIS for Larimer County , reflecting the RiskMAP program, was issued October 16,
2023 [08069CV001F].
In September 2021, ACE completed a LOMR (Case No. 21-08-0277P) for a proposed development directly
east of the project area. This request used HEC-RAS v5.0.7 and delineated 1- and 0.2-PAC floodplains, as
well as a half-foot floodway. The LOMR became effective on February 15, 2022, and serves as the effective
baseline hydraulics and floodplain mapping for the current study.
1.3 Mapping
The Duplicate Effective topographic surface utilized effective data. Topographic surfaces for the Corrected
Effective and Revised Condition models were developed using updated survey data to reflect existing and
proposed conditions within the project reach. Digital copies of the CE and RC topography, along with
surveyor certifications, are included in Appendix A.
1.3.1 Effective (EC) Topography
The topography used in the 2022 Harmony at I-25 LOMR site was derived from post-2013 flood topography
supplied by the City of Fort Collins and overlaid with 1 -foot survey data from 2020, provided by King
Surveyors. The survey covered the subject property at the southeast corner of Harmony Road and Strauss
Cabin Road.
1.3.2 Corrected Effective (CE) Topography
In June 2021 and in August 2022, Northern Engineering conducted field surveys that were used to develop
the corrected effective topographic surface in the project area. The portion of the corrected effective surface
located outside of the project area utilized the effective topography.
1.3.3 Revised Condition (RC) Topography
The Revised Condition topography was based on the CE topography with a proposed overlot grading plan
and other improvements designed by Kimley-Horn and Associates, Inc. (Kimley -Horn) of Fort Collins,
Colorado.
1.3.4 Vertical Datum and Horizontal Coordinate System Considerations
Regulatory water surface elevations for the 1-Percent Annual Chance (PAC) (aka 100-year) floodplain, as
provided in the Larimer County FIS, are referenced to the North American Vertical Datum of 1988
(NAVD88). All elevation data, topography, maps, and models developed for this study are projected in the
Colorado North State Plane Coordinate System, based on the North American Datum of 1983 (NAD83)
and NAVD88. Maps and models presented in the current study are also projected in Colorado State Plane
North.
Commented [CP2]: Lable Strauss C Rd on Fig 1.2 and
show FEMA Case No. for the LOMR-F on the parcel in Figure
1.2
Commented [CP3]: Do we need to add the Date of last rev
prelim??
Commented [CP4]: How does the 2022 LOMR relate to the
LOMR-F???
Commented [CP5]: New/Updated survey data was the
basis of the DE surface???
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1.4 Purpose and Scope of Study
The CLOMR submittal was prepared for the City of Fort Collins to update the effective floodplain delineation
of the CLPR I-25 DFP at the Serfer property. The study evaluates proposed grading for an overflow channel
and a main channel, a secondary access road and bridge crossing, and localized channel protection where
velocities exceed 5 feet/second. The current hydraulic analyses address water surface elevations for the
2-, 1-, and 0.2-percent annual chance (PAC) events, as well as the mapped half -foot floodway, and have
been completed in acc ordance with FEMA, State of Colorado, Larimer County, and City of Fort Collins
regulatory requirements.
The study reach extends beyond the project site to ensure analytical tie -ins to the effective model at Cross
Sections 28848 and 25775 at the upstream and downstream study limits respectively. The project reach
encompasses the Serfer property and includes Cross Sections 28678 through 27890 (I25 DFP West DS
Reach) and Cross Section1489 (I25 DFP East DS Reach).
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II. HYDROLOGY
The hydrology for this study originates from the original HEC -2 models developed for the Cache la Poudre
River (CLPR). Anderson Consulting Engineers (ACE) carried this hydrology forward in the 2021 LOMR
(FEMA Case No. 21-08-0277P). The peak discharges from that analysis, summarized in Table 2.1, have
been adopted without modification for the current study.
Table 2.1 Effective Hydrology from 2021 LOMR
Reach
Cross
Section
ID:
Station
Peak Discharge (cfs)
Location 2-
Percent
Annual
Chance
1-
Percent
Annual
Chance
0.2-
Percent
Annual
Chance
CLPR I25DFP 30909 1,862 4,353 17,858 --
CLPR I25DFP 30370 1,342 2,368 11,858 --
CLPR I25DFP 28848 1,862 4,725 16,000 Upstream toe of Harmony Road
CLPR I25DFP
East Flow Path 2362 687 1,888 - Serfer Property
CLPR I25DFP
East Flow Path 2123 695 2,385 - Serfer Property
CLPR I25DFP
East Flow Path 2049 741 2,641 - Serfer Property
CLPR I25DFP
West Flow Path 28320 1,175 2,837 - Serfer Property
CLPR I25DFP
West Flow Path 28193 1,167 2,340 - Serfer Property
CLPR I25DFP
West Flow Path 27978 1,121 2,084 - Serfer Property
CLPR I25DFP
West Flow Path 27890 1,121 2,083 - Serfer Property
CLPR I25DFP 25775 1,862 4,725 16,000 --
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III. DUPLICATE EFFECTIVE CONDITION
Per FEMA guidelines, the duplicate effective (DE) analysis may involve: 1) obtaining the presumed effective
model(s); 2) creating a DE model by running a copy of the effective model in the same hydraulic modeling
software as was used in the effective study ; and 3) if necessary, converting the DE model to a newer version
of the same hydraulic modeling software or to a different accepted hydraulic modeling software; and 4)
comparing the modeling results to FEMA published values (typically found in the effective FIS fo r the
community). If any errors are noted, they may be explained and/or addressed at the CE step. The purpose
of the DE model is to establish that the presumedly effective model(s) can reproduce the information
published in the effective flood ins urance study. The DE step also ensures that the hardware and software
used to conduct the current study are compatible with those utilized in the effective study. For the current
study, the effective hydrologic and hydraulic information from the effective 2021 LOMR was used as the
basis for the DE analysis.
4.1 Definition of Hydraulic Plans
The effective 2021 LOMR for CLPR I25 DFP utilized HEC -RAS, version 5.0.7. A copy of the model was
created and executed in HEC-RAS, version 5.0.7 to develop the DE model. The DE model was
subsequently converted to HEC-RAS, version 6.6 for use in this CLOMR submittal to FEMA. The following
HEC-RAS, version 6.6 plans are associated with the DE model:
1. DE 1 and 2% – a multi-profile plan modeling the 2- and 1 PAC events.
2. DE 0.2% – a plan modeling the 0.2 PAC event.
3. DE Floodway – a half-foot 1-PAC floodway run.
4.2 Boundary Conditions, Tie-ins, Roughness Coefficients, and Encroachments
For the DE analysis, all boundary conditions, tie -ins, roughness coefficients, and encroachments are from
the effective model.
4.3 Duplicate Effective Analysis Results
At the beginning of the analysis, it is assumed that the model obtained serves as the basis for the effective
FIS. Upon running the duplicate analysis and comparing the result s to published information, the resulting
DE WSEs within the study reach matched those found in the published FIS (see Appendix A).
After comparing the Duplicate Effective model to the published flood profiles in FIS 08069CV005E (195P –
197P) and verifying that the provided effective model reflects the current conditions, the model was adopted
as the basis for subsequent analyses. Confirmation that the current version of the model used in this study
is an accurate DE model for future analyses is supported by achieving a 0.0 -foot difference between the
DE model results and the published effective data. The full Serfer DE model is included within the electronic
appendices (see Appendix B). The results for the DE Floodplain and DE Floodway are presented in
Appendix D.
Commented [CP6]: Guessing the ‘results’ are for the
floodplain evaluations; what about the floodway DE run and
results. Floodway DE should be documented also.
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IV. CORRECTED EFFECTIVE CONDITION
The purpose of the corrected effective (CE) analysis is to update the DE model with new data, as well as
correcting errors noted within the study reach. The DE model was used as the basis for the CE analysis.
During the CE analysis, the following changes were made to the DE model within CLPR I25 DFP:
1. Cross Sections 28320, 28193, 27978, 27890 2362, 2123, 2049, and 1671 were resampled using
CE topography, and roughness coefficients, bank stations, and reach lengths were adjusted to
represent current conditions.
2. Cross Sections 27949 and 27930 were added to provide additional detail entering the west lake.
3. Cross Sections 27006 and 704 were removed and Cross Section 26873 was added to provide
hydraulic connectivity between the east and west splits.
5.1 Definition of Hydraulic Plan
The CE hydraulic analysis utilized HEC-RAS, version 6.6. The CE condition was developed by duplicating
the DE geometry and flow files, with updates made to the geometry to reflect current natural conditions.
The flow file was updated at cross sections connected to the lateral structure to reflect changes due to
topography. The following are the hydraulic plans constructed for the CE condition analysis:
1. CE 1 and 2% – a multi-profile plan modeling the 2- and 1 PAC events.
2. CE 0.2% – a plan modeling the 0.2 PAC event.
3. CE Floodway – a half-foot 1-PAC floodway run.
5.2 Boundary Conditions, Tie-ins, and Roughness Coefficients
For the CE analysis, the boundary conditions , tie-ins, and roughness coefficients from the DE model were
used; however, where cross-sections were added manning’s roughness coefficients were updated based
on roughness coefficients found in the DE model and verified using Chow 1959.
5.3 Corrected Effective Analysis Results
The comparative water surface elevation table presents the results of the 1 -PAC Corrected Effective (CE)
analysis. When compared to the Duplicate Effective (DE) model, the CE model produced changes in water
surface elevations due to modifications in cross -section geometry and the corresponding flow distribution.
Differences between the CE and DE models range from 0.0 feet to 0.7 feet. These changes occur at cross
sections both within the Serfer property and elsewhere in the study reach. A workmap comparing the CE
and DE 1-PAC floodplain and half-foot floodway delineations is provided in Appendix C.
The most notable increases in water surface elevation are 0.7 feet at Cross Section 27978 and 0.7 feet at
Cross Section 2049. These differences are attributed to updated topography within the project area. For
the CE analysis, floodway encroachments were not modified and therefore remain consistent with those in
the DE model. However, for cross sections added, floodway encroachments were based on the DE
floodway delineation.
Commented [CP7]: Did we verify that this CE topo did not
represent any man-made changes since the date of the
effective study (we will need to discuss if this is the LOMR or
the original FIS study).
Commented [CP8]: Non-man made changes?? Otherwise
this may need to be an existing condition step.
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V. REVISED CONDITION
The purpose of the Revised Condition (RC) analysis is to incorporate proposed topography and other
proposed improvements into the CE analysis. During the RC analysis, the following changes were made
to the CE model:
1. Cross Sections 28615, 28320, 28193, 27978, 2362, 2123, 2049 , 1671, and the associated lateral
structures were removed.
2. Reach I25 DFP West was split into two reaches: I25 DFP West and I25 DFP West DS. The
proposed channel is located in both reaches.
3. Reach I25 DFP East was split into two reaches: I25 DFP NE and I25 DFP East. One of the
proposed channels is located in reach I25 DFP NE.
4. Reach South_Channel was added.
5. A proposed private drive crossing was included near the southwest corner of the site to provide a
secondary/emergency access.
6.1 Definition of Hydraulic Plans
The RC hydraulic analysis for the current study utilized HEC -RAS version 6.6. The RC geometry was
created by modifying the CE model geometry and steady flow files to reflect the proposed improvements
of the project. The hydraulic plans below were used in the RC analysis:
1. RC 1 and 2% – a multi-profile plan modeling the 2- and 1-PAC events.
2. RC 0.2% – a plan modeling the 0.2-PAC event.
3. RC Floodway – a half-foot 1-PAC floodway run.
6.2 Boundary Conditions, Tie-ins, and Roughness Coefficients
Starting water surface elevations, tie -ins, and roughness coefficients from the CE analysis were preserved
in the main channel and overbanks as much as possible. Where the proposed grading updated the cross
section geometry, the Manning’s roughness were based on Chow 1959. The revised boundary conditions
matched those in the CE model. The flow splits for the RC model were determined by optimizing all of the
splits.
6.3 Results
Due to proposed channel modifications, a direct one-to-one comparison between the DE, CE, and RC
models across the Serfer property was not feasible. However, for cross sections common to both the CE
and RC models within the study reach, a comparison of water surface elevations was conducted. The
resulting differences in water surface elevation ranged from -0.6 feet to 0.0 feet.
At Cross Sections 1489 and 27890 (downstream of the site) and Cross Section 28822 (upstream of the
site), the water surface elevations in the CE and RC models matched within 0.0 feet. Results are presented
in the comparison table in Appendix D and the RC verses CE workmap in Appendix C.
6.4 Scour Analysis and Mitigation
A detailed scour analysis will be conducted for the primary channel and the proposed emergency access
crossing. This analysis will follow applicable Local (City of Fort Collins and Larimer County), State (C DOT
and CWCB), and Federal (FHWA) methodologies and guidelines.
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A preliminary assessment was performed to identify areas where local velocities exceed 5 ft/s under the
modeled conditions. These areas are shown in Figure 6.4, where scour mitigation measures are
recommended.
Recommended measures include the use of riprap and/or launch rock in high -velocity zones to protect
channel banks, culvert crossings, and berms, and to prevent upstream headcut migration toward the
proposed emergency access crossing and East Harmony Road. Final design of scour countermeasures
will be completed and submitted as part of a future submittal once detailed scour computations are
performed.
Figure 6.4: Scour Mitigation Map
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VI. FLOODPLAIN MANAGEMENT AND COMPLIANCE
Communities that choose to participate in the National Flood Insurance Program (NFIP) agree to abide by
FEMA’s minimum requirements for floodplain management. The City of Fort Collins and Larimer County
are both NFIP participating communities.
7.1 Local Floodplain Management
The current study covers two local jurisdictions with responsibilities for floodplain management: Larimer
County and the City of Fort Collins. Most of the project site is within the City of Fort Collins, however a
portion of the northeast corner is within Unincorporated Larimer County as previously shown in Figure 1.2.
7.1.1 City of Fort Collins
The City of Fort Collins regulates the floodplain provisions found in Chapter 10 of the City’s Code. The
City’s floodplain ordinance generally follows FEMA’s minimum standards for participation in the NFIP and
is in concurrence with Larimer County’s and the State of Colorado’s floodplain regulations . See the
previous section for the conclusions that support the City’s floodplain regulations.
7.1.2 Larimer County
Larimer County regulates the floodplain provisions found in Article 12.0 Floodplain of the Larimer County
Land Use Code. Based on the hydraulic analysis documented in this report, the following conclusions are
provided in support of Larimer County’s regulations regarding the proposed condition impacts on the CLPR
I25 DFP floodplain:
a) In areas where improvements exist, the proposed condition will generally reduce flood depths and
velocities when compared to existing condition; therefore, decreasing the flood risk to life and
properties in those areas.
b) The proposed project will not add substantial solid debris or other materials that could be carried
away during a flood event, potentially causing adverse impacts downstream.
c) The proposed project is consistent with identified land uses and will not prevent access to property
during a 1% annual chance flood event.
d) Access to properties located in the proposed 1% annual chance floodplain will be like that in the
existing condition or improved.
e) The expected height, velocity, duration, rate of rise and sediment transport of flood waters in the
project reach are consistent between the existing condition and the proposed condition.
f) Based on the hydraulic analyses performed, p otential reduction in river channel and/or floodplain
stability is not anticipated.
7.3 State of Colorado Floodplain Management
The State of Colorado’s floodplain provisions are found in Rules and Regulations for Regulatory Floodplains
in Colorado, 2 CCR 408-1 [CWCB, January 14, 2022].
7.4 Federal Emergency Management Agency
7.4.1 MT-2 Forms
FEMA requires the submittal of the MT-2 forms for a CLOMR. The completed MT-2 forms and the required
documentation are contained in Appendix E. The FEMA review fee required on page 2 of MT -2 Form 1 will
be paid in full by Serfer Land Ventures LLC once the request has been submitted . The annotated FIRM
panel is presented in Appendix E as part of the application indicated on MT -2 Form 2, page 2 of 3.
Commented [CP9]: Need to describe what portions of the
study reach are in each community. Reference to one of the
previous figures with the community boundaries clearly shown
would be real good.
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Community boundaries, obtained from local jurisdictions, are shown on the workmaps presented in
Appendix C. As the primary jurisdiction with responsibility for floodplain management, the City of Fort
Collins was forwarded a copy of the current study and apon approval will subsequently provided their
concurrence by signing MT -2 Form 1. As the adjacent jurisdiction, Larimer County’s signing of an MT-2
Form 1 will also be needed.
7.4.2 Property Owner Notifications
Once FEMA has completed its technical review of the CLOMR, they will request that property owner
notifications (PONs) be submitted for all properties located within the study limits. Galloway will work with
the local jurisdictions to draft and send out property owner notifications. Draft PONs will be located in
Appendix E.X.
7.5 Conclusions
This pre-CLOMR report provides a proposed design and hydraulic analyses supporting a revision of the 1 -
and 0.2-PAC floodplains and floodway on the Serfer property. The proposed improvements detailed in this
report also facilitated a channelization of the 1 -PAC floodplain within the current project reach. Additionally,
no insurable structures adjacent to the effective floodplain were brought i nto either the CE or RC 1-PAC
floodplains.
It is therefore concluded that this study complies with all federal, state, county and local floodplain criteria
including:
(a) Section 44 of the Code of Federal Regulations (CFR), Chapter 1, Parts 60, 65, and 73;
(b) Rules and Regulations for Regulatory Floodplains in Colorado;
(c) The City of Fort Collins Municipal Code; and
(d) Larimer County’s Land Use Code.
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VII. REFERENCES
1. AECOM, Inc., Cache la Poudre and Boxelder Creek RiskMAP Project , Ongoing, Best Available
data as of January 26, 2021.
2. Anderson Consulting Engineers, Inc., Hydraulic Analysis for the Cache La Poudre River at
Harmony and Interstate 25, FEMA Case No 21-08-0277P, Effective January 15, 2022
3. Chow, V.T. (1959) Open Channel Hydraulics. McGraw -Hill, New York.
4. City of Fort Collins, City Code Chapter 10: Floodplain Regulations, June 27, 2023
5. City of Fort Collins, Fort Collins Stormwater Criteria Manual, December 2018.
6. Colorado Water Conservation Board, Rules and Regulations for Regulatory Floodplains in
Colorado, Department of Natural Resources, November 10, 2010.
7. Federal Emergency Management Agency, 44 CFR Parts 59-78, NFIP Final Rules and Regulations,
Part 60-Criteria for Land Management and Use & Part 65 -Identification and Mapping of Special
Hazard Areas.
8. Federal Emergency Management Agency, Flood Insurance Rate Map, Larimer County, Colorado
and Incorported Areas, Panel 1013 of 1420, Community -Panel No. 080101 1013 F, December 19,
2006.
9. Federal Emergency Management Agency, Flood Insurance Study, Larimer County, Colorado and
Incorporated Areas, Vol.s 1-2, Revised: January 15, 2021.
10. Federal Emergency Management Agency, Flood Hazard Mapping Program Guidelines and
Specifications for Flood Hazard Mapping Partners , April 2003.
11. Federal Highway Administration (FHWA) (2009). HEC -23: Bridge Scour and Stream Instability
Countermeasures, 3rd Edition, Volume 1, Chapter 3. FHWA-NHI-09-111.
12. Federal Highway Administration (FHWA) (2012). HEC-18: Evaluating Scour at Bridges, 5th Edition,
Chapters 2, 4, 8. FHWA-HIF-12-003.
13. Larimer County Land Use Code, Article 12: Floodplain, June 1, 2023
14. U.S. Department of the Army, Corps of Engineers, Hydrologic Engineering Center, HEC -RAS River
Analysis System Hydraulic Reference Manual, Ver. 5.0.7, February 2016.
15. U.S. Department of the Army, Corps of Engineers, Hydrologic Engineering Center, HEC -RAS River
Analysis System Hydraulic Reference Manual, Ver. 6.4, June 2023.
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APPENDIX A
APPENDIX CONTENTS