HomeMy WebLinkAboutA1 )FOX
MEMO
June 29, 2012
TO: City of Ames, Planning&Zoning and Public Works
FR: Scott Renaud, P E. :`
RE: No Rise Certification
Deery Brothers Site
FOX Re`..No.5174 12h.410
Attached are the draft calculations for the no-rise certification. There are 3 parts to the attached
documentation, First is the existing condition. Second is the fill without the channel modification. Third
is the fill and the channel modification. We are having this work done by Aaron Bousselot, P.E., of ICON
in Denver who had done all the work at FOX prior to leaving and going to ICON. Below are his
cornrnents:
The NEC RAS files.have been set up to model several scenarios:
Existing conditions
Proposed Deery site(no channel work)
Proposed Deery site with channel repair
Please note that the FEMA effective model was not obtained. 1'nsteod, recent survey and LiDAR was used
to develop the existing conditions model. Additionally: bridge structures were not included in the models.
in order utilize effective data, the tailwater at downstream cross section was set of elevation 882.0 to
match the effective BFE. As we discussed before, backwoterfrom the Hwy 30 bridge controls flood
elevotions.
Attached ore.pdf NEC:RAS output files for eocti scenario. Also ottoched is summary spreadsheet showing
changes to 100 year water surfacf elevations(U 5EL). if the Decry site isrorrsfruc ted without channel
mprovements, a minimal rise(less than o.1 ft)is anticipated. With channel improvements, the WSEL is
less and no-rise con be achieved.
FEMA instructions for No Rise Certification are attached. The last page of the.doc has on exompie form
that con be used for a No-Rise submittal.
Once you have had tirne to review this information and have someone on board to do the technical
review we will exchange the electronic files so the calculations can be verified. We are in the process of
getting the Corp of Engineers and IDNR approval of the channel modifications.
74 _.. :a. ,,:n s�, tt:j:y :,F.C is r,_,�;,r.:;3 z�';�nk k�ti.., N ;
REVVIE
I
1 Y OF AMES, iOWA
E
MA
3 '
Federal Emergency Management Agency
3003 Clramiflec-Tucker Road
At1315t.a,6A 3{)34]
CA IRANC'E FOR "NO-RISE/"tiT0-Ii11!'AC T" C;ERTIVIC A'['[ON
FOR PROPOSED DEVELOPMENTS IN IREGULA'I'ORYFt-C3C3I)10` YS
The National. Flood Insurance Program (NFII') floodplain management criterion that is
adopted by all participating communities in their local ordinances—as described in Title 44 of
the Code of Federal Regulations:.. Section 60.3(d)(3).. states:
"A community shall prohibit encroachments, including fill, new construction,
substantial improvements. and other development within the adopted regulatory
fl0()Cl'Waay t:i.nless it has been demonstrated through hydrologic and hydraulic analyses
performed in accordance with standard engineering,practice that the proposed
encroachment would not result in any increase in flood levels within the community
during the occurrence of'the base flood discharge.",
Prior to issuing.; any development permits involving activities in a regulatory floodway,
the community must obtain a cei-tifiication stating,the proposed development will riot
impact the:pre-project base flood elevations. regulatory floodway elevations. or
regulatory floodway widths. The certification should be obtained txoln the permittee and
be sighed and sealed by a professional engineer in accordance:: with State Licensing Board
speciticxations.
The engineering oI "No.-Rise ! No-Impact" certification must be supported by technical
data. File supporting technical data should be based upon the standard step-backwater
hydraulic model utilized to develop the res.=ulat.ory° floodway shown on the community's
effective Flood insurance Date Vvlap(FIRM) or Flood Boundary and Floodway Map
(FI3P`,1) and the results tabulated in the community's Flood Insurance Study(FIS).
Communities are required to review and approve or disapprove the "No-RiseiNo-
Inipact" submittals; however, they may request technical assistance and review*,
from the FI 11 A regional office. If this alternative is chosen, the submittal will be
treated as a Conditional Letter of Map Revision f t j1,O yl R i by the National Service
Provider, and will be subject to the satire fees as ouch.
TO support ai "No-Rise; No-Impact" certification for proposed developments encroaching
unto the re'*ulatelry 1:100dwaay. a community will require that the 'following procedures be
f Alowed:
Page I
1. Current]v Effect1ve Model
Furnisft a written request for the. step-back\--ater hydraulic model for the specified
stream and community. identifying the limits of the requested data. A fee will be
assessed for providing the data. Send data requests to:
Federal Erncrgencv N'lana-etncnt Agency
http, 'u w\\.ftma.gov.fhlrlist_alcler.shtna
or to:
MOD RMC Region 4
Faxed to (678) 45Q--1030 to the attention of':
"Back-Up 'Feclltaical Data Requesi"
?. Duplicate Effective Model
Upon receipt of the step-backwater hydraulic model.. the engineer should run the
effective hydraulic model to duplicate the data in the effective FIS.
>. Fx'stin�� Conditions Model
Revise the duplicate effect VC model to reflect site-specific existing conditions by
Adding:.new cross-sections (two or mare) in the area ofthe proposed develolprrlent;
Without the. proposed &V fopment in place. Re('Lilatory floodway limits 4hould be
manually set at the nc)v crass-section locations by measuring from the effective
FIRM or F 13FM. The c1a1a1ulative reach len<uths of the waterway should remain
unchanged. Tltc results of these analyses \\ill indicate the base flood clevations and
the regulatory floodtivay elevations for the effective hvdracllic lrtodel I-evised to
Incorporate existing Conditions at the proposed project site,
4. Proposed Conditions Model
Modifv the existing; conditions models to reflect the proposed development using the
neNv cross-sections. uhflc rctaininf', the currently adopted regulatory floodway �Nidths,
The overbank rOU hlIess parameters should remaill the salzac unless, a valid
explanation of'how the proposed detieloprnent \vi11 impact the rougliness parameters
Is included with the supporting data. "The results of this floodway hydraulic model
will indicate:, the rcgtllatory floodhvav elevations for proposed conditions at the project
site. These results must indicate .NO impact (m the,base flood elc\,atlons. m-1LJIat0ry'
floodway elevations, or regulatory- floodway widths shown in the duplicate Eftc;etiv e
Model or in the Existing Conditions Model (item, ? and y above, respectively;).
Pate
...........- .......
The"no-impact" analysis along with supporting data and.the original eninnecring
certification must be re-viewed by tile appropriate community official prior to iSSLIIII(F
a.
de,velopryient permit. The original effective FIS model, the duplicate efTective FIS model.
the Existing Conditions Model. and the Proposed Conditions Model should he re-viewed for
any changes in the base flood elevations,regulatory-I'loodway elevations and Iloodway
widths.
The "No-Rise No-Impact" supporting data shOUld inc]LICIC, but may not be limited to:
(1) Copy of.,the Currently eflective FIS hydi-LIL111C niodels(leZ=11gible hard.copy and
a disc("if available))
(2) Duplicate effective FIS hydraulic models(hard copy and a disc).
Existing conditions hydraulic models(hard ooliv, and a disc).
(4) Proposed conditions hydraulics models(hard copy and a disc)
Annotated effective FIR.I'M or FL FVI and topographic map. showing
regulatoryfloodplain and floodway boundaries. the additional ccross-sections.and the site location along with the proposed topographic I i fcations.(6) Documentation clearly stating analysis procedures. All m(:)djfications made
to the duplicate effective hydraulic models to correctly represent existing,
conditions, as well as those made to the existing
, conditions, models to
represent proposed conditions should be well documented and submitted
with all supporting data.
(7/ Annotated effective Floodway Data Table(from the FIS report).
O Statement defining source ot'additional cros's-sections, topographic data. and
other supporting,inf6rniati(?ll.
(9) Cross-section plots of the add't'ojjal cr(iss sections I
on.s for existing and proposed
condition", hydraulic niodels.
Certifle(I ptanimetric (boun(lar%'SLII-\C�) inf'(.)rmLitjon indicating the location
ot'structurLs on the property,
(11) Hard copy ot'all OUtnUt files.
(12) Clear explanation ot'ho-vv roUL11111CSS parameters were obtained (if different
front those used In the effCctive hydraulic models).
13) Em-nneering certification(sample attached).
..........I.............
The emulnecring "No -Rise ' No-Impact" certification and supporting technical data must
stipulate NO impact or NO changes to the base flood elevations. regulatory flood ay
elevations, or regulator' floodwav widths at the new crass-sections and at all existing
cross-sections anywhere in the model. Therefore, the revised computer model should be
run for a sufficient distance upstream and downstream of the development site to insure
proper"No-Rise No-Impact, certifications.
Attached is a SAMPLE "No-Rise No-Impact" c.ertitication form that can be completed
by a registered professional engineer and supplied to the community along with the
supporting technical data when applying for a development permit. This foam does not
have to be utilized to submit for a "No-Rise ' No-Impact" certification. it is provided as a
guide, if needed.
Note: Definitions of terms base flood, development, and regulatory floodway are same as
those include(] in Title.44 of the Code of l=ederal Reilulat.ions Section :9.1. Additional
regulations pertaining;to this Certification are described in Title 44 of the Code of Federal
Regulations. Section 67.1.
Page 4
FLC>c3nWAY "NO->r ISE %NO-1,Nll AC'F" (.,E►Z'I'I IC'A'r'i Ceti
This document is to certify,,that I ant duly qualrlicd en,t-lincer licensed to practice in the State of
it is to further certify that the attached technical data supports
(State)
the fact:that,proposed _........ will not impact the base flood
(.'Ve"wic of Devviormrc,1�11)
elevations. floodway elevations, and floodway widths on at published
(1^trrrrc ear Stream)
cross sections in the Flood Iztsurance Study for, dated
A'trrrrr^r�jcnrrrrrrrrrrit )
rl�rzaej
and will not impact the base flood elevations. floodway elevations, and flood\ ay widths at the
unpublished crass-sections in the area ol'the proposed development.
......................... ......_.......................................
''emir
_-. _............... ................. ......_......_.............
.
Tide
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_........._................................ - ._.........._._.....................................................-.......
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XL: , '!)f),iTl, •ddress
. __. __............ ... ........ .. ... . ._- _--- . ...... ..... _..........-
. ........ .... _.-.._._
C�i)S11n3UtiiC�' Approval
i
i
i
t:c7rnn1unrt} t)itI a]'s ar,ii. (.'?fuc ial's wr matur 1 itke
.... __....... . ..... ......... ._... .............. ._.... ........... .__..__
lEMA, MT
D'TD.09 -004
Skunk River at Hwy 30
5174-12A
HEC RAS Hydraulic Analysis
Station Existing Conditions Proposed Deery Site WSEL Compare
100-YR WSEL(a) 100-YR WSEL(b) (b-a)
585 882.95 883.03 0.08
320 882.83 882.88 0.05
193 882.75 882.75 0.00
0 882.00 882.00 0.00
Proposed Site and Channel Repair WSEL Compare
100-YR WSEL(c) (c-a)
882.90 -0.05
882.80 -0.03
882.75 0.00
882.00 0.00
....._. ._.
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