HomeMy WebLinkAbout10 Concept Review Response REF # 40 - Floodplain CorrespondenceFloodplain Narrative
Revised 1-16-2026
Applicant: WAM Dev Group
544 E Main St Suite A
Bozeman, MT 59715
Representative: Jillian Bertelli, AIA 406-600-6755
Project Identification:112 S Church Avenue
Bozeman, MT 59175
Lot legal description: Parcel 1& 2 Block A Rouse’s Second Addition
Please review the following narrative as it summarizes how the Depot on Church project addresses the
City of Bozeman’s floodplain development regulations for a mixed-use building.
The site is shown in red outline on Flood Insurance Rate Map (FIRM) panel number 30031C0817E
effective date 4/21/2021 and the flood source is mapped as the Church Avenue Split (a Split from
Bozeman Creek).
Floodplain Context:
The property boundary nor the proposed building footprint intersect with the regulatory floodway.
However, there will be work within the floodway, for underground utilities, bike parking, and sidewalk
improvement. As shown above, there is no regulatory flood fringe shown on the FIRM.
Per BMC 38.600.130, a Base Flood Elevation was interpolated at the southern boundary corner
(maximum flood elevation) using the closest regulatory BFE data. The interpolated elevation was
calculated to be 4816.2’, shown by the light blue contour line. The contour was developed using the 2021
LiDAR (USGS). - See Interpolation Figure Map for visual detail. Details on the BFE calculation are
included in the FEMA Profile, and Floodway Data Table attached.
Existing Conditions: The revised sheet C100 Existing Topography shows where the delineated
floodplain boundary lies on the site. This drawing shows current site grading and drainage patterns and
existing utilities. The site has been cleared of residential structures with demo approval from the City of
Bozeman, February 26, 2024, file number 24643. No history of flooding or drainage complaints since
WAM Dev Group has owned the property mid-year 2018.
Proposed Development Description: Revised sheet C300 Site Plan shows where the delineated
floodplain boundary lies in relation to the building footprint. The western portion of the building will
encroach into the delineated flood fringe boundary. No building elements will encroach into the regulatory
floodway.
The proposed project, The Depot on Church, is proposed as a mixed-use, new construction building with
six stories above grade plus one lower story basement. It is in the B-3 zoning district and in the
Traditional Core of the Future Land Use Map. The mix of occupancies planned for the building are retail,
office, parking, residential and storage. Using a non-residential classification, BMC 38.600.270.D
(requirements for non-residential building within flood fringe) was applied for design considerations.
The finished floor elevation of the ground floor at the entrance from Church Ave will be 4815.5’. The
ground floor steps 0.92’ and uses an ADA compliant circulation ramp to the mid parking level of 4816.42’
and further slopes in the parking level of 0.2’-1’ to exit at the east alley 4817.0’.
Compliance Measures: The building will meet all FEMA NFIP and local flood plain regulations. The
lobby and retail space entered from the western entrance from Church Avenue will be located below the
base flood elevation, therefore complying with BMC 38.600.270.D.8,the lowest floor will be dry
floodproofed and professionally designed in accordance with FEMA NFIP Technical Bulletin 3. There are
separate pedestrian and vehicular entrances above the BFE that exit to the public alley right of way.
The building will be dry floodproofed to a height 2’-0” above the BFE of 4816.2 to 4818.2. Dry
floodproofing will follow FEMA ASCE 24-14 and ASCE 24-05 as the accepted standard of practice and
construction will follow IBC 2021 and all City of Bozeman requirements. The owners agree to provide
certification that the structural designs, specifications and plans for construction of dry floodproofing
measures will be developed and reviewed by registered professional engineers and architects and follow
guidance from FEMA Form 086-0-34.
Dry Floodproofing Measures will include but not be limited to the following, outlined in FEMA Technical
Bulletin 3, section 1.4:
• Portions of a building, including walls and slabs, reinforced to resist water pressure and
floating debris impacts
• Doors and windows that are specially designed to be watertight when closed without
flood shields
• Removable substantially impermeable panels to cover doors, windows, and other
openings
• Paints, membranes, gaskets, and other sealants that reduce water seepage
• Sump pumps or self-priming pumps that control the level of seepage water
• Backflow (non-return) valves or shutoff valves that prevent floodwater from
entering through sewer and drainage pipes and/or sewage ejectors that pump sewage to
above the flood protection level before the pipes connect to a vertical sewer line
• Seals that prevent the entrance of floodwater through joints and utility penetrations
• Electrical equipment and circuits that are protected to the flood protection level
• Backup or emergency power for sump pumps and other seepage control
measures that is protected to the flood protection level
Sheet C601 shows erosion control details currently planned. A construction logistics plan is being
developed with our team of architects, builders, civil and floodplain engineers, and will be submitted as
part of the floodplain permit requirements. This plan will describe how the project will use best
management practices to limit impacts on flood sources.
The project is currently submitted for Site Plan adequacy and approval and it is understood that a
separate Floodplain Development Permit application is required (BMC 38.600.180). This permit will need
to be submitted and approved prior to final site plan approval. As part of the Floodplain Permit, No-Rise
analysis will be completed to discuss proposed work being done within the floodway, per BMC
38.600.260. The work within the floodway will be temporary, and all infrastructure will be replaced at
existing elevations, and therefore it is anticipated that a qualitative no-rise will be adequate for
compliance.
BMC 38.600.180. – Floodplain Permit Application Requirements
A floodplain permit application will be filed with the floodplain administrator through the PDox electronic
plan review system. The floodplain administrator will be notified of the submitted application by directly
emailing llehigh@bozeman.net and include the following information:
B. The floodplain administrator may require additional information for the floodplain permit application
depending on the nature of the proposed use, activity or artificial obstruction, including but not limited to:
1. Scaled topographic plan view exhibit(s) of the project area with one-foot contours and
elevation values displayed in NAVD88 vertical datum depicting:
a. Linetype legend, drawing scale, and north arrow
b. Existing ground contours certified by a professional engineer or
registered land surveyor
c. Location of watercourse or drainway channel and banks
d. Delineated boundary of the regulated flood hazard area pursuant to
38.600.130.B
e. Proposed ground contours and delineation of proposed regulated
flood hazard boundaries pursuant to a conditional letter of map change
issued by FEMA; and f. Location of all proposed improvements and
artificial obstructions
2. Cross sections of the proposed project that clearly differentiate between existing site
conditions and proposed site conditions
3. Proposed building elevations showing the elevation of the lowest floor, including any
basement or crawlspace, proposed finished ground elevation, and the base flood
elevation
4. Specifications for floodproofing, filling, excavating, grading, bank stabilization, storage
of materials and location of utilities
9. A floodway encroachment analysis and no-rise certification prepared in accordance
with and signed by a professional engineer together with any hydraulic modeling utilized
for the no-rise analysis
11. For a new building, or alteration or substantial improvement to an existing building, a
completed FEMA elevation certificate based on construction drawings
13. A professional engineer's or registered architect's certification within their respective
areas of expertise that the proposed use, activity, or artificial obstruction has been
designed to be in compliance with this division
BMC 38.600.260 Requirements for Permitted Uses in the Floodplain
A. Proposed development in the floodway includes replacement of streetscape elements, (ie
sidewalk, tree planting) and will add utility connections and bike racks. All elements will meet
COB downtown district development standards.
B. Improvements in the floodway will be designed and constructed to minimize flood damage and
ensure they do not adversely affect the flood hazards of other properties or be swept downstream
to the injury of others.
C. The project assures that all uses, activities and artificial obstructions do not reduce the carrying
capacity of the regulatory floodway.
As stated above, a floodplain permit will be submitted separately, prior to final site plan approval. The
floodplain permit will show compliance with all applicable parts of section 38.600.270 listed below. With
the floodplain permit, a construction logistics plan will be included for review, minimizing work within the
regulatory floodway.
BMC 38.600.270.D: Requirements for New Buildings Permitted in the Flood Fringe
1. The new construction of the mixed-use building will conform to the requirements of this chapter
and BMC Chapter 10 and is not prohibited by any other statute, regulation, ordinance or
resolution.
2. Such buildings and structures are compatible with local growth policies, the Future Land Use
Map, the Bozeman 2020 Community Plan, and the B-3 zoning district guidelines.
3. The building and structures will be constructed by methods and practices that minimize flood
damage and are professionally designed to be safe from flooding and structured to flotation,
collapse and lateral movement.
4. Grading around such buildings and structures is designed with adequate surface drainage.
5. All materials used for construction are resistant to flooding to an elevation at least two feet
above the base flood elevation of 4816.2.
8. This non-residential building shall be certified by a professional engineer or registered architect
to be adequately floodproofed in accordance with the following:
a. The lowest floor of the building or structure must be adequately wet or dry floodproofed
to an elevation at least two feet above the base flood elevation
b. The building or structure shall be designed to withstand hydrostatic, hydrodynamic,
and buoyancy forces of the base flood
c. Wet floodproofing is only permitted when the lowest floor of a building or structure is
used for parking, loading, or storage of equipment or materials not appreciably affected
by floodwater
d. Wet floodproofing must provide adequate openings to equalize hydrostatic forces; and
e. Dry floodproofing will not allow floodwaters to cause internal flooding of the building or
structure by using impermeable membranes and materials for construction of floors and
walls, and must ensure that all windows, doors and other openings are watertight and do
not allow the passage of floodwaters.
12. All electrical systems shall be certified by a professional engineer to satisfy all applicable flood
hazard area provisions of the current adopted building codes set forth in chapter 10 along with
the following requirements.
a. All incoming power service equipment including all metering equipment, control
centers, transformers, distribution and lighting panels, and all other stationary equipment
is shown to be located at least two feet above the base flood elevation.
b. Portable and movable electrical equipment may be placed below the base flood
elevation, provided that the equipment can be disconnected by a single plug and socket
assembly of the submersible type
c. The main power service lines must have automatically operated electrical disconnect
equipment or manually operated electrical disconnect equipment located at an accessible
remote location outside the regulated flood hazard area or shall be two feet above the
base flood elevation
d. All electrical wiring systems installed below the base flood elevation shall be suitable
for continuous submergence and may not contain fibrous components
13. All mechanical systems shall be certified by a professional engineer to satisfy all applicable
flood hazard area provisions of the currently adopted building codes set forth in chapter 10 along
with the following requirements.
a. Float operated automatic control valves shall be installed so that fuel supply is
automatically shut off when flood waters reach the floor level where mechanical systems
are located
b. Manually operated gate valves shall be installed on gas supply lines. The gate valves
shall be operable from a location above the base flood elevation
c. Electrical components of the HVAC systems shall meet the requirements of D.12
above; and
d. Furnaces, cooling units, and all associated ductwork shall be installed at least two feet
above the base flood elevation
14. All plumbing systems shall be certified by a professional engineer to satisfy all applicable
flood hazard area provisions of the current building codes set forth in chapter 10 along with the
following requirements.
a. The building sewer line shall have a backwater valve installed to prevent sewage
backup into the building.
FEMA Technical Bulletin 3 allows this building to be dry floodproofed through section 1.3, “Dry
floodproofing is permitted for new and substantially improved non-residential and non-residential portions
of mixed-use buildings in Zone A,” but there are definitions of use by inhabitants that are allowed to
occupy dry floodproofed areas are defined in FEMA P-2037. It should also be noted here, that according
to Technical Bulletin 3, page 7, the use of the term “Zone A” refers to Zones A, AE, etc. The floodway on
Church Avenue is classified as a Zone AE.
FEMA P-2037 section 1.7 Dry Floodproofing states; “when properly designed, constructed, and certified
to be dry floodproofed, the lowest floor of a mixed-use building is allowed below the BFE; however, the
lowest floor can only be used for non-residential purposes. While access to the residential spaces is
allowed from a dry floodproofed lobby that serves both commercial and residential spaces, the lowest
floor of all residential areas must be elevated to or above the BFE.”
FEMA P-2037 Table 5-9 shows the mitigation measure for new construction in Zone A to allow dry
floodproofing of non-residential areas of mixed-use buildings. The table also shows the mitigation
measure for new construction in Zone A to allow dry floodproofing MEP components (vaults).
Sheet SP200 Basement Floor Plan shows that use is limited to mechanical use, bathrooms with showers
for use by office inhabitants and primarily storage. Sheet SP201 shows use of the ground floor as lobby,
retail and parking.
The project will follow the requirements of ASCE 24 Chapter 7 that applies to attendant utilities and
equipment for new construction in collaboration with all utility providers including but not limited to; City of
Bozeman, Northwest Energy, Yellowstone Fiber, Spectrum and Blackfoot.
Mechanical/electrical equipment and plumbing fixture installations will be designed per floodproofing
standards. Elevator equipment will follow the current building code including applicable ASCE 24
standards for Flood Resistant Design and Construction. There is no gas service planned for the building
and electric service will enter the building from the alley to the east.
Mechanical and electrical design and construction will follow FEMA Technical Bulletin 3, Section 6.6: The
NFIP regulations and ASCE 24 permit equipment and service facilities to be below the flood protection
level when “designed … to prevent water from entering or accumulating within the components during
conditions of flooding” (44 CFR § 60.3(a)(3)(iv)). The expectation is that after being submerged,
equipment and facilities below the flood protection level will be able to be restored to functioning with
minimal cleaning and repair.
Connections for temporary equipment will be installed above the Flood Protection Level (FPL) of 4818.2’.
A good practice is to install connections for temporary equipment above the flood protection level or
design interior core areas, as discussed in Section 3.3 of FEMA P-936. Additional guidance is available in
FEMA P-348,Protecting Building Utility Systems from Flood Damage (2017).
See below for:
Floodway Data
BFE Calculation Table
BFE Calculation Map