STORMWATER MASTER PLAN - City of Fort Walton Beachfwb.org/wp-content/uploads/2013/11/1-59-Stormwater-Master-Plan... · STORMWATER MASTER PLAN CITY OF FORT WALTON BEACH 107 Miracle

STORMWATER MASTER PLANSTORMWATER MASTER PLAN

CITY OF FORT WALTON BEACHCITY OF FORT WALTON BEACH107 Miracle Strip Parkway SW107 Miracle Strip Parkway SW

Fort Walton Beach, FL 32548Fort Walton Beach, FL 32548

STORMWATER MASTER PLANSTORMWATER MASTER PLAN

FINAL DRAFTFINAL DRAFT

JULY JULY 20132013

1545 Raymond Diehl Rd, Suite 200

Tallahassee, Florida 32308

T: 850.222.0334 F: 850.561.0205

HMM Project No. 297786

TABLE OF CONTENTS

1

Section Page Number

1.0 Executive Summary.. 1

2.0 Introduction 4

2.1 Project Background.. 4

2.2 Goals and Objectives 4

3.0 Model Development. 7

3.1 Model Platform 7

3.2 Data Gap Identification.. 11

3.3 Model Construction.11

3.4 Basin Delineation 12

3.5 Hydrologic Model.. 14

3.6 Hydraulic Model.. 16

3.7 Water Quality... 17

4.0 System Flood Analysis. 18

5.0 Design Alternative Development 21

5.1 System Improvements Methodology.. 21

5.2 Proposed System Improvements .. 21

5.3 Conceptual Cost Estimates.. 46

5.4 Evaluation Matrix.. 48

5.5 Improvement Priority 50

6.0 Rehabilitation and Replacement. 52

7.0 Capital Improvements Plan (CIP).55

8.0 Funding and Recommendations.. 57

8.1 Funding. 57

8.2 Recommendations. 58

Appendix A HEC-RAS to InfoSWMM Conversion Methodology

Appendix B Data Gap Analysis Document

Appendix C Flood Analysis Document

Appendix D Maps

Appendix E HGL Profiles and Junction Graphs

Appendix F Project Conceptual Cost Estimates

Appendix G Project Evaluation Matrix

Appendix H Rehabilitation and Replacement Pipe List

EXECUTIVE SUMMARY

2

1.0 EXECUTIVE SUMMARY

This report presents the City of Fort Walton Beach Stormwater Master Plan. The report

describes the review and analysis of the Citys stormwater infrastructure conducted by Hatch

Mott MacDonald (HMM) and includes recommendations for improvements. The primary

objective of the study was to develop a document to be used as guidance for eliminating or

reducing flooding within the City in consideration of health and safety. A second phase of the

Master Plan will be completed at a later date which will address Water Quality.

A summary of the efforts undertaken to complete the master plan process is as follows:

The InfoSWMM modeling software was selected for use in this master planning effort, per HMMs recommendation to City staff, after evaluation of multiple software

platforms.

HMM reviewed the Citys GIS data and made recommendations to improve model performance and ease of data transfer.

Field work was performed by both HMM and City staff to obtain missing data identified by HMM.

The model was constructed to include inlets, junction boxes, drainage ditches, pipes that are 15-inches in diameter or larger, stormwater basins, and rainfall data for storm

events up to and including the 100 yr-24hr storm event.

The City of Fort Walton Beachs InfoSWMM stormwater system model represents a valid working model of the existing system as of May 2012 along with the proposed

improvements. All model entities are matched one-to-one with the Citys GIS, where

possible.

Initial flood analysis discovered flooding in several areas throughout the City.

System improvements, based on the 25-yr critical storm event, were proposed to increase the conveyance system capacity to eliminate or reduce system flooding.

A flood reduction analysis was performed to identify the percent of flood reduction that would be achieved during the 100-yr critical storm event based on completion of the

improvements to eliminate flooding during the 25-yr storm event.

A conceptual cost estimate was developed for the areas with proposed system improvements. The cost estimates include a 35% construction contingency and 10%

engineering & administration fee.

An evaluation matrix was created to establish priorities for each area of proposed improvement based on key criteria established by HMM and City staff.

A Rehabilitation and Replacement (R&R) analysis was completed on the existing stormwater conveyance system to determine maintenance priorities. The analysis

included pipe material, age, diameter, conflicts, and conceptual costs.

A 25 Year Capital Improvements Plan (CIP) was developed based on 5 year improvement periods and a budget of $500,000 per year.

EXECUTIVE SUMMARY

3

There are 85 recommended improvements which are identified and discussed in Section 5.2 of

this report. Also, a summary of the recommended improvements is provided in Table 7.1,

which is prioritized and includes estimated costs. Appendix H includes a spreadsheet for 2,360

pipe segments which have been prioritized for maintenance consideration. Recommendations

are provided in Section 8.0, which generally include:

1. Implement the proposed system improvements as identified in the Capital Improvement Plan (Table 7.1) as funding allows. The list of improvement projects is prioritized and

should be used as guidance. There are circumstances, such as change in conditions,

development, and property damage, which may justify a change in the order of

implementation.

2. Implement a maintenance program for the proposed rehabilitation and replacement of storm water pipe as identified in the Pipe Maintenance Schedule included in Appendix

H. The list of maintenance projects is prioritized and should be used as guidance. When

practical, the maintenance projects should be coordinated with other construction

projects to prevent an area from being damaged twice and to reduce construction cost.

3. Update the models physical data and operating scenario(s) to reflect evolving system

conditions and operating protocol(s). Consider including additional County and FDOT

stormwater data in the model as it becomes available.

4. Utilize the InfoSWMM software to include the Water Quality component of the

stormwater system. Use the water quality data to seek grant opportunities.

5. Develop a model maintenance guideline to ensure modifications are uniformly made to

the model by all whose use of the model is authorized by the City. This protocol should

also contain procedures to ensure the model is able to seamlessly update the Citys GIS

data as applicable, and vice-versa.

6. Update the stormwater master plan in five (5) year increments.

INTRODUCTION

4

2.0 INTRODUCTION

2.1 Project Background

The City of Fort Walton Beach is located in southern Okaloosa County, Florida. The City has a

population of approximately 19,500 people and includes a total area of 8.2 square miles

according to the United States Census Bureau. Of the 8.2 square miles, 7.4 square miles is land

and the remaining 0.8 square miles is water. The City limits are divided into two separate

sections with the area in between belonging to Okaloosa County. The southern area of the City

is generally located along the Gulf of Mexico and Cinco Bayou with elevations ranging from sea

level to elevation 40. The northern area of the City is generally located along Bass Lake and

Dons Bayou to the Lewis Turner Boulevard area with elevations ranging from sea level to

elevation 74. A map of the city limits is included as Figure 2.1.

During certain storm events, flooding occurs in areas along the coast, streams, and streets

within the City, resulting in flood damage that impacts homes and businesses. As the City

continues to develop, flood impacts will increase due to additional runoff generated as a result

of increased urbanization.

As a result of the flood impacts, the City decided to proceed with a stormwater master plan

development that would have specific goals and objectives in place to target and eliminate /

reduce flooding.

2.2 Goals and Objectives

This report describes the review and analyses conducted by Hatch Mott MacDonald (HMM) on

the Citys stormwater infrastructure. The primary objectives of the study include the following:

1. Develop a large scale hydraulic and hydrologic model of the existing stormwater

infrastructure.

2. Analyze the existing infrastructure during the 10, 25, 50, and 100 year critical storm

frequencies to identify areas prone to flooding.

3. Develop design alternatives, where practical, for the areas prone to flooding to

determine necessary improvements required.

4. Provide opinions of probable cost for each design alternative.

5. Evaluate each design alternative based on established ranking criteria for inclusion in

the Citys Capital Improvements Plan (CIP).

6. Develop a comprehensive stormwater master plan document.

INTRODUCTION

5

The original project goals were altered slightly based on software limitations within InfoSWMM.

Many of the goals focus upon flood levels. The base InfoSWMM software does not provide

actual flood levels outside of the conveyance system. Due to this limitation, HMM and the City

adjusted the goals to focus on eliminating flooding completely where practical and otherwise

reducing flooding as much as possible.

INTRODUCTION FIGURE 2.1

6

MODEL DEVELOPMENT

7

3.0 MODEL DEVELOPMENT

3.1 Model Platform

At the City of Fort Walton Beachs invitation, on October 13, 2011, representatives from

Bentley Systems, Inc., and Innovyze, Inc., made presentations showcasing the features of their

respective stormwater modeling applications:

Bentley: SewerGEMS

Innovyze: InfoSWMM and InfoWorks ICM

Based on the information relayed during the presentations, answers to follow-up questions by

representatives from each vendor, feedback from City staff, and HMMs experience with these

platforms, HMM developed a comparison summary (see Table 3.1) that lists the advantages

and disadvantages of each program.

MODEL DEVELOPMENT

8

TABLE 3.1

COMPARISON OF STORMWATER MODELING SOFTWARE

Bentley SewerGEMS, Innovyze InfoWorks ICM, Innovyze InfoSWMM

System Advantages Disadvantages

Client familiarity with Bentley productsManual mods to RTK tables required for

model calibration

Bentley's support and training programs

seem preferable to Client

Manual catchment/ sub-catchment

delineation required (via ArcGIS tools)

Bentley bundles other Haestad/ Bentley

products within SewerGEMS

Does not model sediment transport as

part of water quality analysis

More output graph features than those

contained in MS Excel2D flood boundary mapping not available

Scenario/ Alternative setup and

management is more intuitive (HMM's

experience)

No built-in tools for importing HEC-RAS

data files or transects

Capability to run in "stand-alone" mode

No additional licenses required by HMM

to perform project modeling

Includes 2D flood boundary mapping Most expensive alternative

Utilizes ArcGIS layers/ shapefiles for data

import

Manual mods to RTK tables required for

model calibration

Combines functionality of InfoWorks CS

and InfoWorks RS

Additional hardware requirements for

optimum performance (e.g., 64-bit, multi-

processor O/ S with GPU capability)

Marketed solely as "stand-alone" program

Built-in Sub-catchment Boundary

Delineation Manager (works with

ArcGIS' Spatial Analyst)

More cumbersome Active Facility/

Topology, and Data Set/ Alternative

management (HMM's experience)Available 2D module for flood boundary

mapping Requires user knowledgable of both

modeling & GIS (no "stand-alone" mode)

InfoSWMM Exchange Menu option for

direct import of HEC-RAS transect data2D module requires separate license/

maintenance agreement

Built-in sediment transport modeling

capabilities via Water Quality Simulation

Options

Innovyze has troublesome output Graph

Control Manager (HMM's experience), but

plans to upgrade in 2012

Built-in Calibrator extension No online training/ webinars offered

Bentley

SewerGEMS v8i SELECT Series 2 (for

ArcGIS v10)

* Includes the following InfoSWMM Suite Extensions: Calibrator, DWF Allocator, Designer, Conduit Storage Synthesizer,

Subcatchment Manager, Risk Assessment Manager. Includes the above InfoSWMM Suite Extensions plus these InfoSWMM ExecuOve Suite Modules: Pond Design

Manager, NetVIEW, RDII Analyst.

FEATURES

Innovyze

InfoSWMM Suite *

InfoSWMM Exec Suite

InfoSWMM 2D

(for ArcGIS v10)

Innovyze

InfoWorks ICM

("stand-alone" only)

MODEL DEVELOPMENT

9

Some key features of InfoSWMM which SewerGEMS currently lacked were noted as follows:

1. Calibrator extension

2. Sub-catchment boundary delineation tool

3. Sediment transport modeling capability

4. Rainfall Derived Infiltration Inflow (RDII) Analyst

The features of the Citys stormwater geodatabase can be mapped one-to-one for creating a

stormwater model in either InfoSWMM or SewerGEMS; this is not possible within InfoWorks

ICM, as this program runs strictly in stand-alone mode.

It should be noted that there was no completely automated method for importing Okaloosa

Countys existing HEC-RAS stormwater model data into any of these platforms; however, the

latest version of InfoSWMM will allow transects to be imported from a HEC-RAS geometry file.

This geometry file is generated via HEC-RAS using the output data from an applicable model

run. ArcGIS tools can then be used to generate a geodatabase mirroring the physical and

geometric characteristics of the existing HEC-RAS stormwater model (see Appendix A for

detailed HEC-RAS to InfoSWMM conversion methodology).

HMM also presented a matrix of costs associated with each potential software package and

combinations thereof as shown in Table 3.2. This matrix included costs for the software,

technical support by the software vendors, training programs offered by the software vendors,

and annual software license renewals.

Based on HMM review and discussions with City staff, it was recommended that the City of Fort

Walton Beach purchase Innovyzes InfoSWMM Executive Suite. HMM reviewed the Citys and

Countys stormwater geodatabases received to-date, and believed the 10,000-pipe version of

the software to be adequate for the Citys needs on the current project, as well as for

expanding the model to include the Countys stormwater infrastructure. HMM advised the City

to purchase the network license-based version, thereby ensuring a centralized location on the

Citys computer network for license maintenance, upgrades, etc.

The City ultimately purchased Innovyzes InfoSWMM Executive Suite 5,000-pipe version with

Okaloosa County agreeing to pay for the software upgrade to 10,000-pipes in the future to

include their stormwater data.

MODEL DEVELOPMENT

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TABLE 3.2

License

Annual

Maintenance First Year's Cost* License

Annual

Maintenance First Year's Cost*

Bentley 5,000 $14,995 $3,600 $23,590 $14,995 $3,600 $23,590 "BentleyLEARN": $4,995 / annum (includes "on demand

SewerGEMS v8i SELECT Series 2 10,000 $19,995 $4,800 $29,790 $19,995 $4,800 $29,790 web-based training, unlimited 24/7 tech support, software

(for ArcGIS v9.3.1) Unlimited N/A N/A N/A N/A upgrades, & network licensing) SewerGEMS Course: $1,500 / person

5,000 $40,500 $6,075 $46,575 $44,550 $6,683 $51,233

10,000 $57,000 $8,550 $65,550 $62,700 $9,405 $72,105

Unlimited $60,000 $9,000 $69,000 $66,000 $9,900 $75,900

5,000 $22,000 $4,500 $26,500 $24,000 $6,750 $30,750

10,000 $29,000 $5,000 $34,000 $31,000 $7,500 $38,500

Unlimited $32,000 $5,500 $37,500 $34,000 $8,250 $42,250

First Year's Cost Annual Cost 4-yr Annual Cost Est. 5-yr Cost

Bentley SewerGEMS (10k pipes) $29,790 $9,795 $39,180 $68,970

Innozyve

InfoWorks ICM (10k junctions) $72,105 $9,405 $37,620 $109,725

RECOMMENDED SELECTION

Network Based License

InfoSWMM Exec Suite &

InfoSWMM 2D (10k pipes)$38,500 $7,500 $30,000 $68,500

Innovyze

InfoSWMM Exec Suite & 2D

(bundled)

No annual training subscipriton program; no online training /

webinars offered.

2-day workshops at Innovyze are $1,600 / person.

2-day workshops at a client's location cost $10,000 for eight (8)

persons max.

Licensing fees include all aoftware upgrades / updates.

** Includes the following InfoSWMM Suite Extensions: Calibrator, DWF Allocator, Designer, Conduit Storage Sythesizer, Subcatchment Manager, Risk Assessment Manager.

*** Includes the above InfoSWMM Suite Extensions plus these InfoSWMM Executive Suite Modules: Pond Design Manager, NetVIEW, RDII Analyst.

* SewerGEMS cost includes annual BentleyLEARN fee of $4,995.

$6,750 $38,750Innovyze

InfoSWMM Suite & 2DUnlimited (est.) $32,000

$5,250 $25,250

Innovyze

InfoSWMM 2DUnlimited (est.) $20,000 $3,000 $17,000

$18,000 $3,750 $21,750

Innovyze

InfoSWMM Exec Suite***Unlimited (est.) $20,000

Number of

Pipes / Nodes

Innovyze

InfoWorks ICM

Innovyze

InfoSWMM Suite**Unlimited (est.)

Fixed-seat License Floating Network License

Training

COMPARISON OF STORMWATER MODELING SOFTWARE

Bentley SewerGEMS, Innovyze InfoWorks ICM, Innovyze InfoSWMM

System

MODEL DEVELOPMENT

11

3.2 Data Gap Identification

Once the InfoSWMM software was selected and the most recent stormwater geodatabase

received, HMM began the process of reviewing the existing data for accuracy, missing

information, and compatibility with the selected software package. The review resulted in the

creation of the Data Gap Analysis document. The complete document is included in Appendix B

and a summary is as follows:

An identifier that is unique to each element was required prior to model creation to

allow data to be transferred between the model and GIS.

No existing drainage basins had been established.

Missing data was noted by element type and categorized as relevant or not relevant.

Object IDs were listed for relevant data necessary for model construction.

Areas with a long run of negative slopes were identified for the City to review for

accuracy.

Areas of City stormwater connection to County and FDOT systems were noted and

mapped.

Based on this document, the City completed additional fieldwork, updated the existing

geodatabase, and created the unique identifier for each element known as the Model ID. The

updated geodatabase was then used to begin the model construction process.

3.3 Model Construction

The InfoSWMM model platform is based within ArcGIS and allows for direct import of existing

GIS data using the GIS Gateway. The gateway allows the user to select the existing data to

import and map the necessary data fields in GIS to the corresponding field in InfoSWMM. The

critical element when using the gateway is having a unique identifier, in this case the Model ID,

for every element within GIS. Otherwise, InfoSWMM will create a unique model identifier and

the connectivity between GIS and the model is lost. The unique identifier allows for data to be

transferred from the model back to GIS and for model maintenance updates as additional

information becomes available.

After the data was imported from GIS, all non-essential elements were removed from the

model (i.e. pipes less than 15-inches in diameter, fittings, etc.). The drainage ditches and ponds

were added at this point based on cross-sections provided by the City and contour data. Minor

fieldwork was also completed by HMM to verify some of the pond outfall structures and ditch

cross-sections. Discharge points were then converted to outfalls with a high water tidal

MODEL DEVELOPMENT

12

elevation of 2-ft established based on conversations with City staff and National Oceanic and

Atmospheric Administration (NOAA) data.

The final step in the physical model construction process involved HMM verifying the model

connectivity. Minor connectivity errors were encountered such as pipes not connected to

nearby node, orphan nodes, and pipes connected in reverse. These errors were corrected using

the built in network review / fix toolbars within InfoSWMM.

3.4 Basin Delineation

A stormwater basin is a surface area that drains during a rainfall event to a point of interest

such as an inlet, culvert, or outfall to surface water or pond. Basin delineation is a critical step

in stormwater model development as it plays a large role in determining the amount of runoff

that enters a system. Surface runoff, in turn, is used to estimate the capacity remaining or

flooding within the conveyance system.

The stormwater basins were delineated for each inlet and drainage ditch in the model using

aerials and 1-ft contour data. InfoSWMM has the capability to create the basins; however, due

to topographic data limitations (i.e. lack of curb and gutter shots, etc) the basin boundaries had

to be created manually. The land use for each basin was then defined using existing GIS data

for use with future pollutant loading. A Curve Number (CN) was defined for each basin based

on land use category and percent impervious as shown in Table 3.3

MODEL DEVELOPMENT

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TABLE 3.3

SCS RUNOFF CURVE NUMBERS

The basin areas were then tabulated automatically within InfoSWMM in square feet and

converted to acres. The slopes for each basin were calculated using a slope raster created using

the Spatial Analyst within ArcGIS and existing contour data. The longest length within each

basin was calculated manually based on basin boundaries, contours data, and street locations.

Based on the input data entered into each basin, the time of concentration was calculated

automatically by InfoSWMM. Finally, each basin was assigned to the corresponding inlet and

rain gages created using the Subcatchment Manager tool.

MODEL DEVELOPMENT

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3.5 Hydrologic Model

Hydrologic models are simplified, conceptual representations of a part of the hydrologic cycle

shown in Figure 3.1 below. They are primarily used for hydrologic prediction and for

understanding hydrologic processes. This model includes precipitation, evaporation,

infiltration, and surface runoff.

FIGURE 3.1

HYDROLOGIC CYCLE

The precipitation portion of the model included rainfall intensity time series curves based on

FDOT rainfall distribution curves for the 10, 25, 50 and 100 year frequency storm events. As an

example, the 25yr-8hr rainfall distribution curve table is shown in Table 3.4. After review of the

1, 2, 4, 8, and 24 hour storm events for each frequency, in most cases the 8 hour storm was

determined to be the critical storm event based on flood duration and frequency within the

service area. A rainfall distribution curve was applied to each rain gage in the model prior to

each model simulation. The rain gages were located within each basin established within the

model.

MODEL DEVELOPMENT

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TABLE 3.4

25YR-8HR RAINFALL DISTRIBUTION CURVE TABLE

8-HR RAINFALL (I = 0.94 IN/HR)

T (HRS) P/P TOTAL i/P TOTAL IDF 8-HR INTENSITY (IN/HR)

0.0 0.000 0.000 7.52 0.00

1.0 0.020 0.020 7.52 0.15

2.0 0.130 0.060 7.52 0.45

3.0 0.280 0.150 7.52 1.13

4.0 0.700 0.420 7.52 3.16

5.0 0.860 0.160 7.52 1.20

6.0 0.920 0.060 7.52 0.45

7.0 0.970 0.050 7.52 0.38

8.0 1.000 0.000 7.52 0.00

The evaporation was applied in the model as a constant rate based on local conditions under

the Climatology tab. This rate can also be modified for each individual storage area (pond) if

varying conditions exist.

Infiltration was included within each stormwater basin by defining a generic sand soil type

based on the USDA Soil Survey of the area. The total surface runoff from each basin was

calculated by the model based on the Curve Number assigned.

InfoSWMM offers the following ten options for modeling surface runoff from a stormwater

basin:

Nonlinear Reservoir each basin surface is treated as a nonlinear reservoir.

Colorado Urban Hydrograph Procedure uses procedures presented in the Colorado

Urban Drainage Criteria Manual of the Urban Drainage and Flood Control District.

NRCS (SCS) Dimensionless Unit Hydrograph commonly used with established Curve

Number (CN) values.

NRCS (SCS) Triangular Unit Hydrograph approximation of the dimensionless unit

hydrograph method that uses only three points.

Delmarva Unit Hydrograph used where local topography is flat and large amounts of

surface storage is available.

Snyder Unit Hydrograph relates lag time to geometric characteristics of the basin to

derive critical points for interpolating the unit hydrograph.

Clark Unit Hydrograph - derives a unit hydrograph by explicitly representing the

processes of translation and attenuation, which are the two critical phenomena in

transformation of excess rainfall to runoff hydrograph.

MODEL DEVELOPMENT

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Espey Unit Hydrograph 10-minute unit hydrograph developed strictly for urban

watersheds.

Santa Barbara Urban Hydrograph Developed for Santa Barbara County and is suited

for urban applications.

San Diego Modified Rational Formula uses a 6-hour storm event for estimation of peak

flows from urban and rural drainage basins.

The widely used NRCS (SCS) Dimensionless Unit Hydrograph method was the one utilized for

this stormwater model as recommended by the software developer. This method utilizes curve

numbers and will also automatically calculate the time of concentration based on input data.

3.6 Hydraulic Model

Hydraulic models simulate the flow and conveyance of fluids, in this case stormwater, in order

to investigate design and operational issues. The results of a stormwater hydraulic model are

based on the amount of surface water runoff entering a system, the conveyance capacity,

conveyance slope, and pond storage capacity. The InfoSWMM model allows a system to be

analyzed over long periods of time following single or multiple storm events.

The hydraulic portion of the model begins once surface water flow from individual basins

enters the conveyance system following a storm event. The hydraulic model includes the flow

characteristics of the stormwater system such as flow, velocity, depth over diameter (d/D),

hydraulic grade line, inlet / ditch flooding, and pond storage capacity. Conveyance and storage

consisted of drainage ditches, inlets, piping, and ponds imported directly from GIS and

supplemented by additional field work.

The hydraulic model analysis was a result of the runoff generated from the hydrologic portion

of the model. The hydrologic model was based on theoretical storm events and not actual

measured rainfall. The results for various storm events were analyzed for areas of known flood

concern as provided by the City. The analysis confirmed that most of the areas of known flood

concern were also shown as flooding areas within the model. Meetings were held with City

staff to review the model output and the flood results were confirmed.

MODEL DEVELOPMENT

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3.7 Water Quality

Stormwater runoff has both a quantity and quality component. Quantity is related to runoff

volume and duration of a storm event. Quality is related to the potential contaminants

contained within the runoff (water pollution).

This master plan deals solely with stormwater quantity in an effort to reduce or eliminate

flooding. The InfoSWMM model has been setup, to the extent possible, to include the quality

modeling component in the future by including land use characteristics within each drainage

basin. Water quality modeling will be completed in Phase 2 of the master plan and will be a

valuable tool to address the proposed rules regarding Total Maximum Daily Load (TMDL).

SYSTEM FLOOD ANALYSIS

18

4.0 SYSTEM FLOOD ANALYSIS

Following completion of the model development process, the simulations were completed and

the results reviewed to determine the extent of flooding up to and including the 100-yr storm

events. Maps and solution sets were created for the 8-hour event first since it was determined

to be the overall critical storm. The remaining rainfall events were then checked and flooding

analyzed as required. The flooding during the critical storm event occurred in several areas

within the city limits and was not isolated to any particular location. The majority of the flood

areas were located in the southeast and central sections of the city.

The model flood results from a small area of the city are shown in Figure 4.1 as an example.

Flooding is shown at inlet or ditch junction locations. The red nodes indicate inlet or ditch

flooding locations during the 25yr-8hr storm and include an identification number. The green

nodes indicate areas with no flooding. The blue lines indicate pipes and ditches. These results

were produced for each storm event and displayed automatically within the model using the

mapping tools.

FIGURE 4.1

SAMPLE FLOOD RESULTS MAP

The rainfall distribution curves were based on theoretical storm events and not actual

measured rainfall. Also, data regarding flood levels for actual rainfall events was not available

for calibrating the model. Therefore, based on meetings with the City, it was decided that the

model would be calibrated by comparing the model results for the 25-yr critical storm event to


19

areas of known flooding. HGL profiles were then created for each area identified along with

flooding / storage graphs for analysis. The detailed flood analysis document is located in

Appendix C. A sample HGL profile and storage graph is shown in Figure 4.2. Based on the

model results, a summary document was then created to compare the known flood area map

provided by the City to the model results. This document confirmed flooding in most areas of

known flood concern. Some of the areas could not be checked as there were no stormwater

elements shown in GIS or the model. A few areas did not flood, but did have inlet surcharging.

The entire stormwater system was reviewed in detail using the same methodology listed above.

These profiles and graphs are included in Appendix E. The results of this analysis were used to

evaluate improvements to reduce / eliminate flooding within the system.

FIGURE 4.2

SAMPLE HGL PROFILE AND STORAGE GRAPH


20

The following observations were made during the course of the stormwater system analysis:

The majority of the inlet flooding occurred for less than 2 hours.

Flooding along the coastal areas was either caused or impacted by the high tide elevation

of 2-ft.

Flooding shown in isolated roadside swale sections with no outfall was largely the result

of a lack of infiltration data available at conduits within the InfoSWMM software.

Infiltration rates needed to be adjusted at some storage (pond) locations in order to

match real world results.

The majority of the stormwater system discharges directly into the surrounding bay at

multiple locations. Due to the outfall elevation in relation to the bay and tailwater

conditions, the flood reduction options available were limited.

Flow is lost from the system once it leaves an inlet during a dynamic model simulation.

The downstream portion of each area will need to be checked carefully once

improvements are made in the model to make sure additional flooding is not created.

DESIGN ALTERNATIVE DEVELOPMENT

21

5.0 DESIGN ALTERNATIVE DEVELOPMENT

5.1 System Improvements Methodology

The most practical method to reduce flooding was determined to be increasing capacity within

the conveyance system (ditches and pipes). This method involved increasing pipe sizes,

removing negative slope pipe sections, increasing pipe slopes, and widening ditches. Each flood

area during the critical storm event was individually numbered and analyzed for potential flood

reduction. The conveyance system capacity was then increased in each identified problem area

until flooding was eliminated or reduced as much as possible. The downstream section of each

identified problem area was checked to make sure additional flooding was not created as a

result of the proposed improvements.

After the proposed system improvements to eliminate flooding during the 25-yr critical storm

event were established within the model, a flood reduction analysis for the 100-yr critical storm

was completed. The purpose of this analysis was to establish the amount of flood reduction

achieved during the critical 100-yr storm event as a result of the proposed system

improvements for the 25-yr critical storm.

An example of the flood reduction analysis is a flood area that has been modeled for the 100-yr

critical event with both the existing conditions and proposed improvements for eliminating

flooding during the 25-yr critical storm. The difference in the flood volume divided by the

volume with no improvements is identified as the flood reduction and shown as a percentage.

The percentage for the 100-yr flood reduction is identified for each flood area identified in the

model of the 25-yr storm event and is included in proposed solution in Section 4.3 for each

individual flood area.

It should be noted that the proposed improvements in upstream areas that discharge through

drainage ditches connected directly to the bay have the potential to increase downstream

flooding along these ditches during extreme storm events due to increased tailwater

conditions. Extreme storm events, such as hurricanes, that cause the tidal elevation to rise

significantly will result in reduced capacity within these drainage ditches. Most of these ditches

appear to run through open areas, such as recreation facilities, that are not heavily populated.

5.2 Proposed System Improvements

The proposed system improvements up to the 25-yr critical storm event are included in this

section for the flood areas shown in Figures 5.1 through 5.6. In areas of flooding that occurred

only during the 100-yr storm events, solutions are also included where flooding could be

eliminated by increasing the conveyance capacity. In areas where flooding occurred during the

25-yr and 100-yr storm events, only the flood reduction analysis is included for the 100-yr

storm.

DESIGN ALTERNATIVE DEVELOPMENT FIGURE 5.1

22


23


24

Area 1

The flooding is located along Mooney Road. The area is within Okaloosa County, so no

improvements are proposed as part of this master plan. Per the County, these areas do have

minor flooding that exceeds the ditch capacity at times. These areas are not a priority for the

County because the flooding does not impact nearby homes.

Area 2





Area 3





Area 4





Area 5





Areas 6 & 7

The flooding is located along Golf Course Drive and Eagle Street NE. The proposed solution for

the 25-yr critical storm is as follows:

Increase pipe size from 18x29-inch elliptical to 22x34-inch elliptical between SWINLE00000000002042 and SWINLE00000000002044

Increase pipe size from 24-inch to 24x38-inch elliptical from SWINLE00000000002051 to SWINLE00000000002048

Increase pipe slope to existing inlet inverts and size from 27x43 elliptical to 42-inch (or elliptical equivalent) between SWINLE00000000002042 and SWINLE00000000002010

Increase pipe size from 36-inch to 48-inch and deepen inlet SWINLE00000000000421 between SWINLE00000000002010 and SWINLE00000000000421

Flooding is reduced during the 100-yr critical storm by approximately 50% after system

improvements.


25

Area 8

The flooding is located along Mooney Road. The proposed solution for the 25-yr critical storm

is as follows:

Increase pipe slope and inlet SWINLE00000000000420 depth between inlets SWINLE00000000001918 and SWNETW00000000000559

Increase pipe size from 24-inch to 30-inch at SWGRAV00000000002339 Additional flooding occurs upstream during the critical 100-yr event. The proposed solution for

the 100-yr critical storm is as follows:

Deepen inlet SWINLE00000000001940 to remove negative slope.

Increase pipe size from 18-inch to 24-inch between SWINLE00000000001939 and SWINLE00000000001948.

Area 9

The flooding is located along Mooney Road and is partially the result of the lack of data on the

upstream FDOT conveyance system. The proposed solution for the 25-yr critical storm is as

follows:

Increase pipe slope and size from 24-inch to 30-inch at SWGRAV00000000002338 Flooding is reduced during the 100-yr critical storm by approximately 60% after system

improvements.


26


27

Area 10

The flooding is located along Highway Ave NE. The proposed solution for the 25-yr critical

storm is as follows:

Increase pipe size of SWGRAV00000000000808 from 15-inch to 24-inch

Increase upstream pipe slopes to max allowable using existing inlets Flooding is reduced during the 100-yr critical storm by approximately 20% after system

improvements.

Area 11

The flooding is located along Beachview Drive NE. The proposed solution for the 25-yr critical

storm is as follows:

Entire branch needs to be re-installed to remove negative slopes from SWINLE00000000000677 to SWINLE00000000000663

Pipe sizes need to be increased from 24-inch to 29x45-inch elliptical between SWINLE00000000000663 and SWINLE00000000000674

Pipe sizes need to be increased from 15/18-inch to 24-inch between SWINLE00000000000674 and SWINLE00000000000677

Peak flooding is reduced by approximately 30% and flood length reduced after system

improvements. Additional flooding occurs on north branch during the critical 100-yr event.

The proposed solution for the 100-yr critical storm is as follows:



Increase pipe size from 15-inch to 18-inch at SWGRAV00000000000795.


28


29

Area 12

The flooding is located along Sudduth Circle NE and is caused by the 2-ft tidal outfall elevation. The proposed solution for the 25-yr critical storm is as follows:

Flooding can be reduced by a small amount by increasing SWGRAV00000000000729 pipe size from 15-inch to 18-inch


improvements.

Area 13

The flooding is located along Yacht Club Drive NE. The model shows minor flooding for less

than 10 minutes that appears to be a result of the 2-ft downstream tidal elevation. There is

also a lack of infiltration along ditch sections in the model. The area is not a flood concern per

the City and has recently been cleaned out.

Area 14

The flooding is located along Hughes Street NE. The proposed solution for the 25-yr critical storm is as follows:

Increase pipe size from 13x21-inch elliptical to 19x30-inch elliptical between SWINLE00000000000572 and SWNETW00000000000510


improvements.

Area 15

The flooding is located along Hughes Street NE and Iowa Drive NE and is impacted by the 2-ft

tidal elevation. The proposed solution for the 25-yr critical storm is as follows:

Increase pipe size of SWGRAV00000000000567 from 30-inch to 29x45-inch elliptical



Increase pipe size of SWGRAV00000000000620 from 11x17-inch elliptical to 14x23-inch elliptical

Increase pipe size of SWGRAV00000000000618 from 18-inch to 24-inch

Increase pipe size of SWGRAV00000000000617 from 15-inch to 24-inch Flooding is reduced during the 100-yr critical storm by approximately 65% after system

improvements.

Area 16

The flooding is located between Hughes Street NE and Ferry Road NE. Ditch flooding cannot be prevented due to the 2-ft tidal elevation in the model.

Area 17

The flooding is located along Hughes Street NE. A surcharge depth was added to the inpoint to

remove flooding at SWINLE00000000001241. The proposed solution for the 25-yr critical storm

is as follows:


30

Increase pipe size from 24-inch to 24x38-inch elliptical between SWNETW00000000000120 and SWINLE00000000000485


improvements.

Area 18

The flooding is located at a commercial property along Eglin Parkway NE. This area only floods

during the 100 year storm events. The proposed solution for the 100-yr critical storm is as

follows:

Increase pipe size from 18-inch to 24-inch at SWGRAV00000000001366

Area 19

The flooding is located along Buck Drive NE. The proposed solution for the 25-yr critical storm is as follows:

Increase pipe size from 24-inch to 30-inch between SWOUTL00000000000049 and SWNETW00000000000182



improvements.

Area 20

The flooding is located along California Drive. The downstream pipe is undersized and at a

negative slope. The proposed solution for the 25-yr critical storm is as follows:

Increase pipe size from 15-inch to 24-inch between SWNETW00000000000366 and SWINLE00000000002345

Increase slope by lowering invert at SWNETW00000000000366 Flooding is reduced during the 100-yr critical storm by approximately 65% after system

improvements.

Area 21

The flooding is located along Oregon Drive NE. The proposed solution for the 25-yr critical storm is as follows:

Increase pipe size from 18-inch to 24-inch between SWINLE00000000000599 and SWNETW00000000000357


improvements.

Areas 22 & 23

The flooding is located along Okaloosa Road NE and Laurie Drive NE. The proposed solution for the 25-yr critical storm is as follows:




31

Increase pipe size from 15-inch to 18-inch between SWINLE00000000000711 and SWINLE00000000000607


Flooding is reduced during the 100-yr critical storm by approximately 50% and flood length

reduced after system improvements.

Area 24

The flooding is located along Kepner Drive NE. The proposed solution for the 25-yr critical storm is as follows:

Increase pipe size from 12/15-inch to 24-inch between SWINLE00000000000616 and SWINLE00000000000706

Increase pipe size from 24-inch to 30-inch between SWINLE00000000000616 and SWOUTL00000000000079

Increase pipe slope / deepen inlets to remove negative / flat slopes between SWINLE00000000000706 and SWOUTL00000000000079.


significantly reduced after system improvements.

Area 25

The flooding is located along Gardner Drive NE. The proposed solution for the 25-yr critical storm is as follows:

Increase pipe slope from SWINLE00000000000703 to SWINLE00000000000695 to establish a positive grade


Increase pipe size from 24-inch to 30-inch at SWGRAV00000000000676 Flooding is reduced during the 100-yr critical storm by approximately 65% after system

improvements.

Area 26

The flooding is located along Kepner Drive NE. The proposed solution for the 25-yr critical storm is as follows:

Increase pipe size from 24-inch to 24x38-inch elliptical between SWINLE00000000001124 and SWINLE00000000000632

Flooding is reduced during the 100-yr critical storm by an insignificant amount after system

improvements.

Area 27

The flooding is located along Bay Drive SE. The proposed solution for the 25-yr critical storm is as follows:

Increase pipe size from 15-inch to 18-inch and increase pipe slope at SWGRAV00000000000664


32


improvements. Additional flooding occurs on the west branch during the 100-yr critical event. The proposed solution for the 100-yr critical storm is as follows:



Area 28

The flooding is located along Bay Drive SE. This area only floods during the 100 year storm

events. The proposed solution for the 100-yr critical storm is as follows:

Increase pipe size from 15-inch to 24-inch between SWOUTL00000000000364 and SWINLE00000000000839

Area 29

The flooding is located along Brooks Street SE. This area only floods during the 100 year storm




Area 30

The flooding is located along Alexandra Place SE. The proposed solution for the 25-yr critical storm is as follows:




Increase pipe size and remove negative slope from 30-inch to 34x53-inch elliptical between SWOUTL00000000000246 and SWINLE00000000000804


improvements.

Area 31

The flooding is located along Brooks Street SE. This area only floods during the 100 year storm



Areas 32 & 33

The flooding is located along Fourth Street SE, Third Street SE, and near Elliot Road SE. The proposed solution for the 25-yr critical storm is as follows:


33

Increase pipe size from 18-inch to 24x38-inch elliptical between SWINLE00000000000922 and SWNETW00000000000284 along with the Area 30 pipe

size increase from 30-inch to 42-inch

Deepen inlet SWINLE00000000001102



Increase pipe size from 18-inch to 24-inch between SWNETW00000000000283 and SWNETW00000000000284


improvements.

Area 34

The flooding is located along Oak Street SE and Elm Avenue SE. The ditch along Oak Street SE

appears to be undersized due to limited right-of-way. This ditch is not an area of flood concern

per City staff, but is a maintenance issue. The proposed solution is as follows:

Increase pipe size from 24-inch to 36-inch to prevent downstream inlet flooding between SWNETW00000000000228 and SWNETW00000000000267

Area 35

The flooding is located along Magnolia Avenue SE. The proposed solution for the 25-yr critical storm is as follows:

The pipe size appears to be adequate. The pipe slope needs to be increased from SWINLE00000000000592 to SWINLE00000000000927.

Area floods during the 100-yr critical event. The proposed solution for the 100-yr critical storm

is as follows:


Area 36

The flooding is located along Buck Drive NE. The proposed solution for the 25-yr critical storm is as follows:



improvements.

Area 37

The flooding is located along Ferry Road SE. The proposed solution for the 25-yr critical storm is as follows:

Pipe slope and size to be increased from 15-inch to 18-inch between SWINLE00000000000884 and SWINLE00000000000879



34


improvements.

Area 38

The flooding is located along First Street SE. The proposed solution for the 25-yr critical storm is as follows:



improvements.

Area 39

The flooding is located along Brooks Street SE. The proposed solution for the 25-yr critical storm is as follows:


Increase pipe size from 18-inch to 24-inch between SWINLE00000000000982 and SWOUTL00000000000380



Area 40

The flooding is located along Third Street SE. The proposed solution for the 25-yr critical storm is as follows:



improvements.

Area 41

The flooding is located along Second Street SE. The proposed solution for the 25-yr critical storm is as follows:

Increase pipe size from 15-inch to 14x23-inch elliptical and remove negative slope at SWGRAV00000000001120


Flooding is reduced during the 100-yr critical storm by approximately 50% and flood length is


Area 42

The flooding is located along Harbeson Avenue SE. The proposed solution for the 25-yr critical storm is as follows:



35


Increase pipe size from 18/24-inch to 36-inch between SWINLE00000000000953 and SWNETW00000000000265

Remove negative slopes through entire pipe run Flooding is reduced during the 100-yr critical storm by approximately 60% after system

improvements.

Area 43

The flooding is located along Park Circle SE. The pipes downstream of the flooding inlet are

undersized. The proposed solution for the 25-yr critical storm is as follows:

Increase pipe size from 15/18-inch to 30-inch between SWNETW00000000000613 and SWNETW00000000000611

Deepen inlet SWINLE00000000000740 to remove negative pipe slope


improvements.

Area 44

The flooding is located along Jackson Street NE. The proposed solution for the 25-yr critical storm is as follows:

Remove negative pipe slope between SWINLE00000000000466 and SWNETW00000000000123



Increase pipe size from 30-inch to 36-inch at SWGRAV00000000000524 Flooding is reduced during the 100-yr critical storm by an insignificant amount after system

improvements.


36


37

Areas 45 - 47

The flooding is located along Beal Parkway SW. The proposed solution for the 25-yr critical storm is as follows:




Increase pipe size from 15-inch to 18-inch at SWGRAV00000000001312 and SWGRAV00000000000380

Flooding is reduced during the 100-yr critical storm by approximately 70% in Area 45, 25% in

Area 46, and eliminated in Area 47 after system improvements.

Area 48

The flooding is located along Miracle Strip Parkway SW. The proposed solution for the 25-yr critical storm is as follows:

Increase pipe size from 15-inch to 18-inch at SWGRAV00000000000346 Flooding is eliminated during the 100-yr critical storm after system improvements.

Areas 49 & 50

The flooding is located along First Street SW and Robinwood Drive SW. The proposed solution for the 25-yr critical storm is as follows:

Increase pipe size from 18/24-inch to 29x45-inch elliptical between SWFITT00000000000020 and SWINLE00000000000217



Increase pipe size from 15-inch to 18-inch at SWGRAV00000000000151 and SWGRAV00000000000157

Flooding is reduced during the 100-yr critical storm by approximately 65% in Area 49 and 85%

in Area 50 after system improvements.

Area 51

The flooding is located along a drainage ditch north of Coral Drive SW and cannot be eliminated

due to 2-ft tidal elevation.

Area 52

The flooding is located along Ranger Street SW. The proposed solution for the 25-yr critical storm is as follows:



38



Area 53

The flooding is located along Ed Brown Street SW and is caused by water levels in main pipe run

and cannot be eliminated. The rim of inlet SWINLE00000000000159 is lower than the crown of

the main pipe run.

Area 54

The flooding is located along a drainage ditch just north of Hollywood Boulevard NW and is

impacted by the downstream 2-ft tidal elevation and undersized outfall piping with a negative

slope. Upsizing the downstream piping and removing the negative slope reduces the ditch

flooding, but increases flooding at a downstream pond / ditch. Flooding cannot be eliminated

without potentially diverting runoff to new area. This area is of flood concern per City staff.

Area 55

The flooding is located along Industrial Street NW. The proposed solution for the 25-yr critical storm is as follows:




Area 56

The flooding is located along Holmes Boulevard NW. The proposed solution for the 25-yr critical storm is as follows:



Increase pipe size from 15-inch to 18-inch at SWGRAV00000000001547 Flooding is reduced during the 100-yr critical storm by approximately 80% and flood length is


Areas 57 - 59

The flooding is located along Highland Drive NW and Silva Drive NW. The proposed solution for the 25-yr critical storm is as follows:

Remove negative slope along entire pipe run


Increase pipe size from 36-inch to 34x53-inch elliptical between SWINLE00000000001752 and SWNETW00000000000455

Increase pipe size from 48-inch to 48x76-inch elliptical between SWNETW00000000000455 and SWOUTL00000000000146


improvements. It should be noted that the improvements in these areas cause increased


39

downstream flooding. The proposed improvements increase flooding along the drainage ditch

behind a recreation area within Area 54. Area 54 flooding cannot be eliminated as previously

discussed.

Area 60

The flooding is located along Rainbow Drive NW. The proposed solution for the 25-yr critical storm is as follows:

Increase pipe size and steepen slope from 30-inch to 36-inch between SWINLE00000000001364 and SWINLE00000000001366





improvements.

Area 61

The flooding is located along Wisteria Court NW. The proposed solution for the 25-yr critical storm is as follows:

Increase pipe size from 18-inch to 24-inch between SWNETW00000000000648 and SWINLE00000000001342 or increase pipe slope of entire branch


improvements.

Area 62

The flooding is located along Beal Parkway NE. This area only floods during the 100 year storm













40

Area 63

The flooding is located along Linstew Drive NW. The proposed solution for the 25-yr critical storm is as follows:



improvements.

Area 64

The flooding is located along Beal Parkway NW. The proposed solution for the 25-yr critical storm is as follows:


Additional flooding occurs during the critical 100-yr event. The proposed solution for the 100-

yr critical storm is as follows:





Area 65

The flooding is located at a pond near Ventura Circle NW and sheet flows directly into the bay.

If the flooding is a concern, the pond volume can be increased.

Area 66

The flooding is located along Holmes Boulevard NW. The proposed solution for the 25-yr critical storm is as follows:




Area 67

The flooding is located within a residential area between Bishop Avenue NW and Martisa Road

NW. This area only floods during the 100 year storm events. The proposed solution for the

100-yr critical storm is as follows:


Area 68

The flooding is located along Linda Lane NW. The proposed solution for the 25-yr critical storm is as follows:


41

Remove the negative slope and / or increase pipe size from 15-inch to 18-inch between SWNETW00000000000505 and SWINLE00000000001427


improvements.

Area 69

The flooding is located along Driftwood Avenue SW. The proposed solution for the 25-yr critical storm is as follows:

Increase pipe size from 15-inch to 18-inch at SWGRAV00000000000117 Flooding is reduced during the 100-yr critical storm by approximately 40% and flood length is


Area 70

The flooding is located along Deluna Road SW. This area only floods during the 100 year storm



Area 71

The flooding is located just north of Holmes Boulevard NW. This area only floods during the

100 year storm events. The proposed solution for the 100-yr critical storm is as follows:


Area 72

The flooding is located at a pond along Wright Parkway NW. This area only floods during the

100 year storm events. Severe flooding occurs and the pond cannot be widened much due to

site constraints.

Area 73

The flooding is located just north of Holmes Boulevard NW. The proposed solution is as follows:

Increase pond volume by adding width / depth, adjust weir, and increase discharge pipe size to 8-inch.

Area 74

The flooding is located at a pond near Olde Cypress Circle NW. This area only floods during the

100 year storm events. Severe flooding occurs and the pond cannot be widened much due to

site constraints.

Area 75

The flooding is located at a mixed use property along Carol Avenue NW. The proposed solution for the 25-yr critical storm is as follows:



42


improvements.

Area 76

The flooding is located at a commercial property along Carol Avenue NW and cannot be

eliminated because entire pipe run is at a negative slope and inlet SWINLE00000000002380 rim

elevation is 2-ft below the pond top elevation.

Area 77

The flooding is located along Deal Avenue NW and Poulton Drive NW. The proposed solution for the 25-yr critical storm is as follows:

Remove negative slope at SWGRAV00000000002084



Increase undersized downstream pipe at SWGRAV00000000001360 from 15-inch to 36-inch


improvements.

Area 78

The flooding is located along Hollywood Boulevard NW. The proposed solution for the 25-yr critical storm is as follows:




improvements.

Area 79

The flooding is located along North Audrey Circle NW. The proposed solution for the 25-yr critical storm is as follows:



improvements.

Area 80

The flooding is located along Jonquil Avenue NW. The proposed solution for the 25-yr critical storm is as follows:

Increase pipe size from 18/21-inch to 24-inch between SWNETW00000000000388 and SWNETW00000000000580


43


improvements.

Area 81

The flooding is located at a pond south of Sullivan Street NW. This area only floods during the

100 year storm events. Ditch and upstream pipe section floods during 100-yr critical event.

Ditch flooding cannot be eliminated due to backflow from downstream system. The proposed

solution for the 100-yr critical storm is as follows:

Remove negative slope through 24-inch pipe and increase pipe size to 30-inch between SWOUTL00000000000249 and SWINLE00000000001641




44


45

Area 82

The flooding is located at a pond near Mary Esther Boulevard. This area only floods during the

100 year storm events. The proposed solution for the 100-yr critical storm is as follows:





Area 83

The flooding is located at a pond west of Poplar Avenue NW. Moderate to heavy pond flooding

occurs. It is a County owned pond with improvements currently under design. Part of the ditch

along Lovejoy to the pond is being improved, pond capacity increased, outfall structure / pipe

upgraded, additional retention basin to be added north of outfall, and road crossing culvert to

be upgraded.

Area 84

The flooding is located along Anchors Street NW. The proposed solution for the 25-yr critical storm is as follows:


Increase pipe size from 18-inch to 19x30-inch elliptical at SWGRAV00000000002299 Flooding is reduced during the 100-yr critical storm by approximately 25% after system

improvements.

Area 85

Inlet floods due to flood level of Gap Creek after addition of County data. 36-inch pipe

(SWGRAV000000000002530) under Burnette Avenue NW is undersized and needs to be

upgraded to three (3) 48-inch pipes.

Area 86

The flooding is located along Lovejoy Road NW and cannot be eliminated because the rim

elevation is below the downstream pipe crown.

Area 87

The flooding is located along Stokes Avenue NW. The multiple small ditch sections show very

minor flooding largely due to lack of outfall and infiltration data in the model. Area is not a

flood concern per City staff since any overflow runs to the nearby creek.


46

5.3 Conceptual Cost Estimates

Upon completion of the full model analysis, conceptual cost estimates were developed for each

flood area which included a proposed system improvement as identified in Section 5.2. A unit

price was developed per linear foot of pipe that included all items associated with pipe

installations such as select fill, asphalt, sod, silt fence, demolition, maintenance of traffic, as-

builts, mobilization and bonds, etc. The only items broken out separately were inlets and

junction boxes. A 35% construction contingency was added due to the conceptual nature of

this analysis. A 10% engineering and administration cost was added to the construction

subtotal to cover design services. The unit prices used to estimate the cost of the proposed

improvements are shown in Table 5.1.

TABLE 5.1

UNIT PRICE LIST

Material

Round RCP Pipe Select Fill Sod Silt Fence Demolition MOT As-builts

Mobilization

& Bonds

35%

Contingency Total

15-inch $45.00 $8.00 $2.50 $3.00 $10.00 $1.37 $0.34 $3.51 $25.80 $99.53

18-inch $50.00 $8.00 $2.50 $3.00 $10.00 $1.47 $0.37 $3.77 $27.69 $106.79

24-inch $60.00 $8.00 $2.50 $3.00 $10.00 $1.67 $0.42 $4.28 $31.45 $121.32

30-inch $75.00 $9.00 $3.00 $3.00 $10.00 $2.00 $0.50 $5.13 $37.67 $145.29

36-inch $95.00 $9.00 $3.00 $3.00 $15.00 $2.50 $0.63 $6.41 $47.09 $181.62

42-inch $115.00 $10.00 $3.50 $3.00 $15.00 $2.93 $0.73 $7.51 $55.18 $212.86

48-inch $140.00 $10.00 $3.50 $3.00 $15.00 $3.43 $0.86 $8.79 $64.60 $249.18

54-inch $175.00 $11.00 $4.00 $3.00 $15.00 $4.16 $1.04 $10.66 $78.35 $302.21

60-inch $210.00 $12.00 $4.00 $3.00 $15.00 $4.88 $1.22 $12.51 $91.91 $354.52

Elliptical RCP

14x23-inch $60.00 $8.00 $2.50 $3.00 $10.00 $1.67 $0.42 $4.28 $31.45 $121.32

19x30-inch $75.00 $8.00 $2.50 $3.00 $10.00 $1.97 $0.49 $5.05 $37.10 $143.11

22x34-inch $100.00 $9.00 $3.00 $3.00 $10.00 $2.50 $0.63 $6.41 $47.09 $181.62

24x38-inch $115.00 $9.00 $3.00 $3.00 $10.00 $2.80 $0.70 $7.18 $52.74 $203.41

29x45-inch $150.00 $9.00 $3.00 $3.00 $15.00 $3.60 $0.90 $9.23 $67.80 $261.53

34x53-inch $200.00 $10.00 $3.50 $3.00 $15.00 $4.63 $1.16 $11.86 $87.20 $336.36

38x60-inch $250.00 $10.00 $3.50 $3.00 $15.00 $5.63 $1.41 $14.43 $106.04 $409.00

43x68-inch $320.00 $11.00 $4.00 $3.00 $15.00 $7.06 $1.77 $18.09 $132.97 $512.89

48x76-inch $390.00 $12.00 $4.00 $3.00 $15.00 $8.48 $2.12 $21.73 $159.72 $616.05

Material

Round RCP Pipe Select Fill Asphalt Silt Fence Demolition MOT As-builts

Mobilization

& Bonds

35%

Contingency Total

15-inch $45.00 $8.00 $45.00 $3.00 $10.00 $2.22 $0.56 $5.69 $41.81 $161.28

18-inch $50.00 $8.00 $45.00 $3.00 $10.00 $2.32 $0.58 $5.95 $43.70 $168.54

21-inch $55.00 $8.00 $46.50 $3.00 $10.00 $2.45 $0.61 $6.28 $46.14 $177.98

24-inch $60.00 $8.00 $46.50 $3.00 $10.00 $2.55 $0.64 $6.53 $48.03 $185.25

27-inch $70.00 $8.00 $46.50 $3.00 $10.00 $2.75 $0.69 $7.05 $51.79 $199.78

30-inch $75.00 $9.00 $48.00 $3.00 $10.00 $2.90 $0.73 $7.43 $54.62 $210.68

36-inch $95.00 $9.00 $50.00 $3.00 $15.00 $3.44 $0.86 $8.82 $64.79 $249.91

42-inch $115.00 $10.00 $52.00 $3.00 $15.00 $3.90 $0.98 $9.99 $73.45 $283.32

48-inch $140.00 $10.00 $53.50 $3.00 $15.00 $4.43 $1.11 $11.35 $83.44 $321.83

Unit Price Per Linear Foot (Sod)

UNIT COST SUMMARY

Unit Price Per Linear Foot (Asphalt)


47

Material

Round RCP Pipe Select Fill Asphalt Silt Fence Demolition MOT As-builts

Mobilization

& Bonds

35%

Contingency Total

54-inch $175.00 $11.00 $55.00 $3.00 $15.00 $5.18 $1.30 $13.27 $97.56 $376.31

60-inch $210.00 $12.00 $57.00 $3.00 $15.00 $5.94 $1.49 $15.22 $111.88 $431.52

72-inch $270.00 $12.00 $57.00 $3.00 $15.00 $7.14 $1.79 $18.30 $134.48 $518.70

84-inch $330.00 $12.00 $57.00 $3.00 $15.00 $8.34 $2.09 $21.37 $157.08 $605.87

Elliptical RCP

14x23-inch $60.00 $8.00 $45.00 $3.00 $10.00 $2.52 $0.63 $6.46 $47.46 $183.07

17x25-inch $70.00 $8.00 $45.00 $3.00 $10.00 $2.72 $0.68 $6.97 $51.23 $197.60

19x30-inch $75.00 $8.00 $46.50 $3.00 $10.00 $2.85 $0.71 $7.30 $53.68 $207.04

22x34-inch $100.00 $9.00 $47.50 $3.00 $10.00 $3.39 $0.85 $8.69 $63.85 $246.27

24x38-inch $115.00 $9.00 $48.00 $3.00 $10.00 $3.70 $0.93 $9.48 $69.69 $268.79

29x45-inch $150.00 $9.00 $50.00 $3.00 $15.00 $4.54 $1.14 $11.63 $85.51 $329.82

34x53-inch $200.00 $10.00 $52.00 $3.00 $15.00 $5.60 $1.40 $14.35 $105.47 $406.82

38x60-inch $250.00 $10.00 $53.50 $3.00 $15.00 $6.63 $1.66 $16.99 $124.87 $481.65

43x68-inch $320.00 $11.00 $55.00 $3.00 $15.00 $8.08 $2.02 $20.71 $152.18 $586.99

48x76-inch $390.00 $12.00 $57.00 $3.00 $15.00 $9.54 $2.39 $24.45 $179.68 $693.05

Unit Price Per Linear Foot (Asphalt)

The conceptual costs were estimated using spreadsheets that included material quantities and

unit prices. A construction cost was estimated as a subtotal and then the 10 percent was

included for engineering and administration for estimating the total conceptual cost. An

example of a calculation spreadsheet is shown in Table 5.2 and the spreadsheets for all the

flood areas are included in Appendix F. The conceptual cost summary for each flood area is

included in Table 5.4, Improvement Priority List.

TABLE 5.2

SAMPLE CONCEPTUAL COST ESTIMATE

Area 41 Construction Cost

Material Quantity Unit Unit Price Total

14x23-inch Elliptical RCP (Asphalt) 35 LF $ 183.07 $ 6,407.45

24-inch RCP (Sod) 299 LF $ 121.32 $ 36,274.76

Junction Box 1 EA $ 3,500.00 $ 3,500.00

Construction Subtotal $ 46,182.22

10% Engineering & Admin $ 4,618.22

Total Project Cost $ 50,800.44


48

5.4 Evaluation Matrix

Each flood area was evaluated based on specific categories for prioritizing the proposed system

improvements. These categories were identified through meetings and conversations with City

staff as well as suggestions by HMM. The categories established were Land Use, Frequency of

City Scheduled Maintenance & Work Orders, Flood Frequency, Infrastructure Material, and

Flood Duration during the 25-yr critical storm event. Each category includes ranking criteria

that ranges from 1 to 5 points.

The land use criteria for each flood area was established using GIS data provided by City staff

and included, from low to high priority, Recreation, Low Density Residential, Medium Density

Residential, Mixed Use, and Commercial / Industrial. Maintenance criteria, from low to high

priority, included never, occasionally, and frequent. The ranking was determined by City staff

based on past scheduled maintenance frequency and volume of work orders generated. Flood

frequency criteria, from low to high priority, included 100-yr flooding, 25-yr flooding, and 10-yr

flooding. The flood frequency was determined using the InfoSWMM model and ranked based

on the storm year in which flooding occurs. Infrastructure material criteria, from low to high

priority, included plastic / concrete, clay / brick, and corrugated metal. The infrastructure

material for the flood area was determined using GIS data provided by City staff. Flood

duration criteria, from low to high priority, included < 1-hr, 2-hr, 3-hr, 4-hr, and 5-hr. The flood

duration for each flood area was determined using the InfoSWMM model and ranked based on

the length of time flooding occurs during the 25-yr critical storm event.

Each category was assigned a Weight Factor based on the importance level determined by

HMM and City staff. The category score was a product of the categorys ranking multiplied by

the Weight Factor. The total score was the sum of the category scores, which had a maximum

value of 50. A sample area evaluation matrix is shown in Table 5.3. The evaluation matrix for

each project area is located in Appendix G.


49

TABLE 5.3


50

5.5 Improvement Priority

A list of the flood areas was compiled that contained the area number, location, improvement

description, total score, and estimated project cost for each flood area as shown in Table 5.4.

For prioritizing the list, the data was sorted based on total score with the higher scores being

the higher priority. In the case of a tie, the flood area with the lowest estimated cost was given

higher priority.

TABLE 5.4

IMPROVEMENT PRIORITY LIST

Area No. Location Improvement DescriptionTotal Score

(max score 50.0)

Estimated

Project Cost

84 Anchors St NW near Forsman Dr NW Increase pipe size 45.5 $401,417.35

49&50 First Street SW and Fourth Ave SW Increase pipe size 43.5 $632,899.58

73 North of Holmes Blvd NW near Wright Pkwy NW

Increase pond volume, adjust

weir, and increase discharge

pipe size

41.0 $39,513.97

85 End of Combs Manor Ct NW Increase pipe size and quantity 41.0 $79,472.05

6&7 Golf Course Drive and Eagle Street NE Increase pipe size 41.0 $649,397.98

40 Intersection of Third St SE and Carson Dr SE Increase pipe size 40.0 $53,787.67

57-59Neighborhood between Highland Dr NW and

Silva Dr NW

Remove negative pipe slope

and increase pipe size39.5 $1,473,068.86

39 Brooks St SE near Alconese Ave SE Increase pipe size 39.0 $160,459.22

38 Intersection of Chestnut Ave SE and First St SE Increase pipe size 38.0 $16,747.87

69 Intersection of Driftwood Ave SW and Iva PL SW Increase pipe size 35.5 $26,420.36

14 Hughes St NE near Walton Dr NE Increase pipe size 35.5 $45,108.48

9 Mooney Rd near Sherwood Rd NW Increase pipe size 34.0 $22,055.59

37 Ferry Rd SE near Chicago Ave SE Increase pipe size and slope 33.0 $99,175.04

24 Kepner Dr NE north of Okaloosa Rd NERemove negative pipe slope

and increase pipe size32.0 $296,266.31

55 Industrial St NW near Robinwood Dr NW Increase pipe size 31.0 $33,991.98

22&23 Anastasia Dr SE and Okaloosa Rd NE Increase pipe size 31.0 $391,225.43

30 Alexandra PL SE near Waynel Circle SERemove negative pipe slope


32&33 Magnolia Ave SE near Third St SEIncrease pipe size and deepen

inlet30.5 $255,297.12

19 Intersection of Hospital Dr NE and Buck Dr NE Increase pipe size 30.0 $227,294.06

77 Poulton Dr NW near Deal Ave NWRemove negative pipe slope


45-47 Beal Pkwy SE near First St SE Increase pipe size 29.5 $329,840.57

15 Hughes St NE near Oregon Dr NE Increase pipe size 29.5 $366,583.90

41 Second St SE near Methodist Ave SE Increase pipe size 29.0 $50,800.44

61 Sleepy Oaks Rd NW near Wisteria Ct NW Increase pipe size and slope 29.0 $70,706.55

42 Harbeson Ave SE near Birch St SERemove negative pipe slope


34 Oaks St SE near Alder Ave SE Increase pipe size 28.0 $68,324.39

75Neighborhood between Carol Ave NW and

Sherry Circle NWIncrease pipe size 28.0 $120,067.12

44 Intersection of Jackson St NE and Mallard Ave NERemove negative pipe slope



51

Area No. Location Improvement DescriptionTotal Score

(max score 50.0)

Estimated

Project Cost

80 Jonquil Ave NW near Sullivan St NW Increase pipe size 27.0 $83,695.37

81 Commercial property north of Sullivan St NWRemove negative pipe slope


60 Rainbow Dr NW near Tula PL NW Increase pipe size 27.0 $503,735.84

66Intersection of Martisa Rd NW and Holmes Blvd

NWIncrease pipe size 26.5 $11,732.62

11 Beachview Dr NE near Greenbrier Dr NERemove negative pipe slope


10 Highway Ave NE near Beachview Dr NE Increase pipe size and slope 26.0 $28,024.98

28 Bay Dr SE near Brooks St SE Increase pipe size 26.0 $32,881.21

29 Brooks St SE near Walkedge Dr SE Increase pipe size 25.0 $26,671.28

36 Buck Dr NE near Vine Ave NE Increase pipe size 25.0 $110,887.68

68 Linda Ln NW near Lula Belle Ln NWRemove negative pipe slope


8 Mooney Rd near Sherwood Rd NW Increase pipe size and slope 24.0 $34,606.57

52 Intersection of Ranger St SW and Fourth Ave SW Increase pipe size 24.0 $56,984.14

79 N Audrey Circle NW north of Sullivan St NW Increase pipe size 24.0 $74,354.51

63 Linstew Dr NW north of Beal Pkwy NW Increase pipe size 24.0 $106,602.02

82 Mary Esther CTO NW south of Sullivan St NW Increase pipe size 23.0 $170,524.88

43 Park Circle SEIncrease pipe size and deepen

inlet22.0 $46,393.53

35 Magnolia Ave SE near Hollywood Blvd SE Increase pipe slope 22.0 $93,244.81

62 Beal Pkwy SE ne

Documents

STORMWATER MASTER PLAN - City of Fort Walton Beachfwb.org/wp-content/uploads/2013/11/1-59-Stormwater-Master-Plan... · STORMWATER MASTER PLAN CITY OF FORT WALTON BEACH 107 Miracle