Using the Power of SWMM Unsteady Modeling for CLOMR

Report
Duval County:
Using the power of SWMM unsteady modeling for
CLOMR applications
José Maria Guzmán, P.E. D.WRE
Gaston Cabanilla, P.E., CFM
Greg McGrath
May 17 2011, Louisville KY
Agenda
•
•
•
•
Project Technical Background
Flood Insurance Study Documents based on SWMM
LOMC Process using SWMM
Conclusions/Discussion
Acknowledgments: Tom Nye, Michael F. Schmidt, Sandeep Gulati,
Seungho Song, Erin Hardin, Katie Lytle.
Project Technical Background
• Community opted to use SWMM for
several reasons
– Previous models with successful model
calibrations
– Complex system with multiple culverts,
ditches and closed conduits
– Hydraulics are driven by tail water
conditions
– Timing between different tributaries is
relevant
– Agreement with local regulations driven
by 24 hour duration storms
– Concurrent TMDL studies
– Public domain software
• By having one single model, the City can keep updated one tool that is
benefiting from continuous work in the LOMC, TMDL, and ongoing activities
Some experienced CFMs might need to get familiar
with results from SWMM
• Model data are structured differently in SWMM than in other more
traditional software:
Variable
HEC RAS
SWMM
Discharge
Cross Section
Link
WSE, Stage
Cross Section
Node
Velocity
Cross Section
Link
Floodway Width
Cross Section
Link
Floodway Surcharge
Cross Section
Node
• Hydrology and Hydraulics are solved simultaneously in SWMM
• No need to solve tributaries separately, and account for backwater
curve with a dynamic stable simulation
Little Cedar Creek
• Hydrology
– Tributary Area: 6
Square Miles
– 14 Subcatchments
• Hydraulics
– 74 Nodes
– 83 Links
2010 DFIRM Panel Generated with SWMM Output
Stream Profile using RASPLOT and showing SWMM
Nodes
FIS Discharge Table
Floodway Data Table in staggered format
Example of Map Revision Application using SWMM
Proposed 4-Lane
Causeway and
Bridge
Proposed Urban
Development
Without Floodplain
Encroachment
LOMC Process, What to submit
• Completed application forms.
• Narrative on project and submittal (optional but very helpful).
• Hydrologic Computations (if applicable) along with digital files of
computer models used.
• Hydraulic Computations (if applicable) along with digital files of
computer models used.
• Certified topographic map with floodplain and floodway (if
applicable) delineations.
• Annotated FIRM and/or FBFM to reflect changes due to project
• Items required to satisfy any NFIP regulatory requirements.
• Fee payment if applicable.
The LOMC process requires the use of several forms
• SUMMARY OF FORMS
• There are six forms plus a payment form that needs to be prepared,
• Form 1 - Overview & Concurrence (All revisions)
– Requester , community official, and engineer signatures
• Form 2 - Riverine Hydrology & Hydraulics
– Scope and methodology of hydrologic and/or hydraulic analyses
• Form 3 - Riverine Structures
– Hydraulic structures in the stream channel or floodplain.
• Form 4 - Coastal Analysis
– Scope and methodology of coastal analyses
LOMC Process
• Form 5 - Coastal Structures
– hydraulic structures constructed along the coast
• Form 6 - Alluvial Fan Flooding
– information for analyses of alluvial fans
• Payment Information
– Information regarding any fees paid for a CLOMR, LOMR, or External
Data Request.
CLOMR Process for this case
• Form 1 - Overview & Concurrence (All revisions)
– Identify that it is CLOMR or LOMR
– Community Number, Name, State, Map Number, Panel Number,
and Effective Date
– Flooding source name , type of flooding (Riverine)
For this example FORM 2 and 3 are required
• Form 2 - Riverine Hydrology & Hydraulics
– Duplicate Effective Model
• Is a copy of the hydraulic analysis used in the effective FIS
– Corrected Effective Model
• is the model that corrects any errors that occur in the Duplicate Effective
Model
– Existing or Pre-Project Conditions Model
• Modifications to produce the Existing or Pre-Project Conditions Model to
reflect any modifications that have occurred within the floodplain since
the date of the Effective model but prior to the construction of the
project
– Revised or Post-Project Conditions Model
• Modified to reflect revised or post -project conditions
For this example FORM 2 and 3 are required
• Form 3 - Riverine Structures
– request involves a new bridge
– Indicate the reason for the new bridge
– Indicate the model used to analyze the hydraulics at the bridge
(SWMM)
– Attach plans of the structure certified by a registered
professional engineer
• Payment Information
– Fees paid for a CLOMR
Effective Model is available in SWMM5
• 100 yr Storm: 12.3 inches in 24 hours
• The model took less than a minute to run 30 hours for the entire
stream
• Peak Flow at proposed project site: + 1,600 cfs , - 150 cfs
Effective Model Peak WSE Results
• Each node
reports the
peak HGL
(WSE)
• Note that many
conduits peak
around hour 21
(9 hours after
the storm peak)
Existing Pre-conditions Effective Model
• In anticipation of the proposed
conditions, the user adds
cross sections at critical
locations
• This represents pre-conditions model
• There could be a BFE change
due to new cross sections
Proposed Model – Bridge Addition in SWMM
• State/Local criteria: no WSE
increase is allowed
• Federal criteria: no increase
allowed in floodway areas
• Peak Upstream WSE : 5.8 ft at
Hour 16
• No encroachment
• Two rows of bridge piers
• Lower Chord Elevation: 6.8 ft
• Adding the bridge takes up to 60
Minutes
SWMM Reports model information differently than
HECRAS and this has implications in the location of
cross sections
• In anticipation of the
proposed bridge,
HECRAS users would
add four cross sections
• In order to extract the
same information from
SWMM the user should
add nodes and links
as shown
LC_Junc
LC20008L2S
LC20008L3
Le_Junc
Node
Link
Cross Section
User estimates the length of contraction and
expansion reaches
• Based on proposed
bridge geometry the
user can determine the
following using
HEC methodology
• Lc = 20 ft
• Le = 40 ft
• Rounded to nearest 10 ft
LC_Junc
LC20008L2S
LC20008L3
Le_Junc
Node
Link
Cross Section
Proposed Model needs to show no WSE increase
• Net 3 cfs decrease in discharge upstream of bridge.
User compares Peak WSE Results with effective
model and compares floodway results
• Floodway Peak Stages:
•
•
•
•
Cannot increase 100 year storm stages per Florida regulations.
Cannot increase Floodway with or surcharge per FEMA regulations.
Florida regulations control for this case.
End result is a proposed bridge with no floodplain encroachment.
An Updated Floodway Table is generated using the
SWMM results
• Floodway widths are also verified
NODES
LINKS
BASE FLOOD WATER SURFACE ELEVATION
FLOODWAY
FLOODING LOCATION
DISTANCE FLOODWAY BASE PEAK
WIDTH (FT) FLOW (CFS)
(FT)
WITHOUT
BASE PEAK
VELOCITY REGULATORY FLOODWAY
(FT NAVD)
(FT NAVD)
(FPS)
WITH
FLOODWAY
(FT NAVD)
SURCHARGE
(FT)
LITTLE CEDAR CREEK
C20007L1
268
2026
2.9
85
2117
0.7
292
1646
1.9
306
7868
1.4
472
31271
1.4
4796
20007L1
C20007
5709
20007
C20008L3
6406
Le_Junc
Le_Chan
6446
20008L3
Lc_Chan
6466
Lc_Junc
C20008L2
200
1765
2.6
343
1615
1.0
7143
20008L2
C20008L1
5.1
5.1
5.4
0.3
5.2
5.2
5.6
0.4
5.4
5.4
5.8
0.4
5.3
5.3
5.7
0.4
5.4
5.4
5.8
0.4
5.8
5.8
6.6
0.8
Conclusions
• SWMM users can find the required information for
FEMA LOMC applications
• When the model for the entire watershed is used,
there is no need to pre-establish the domain of
influence of new developments
• The dynamic simulation requires attention to model
results to verify timing, direction and magnitude of
flows.
• Duval County has developed a tool that can assist in
FEMA mapping, urban planning, permitting, and
water quality evaluations

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