responsible for its content.
Policy 21 NO-FILL LINE
Policy-21-1
Appendix C
Land Development Manual
June 2003
City of Knoxville, Tennessee
Stormwater Engineering Division
http://www.ci.knoxville.tn.us/engineering/
Policy 21
NO-FILL LINE
The purpose of this policy is to clarify the requirements for the
No-Fill Line
within the City of
Knoxville. The no-fill line, which is defined in Section 22.5-23(f)(1) of the Stormwater and Street
Ordinance (Chapter 22.5 of the Knoxville City Code), must be clearly shown and labeled on the
site development plans and also on the recorded survey plat.
A
No-Fill Line
is defined for studied streams where a floodway profile has been computed; it is
a continuous line halfway between the 100-year floodway and the 100-year floodplain
boundaries. Any type of fill which alters the conveyance or the flood storage capacity of the
regulated floodplain is prohibited within the no-fill line. This includes buildings, structures,
construction fill, soil, riprap, pavement, concrete, signs, other materials, etc. that reduce the
stream cross-section anywhere within the no-fill line. See Policy 23 for the list of studied
streams and maximum extent of floodway profiles.
The requirement for a
No-Fill Line
may be waived if a drainage study shows a rise of 0.00 feet
on all existing properties within 0.5 miles (upstream and downstream) of the proposed site
development using a method widely accepted among engineering professionals. The drainage
study (also called a
no-rise certification
) must be prepared, signed and stamped by a
registered professional engineer licensed to practice in the State of Tennessee. The procedure
for proving a no-rise certification for encroachment of the no-fill line is part of this policy. This
no-rise certification uses the 100-year flood model (without floodway) to demonstrate no impacts
on the 100-year water surface elevation.
This type of no-rise certification is very different than the one described in Policy 20 (No-Rise
Certification For Floodway Encroachment). The
regulatory floodway
is established by the
Federal Emergency Management Agency (FEMA) by the mechanism of an official Flood
Insurance Study (FIS), Flood Boundary and Floodway Maps (FBFMs), and Flood Insurance
Rate Maps (FIRMs). The regulatory floodway is thus defined by federal regulations to be
absolutely necessary for conveying the fast-moving central portion of the flood event. The basis
for a no-rise certification for floodway encroachment is the 500-year flood event per City Code.
Instructions for the No-Rise Certification of Encroachment of the No-Fill Line:
Procedures for No-Rise Certification for Proposed Developments (3 pg) Adapted from R4-MT
Example of an Engineering No-Rise Certification
(1 pg) Adapted from R4-MT
(Step 1) -- The City of Knoxville Engineering Department (215-2148) or the Tennessee Valley Authority
(632-6851) can furnish the current HEC-2 or HEC-RAS 100-year flood model for a specified stream or
creek, free of charge, other than mailing charges if needed. The City of Knoxville Engineering Department
can furnish photocopied pages of the Flood Insurance Study (profile, floodway tables) and Flood Insurance
Rate Maps (1=1000 scale) to customers who request these items in person. Or portions of the FIS and
FIRMs can be obtained from the FEMA Map Service Center.
The no-rise certification must have the supporting data as described in form R4-MT, including:
plots of each cross section
list of modifications to the original HEC-2 or HEC-RAS file
a plan drawing containing cross section locations and both existing & proposed topography
electronic input and output files on diskette or CD (effective, existing and proposed models) Policy-21-2
Appendix C
City of Knoxville, Tennessee
Stormwater Engineering Division
Land Development Manual
June 2003
Federal Emergency Management Agency
Region IV
3003 Chamblee-Tucker Road
Atlanta, Georgia 30341
Modified version of R4-MT (City of Knoxville)
Original - January/92
PROCEDURES FOR NO-RISE CERTIFICATION
FOR PROPOSED DEVELOPMENTS WITHIN THE NO-FILL LINE
Section 60.3 (d) (3) of the National Flood Insurance Program (NFIP) regulations states that a community shall
prohibit encroachments, including fill, new construction, substantial improvements, and other developments within
the adopted regulatory floodway unless 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 (100-year) flood discharge.
Prior to issuing any building grading or development permits involving activities within the regulatory no-fill line,
the community must obtain a certification stating the proposed development will not impact the pre-project base
flood elevations, floodplain elevations, or floodplain data widths. The certification should be obtained from the
permittee and signed and sealed by a professional engineer.
The engineering or no-rise certification must be supported by technical data. The supporting technical data should
be based upon the standard step-backwater computer model utilized to develop the 100-year floodplain shown on
the communitys effective Flood Insurance Rate Map (FIRM) or Flood Boundary and Floodway Map (FBFM) and
the results tabulated in the communitys Flood Insurance Study (FIS).
Although communities are required to review and approve the no-rise submittals, they may request technical
assistance and review from the FEMA regional office. However, if this alternative is chosen, the community must
review the technical submittal package and verify that all supporting data, listed in the following paragraphs, are
included in the package before forwarding to FEMA.
To support a no-rise certification for proposed developments encroaching into the regulatory no-fill line, the City
of Knoxville Engineering Department will require that the following procedures be followed:
Currently Effective Model
1.
Furnish a written request for the step-backwater computer 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 Emergency Management Agency
or
FIS Information Specialist
Region IV HIRA Branch
Dewberry & Davis
3003 Chamblee-Tucker Road
8401 Arlington Boulevard
Atlanta, GA 30341
Fairfax, VA 22031-4666
* The minimum flood required for FEMA floodplain analysis is the 100-year flood, unless local regulations are stricter.
** The base flood for the No-Fill Line only, in the City of Knoxville, is defined as the 100-year flood, without floodway.
*** Step-backwater models may also be obtained from TVA or City of Knoxville Engineering Department without charge. Policy-21-3
Appendix C
City of Knoxville, Tennessee
Stormwater Engineering Division
Land Development Manual
June 2003
Duplicate Effective Model
2.
Upon receipt of the step-backwater computer model, the engineer should run the original step-backwater
model to duplicate the data in the effective FIS.
Existing Conditions Model
3.
Revise the original step-backwater model to reflect site specific existing conditions by adding new cross-
sections (two or more) in the vicinity of the proposed development, without the proposed development in
place. Floodplain limits should be manually set at the new cross-section locations by measuring from the
effective FIRM or FBFM. The cumulative reach lengths of the stream should also remain unchanged. The
results of these analyses will indicate the 100-year floodplain elevations for revised existing conditions at
the proposed project site.
Proposed Conditions Model
4.
Modify the revised existing conditions model to reflect the proposed development at the new cross-
sections, while retaining the currently adopted floodplain widths. The over-bank roughness coefficients
should remain the same unless a reasonable explanation of how the proposed development will impact
Mannings n values should be included with the supporting data. The results of this floodplain model run
will indicate the 100-year floodplain elevations and widths for proposed conditions at the project site.
These results must indicate NO impact on the 100-year flood elevations, floodplain elevations, or
floodplain widths shown in the Duplicate Effective Model or in the Existing Conditions Model.
The original FIS model, the duplicate effective FIS model, the revised existing conditions model, and the proposed
conditions model should all produce the same exact results.
The no-rise supporting data and a copy of the engineering certification must be submitted to and reviewed by the
appropriate community official prior to issuing a permit.
The no-rise supporting data should include, but may not be limited to:
a.
Duplicate of the original FIS step-backwater model printout or floppy disk.
b.
Revised existing conditions step-backwater model.
c.
Proposed conditions step-backwater model.
d.
FIRM and topographic map, showing floodplain and floodway, the additional cross-sections, the
site location with the proposed topographic modification superimposed onto the maps, and a
photocopy of the effective FIRM or FBFM showing the current regulatory floodway.
e.
Documentation clearly stating analysis procedures. All modification made to the original FIS
model to