LANTERN PARK STORMWATER

RETROFIT

DRAINAGE REPORT

Prepared for

City of South Daytona 1672 S Ridgewood Avenue South Daytona, Florida 32119

Volusia County Public Works Department 123 West Indiana Avenue DeLand, Florida 32720

Prepared by

Geosyntec Consultants, Inc.

11301 Corporate Boulevard, Suite 305 Orlando, Florida 32817

Project FW11762

May 2026

Lantern Park Stormwater Retrofit ii May 2026

Lantern Park Stormwater Retrofit

Drainage Report

Prepared for City of South Daytona 1672 S Ridgewood Avenue South Daytona, Florida 32119

Volusia County Public Works Department 123 West Indiana Avenue DeLand, Florida 32720

Prepared by Geosyntec Consultants, Inc.

11301 Corporate Boulevard, Suite 305 Orlando, Florida 32817

Nick Hartshorn, PE Mark Ellard, PE, CFM, D.WRE, ENV SP Water Resources Engineer Senior Principal

Project Number: FW11762

May 2026

The engineering material and data contained within the enclosed report was prepared by

Geosyntec Consultants, Inc. for sole use by the Volusia County Public Works Department and

City of South Daytona. This report was prepared under the supervision and direction of the respective undersigned, whose seal as a registered professional engineer is affixed below.

Nicholas Hartshorn, PE Project Manager

Florida PE# 90368

Lantern Park Stormwater Retrofit iii May 2026

TABLE OF CONTENTS

1. INTRODUCTION AND BACKGROUND ......................................................................... 1-1

1.1 Introduction ................................................................................................................. 1-1

1.2 Background and Location ........................................................................................... 1-1

1.3 Purpose and Goals ....................................................................................................... 1-1

2. DATA COLLECTION AND EVALUATION .................................................................... 2-1

2.1 General Description of Project Area ........................................................................... 2-1

2.2 Topography ................................................................................................................. 2-1

2.3 Soils ............................................................................................................................. 2-1

2.4 Land Use ...................................................................................................................... 2-1

2.5 Existing Drainage Infrastructure ................................................................................. 2-1

2.6 FEMA Flood Zones ..................................................................................................... 2-2

2.7 Surface Water and Wetlands ....................................................................................... 2-2

2.8 Water Quality Treatment ............................................................................................. 2-2

2.9 Previous Studies .......................................................................................................... 2-8

2.10 Project Survey ............................................................................................................. 2-8

2.11 Geotechnical Investigation .......................................................................................... 2-8

3. EXISTING CONDITIONS EVALUATION ....................................................................... 3-1

3.1 Hydrologic and Hydraulic Model Development ......................................................... 3-1

3.2 Hydrologic Model Development ................................................................................. 3-1

3.2.1 Subbasin Delineation ....................................................................................... 3-1

3.2.2 Time of Concentration ..................................................................................... 3-1

3.2.3 Peaking Factor ................................................................................................. 3-2

3.2.4 Curve Number Development ........................................................................... 3-4

3.2.5 Rainfall Distribution, Depth, Duration, and Frequency .................................. 3-4

3.3 1D Hydraulic Model Development ............................................................................. 3-5

3.3.1 1D Nodes ......................................................................................................... 3-5

3.3.2 Links ................................................................................................................ 3-6

3.4 Existing Conditions Model Results ............................................................................. 3-9

3.5 Existing Conditions Conclusions ................................................................................ 3-9

4. PROPOSED CONDITIONS EVALUATION ..................................................................... 4-1

4.1 Improvement Design ................................................................................................... 4-1

4.2 Proposed Conditions Stormwater Model .................................................................... 4-2

4.3 Proposed Conditions Model Results ........................................................................... 4-3

4.4 Pump Station Design Basis Report ........................................................................... 4-13

4.5 Proposed Conditions Conclusions ............................................................................. 4-14

5. CONCLUSION ..................................................................................................................... 5-1

Lantern Park Stormwater Retrofit iv May 2026

LIST OF TABLES

Table 3-1: Curve Number Lookup Table ..................................................................................... 3-4 Table 3-2: Summary of Land Use Imperviousness and Percent DCIA ....................................... 3-4 Table 3-3: Summary of Simulated Design Storms ...................................................................... 3-5 Table 3-4: Existing Node Maximum Conditions Summary ...................................................... 3-10 Table 4-1: Proposed Conditions Node Maximum Conditions Summary .................................... 4-5 Table 4-2: Flood Duration Summary Table ............................................................................... 4-11 Table 4-3: Summary of Peak Discharge Rates to Reed Canal ................................................... 4-12

LIST OF FIGURES

Figure 1-1: Vicinity Map ............................................................................................................. 1-2 Figure 1-2: Site Map .................................................................................................................... 1-3 Figure 2-1: Digital Elevation Model (DEM) Map ....................................................................... 2-3 Figure 2-2: Soils Map .................................................................................................................. 2-4 Figure 2-3: Land Use Map ........................................................................................................... 2-5 Figure 2-4: Drainage Infrastructure Map ..................................................................................... 2-6 Figure 2-5: FEMA Flood Zones Map .......................................................................................... 2-7 Figure 3-1: Subbasin Delineation Map ........................................................................................ 3-3 Figure 3-2: Existing Conditions Model Map ............................................................................... 3-8 Figure 3-3: Existing Conditions Inundation Results Map ......................................................... 3-11 Figure 4-1: Improvement Design Map ........................................................................................ 4-4 Figure 4-2: Proposed Conditions Model Map ............................................................................. 4-5 Figure 4-3: 10 Year / 24 Hour Proposed Inundation Results Map .............................................. 4-6 Figure 4-4: 25 Year / 24 Hour Proposed Inundation Results Map .............................................. 4-7 Figure 4-5: 100 Year / 24 Hour Proposed Inundation Results Map ............................................ 4-8

LIST OF APPENDICES

Appendix A: Project Survey

Appendix B: Geotechnical Investigation Report

Appendix C: Existing Conditions Model Input/Output Files

Appendix D: Proposed Conditions Model Input/Output Files

Appendix E: Pump Station Design Basis Report

Lantern Park Stormwater Retrofit 1-1 May 2026

1. INTRODUCTION AND BACKGROUND

1.1 Introduction

This drainage report presents the results of a design evaluation for the Lantern Park Stormwater Improvements project. Geosyntec Consultants, Inc. (Geosyntec) was tasked by Volusia County (County) Public Works Department to perform this assessment under the Professional Stormwater and Environmental Engineering Services Contract 24-SQ-101KW. It is noted that this project is being performed for the City of South Daytona (City) through Geosyntec’s existing contract with the County.

1.2 Background and Location

Lantern Park is a 168-home subdivision located off of Reed Canal Road in South Daytona. The subdivision was constructed in the 1960s without stormwater attenuation or treatment.

Stormwater is collected in a series of inlets that direct water to two large pipes that run parallel along the western edge of the subdivision. One of the pipes is 42-inch and the other pipe is 48-inch. The pipes discharge to the existing stormwater pond discussed below.

Prior to Hurricane Ian in 2022, the City purchased a 1.42 acre vacant lot in front of the subdivision and constructed a stormwater pond. The existing 42-inch and 48-inch pipes discharge to this pond and a pump station conveys water into Reed Canal. There is a high flow bypass which also allows the pipes to discharge directly to Reed Canal, however this is restricted at times due to tailwater conditions. During Hurricane Ian, the pond became overwhelmed and the majority of the homes in the subdivision flooded. During Hurricane Milton, the pond once again became overwhelmed and most of the homes that flooded during Hurricane Ian flooded yet again.

A Vicinity Map and Site Map are presented as Figure 1-1 and Figure 1-2, respectively.

1.3 Purpose and Goals

The purpose of this project is to provide a flood mitigation retrofit to reduce the occurrence of flooding in the subdivision. The proposed improvement involves the purchase of undeveloped land to construct a second stormwater pond to provide additional storage capacity with the ultimate goal of mitigating flooding in the subdivision. The target parcels for this proposed pond were designated by the City. The pond will have a proposed electric pump station that is capable of lowering the pond before a forecast storm event and run continuously during and after a storm until the roads are cleared. The pump station will have a backup generator in case of power loss set at an elevation higher than the estimated flood stage so it can continue to work even though the surrounding ground may be flooded. The generator must have the capability to run the pump station for at least 12 hours before needing to be refueled. The proposed pump station will discharge to Reed Canal, similar to the existing pump station.

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Sources Aerial & Streets: Esri, 2025 County Boundary: Volusia County, STR: Volusia County, 2025 WMD Boundary: SJRWMD, 2025

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Notes:

1. Reported flooding has been identified at the intersections of Lantern Drive and Gaslight Drive and the intersection of Colonial Drive and Gaslight Drive.

2. The Lantern Park Subdivison discharges into the existing stormwater pond that discharges into the Reed Canal and eventually discharges into the Halifax River.

Outfall to Halifax River

Lantern Park Stormwater Retrofit 2-1 May 2026

2. DATA COLLECTION AND EVALUATION

2.1 General Description of Project Area

The project area is located in east Volusia County, within the City limits of South Daytona, and on the south side of Reed Canal Road. The subdivision drains to Reed Canal which ultimately discharges to the Halifax River to the east. The project area consists primarily of residential areas.

2.2 Topography

Elevations in the project area generally slope to the north towards Reed Canal and to the west where drainage infrastructure collects stormwater runoff. The project area is bounded to the west by residences along Lantern Drive, to the east by residences along Gaslight Drive, to the north by Reed Canal, and to the south by a local ridge. In general, the elevations of the streets throughout the subdivision are lower relative to the residences. A digital elevation model (DEM) dated 2018 was downloaded for the project area from US Geological Survey. Elevations in the project area are depicted in Figure 2-1. The vertical datum referenced throughout this memo is the North American Vertical Datum of 1988 (NAVD88).

2.3 Soils

Based on data downloaded from the NRCS Web Soil Survey, soils in the project area are primarily classified as fine sands. Soil classifications are depicted in Figure 2-2. The entire project area is classified as hydrologic soil group (HSG) B/D, which indicates that the soils are moderately well draining but elevated groundwater elevations during certain times of the year may restrict infiltration leading to higher rates of runoff. Results of the project geotechnical investigation are discussed in Section 2.9.

2.4 Land Use

Land use data were downloaded from SJRWMD that reflect 2020 conditions in the project area.

Land use classifications were reviewed and updated by Geosyntec based on review of aerials and field reconnaissance. Land use classifications are depicted in Figure 2-3. Land use in the project area is classified primarily as medium density residential.

2.5 Existing Drainage Infrastructure

Existing drainage infrastructure in the project area consists primarily of a closed system comprised of inlets and pipes. In general stormwater runoff is conveyed toward the west side of the subdivision where it is collected and conveyed into the trunkline running south to north which consists of the 42-inch and 48-inch pipes that run parallel to one another. Stormwater runoff is then discharged to the existing stormwater pond located in the northwest corner of the subdivision where a pump station conveys it to Reed Canal. The 42-inch and 48-inch pipes also have a gravity outfall to Reed Canal and are able to bypass the stormwater pond during high flow events. The pipes and force main from the pump station are retrofitted with flap gates to prevent backflow from Reed Canal. The stormwater pond has a gravity outfall located near the west side of the pond that also discharges to Reed Canal. As-built plans from ERPs, field observations by

Lantern Park Stormwater Retrofit 2-2 May 2026

Geosyntec staff, and survey data were utilized to supplement, refine, and modify the drainage infrastructure depicted in Figure 2-4.

2.6 FEMA Flood Zones

FEMA Flood Insurance Rate Map (FIRM) panel 12127C0369J covers the project area and has an effective date of September 29, 2017. Parts of the project area are classified as Zone A and Reed Canal to the northeast is classified as Zone AE with a base flood elevation equal to 4 feet. FEMA flood zones in the vicinity of the project area are depicted in Figure 2-5. It is noted that Zone A areas correspond with the streets in the subdivision, which is consistent with reports from the City that the streets experience frequent inundation.

2.7 Surface Water and Wetlands

There are no wetlands present in the project area. Reed Canal is a surface water that ultimately drains to the Halifax River.

2.8 Water Quality Treatment

The subdivision was originally constructed before permitting requirements and did not have water quality treatment. In 2011, the existing stormwater pond was constructed providing a water quality benefit for the project area. However, this stormwater pond was primarily implemented for flood control and may not be meeting current requirements for water quality treatment.

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Existing Stormwater Pond

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MUKEY Soil Name HSG Percent of Project Area

1544130 Immokalee Sand B/D 9.50% 1544174 Tuscawilla Fine Sand, 0 to 2 Percent Slopes B/D 88.80% 1544176 Tuscawilla-Urban Land Complex B/D 1.70%

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Land Use Code Description Percent of Project Area

1100 Residential Low Density 2.03% 1200 Residential Medium Density 88.33% 4340 Upland Mixed Coniferous Hardwood 9.64%

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Sources Aerial: Esri, 2025 Roads: Volusia County, 2025 Parcels: Volusia County, 2025 Infrastructure: Geosyntec, 2025

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Sources Aerial: Esri, 2025 Roads: Volusia County, 2022 Parcels: Volusia County, 2023 FEMA FIRM Panel: 12127C0369J Effective Date 9/29/2017

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Lantern Park Stormwater Retrofit 2-8 May 2026

2.9 Previous Studies

The City provided Geosyntec with data from the Lantern Park Stormwater Improvements project performed in 2011 by John A. Dillard, Jr. This information included as-built information for the existing stormwater pond and pump station as well as modeling data that was referenced for developing the model for this project. No environmental resource permits (ERPs) were referenced for this project.

2.10 Project Survey

The project survey was performed by ECHO UES, Inc. (ECHO) in August 2025. The project survey is provided in Appendix A. The project survey vertical datum is NAVD88. The conversion factor from NGVD29 to NAVD88 for the project area is -1.19 feet. Information collected during the project survey included drainage infrastructure, topographic information, right of way and easements, utility designations, geotechnical boring locations, etc. This information was collected to aid in the development of the project model and improvement design.

2.11 Geotechnical Investigation

The project geotechnical investigation was performed by Geotechnical and Environmental Consultants, Inc. (GEC) in October 2025. The geotechnical investigation reports are provided in Appendix B.

Groundwater was measured 24 hours after completion of the soil borings at depths ranging from

4.7 to 5.3 feet below the ground surface. Seasonal high groundwater levels are estimated to range from 2.2 to 2.6 feet below the ground surface. Dense sand and shell layers were encountered in the borings at various depths. These soils may be difficult to excavate and may require special consideration from the Contractor in choosing the proper equipment for excavation. Additional information related to the geotechnical investigation is provided in Appendix B.

Lantern Park Stormwater Retrofit 3-1 May 2026

3. EXISTING CONDITIONS EVALUATION

3.1 Hydrologic and Hydraulic Model Development

Geosyntec developed a hydrologic and hydraulic (H&H) model to simulate design storm events and assess modeled flooding conditions. The model was utilized to assess existing conditions and evaluate different storage and pump scenarios to alleviate flooding in the subdivision. The existing conditions evaluation aided in the identification / confirmation of areas of flooding, causes of flooding, and provided a foundation for the development of the proposed improvements.

The drainage area hydrologic features of interest for modeling of rainfall excess (runoff) included soil data with hydrologic group classifications indicating relative runoff infiltration capacity, land use data to provide estimated curve numbers (CN) and percent imperviousness, and subbasin delineations. The hydrologic parameters of each individual subbasin (contributing area, CN, time of concentration, etc.), were developed to simulate rainfall-derived runoff hydrographs.

Data collected from existing GIS drainage inventories and the project survey were utilized to inventory the hydraulic features that convey runoff throughout the project area. These hydraulic features were used to develop the model network schematic with a sufficient level of detail to accomplish the objectives of the existing conditions analysis. The model level of detail was developed to each existing inlet in the subdivision to help pinpoint drainage issues in the subdivision and better characterize potential benefits.

Stormwater hydrology and hydraulics were simulated using StormWise [version 4.08.03], which is a comprehensive hydrodynamic stormwater modeling software. The StormWise model utilized the hydrology procedures presented in the Soil Conservation Service’s TR-55 [NRCS TR-55, 1986]. Stormwater runoff hydrographs were generated from subbasins and then assigned to nodes in the drainage network. The nodes are used to represent specific locations in the drainage network and are connected by links, which include pipes, weirs, etc. Specific hydrologic parameters are discussed below.

3.2 Hydrologic Model Development

3.2.1 Subbasin Delineation

Subbasins were delineated by Geosyntec for each area of interest within the project area. The approximately 49.5-acre project area was discretized into 25 subbasin areas for use in the hydrologic model. The subbasin boundaries were determined using the project DEM, drainage infrastructure data, and survey data. Refer to Figure 3-1 for a map of the subbasin delineations.

Delineation of individual subbasins allows for a more detailed analysis and the opportunity to pinpoint specific areas with potential drainage deficiencies.

3.2.2 Time of Concentration

The Soil Conservation Service (SCS) Unit Hydrograph method requires a time of concentration (Tc) be specified for each subbasin. The Tc represents the amount of time it takes a particle of water to travel from the hydraulically most distant point in the drainage basing to its outlet. The Tc is computed by summing all travel times for consecutive flow components (i.e., sheet flow, Lantern Park Stormwater Retrofit 3-2 May 2026 shallow concentrated flow, and channel flow) of the subbasin conveyance system in accordance with TR-55. Sheet flow is flow over plane surfaces with flow length of less than 100-feet. After 100-feet, sheet flow is assumed to become shallow concentrated flow. Shallow concentrated flow is also used for flow in very small channels such as water flowing along a street curb. Open channel flow is used for flow in ditches or pipes. A minimum Tc of 10 minutes was used in the calculations. Due to the relatively small size of each subbasin, all subbasins were assumed to have a Tc equal to the minimum value of 10 minutes.

3.2.3 Peaking Factor

The SCS Unit Hydrograph Method requires a unit hydrograph peak rate factor (K’) be specified.

The selection of a K’ depends on the geographical area and local conditions. Selection of K’ was based on the procedures outlined in the document entitled “Procedure for Selection of SCS Peak Rate Factors for Use in MSSW Permit Applications”, SJRWMD, April 1990. Specifically, the K’ value of 256 was used in the watershed, which based on the SJRWMD 1990 report is “an average of peak rate factors determined for several measured runoff hydrographs from several basins (in addition to the Kissimmee) in central and southern Florida by the U.S. Army Corps of Engineers.”

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Sources Aerial: Esri, 2025 Roads: Volusia County, 2025

Legend Subbasins

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Lantern Park Stormwater Retrofit 3-4 May 2026

3.2.4 Curve Number Development

The Curve Number (CN) approach was used as the rainfall excess and runoff method. CN values were assigned to each land use and soil combination in a Curve Number Set table in the model.

The CN for each sub-polygon is determined by the model by looking up the matching land use and soil combination in the Curve Number Set table.

Approximate impervious area percentages were estimated by Geosyntec by performing takeoff calculations at representative locations for each land use type. Approximate directly connected impervious area (DCIA) percentages were also estimated by Geosyntec by performing takeoff calculations. Waterbodies were given a CN of 100. The CN representative of open space was used for pervious areas rather than a land use specific CN to avoid double counting impervious area in the model. CN values for pervious areas are summarized in Table 3-1. It is noted that the entire project area is classified as HSG B/D.

Table 3-1: Curve Number Lookup Table

Curve Number Lookup Table Open Space HSG Classification Open Space Curve Number

HSG B/D 80

A summary of imperviousness and percent DCIA for the different land use types is provided in Table 3-2.

Table 3-2: Summary of Land Use Imperviousness and Percent DCIA

Summary of Land Use Imperviousness and Percent DCIA Land Use Classification % Impervious % DCIA

1100: Residential low density 10 0 1200: Residential medium density 15 5 4340: Upland mixed coniferous hardwood 0 0 5300: Reservoirs 100 100

3.2.5 Rainfall Distribution, Depth, Duration, and Frequency

The SCS Unit Hydrograph Method was used for the project. To implement the SCS Unit Hydrograph Method, a rainfall distribution must be specified for the desired storm event as a function of time for the subbasin’s unit hydrograph. Standard SCS, Florida Modified, SFWMD, or SJRWMD rainfall distributions are commonly used in this region of Florida if no local distribution has been established. The Florida Modified rainfall distribution was utilized for this project. Rainfall depths for the different design storms were referenced from the National Oceanic and Atmospheric Administration (NOAA) Atlas 14 precipitation frequency estimates.

The design storms simulated for this project are summarized in Table 3-3.

Lantern Park Stormwater Retrofit 3-5 May 2026

Table 3-3: Summary of Simulated Design Storms

Summary of Design Storms Design Storm Rainfall Amount (inches) Rainfall Distribution

Mean Annual, 24 hour 3.84 Florida Modified 10 year, 24 hour 6.96 Florida Modified 25 year, 24 hour 8.92 Florida Modified

100 year, 24 hour 12.6 Florida Modified

3.3 1D Hydraulic Model Development A total of 32 nodes and 68 links were included in the model network. It is noted that the model hydraulic features were modeled in a maintained design condition, assuming all conveyance is free of sedimentation or other flow obstructions. The model node-link schematic is shown in Figure 3-2. Specific information pertaining to development of the node-link network is provided below.

3.3.1 1D Nodes Nodes in the model are typically either defined as Stage/Area or Time/Stage. Stage/Area nodes are used to model storage areas such as stormwater ponds and can also be used as junctions in channels and manholes in pipe networks. Time/Stage nodes typically represent the discharge point(s) or boundary condition(s) in the model. A total of 30 Stage/Area nodes, one Time/Stage node, and one Stage/Volume node were utilized in the existing conditions model. The one Stage/Volume node represents the existing stormwater pond and was referenced from the previous project performed in 2011.

Initial Stages

Initial stages of nodes were set such that the model simulation would begin in static equilibrium.

For nodes connected to a waterbody, the initial stage was set at the greater of the waterbody initial stage or pipe/weir invert elevations.

Warning Stages

Warning Stages were set at the elevation at which flooding of concern is expected to occur.

Typically, this would include pond berm overtopping, roadway flooding, manhole tops, structure flooding elevation, etc.

Lantern Park Stormwater Retrofit 3-6 May 2026

Stage vs. Area

Stage vs. area relationships for each Stage/Area type node was defined below the node initial stage and above the peak node stage from the model results for each node. This was done to accurately define the available storage in each node and prevent extrapolation or performance issues in the model. The stage vs. area information for storage nodes was extracted from the project DEM using the native StormWise modeling tools and adjusted by Geosyntec to account for the small amount of storage provided in the drainage structures.

Boundary Conditions

The project area discharges to Reed Canal. Based on the previous model completed for this area (John A. Dillard, Jr., 2011), the boundary condition for Reed Canal was assigned an initial stage of 0.81 feet that increased up to a stage of 5.31 feet at hour 18 of the design storms. These boundary conditions were used for all design storm simulations.

3.3.2 Links

The model simulated flow in links allowing the evaluation of conveyance effectiveness between nodes. A description of the various model links is provided below.

Pipes

Pipe links were used to represent the various pipes and culvert sections included in the model. A total of 34 pipe links were used in the existing conditions model. Pipe inverts, dimensions, geometry, and material data were referenced from available information. Roughness coefficients (Manning’s n) were based on the material as follows:

• Corrugated Metal Pipe (CMP) 0.022.

• Reinforced Concrete Pipe (RCP) 0.012.

• High Density Polyethylene Pipe (HDPE) 0.009.

Entrance and exit losses were assigned to pipes where appropriate based on the outlet condition at the end of the pipe. These values were assigned based on literature values, or default values were used where exact conditions were uncertain. In general, the values were applied as follows:

• Entrance Losses – A representative average value of 0.5 was assigned to all pipes.

• Exit Losses – A value of 0 was used for open discharge, and an exit loss of 1.0 was used for discharge into a static waterbody.

Weirs

Weir links are used to represent outflow weirs at ponds, inlet characteristics to some outfall structures, and to represent overland flow. A total of 32 weir links were used in the model for this project. The specific geometric of the weir was input into the model. Vertical weirs were used to model overtopping situations. Each weir was assigned a specific weir coefficient based on its geometry. Weir coefficients were applied as follows:

• Weir Coefficient – A value of 2.8 was assigned for broad-crested weirs and 3.2 was assigned for sharp-crested weirs.

Lantern Park Stormwater Retrofit 3-7 May 2026

• Orifice Coefficient – A value of 0.6 was assigned.

Drop Structure

A single drop structure link was utilized to model the existing pond’s control structure that provides a gravity outfall to Reed Canal. In the model, a drop structure link simply represents a weir link in series with a pipe link.

Rating Curve

A single rating curve link was utilized to model the existing pump station that conveys water from the existing stormwater pond to Reed Canal. An operating table was assigned to the rating curve link that relates head conditions to flow rates. Information pertaining to the existing pump station was obtained from the 2011 model completed for this area and was utilized to parameterize the rating curve link and associated operating table.

Cross Sections

Location specific irregular cross-sections are typically extracted from a project DEM, topographic survey, or as-built plans for use in the model. Cross-sections are typically assigned to specific weir or channel links in the model to provide the irregular geometric properties for these links. For the case of cross-sections used in channel links, the cross-sections are used to sort Manning’s roughness values as well as geometric data. For this project 31 overland weir cross sections were developed in the model and elevations were extracted from the project DEM.

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Sources Aerial: Esri, 2025 Roads: Volusia County, 2025

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Lantern Park Stormwater Retrofit 3-9 May 2026

3.4 Existing Conditions Model Results

Peak stage results for the simulated design storms are summarized in Table 3-4. Modeled inundation results are depicted on Figure 3-3. Model input/output files are provided as Appendix C.

As seen in Figure 3-3, there is significant inundation throughout the subdivision beginning at the 10 year, 24 hour design storm. As seen in Figure 3-3, with increasing intensity of the simulated design storms, the extent of flooding extends outward from the street, and the number of potentially impacted structures increases. A significant number of potentially impacted structures is observed during the 100 year, 24 hour design storm.

These results appear to be due to not only a lack of storage in the project area, but also undersized drainage infrastructure throughout the subdivision. There are a number of undersized pipes as well as mismatched pipe sizes that appear to be restricting stormwater runoff generated in the subdivision from reaching the 42-inch and 48-inch pipes that convey stormwater north towards Reed Canal. An example of this is the drainage infrastructure near the intersection of Lantern Drive and Gaslight Drive. Pipe sizes in this location decrease from 24”x38” in the upstream area to 19”x30” at the connection to the trunkline. Generally, pipe sizes should not decrease relative to upstream sizes with the understanding that more runoff will be added to the system in downstream areas. Observations similar to this as well as undersized pipes such as 12-inch, 15-inch, and 18-inch throughout the subdivision may be exacerbating flooding. Refer to Figure 2-4 for a map of existing drainage infrastructure.

Peak discharge rates to Reed Canal for each design storm event are summarized below.

• Mean Annual, 24 hour: 5.67 cubic feet per second (cfs).

• 10 year, 24 hour: 28.61 cfs.

• 25 year, 24 hour: 37.92 cfs.

• 100 year, 24 hour: 47.47 cfs.

3.5 Existing Conditions Conclusions

An existing conditions assessment was performed for the project area. Model results indicated that there is significant inundation occurring throughout the subdivision due to a lack of storage and inadequate drainage infrastructure. These observations are consistent with City reports of flooding in the subdivision. Based on both the simulated and reported flooding in the project area, additional storage, infrastructure upgrades, and additional pumping are warranted and are presented in Section 4.

STAGE/AREA NODE INITIAL STAGE WARNING STAGE

NAME ELEVATION ELEVATION

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LP0010 -0.05 6.45 3.30 - 4.97 - 5.03 - 5.10 -

LP0020 0.65 6.03 3.31 - 5.03 - 5.22 - 5.49 -

LP0030 0.35 6.14 3.32 - 5.07 - 5.32 - 5.63 -

LP0040 0.70 5.71 3.32 - 5.11 - 5.39 - 5.73 0.02

LP0050 1.27 5.48 3.32 - 5.11 - 5.40 - 5.74 0.26

LP0060 1.19 3.92 3.32 - 5.06 1.14 5.51 1.59 6.09 2.17

LP0070 1.00 3.67 3.32 - 5.05 1.38 5.50 1.83 6.09 2.42

LP0080 1.06 3.78 3.32 - 5.06 1.28 5.51 1.73 6.09 2.31

LP0100 0.70 3.58 3.48 - 5.10 1.52 5.41 1.83 5.80 2.22

LP0110 0.86 3.55 3.40 - 5.10 1.55 5.41 1.86 5.80 2.25

LP0120 0.70 3.66 3.40 - 5.09 1.43 5.41 1.75 5.80 2.14

LP0130 1.42 3.97 3.67 - 5.10 1.13 5.41 1.44 5.80 1.83

LP0140 1.53 4.2 4.20 - 5.10 0.90 5.41 1.21 5.80 1.60

LP0150 2.25 4.87 5.23 0.36 5.29 0.42 5.42 0.55 5.81 0.94

LP0160 2.16 4.94 5.20 0.26 5.29 0.35 5.42 0.48 5.81 0.87

LP0170 2.02 4.83 5.01 0.18 5.21 0.38 5.42 0.59 5.80 0.97

LP0180 2.1 4.73 5.02 0.29 5.22 0.49 5.42 0.69 5.81 1.08

LP0190 1.3 3.63 3.88 0.25 5.31 1.68 5.66 2.03 6.04 2.41

LP0200 1.21 3.61 4.02 0.41 5.31 1.70 5.66 2.05 6.04 2.43

LP0210 1.1 3.68 3.85 0.17 5.30 1.62 5.66 1.98 6.04 2.36

LP0220 1.68 4.17 4.17 - 5.31 1.14 5.66 1.49 6.04 1.87

LP0230 1.92 4.33 4.31 - 5.31 0.98 5.66 1.33 6.05 1.72

LP0240 2.05 4.31 4.38 0.07 5.31 1.00 5.67 1.36 6.05 1.74

LP0250 1.53 3.78 3.59 - 5.30 1.52 5.66 1.88 6.04 2.26

LP0260 1.47 3.73 3.55 - 5.30 1.57 5.66 1.93 6.04 2.31

LP0270 2.24 4.88 4.31 - 5.31 0.43 5.66 0.78 6.05 1.17

LP0280 2.44 4.94 4.39 - 5.32 0.38 5.67 0.73 6.05 1.11

LP0290 2.57 4.92 4.42 - 5.32 0.40 5.67 0.75 6.05 1.13

LP0300 0 6.02 6.14 0.12 6.29 0.27 6.34 0.32 6.40 0.38

LP0310 0 7.2 3.30 - 4.97 - 5.03 - 5.11 -

LP0330 0 7.2 3.30 - 4.95 - 4.96 - 4.99 -

REED CANAL 0.95 6.45 4.95 - 4.95 - 4.95 - 4.95 -

- Bold red peak stages represent nodes that exceed the warning stage

TABLE 3-4: EXISTING CONDITIONS NODE MAXIMUM CONDITIONS SUMMARY

MEAN ANNUAL / 24 HOUR 10 YEAR / 24 HOUR 25 YEAR / 24 HOUR 100 YEAR / 24 HOUR

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Sources Aerial: Esri, 2025 Roads: Volusia County, 2025

Legend Subbasins

Mean Annual / 24 Hour Inundation

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Figure 3-3

Lantern Park Stormwater Retrofit 4-1 May 2026

4. PROPOSED CONDITIONS EVALUATION

4.1 Improvement Design

Based on the results of the existing conditions analysis, the Lantern Park project area lacks storage for the amount of stormwater runoff that is generated, in addition to the existing drainage infrastructure being inadequate to convey runoff without street inundation. Based on these findings, a design was developed and is described below. The location of the proposed pond was conveyed to Geosyntec by the City, and the pond was sized to maximize the utilization of the site. The goal of the design is to perform pre-storm drawdown of the proposed pond to provide additional storage which will reduce inundation in the subdivision. Additionally, pumping during and after the storm will improve overall conveyance of runoff and reduce the duration of flood impacts.

A stormwater pond will be constructed in the vacant area behind 2825 Sauls Street. The stormwater pond will be constructed to a depth of 10 feet with 3:1 side slopes. A junction box will be added to the existing 42-inch and 48-inch trunkline that will convey water to the proposed pond. A second pump station is proposed at the proposed stormwater pond that will convey water to Reed Canal via a proposed force main. Water will flow from the proposed pond to a wet well where the submersible pumps will be located. The proposed force main will be retrofitted with a flap gape due to tailwater conditions, similar to the existing system.

The proposed pump station was sized so that it would have the ability to pump down the proposed stormwater pond to the proposed bottom elevation of -4.72 feet ahead of a significant storm event (e.g., 100 year, 24 hour event) within 3 days. The proposed pump station will also run during and after the storm event until inundation has been cleared from the subdivision. The proposed pond will start at its control elevation equal of 1.16 feet based on the invert of the connected pipes that convey runoff north to the existing pond. To pump down the pond within 3-days, a pump was sized while also considering influx of groundwater during drawdown. The volume of the proposed pond relative to the existing ground surface is also provided for reference.

• Storage = 47,986 cubic yards (cy). Pump = 2,400 gallons per minute (gpm).

During more routine storm events where the pond is not drawn down ahead of time, the pond would still provide a benefit via the additional storage provided above the control elevation of

1.16 feet. However, the benefit is only maximized when the pond is pumped down to provide all available storage. It is noted that the proposed pond is also expected to provide a water quality benefit by reducing pollutant loads discharged to Reed Canal; however, the pond is not expected to meet new development standards for water quality as it is a retrofit to an already existing system.

The design also includes drainage infrastructure improvements in the subdivision. Specifically, the connections from the subdivision along Lantern Drive to the trunkline were upsized with the goal of improving the rate at which stormwater is discharged into the trunkline. As noted previously, the undersized and mismatched drainage infrastructure in the subdivision worsens flooding by restricting the conveyance of runoff from the subdivision to the trunkline, in addition to the lack of storage in the project area.

Lantern Park Stormwater Retrofit 4-2 May 2026

The proposed improvement design is depicted on Figure 4-1. Additional information related to the design of the pump station is provided in the Pump Station Design Basis Report, included as Appendix E. Information related to the pumps, instrumentation and controls, vaults, force main, and generator is provided in this document.

4.2 Proposed Conditions Stormwater Model

The existing conditions model, discussed in Section 3, was used as a starting point for the stormwater model development for the proposed design. The proposed conditions model network is depicted in Figure 4-2. Updates to the model included the following:

• Reflecting the proposed pond storage in the stage/area table for Node LP0300. The control elevation of the proposed pond was set at 1.16 feet which is equal to the invert of the first downstream pipe from the proposed pond. This is the elevation that the pond would drain to by gravity, not considering pumping.

• A pipe link was added between Node LP0020 and Node LP0300 representing the connection from the existing trunkline to the proposed pond. The proposed pipe was modeled as a 53”x83” elliptical concrete pipe.

• A rating curve link was added from Node LP0300 to the time/stage node representing Reed Canal representing the proposed pump station.

• Pipe links were updated in the subdivision to reflect the infrastructure upgrades.

The node representing the proposed pond began the simulation with an initial stage equal to the proposed pond bottom. This was done with the understanding that the City would pump down the pond ahead of significant storm events in order to maximize the available storage in the…