A Simplified Method of Implementing
No Rise Analysis in
Unnumbered A-Zones
Based Upon No Loss of Conveyance
Second National Flood Workshop, Houston, TX
Session C4 - Public Awareness/Mitigation
Dwayne E. Culp, Ph. D., P.E., CFM
A Simplified Method of
Implementing No Rise
Analysis in Unnumbered
A-Zones Based Upon
No Loss of Conveyance
CFR 60 Requirements
44 CFR 60.3(a)(3)
Second National Flood
Workshop, Houston, TX
Review all permit applications to determine whether proposed building
sites will be reasonably safe from flooding. If a proposed building
site is in a flood-prone area, all new construction and substantial
improvements shall (i) be designed (or modified) and adequately
anchored to prevent floatation, collapse, or lateral movement of
the structure resulting from hydrodynamic and hydrostatic loads,
including the effects of buoyancy, (ii) be constructed with materials
resistant to flood damage, (iii) be constructed by methods and
practices that minimize flood damages, and (iv) be constructed
with electrical, heating, ventilation, plumbing, and air conditioning
equipment and other service facilities that are designed and/or
located so as to prevent water from entering or accumulating
within the components during conditions of flooding.
A Simplified Method of
Implementing No Rise
Analysis in Unnumbered
A-Zones Based Upon
No Loss of Conveyance
CFR 60 Requirements
44 CFR 60.3(a)(4)
Review subdivision proposals and other proposed new development,
including manufactured home parks or subdivisions, to determine
whether such proposals will be reasonably safe from flooding. If a
subdivision proposal or other proposed new development is in a
flood-prone area, any such proposals shall be reviewed to assure
that (i) all such proposals are consistent with the need to minimize
flood damage within the flood-prone area, (ii) all public utilities and
facilities, such as sewer, gas, electrical, and water systems are
located and constructed to minimize or eliminate flood damage,
and (iii) adequate drainage is provided to reduce exposure to flood
hazards.
Second National Flood
Workshop, Houston, TX
A Simplified Method of
Implementing No Rise
Analysis in Unnumbered
A-Zones Based Upon
No Loss of Conveyance
CFR 60 Requirements
44 CFR 60.3(b)(7)
Assure that the flood carrying capacity within the altered or relocated
portion of any watercourse is maintained;
44 CFR 60.3(c)(10)
Second National Flood
Workshop, Houston, TX
Require until a regulatory floodway is designated, that no new
construction, substantial improvements, or other development
(including fill) shall be permitted within Zones A1-30 and AE on the
communities FIRM, unless it is demonstrated that the cumulative
effect of the proposed development, when combined with all other
existing and anticipated development, will not increase the water
surface elevation of the base flood more than one foot at any point
within the community.
A Simplified Method of
Implementing No Rise
Analysis in Unnumbered
A-Zones Based Upon
No Loss of Conveyance
Basis of Method
Determine Base Flood Elevation
– Use Maps and Profiles with BFEs if available.
– Use the survey methods with local agreement if
BFEs are not available.
• Demonstrate No Net Fill (no loss of storage)
• Demonstrate No Loss of Conveyance
Capacity (no loss in carrying capacity of the
system)
Second National Flood
Workshop, Houston, TX
A Simplified Method of
Implementing No Rise
Analysis in Unnumbered
A-Zones Based Upon
No Loss of Conveyance
Determine Base Flood Elevation
• When there are elevations
– From Profiles (preferred)
– From FIRM Panel
• When there are no elevations
– From FIRM Panel overlaid over a topographical
map
– From a FIRM Panel with staked elevations of the
lines of the FIRM panel
Second National Flood
Workshop, Houston, TX
A Simplified Method of
Implementing No Rise
Analysis in Unnumbered
A-Zones Based Upon
No Loss of Conveyance
Determine Base Flood Elevation
BFE=57.0 feet
Bridge upstream
Second National Flood
Workshop, Houston, TX
Bridge downstream
Property
A Simplified Method of
Implementing No Rise
Analysis in Unnumbered
A-Zones Based Upon
No Loss of Conveyance
Determine Base Flood Elevation
BFE=57.0 feet from profile
Bridge
upstream
Second National Flood
Workshop, Houston, TX
Bridge downstream
A Simplified Method of
Implementing No Rise
Analysis in Unnumbered
A-Zones Based Upon
No Loss of Conveyance
Determine Base Flood Elevation
If there are No Elevations
Property
Second National Flood
Workshop, Houston, TX
A Simplified Method of
Implementing No Rise
Analysis in Unnumbered
A-Zones Based Upon
No Loss of Conveyance
Determine Base Flood Elevation
Property
Second National Flood
Workshop, Houston, TX
A Simplified Method of
Implementing No Rise
Analysis in Unnumbered
A-Zones Based Upon
No Loss of Conveyance
Determine Base Flood Elevation
53.55
54.15
54.35
55.05
54.75
Second National Flood
Workshop, Houston, TX
54.35
55.15
55.10
55.00
54.15
Property
A Simplified Method of
Implementing No Rise
Analysis in Unnumbered
A-Zones Based Upon
No Loss of Conveyance
Conveyance
Manning’s Equation
K
Q  AR 2 / 3 S 1f / 2
n
Conveyance
X
Second National Flood
Workshop, Houston, TX
K
AR 2 / 3
n
Where, Q is flow (cfs / cms), A is area of flow
perpendicular to flow direction (ft2 / m2), R is hydraulic
radius (ft / m), n is Manning’s n, K is a conversion
factor (1.49 in English units, 1.00 in metric), and X is
the conveyance.
A Simplified Method of
Implementing No Rise
Analysis in Unnumbered
A-Zones Based Upon
No Loss of Conveyance
Second National Flood
Workshop, Houston, TX
Conveyance
Note:
If the Manning’s n increases, conveyance decreases.
If depth of flow increases, both A and R will also
increase, and therefore conveyance increases.
If depth of flow increases but A decreases, it may be
possible to have conveyance increase or decrease.
K
2/3
X  AR
n
A Simplified Method of
Implementing No Rise
Analysis in Unnumbered
A-Zones Based Upon
No Loss of Conveyance
Goal of the Conveyance Analysis
• Demonstrate for multiple cross sections that
there is no decrease in conveyance.
– Note: City of Houston requires that there is no
significant increase in Conveyance too. The City
of Houston does allow the most restrictive cross
section to demonstrate no significant increase.
– For jurisdictions with unnumbered A zones with
unmodelled streams, it should be adequate to
demonstrate that there is no loss of conveyance.
Second National Flood
Workshop, Houston, TX
A Simplified Method of
Implementing No Rise
Analysis in Unnumbered
A-Zones Based Upon
No Loss of Conveyance
How to Select Cross Sections
• Representative
– Existing conditions
– Proposed conditions
Second National Flood
Workshop, Houston, TX
• Perpendicular to direction of channel flow
• Include both onsite and offsite areas if
necessary
• More than one. There will be a need for
multiple cross sections. It is suggested that a
minimum of two are needed per 500 feet of
property width perpendicular to channel flow
direction
A Simplified Method of
Implementing No Rise
Analysis in Unnumbered
A-Zones Based Upon
No Loss of Conveyance
Second National Flood
Workshop, Houston, TX
Example
A Simplified Method of
Implementing No Rise
Analysis in Unnumbered
A-Zones Based Upon
No Loss of Conveyance
Second National Flood
Workshop, Houston, TX
Example
A Simplified Method of
Implementing No Rise
Analysis in Unnumbered
A-Zones Based Upon
No Loss of Conveyance
Conveyance
• Calculate Conveyance for Each Section
• Wetted Perimeter
• In CADD do not use a distorted cross section
• Calculate edge of buildings if the buildings act as restrictions
to flow
• When flow is under buildings without restriction – be aware
that piers increase wetted perimeter
• Area
• Mannings n
• Use values for floodplain areas where possible. TxDOT
tables or the tables from Chou work good.
Second National Flood
Workshop, Houston, TX
A
R
WP
K
2/3
X  AR
n
A Simplified Method of
Implementing No Rise
Analysis in Unnumbered
A-Zones Based Upon
No Loss of Conveyance
Example
Existing Cross Section 1
Description
Sta.1
(ft)
Sta. 2
(ft)
Material
Manning's
n
Area
(ft2)
Wetted
Perimeter
(ft)
Conveyance
(cfs)
Open space
0+00.00
1+02.32
Grass
0.040
169.9
102.3
8851.2
Driveway
1+02.32
1+85.11
Gravel with
Vegetation
0.024
148.5
82.8
13682.1
Open space
1+85.11
2+00.00
Grass
0.040
34.4
14.9
2227.0
Total:
24760.4
Proposed Cross Section 1
Second National Flood
Workshop, Houston, TX
Material
Manning's
n
Area
(ft2)
Wetted
Perimeter
(ft)
Conveyance
(cfs)
0+64.88
Grass
0.023
112.4
66.7
10196.6
0+85.72
Brick
0.000
0.0
0.0
0.0
0+85.72
0+91.89
Grass
0.023
10.6
9.6
725.7
0+91.89
1+12.72
Brick
0.000
0.0
0.0
0.0
Open space
1+12.72
1+16.49
Grass
0.023
6.5
5.1
493.2
Driveway
1+16.49
1+36.57
Concrete
0.011
46.5
22.6
10166.0
Garage
1+36.57
1+60.53
Brick
0.000
0.0
0.0
0.0
House
1+60.53
1+68.53
Under House
0.000
0.0
0.0
0.0
Post
1+68.53
1+69.53
Wood
0.000
0.0
0.0
0.0
House
1+69.53
1+76.53
Under House
0.000
0.0
0.0
0.0
Post
1+76.53
1+77.53
Wood
0.000
0.0
0.0
0.0
House
1+77.53
1+88.03
Under House
0.000
0.0
0.0
0.0
Post
1+88.03
1+89.03
Wood
0.000
0.0
0.0
0.0
Open space
1+89.03
2+00.00
Grass
0.023
29.9
13.8
3211.4
Open space
0+00.00
0+64.88
Grass
0.023
112.4
66.7
10196.6
Description
Sta.1
(ft)
Sta. 2
(ft)
Open space
0+00.00
Garage
0+64.88
Open space
Garage
Total:
24792.9
A Simplified Method of
Implementing No Rise
Analysis in Unnumbered
A-Zones Based Upon
No Loss of Conveyance
No Storage Loss
• Demonstrate no storage loss
– CADD
– Cross Sections and area volume calculations
– 3D surfaces
Second National Flood
Workshop, Houston, TX
A Simplified Method of
Implementing No Rise
Analysis in Unnumbered
A-Zones Based Upon
No Loss of Conveyance
Second National Flood
Workshop, Houston, TX
No Storage Loss
A Simplified Method of
Implementing No Rise
Analysis in Unnumbered
A-Zones Based Upon
No Loss of Conveyance
Second National Flood
Workshop, Houston, TX
No Storage Loss
A Simplified Method of
Implementing No Rise
Analysis in Unnumbered
A-Zones Based Upon
No Loss of Conveyance
Why should Agencies Use a
Method Like This?
• The method is simple to implement
– It does not require that the reviewer have significant
mathematic ability, or knowledge of specific programs.
Second National Flood
Workshop, Houston, TX
• It is reproducible
• It is more accurate on a site basis than hydrologic or
hydraulic models that average conveyance and
storage over very large areas
• It complies with 44 CFR 60.3(b)(7) as it demonstrates
no loss of carrying capacity
• It complies with 44 CFR 60.3(c)(10) as it
demonstrates that the cumulative effect of the
proposed development, will not increase the water
surface elevation of the base flood
A Simplified Method of
Implementing No Rise
Analysis in Unnumbered
A-Zones Based Upon
No Loss of Conveyance
Second National Flood
Workshop, Houston, TX
References
Managing Floodplain Development in
Approximate Zone A Areas, a guide for
obtaining and developing Base (100-year)
Flood Elevations, FEMA April 1995.
Rules and Regulations for Chapter 19, City of
Houston, February 2009.
Hydraulic Design Manual, Texas Department of
Transportation, October 2011.
Chou, Ven Te, Open-Channel Hydraulics,
McGraw Hill, 1988.
A Simplified Method of
Implementing No Rise
Analysis in Unnumbered
A-Zones Based Upon
No Loss of Conveyance
Second National Flood
Workshop, Houston, TX
Questions
Dwayne E. Culp, Ph.D., P.E., CFM
Jacobs Engineering Group Inc.
5995 Rogerdale Road, Suite B3014B
Houston, TX 77072
713-898-1977