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CIVCO Engineering, Inc.
Vernal, Utah
CIVCO Engineering, Inc.
Civil Engineering Consultants
PO Box 1758 * 1256 W 400 5, Suite 1
Vernal, Utah 84078
September 27, 2016
RE: Resource Engineering Inc. Comment letter and Staff Report, both dated August 16, 2016
Resource Comment 1
The anchoring system is listed as an over the top tie clown in the CIVCO report, but the design
drawings show a foundation system with tie straps to the floor joists. Both systems are
acceptable, but the Applicant should clarifi' the design so that the floodplain permil and building
permit are consistent for the project.
Response
The text of the flood plain report has been revised to say "the structure VI, i I I be anchored using tie
straps on the chassis frame anchored to the exterior concrete foundation".
Resource Comment 2
The grading plan on Street 2 of the CIVCO drawings calls out a high point on the gyres! fence line
with half the drainage flowing north and liar f flotit'ing to the south. The existing topography does
not appear to support this label. RESOURCE agrees with this approach so as to not impact the
property to the gest. 11 is recommended that the drawings indicate specific elevations al the high
point and at the northwest and southwest corners for the contractor to provide the intended
drainage concept.
Response
The grading plan has been revised to include the spot elevations at the high point and the corners
of the lot.
Resource Comment 3
The plans indicate a crawl space for the foundation system. The Applicant should address
location, elevation and size of openings and address compliance with enclosure openings if
appropriate. Specifically, the east side of the structure foundation could be subject to flooding in
the crawl space.
Response
The foundation plan has been revised to show the flood openings.
Phone (435)789-5448 * Fax (435)789-4485
Email: civcoia civcoengineering.com
Staff Comment 4 a
Confirmation that all utility connections are designed and protected front infiltration by flood
waters and confirmation that all utilityfacilities and equipment such as air conditioning units
will be elevated al least one foot above the FEU/1 anticipated level offlood waters. This
information ormation shall be provided with the building permit application.
Response
Utility Note 5 has been added to Sheet No. 1 - Site Layout and Utility. Plan addressing this
comment.
Staff Comment 4 b
Plans for landscaping or re -vegetation of disturbed areas to minimize the potential for soil
erosion in the event of a flood Evidence of initial re -seeding shall be required prior to issuance
of a certificate of occupancy.
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Response
Staff Comment -1 c
A determination that the proposed grading plan will not adversely affect any adjacent property
owners.
Response
The site plan has been designed to eliminate adverse impacts to adjacent Tots and it is the opinion
ofCIVCO Engineering, Inc. that if constructed according to plans, the grading will not adversely
affect any adjacent property owners.
Page 12
CIVCO Engineering, Inc.
Vernal, Utah
CIVCO Engineering, Inc.
Civil Engineering Consultants
PO Box 1758 * 1256 W 400 5, Suite 1
Vernal, Utah 84078
May 4, 2016
Amended September 27, 2016
RE: CMH Flood Plain Development Permit (File No. FDPA-04-16-8445)
1.0 Summary
The Chavez residence will be located on Lots 8 & 9 Rifle Village South; on Remington Ave. in
Garfield County. This property is situated within a Zone AO Special Flood Hazard Area
(SFHA) subject to inundation by the 100 annual chance flood. Zone AO is defined as "Flood
depths of I to 3 feet (usually sheet flow on sloping terrain); average depths determined. For areas
of alluvial fan flooding, velocities also determined." The flood zone is associated with alluvial
fan flooding from Helmer Gulch, and the 100 year discharge is defined as 760 cubic feet per
second (cfs). The flood depth in this area is defined as 1 foot with a velocity of 4 feet per second
(fps). The entire parcel is located within the flood zone.
The proposed residence will be a single story manufactured home with treated lumber framed
perimeter foundation walls on concrete footings and chassis supports on spot footings throughout
the crawl space. The structure will be anchored to resist flotation using tie straps on the chassis
frame anchored to the exterior foundation. The finished floor elevation (FFE) will be 2 feet
higher (5365.37) than the highest adjacent ground elevation (5363.37). The lot will be graded to
provide positive drainage away from the structure in all directions.
2.0 County Floodplain Overlay Regulations
The Garfield County Land Use and Development Code specifies general standards for
development within a floodplain and specific standards that apply to the different types of SFHA
zones that have been defined. The sections of that code that apply to the proposed project are 3-
301 B -G, 4-109, and 4-203. These sections are discussed in sections 2.1, 2.2 and 2.3 of this
report.
2.1 Garfield County Land Use and Development Code 3-301
3-301 B. General Standards.
In the Floodplain Overlay, the fallowing provisions are required for all New Construction
and Substantial Improvements:
1. All New Construction or Substantial Improvements shall be designed (or modified) and
adequately anchored to prevent flotation, collapse, or lateral movement of the
structure resulting from hydrod}mantic and hydrostatic loads, including the effects of
buoyancy.
Phone (435)789-5448 * Fax (435)789-4485
Email: civco@civcoengineering.com
The proposed residence will be a single story manufactured home with treated lumber framed
perimeter foundation walls on concrete footings and chassis supports on spot footings throughout
the craw I space. The structure will be anchored to resist Flotation and lateral movement using tie
straps on the chassis frame anchored to the exterior concrete foundation. Refer to attached
foundation plans.
2. All New Construction or Substantial Improvements shall be constructed by methods
and practices that minimize food damage.
The proposed project site has been designed to minimize the probability for floodwaters to
impact the proposed structure. Refer to sections 4.0 Site Grading and 5.0 Flood Damage
Protection. Construction materials have been specified according to the International Residential
Code Section R401. Refer to attached foundation plan.
3. All New Construction or Substantial Improvements shall be constructed with materials
resistant to flood damage.
Foundation materials have been specified per the International Residential Code Section R401.
Refer to section 4 Site Grading and to the attached foundation plan.
4. All New Construction or Substantial Improvements shall be constructed with
electrical, heating, ventilation, plumbing, and air conditioning equipment, and other
service facilities that are designed annd`or located so as to prevent water from entering
into or accumulating within the components during conditions of flooding.
The finished floor elevation of the structure swill be 5365.37 feet which is 1 foot higher than the
reported flood water depth. A concrete slab for the air conditioning unit will be constructed with
a finished top of slab elevation of 5364.37 feet. All electrical, heating, ventilation, plumbing.
and air conditioning equipment, and other service facilities have been designed to keep those
systems higher than the 100 -year floodwater elevation. Refer to section 5.0 Flood Damage
Protection.
5.1111 Manufactured Homes shall be installed using methods and practices which
minimize flood damage. For the purposes of this requirement, Manufactured Homes
must be elevated and anchored to resist floatation, collapse, or lateral movement.
Methods of anchoring may include, but are not limited to, use glover -the -top or frame
ties to ground anchors. This requirement is in addition to applicable State and local
anchoring requirements for resisting wind forces.
The structure will be anchored to resist flotation and lateral movement using tie straps on the
chassis frame anchored to the exterior concrete foundation. The foundation has been designed
according to the International Residential Code section R401. Refer to section 5.0 Flood
Damage Protection and to the attached foundation plans.
Page 2
6. All new and replacement water supply systems shall be designed to minimize or
eliminate infiltration offload waters into the system.
The proposed project w ill connect to the Rifle City culinary water system. The water service
lateral will be water tight and will terminate above the finished floor.
7. New and replacement sanitary,, sewage systems shall he designed to minilnize or
eliminate infiltration of flood waters into the system and discharge from the systems
into flood waters.
The proposed project will connect to the Rifle City sanitary sewer system. The sewer service
lateral will be water tight and will terminate at or above the finished Floor.
8. On-site ~taste disposal systems shall be located to avoid impairment to them or
contamination from them duringflooding.
Does not apply. There is no on-site waste disposal system.
3-301 C. Specific Standards. In the Floodplain Overlay, where BFE data hav been provided.
Does not apply. Base flood elevation has not been provided on FIRM.
3-301 D. Floodiray.
The proposed structure is not located within the floodway. The floodway will not be altered in
any way by this project. Refer to attached FIRM.
3-301 E. Standards for Areas of Shallow Flooding.
Areas designated as shallow flooding are located within the SFHAs. These areas have
special flood hazards associated with Base Flood depths of 1 10 3 feet where a clearly
defined channel does not exist and where the path of flooding is unpredictable and where
velocityflow may be evident. Such flooding is characterized by' ponding or sheet flow;
therefore, the following pro visions apply:
1. A11 New Construction and Substantial Improvements of residential structures have the
Lowest Floor (including Basement) elevated above the highest adjacent Natural
Grade at least 1 foot above the depth number specified in feet on the community's
FIRM (at least 3 feet if no depth number is specified).
The high point of the lot around the perimeter of the proposed structure has an elevation of
5363.37 feet and is located at the south east corner of the proposed structure. The finished floor
elevation of the structure will be 5365.37 feet which is 1 foot higher than the reported flood water
depth of I foot.
Page j 3
2. All New Corn.struction and Substantial Improvements of nonresidential structures:
Does not apply. This is a residential structure.
3. Adequate drainage paths around structures are required to guide flood waters around
and aii cn from proposed structures_ Drainage shall not adversely impact adjacent
properties.
The lot will be graded to provide positive drainage away from the structure in all directions. The
existing site is crowned and approximately one quarter of the lot drains northerly toward
Remington Avenue. The remaining three quarters of the lot drains to the alley on the northern
side of the lot. Proposed site grading will maintain the same general grading pattern. Refer to
section 4.0 Site Grading and the grading and drainage plan attached to this document.
3-301 F. Properties Removed from the Floodplain bt' Fill.
Does not apply.
3-301 G. Alteration of a Watercourse.
Does not apply.
2.2 Garfield County Land Use and Development Code 4-109
4-109. DEVELOPMENT IN THE 100 -}EAR FLOODPLAIN.
4-109A. Overview. Applications for development within the 100 -year Floodplain must
receive a Floodplain Development Permit prior to any development.
A floodplain development permit has been applied for.
4-10913. Review Process. Development in the 100 -)'ear Floodplain shall be processed
pursuant to section 4-103, Administrative Review. A Floodplain Development Perrllit shall
be issued upon approval of the application.
Pending review by county.
4-109C. Review Criteria. A Floodplain Development Permit may be issued by the Director
or designated Floodplain Administrator if it is found that the application is in conformance
with section 3-301, Floodplain Overlay Regulations, and upon weighing the following
relevant factors:
1. The danger to life and property due to flooding or erosion damage;
Refer to section 3.0 Flood Plain Analysis.
Page 14
2. The susceptibility of the proposed facility and itv contents to flood damage and the
effect of such damage on the individual owner;
Refer to sections 3.0 Flood Plain Analysis, 4.0 Site Grading and 5.0 Flood Damage Protection
and the attached site plan drawings.
3. The danger that materials may be swept onto other lands to the injury of others;
Refer to sections 3.0 Flood Plain Analysis, 4.0 Site Grading and 5.0 Flood Damage Protection
and the attached site plan drawings.
4. The compatibility of the proposed use with existing and anticipated development;
The proposed single family dwelling is located within a residential subdivision.
5. The safety of access to the property in tines of flood for ordinary and emergency
vehicles;
The proposed project will have no effect on the safety of access to the property by ordinary or
emergency vehicles.
6. The costs of providing governmental services during and after flood conditions,
including maintenance and repair of streets and bridges, and public utilities and
facilities such as sewer, gas, electrical, and water systems;
The proposed project will not increase the costs of providing governmental services during and
after flood conditions.
7. The expected heights, velocity, duration, rate of rise, and sediment transport of the
flood waters and the cif -eels ofwave action, if applicable, expected al the site;
Refer to section 3.0 Flood Plain Analysis.
8. The necessity to the facility of a waterfront location, where applicable;
Does not apply.
9. The availability of alternative locations, not subject to flooding or erosion damage, for
the proposed use;
Does not apply.
10. The relationship of the proposed use to the Comprehensive Mania,- that area.
The proposed single family dwelling is located within a residential subdivision.
Page 1 5
2.3 Garfield County Land Use and Development Code 4-203
4-203 4. Floodplain Analysis. When a project is located within a Special Flood Ha_ard
Area, if there is an indication or suggestion that a project is located in a SFHA, or if a
project is a division of land or a PUD over 5 acres in size or proposes 50 lots or greater, the
application mast include a Floodplain Analysis.
L Floodplain Specific Site Plan. The Applicant shall submit a Site Plan ii'ith specific
information pertaining to the SFHA and shall include the following elements. The
Floodplain Administrator may require, or the Applicant may choose to submit, a more
detailed version of till or part of the Site Plan. Any elevation information shall be
provided in the North American Vertical Datum of 1988.
a. Base Flood hoiindary and water surface elevations;
Refer to attached FIRM.
b. Floodway boundary;
Refer to attached FIRM.
c. Channel of water course;
Refer to attached FIRM.
d. Existing and proposed topographic contours shown al vertical intervals of no
greater than ? feet;
Refer to the attached site plan draw ings.
e. Elevation of the Lowes! Floor, including Basement and garage, or each existing and
proposed structure;
Refer to the attached site plan drawings.
f. Proposed elevations to which structures will be flood -proofed;
Refer to the attached site plan drawings.
g. Existing and proposed location, dimension, and elevation of proposed landscape
alterations, structures, streets, water supply and any sanitation facilities;
Refer to the attached site plan drawings.
Page ; 6
h. Boundaries and total land area of existing and proposed impervious surfaces,
including structures; and
Refer to the attached site plan drawings.
i. Location of existing crater supply ditches, irrigation ditches and laterals.
Refer to the attached site plan drawings.
2. A certificate from a qualified professional engineer or architect that the nonresidential
flood -proofed structure shall Inca the flood -proofing criteria in section 3-301.C.2.,
Specific Standards for Nonresidential Construction.
Does not apply. This is a residential structure.
3. An elevation certificatefrom a qualified professional surveyor, engineer or architect
that certifies that all residential construction and mechanical equipment will be at
least 1 foot above BFE.
Refer to the attached elevation certificate, prepared by Kipp Land Surveying.
4. Description of the extent to which any watercourse or natural drainage ti, i11 be altered
or relocated as a result of proposed development.
No watercourse or natural drainage will be altered or relocated as a result of the proposed
development. Refer to the attached grading and drainage plan and FIRM.
5. An engineer's report completed by a qualified professional engineer experienced in
hydrology or hydraulics, using a methodology acceptable to FERIA or the CWCB, that
address the standards in section 3-301. B -G. of this Code.
This report has been prepared to specifically address the requirements of the Garfield County
Land Use and Development Code 3-301.8-G and standard level of care for development within
an SFHA.
3.0 Flood Plain Analysis
The Zone AO SFHA is an alluvial fan shallow flood plain. In an alluvial flood plain, the entire
plain is not inundated during every flood event. An alluvial flood plain is formed over thousands
of years. High velocity, sediment laden flood waters enter the flatter flood plain and gradually
slims until the waters no longer have the energy required to transport the sediment they contain.
When the waters slow sufficiently, the sediment settles out of the water creating deposits on the
flood plain. As this process occurs over many years the alluvial fan changes shape
topographically and flow paths are changed for each succeeding flood event.
Page 7
The 100 year flood discharge at the mouth of Helmer Gulch is 760 cfs with a flood depth defined
at a depth of 1 foot with a velocity of 4 fps. The width of the flood plain at the project. scaled
from the firm map, is approximately 3500 feet. Using the continuity equation (Q ® vA) we can
solve for the width of flow of the 100 year flood, which will be approximately 190 feet. From
this, in the event of a 100 year flood (0.1% chance) the percent chance for this property to be
inundated is approximately 5% (190ft/3500ft).
Other factors influencing flooding in this area include roads, grading due to land development
and farming activities and the development of 1 Telmer Gulch itself. The alluvial fan has been
developed significantly over the past 40 years. The roads in the Rifle Village South Subdivision
alone will do much to channelize and potentially split the flow of flood waters through this area.
This report does not include the analysis of these impacts, but merely mentions them to show
that by following the standards specified in the Garfield County Land Use and Development
Code, the proposed residence will be reasonably protected from damage caused by flooding.
A flood plain report prepared by Jerome Gamba & Associates in May of 1996 was referenced in
the preparation of this report. A copy of that report has been attached to this document.
4.0 Site Grading
The project site is currently vacant. Remington Avenue drains generally from east to west. The
existing site is crowned and approximately one quarter of the lot drains northerly toward
Remington Avenue. The remaining three quarters of the lot drains to the alley on the northern
side of the lot. Proposed site grading will maintain the same general grading pattern.
The high point of the lot around the perimeter of the proposed structure has an elevation of
5363.37 feet and is located at the south east corner of the proposed structure. The finished floor
elevation of the structure will be 5365.37 feet w hick is l foot higher than the reported flood water
depth of 1 foot. Finished grade eleNations around the structure will be 18 inches below the FFE
or 6 inches above the existing grade. A concrete slab for the air conditioning unit will be
constructed with a finished top of slab elevation of 5364.37 feet. The lot will be graded to
provide positive drainage away from the structure in all directions. Refer to the grading and
drainage plan attached to this document.
5.0 Flood Damage Protection
The proposed project will connect to the Rifle City culinary water and sanitary sewer systems.
Service laterals will be water tight and will terminate at or above the finished floor, thereby
minimizing or eliminating the infiltration of potential flood waters into either system.
To protect the proposed structure from flotation, collapse or lateral movement. the structure will
be anchored using tie straps on the chassis frame anchored to the exterior concrete foundation at
regular intervals along the north and south sides.
Openings in the foundation wall have been designed to automatically equalize hydrostatic flood
forces on exterior walls by allowing for the entry and exit of flood waters. Openings have been
Page ! 8
designed using guidance found in FEMA Technical Bulletin 1-08 Openings in Foundation Walls
and Walls of Enclosures. Refer to foundation plan.
6.0 Conclusion
The proposed project has been designed with flood protection in mind. The Garfield County
Land Use and Development Code and FEMA Technical Bulletin 1-08 have been used as for
guidance in the selection of measures used to protect the proposed structure from flood damage.
By constructing the site according to the proposed site plan and the Development Code, and
following FEMA guidelines, the home will be reasonably protected from damage caused by
flooding.
Prey red by:
hn B. Barras
Approved by:
Vance V. King, P.E.
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