HomeMy WebLinkAboutFloodway Impedance Analysis (Supplemental Report)'-FLOOD,WAY IMPEDANCE ANALYSIS` OF THE
.10 MILE CREEK FLOODWAY
,AT
-11258. MUL(EIR ROAD
(Supplemental Report)
Si. Lucie Cbunty, Florida
Prepared " By::
Culpepper &.Terpeningi Inc.
March 2015
C—rjO'b, Number 52-19LbO1.
Introduction
In September 2012, the firm of Culpepper & Terpening, Inc., was retained to perform an analysis and review
of the impacts upon a portion of the 10-Mile Creek Floodway through the redevelopment of an existing
residentially used property located at 11298 Muller Road, in unincorporatediSt. Lucie County, Florida. In the
pre -redevelopment condition of the subject property, the property contained a single family residence with
accessory structures. Through the planned re -development activity of the property, the new property
owner sought to remove and replace the existing structures on the property with a new single family
residence with new accessory use structures.
In the September 2012 report of the subject property, Culpepper & Terpening, Inc., identified that there was
a 'pre -redevelopment' floodway impedance area of approximately 118.5 square feet on the subject property.
Through the initial redevelopment of the property, that area of impedance was reduced to 113.4 square feet,
leaving a difference of 5.1 square feet that 'could potentially' be used to address any future expansions on
the property.
Historic Aerial Photographs
We have attached historical site aerials of the petitioned property. "Exhibit A— Historical Aerials", depicts a
site aerial that was taken in 1944 prior to the construction of the existing residence. The second part of this
aerial is an image of the property taken in 1958, which shows the existing home located at what is now
referenced as 11298 Muller Road, in unincorporated St. Lucie County, Florida.
Boundary and Topographic Survey
We have attached as "Exhibit B" a copy of the Boundary & Topographic Survey performed by Culpepper &
Terpening, Inc., dated July 18, 2012, for the property located at 11298 Muller Road, in unincorporated St.
Lucie County, Florida.
FEMA Map
We have attached as "Exhibit C" a copy of the FEMA FIRM Map No. 1211C0164J, Dated 02/16/12, which
identifies the area of floodway designation along Ten Mile creek and provides an approximate base flood
elevation of 18.2 NAVD at the property located at 11298 Muller Road, in unincorporated St. Lucie County,
Florida..
Pre -Development Floodway Impedance
Per FEMA definitions, a Floodway is defined as " The channel of a river or other watercourse and the
adjacent land areas that must be reserved in order to discharge the base flood without cumulatively
increasing the water surface elevation more than a designated height". Floodway Impedance, is described as
being a structure or feature located within a designated floodway that will impede the floodwaters of given
river or stream causing a rise in the base flood elevation of the area impacted. In the case of the subject
property, "Floodway Impedance" has been calculated based on the cumulative area, in square feet (sf), of
the existing structures on the property as measured perpendicular to the stream flow. In calculating the
Floodway Impedance, it is first necessary to determine the "vertical impedance" of each structure. Vertical
Impedance is defined as the difference between existing grade and the Floodway Elevation, measured in
Floodway Impedance Analysis Report
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feet. The horizontal impedance of each structure is calculated based on, the horizontal distance of the
structure as measured perpendicular to the stream flow.
In accordance with FEMA analysis standards, if a structure is in the shadow of another upstream structure
then the downstream structure doesn't add additional impact to the Floodway. In addition, structures such
as carports, pole barns, and sheds which have open sides that do not impede the stream flow, were
considered as no additional impact to the Floodway.
In the case of the subject property located at 11298 Muller Road, in unincorporated St. Lucie County, Florida,
the "Floodway Impedance" for each structure was calculated in square feet (SF) by multiplying the vertical
impedance by the horizontal impedance. in the pre -redevelopment condition, the "Pre -Development
Impedance" was calculated as 118.50 square feet as shown below in Table 2.
Table 2
Pre -Re -Development Impedance
111101�I� � � •�"" �r �
iv.`S3.�' M�a
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1�/y^H•r.�-�.z���},wlKiuyaYk.1J"�%YA.'�r`�.
og
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ax !i
.Fs��c
Residence
18.62
18.20
17.10
1.10
63.00
69.30
Pump House
18.58
18.20
16.70
1.50
19.00
28.50
Pole Barn
17.36
18.20
17.05
1.15
18.00
20.70
Garage
N/A
N/A
N/A
N/A
N/A
N/A
Carport
N/A
N/A
N/A
N/A
N/A
N/A
TOTAL
118.50
Initial Redevelopment Impacts on 10 Mile Creek Floodway:
The Initial Redevelopment Plan of the subject property called for the following uses to be located on the
property:
Table 3
New Structures to be Built
,yrcF d �..H 5 P Y is 3r iikvJ' 'J
"' �f p.�5rw}�°Yli..,,
,xt,Ae d}�`lY�r�.�.SF2�t�'�w
w�' 4"'
Single Family Residence
2,700 'SF
Garage
800 SF
Pump House
180 SF
Pole Barn (FUTURE)
640 SF
TOTAL
4,320 SF
Post ReDevelopment Floodway Impedance
Based on the above planned uses, a post re -development Floodway Impedance for the subject property was
calculated utilizing the same methodology in calculating the Pre -Development Floodway Impedance. The
new structures that were built on the property are shown in the attached "Exhibit ,Fort.&VARRJ
Floodway Impedance Analysis Report
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Impedance." The original Post Development Floo6wayImpedance associated with the redevelopment nfthe
subject property has been calculated as 6aing113.4D square feet. Howthis number was determined is
depicted in Table 4 below, "Post Development Impedance".
Table 4
Post Development Impedance (initial Review)
FAWN
ir
Garage
18.29
18.20
N/A
N/A
N/A
TOTAL
113.40
mmz: Foie barn indownstream im,eci"=ce snaeow Or eXiSlIng "MI"re"
The Property Owner is now proposing a small expansion to the existing residence on the subject property and
since the subject property remains |mddo the designated floudwayfor 10'W1i|u Creek at Muller Road, an
updated calculation has been made using the same methodology as in the original computations. Table
depictsthecom6inationoftheedobngareaoficnpaot(impedanoe)withtheeveaofaddition.
Table 5
Post Development Impedance (Supplemental Review)
Garage
18.29
18.20
N/A
N/A
N/A
TOTAL
116.70
Note: �Pole barn mdownstream impedance snaavwwexisting stru�"�"
Based on the initial, pre -redevelopment, impedance area of11D.5 square feet, the new calculated area of
impedance, including the new addition to the existing home on the subject property, is 116.7 square feet.
Even with this area of addition, the overall area of impedance is still below I the initial base condition used to
determine base f(uodvvoyarea for this portion of1O'K8UeCreek. .,m* w A9,
noodway Impedance Analysis Report Prepared By: Culpepper & Terpening, Inc.
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than, orequal to,the'�ra.beuebpmeotencroachments (those prior to, 2O122)"foundonfhe.prope | and thus
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Floodway Impedance Analysis Report
Prepared By: Culpepper & Terpening, Inc.
END OF DOCUMENT
Page 10 of 10
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April 2, 2015
C&T Project No. 12-191.001
p.\pro]-2015U5-000 drawdy -11298 muller rd - floodway imped report\15-000 drawdy, 001a, floodway report 150326- draft 2.doc