4. Background
● Mexico Beach is a small town in
Northwestern Florida on the coast of the
Gulf of Mexico
● The town was devastated by Hurricane
Michael in 2018 due to poor stormwater
management and is still in the process of
recovering
● Mexico Beach has taken this as an
opportunity to rebuild with increased
storm resiliency and green development
in mind
Figure 2: Location of Mexico Beach in the
state of Florida
Figure 3: Property Damage from Hurricane
Michael (2018)
5. Background
● The City of Mexico Beach recently
purchased an 80 acre plot of land
● This was done as part of stormwater
resiliency plan developed with help
from the EPA
● Land can only be developed for use in
stormwater management and passive
recreation applications
● Additionally, the city would like to
divert flow from an existing outfall
Figure 4: Location of project site in Mexico Beach, FL.
7. Rationale
● Mexico Beach, FL is still in the process of rebuilding from the
catastrophic damage Hurricane Michael caused in 2018
● Our project will be a crucial step in this recovery
○ Mitigates future storm surge impacts and regulates stormwater during their
frequent high intensity rainfall events
○ Prevents flooding on residential properties
○ Will naturally filter some amount of pollutants out of the stormwater
8. Objectives
The objectives of this project are to
1. Determine hydrologic conditions of the surrounding watershed
2. Design a stormwater wet detention pond accommodating for current flooding and
flow that will be diverted to the property
3. Evaluate the cost of stormwater management project
Figure 5: Current stormwater channel flow
Figure 6: Aerial imagery of the stormwater filled
with tannins flowing into the Gulf of Mexico
Figure 7: Current stormwater channel flow
9. Approaches
To achieve these objectives, the following tasks are planned:
1. Review information provided by Mexico Beach, FL
a. Mexico Beach Recovery and Resiliency Partnership Plan
b. Master Stormwater Plan
c. Municipal Plans
d. GIS Maps
2. Determine stormwater parameters for the area
a. Soil type data
b. Land cover data
c. Rainfall data
d. Water table depth
e. Delineate watershed to determine drainage basins using ArcGIS Pro
f. Develop hydrograph models to determine inflows to the property using
WINTR-55
10. Approaches
3. Design a stormwater retention pond on the property
a. Determine the size of pond
b. Determine the depth of pond
i. Design a raised wet detention pond
● Perform structural analysis of berms surrounding pond
● Design pumping structure for inflow to pond
● Design sedimentation structures within pond
c. Determine outflow from pond
i. Design outflow structure and emergency spillway
4. Create cost estimate of project components
d. Pond
i. Construction
ii. Pump utilities
e. Maintenance
11. Deliverables
● Creation of stormwater management plan including
○ Hydrological modeling and data
○ Wet detention pond design shown with AutoCAD drawings
■ Shape and size of pond
■ Inflows and outflows
● Water volume
● Structure shape
■ Raised berm structures
■ Pump utility
○ Visual rendering of what the pond would look like with native plants
● Presentation to EPA and stakeholders
12. Table 1: Gantt Chart for Mexico Beach, Florida - Land Development Project
Timeline
14. Literature Review
Our literature review will cover all the elements of:
● Coastal stormwater history
○ Florida stormwater standards
● Pond design
○ Types (dry, wet, retention, detention)
○ Size (depth, area, volume, flows)
○ Pumps
○ Outlets
○ Berms/Levees
○ Sedimentation
○ Native plants
15. Literature Review ● Flooding is one of the largest
environmental issues that combat coastal
communities around the world.
● With global warming causing sea level rise
and more frequent high intensity storm
patterns, flooding has been devastating
many areas of the Caribbean and the state
of Florida in recent years.12
● Due to its location relative to the warm
waters of the North Atlantic, Florida is
more likely to get hit by a hurricane than
any other state.11
● On average at least one hurricane strikes
Florida every two years and a strong
hurricane hits Florida on average once
every four years.11
Figure 8: Hurricane Michael in 2018
16. Literature Review
● Impacts of hurricanes and tropical
storms on hydrological processes in
coastal watersheds primarily include
“high peak discharge, reduced
evapotranspiration, overbank
flooding and groundwater table rise
for weeks to month due to storm
surges and heavy precipitation”.12
Figure 9: Catastrophic Damage caused by
Hurricane Ian in 2022
17. Literature Review
● Wet detention systems5
(retention pond)
○ Recommended best management
practices (BMPs) for moderate to high
water table conditions
■ Constant water level in pond
○ Unique advantages
■ Significant removal of dissolved and
suspended solids
■ Opportunities for nearby passive
recreation
● Raised retention pond5
○ Due to high water table, raised berm may
be included around edges to increase
available dry space
Figure 10: Raised wet detention system
18. Literature Review
● Northwest Florida Water District Design Standards 5
○ No more than half of the treatment volume should be discharged in the first 48 to 60
hours after the storm event
● Florida Administrative Code Sec. 62-610.41413
○ Minimum of 20 year storm must be considered
○ Storage capacity must be at least three times the average daily flow
○ Must be lined or sealed to prevent seepage
■ Liner must be adequate for given pressure and climatic conditions
○ Minimum 3 feet of freeboard with emergency discharge device to prevent water from
reaching one foot to the top of embankment
○ Minimum pond depth (excluding freeboard) is 6ft, inside bank side slopes steeper than
3:1 (horizontal to vertical) but no steeper than 1:1
○ Minimum water depth of 18 inches
○ Routine aquatic weed control and regular maintenance is required
○ Ponds above natural grade shall be designed to prevent failure of embankment
19. Literature Review (Pond Sizing)
● The U.S. Soil Conservation Service
developed an approximate
method for required storage
volume of detention basins (The
SCS method)10
● The SCS method relates a
discharge ratio to a volume ratio
● Peak outflow discharge can be
found be using the stormwater
detention pond guidelines for
Northwest Florida
○
Figure 11: SCS Method for Sizing Detention Ponds
20. Literature Review
● Sedimentation
○ Stormwater sediment is removed by settling
○ Sediment is deposited and stored throughout the pond
● Increases water quality by sequestering particles6
and excess nutrients in stormwater8
● Accumulated sediment must be removed as
frequently as every 16-17 years7
● Various BMP’s are utilized in order to decrease
maintenance costs and to reduce resuspension6
○ Sediment forebays
○ Upstream oil/grit separators
○ Bottom grid structure (BGS)
○ Sediment traps downstream from inlet
○ Level spreader
Figure 12: Bottom grid structure
22. Literature Review Sources
The sources that are currently under review for the project:
1. USDA. (1986). Urban Hydrology for Small Watersheds. 2nd ed.. United States Department of Agriculture
2. Preble-Rish Inc. (2015). City of Mexico Beach Stormwater Master Plan. Panama City, FL.
3. A. Ivanovsky, A. Belles, J. Criquet, D. Dumoulin, P. Noble, C. Alary, G. Billon, (2018). Assessment of the treatment efficiency of an urban stormwater pond and its impact on the
natural downstream watercourse, Journal of Environmental Management, Volume 226, Pages 120-130, ISSN 0301-4797, https://doi.org/10.1016/j.jenvman.2018.08.015.
4. Buchberger, S., Avadhanula, K., Pal, C., Wang, X., Shuster, W., & Bonta, J. (2010). Low Impact Development Design—Integrating Suitability Analysis and Site Planning for
Reduction of Post-Development Stormwater Quantity. Sustainability, 2(8), 2467-2482. 10.3390/su2082467
5. Northwest Florida Water Management District, Florida Department of Environmental Protection. (2013). Environmental Resource Permit Applicant’s Handbook Volume II.
Obtained from https://nwfwater.com/Permits/Environmental-Resource-Permits/Applications-Forms
6. Milovanović, I., Bareš, V., Hedström, A., Herrmann, I., Picek, T., Marsalek, J., & Viklander, M. (2020). Enhancing stormwater sediment settling at detention pond inlets by a
bottom grid structure (BGS). Water Science and Technology, 81(2), 274–282. https://doi.org/10.2166/wst.2020.101
7. Rishon R. 2013 Investigation of the Sediment Removal Frequency for Wet-Detention Stormwater Management Pond. M.A.Sc. Thesis, Ryerson University, Toronto, Canada.
8. Rosenquist, S. E., Hession, W. C., Eick, M. J., & Vaughan, D. H. (2010). Variability in adsorptive phosphorus removal by structural stormwater best management practices.
Ecological Engineering, 36(5), 664–671. https://doi.org/10.1016/j.ecoleng.2009.12.008
9. Winston, R. J., & Hunt, W. F. (2008). Field evaluation of level spreaders for runoff reduction and water quality impacts. Low Impact Development for Urban Ecosystem and
Habitat Protection. https://doi.org/10.1061/41009(333)100
10. Mays, L. W. (2001). Stormwater collection systems design handbook. McGraw Hill Professional.
11. Jill Malmstadt, Kelsey Scheitlin, & James Elsner. (2009). Florida hurricanes and damage costs. Southeastern Geographer, 49(2), 108–131.
https://doi.org/10.1353/sgo.0.0045
12. Ouyang, Y., Grace, J. M., Parajuli, P. B., & Caldwell, P. V. (2022). Impacts of multiple hurricanes and tropical storms on watershed hydrological processes in the Florida
panhandle. Climate, 10(3), 42. https://doi.org/10.3390/cli10030042
13. Florida Administrative Code, 62-610.414 (2021). https://www.flrules.org/gateway/ruleno.asp?id=62-610.414&Section=0
23. Materials and Methods
Geospatial Analysis
● Delineated sub-watershed basins that drain into our plot
from Mexico Beach Stormwater Plan (Figure 8)
● Retrieved land use data (Bay County GIS) and hydrologic
soil group (HSG) data (SSURGO)
● Used the union intersect analysis tool to create a new
layer combining basins and land use (Figure 9)
● Extracted data into an Excel spreadsheet
● Visually determined HSG for each land use/basin
sub-group and added into column on spreadsheet
Figure 17: Watershed basins
Figure 18: Watershed basins
intersected with land cover types
25. ● We chose the basins shown in Figure 10 for our
hydrologic modeling
○ In the Resilience and Recovery Partnership, they
said all drainage areas east of 15th street will be
rerouted to our pond
○ These are the basins that either currently drain or
will drain after the rerouting
○ Basins to the north and to the east are primarily
wetlands and will not add flow
○ Intending to put storm surge gate on the original
canal in case of emergencies
Figure 19: Drainage basins that will
drain into our pond
Materials and Methods
Geospatial Analysis
26. Materials and Methods
Hydrologic Modeling
● WINTR-55
○ Models single event rainfall runoff
hydrologic models
○ Used for unit hydrographs in order to
determine inflow to property for a 25
year, 24 hour storm event
● Area
○ Land use, land cover and soil type
acreage inputted for each sub basin
○ Obtained from GIS
Figure 20: Example land use data inputted to WINTR-55
27. ● Weighted CN
○ Each combination of land use and soil type have a uniquely designated
runoff curve number (CN)
○ Weighted value is calculated by WinTR based on inputted area values for
each sub basin
Figure 21: Example CN values based on soil type and land use
Figure 22: Weighted curve number equation
Materials and Methods
Hydrologic Modeling
28. ● Time of concentration (tc
)
○ Time required for runoff to travel from most distant point to the outlet in each sub-basin
■ Calculated by WinTR based on the following inputs obtained from Stormwater
master plan
● Length
● Slope
● Manning’s n value (surface roughness)
Figure 23: Example tc
data
inputted to WinTR
Materials and Methods
Hydrologic Modeling
29. ● Total flow in basin is calculated by WinTR based on inputted values
and NRCS Storm Data
● Rainfall types are designated based off of historical data in order to
estimate peak flow rate and runoff volumes.
Figure 25: Bay County NRCS Storm Data
Figure 24: Rainfall distribution map
Materials and Methods
Hydrologic Modeling
30. ● Pre development inflow
● Total discharge: 4085 cfs
Figure 26: Total output hydrograph Figure 27: Sub-basin output hydrograph
Results
Hydrologic Modeling
31. ● Post development inflow
● Total discharge: 4131 cfs
Figure 28: Total output hydrograph
Figure 29: Sub-basin output hydrograph
Results
Hydrologic Modeling
32. To compute Vs
(Volume storage) of a wet detention pond, we use the SCS
method, using the values for discharge from WinTR-55
● Pre-development discharge = 4085 cfs
● Post-development discharge = 4131 cfs
● Outlet discharge = 2065.5 cfs
● Acreage of watershed = 511.09 ac
● Rainfall for 25 year storm = 10.5 in
● Storm type = type III
Figure 30: SCS Method
Results
Stormwater Modeling
33. - Then we find the discharge ratio:
Qp
/Ip
= 2065.63/4131.25 = 0.5
- Plug the discharge ratio into the volume ratio
Vs
/Vr
= 0.683 - 1.43(Qp
/Ip
) + 1.64(Qp
/Ip
)2
- 0.804(Qp
/Ip
)3
Vs
/Vr
= 0.275
- We know Vr
Vr
= R*A = (10.5/12)(511.09) = 447.2 ac.ft
- Rearranging the volume ratio equation we get
Vs
= 0.275 * 447.2
Vs
= 123 ac.ft
Results
Stormwater Modeling
34. ● Since the water table is only 6-18
inches below soil, the pond will
need to be above ground to
achieve varying depths
○ 1 foot dry depth = 123 ac pond
○ 2 foot dry depth = 61.5 ac pond
○ 3 foot dry depth = 41 ac pond
Figure 31: Proposed
Pond Size and
Location on Lot
Results
Stormwater Modeling
35. Future Steps
What’s next in our design process?
● Design outflow structure
○ produce a post-development outflow hydrograph
● Design Berm structures
○ Investigate liners
○ perform a structural analysis on berms surrounding pond
● Design Sedimentation structures
● Size and investigate pumps
● Investigate planting
36. Acknowledgements
We would like to thank Dr. Christophe Darnault, Dr. Tom Dodd and Dr.
Tom Owino for their extraordinary guidance through the entirety of this
project. We would also like to thank Jeannie Williamson, Douglas Baber,
and Tim Linderman for the amazing opportunity it has been to work on
such an important project. We would also like to thank Chuck Jarman for
his excellent guidance in stormwater management design. This project
would not be what it is today without their guidance and assistance
along the way!
