City of Dunedin Dredging Feasibility:

Cedar Creek and Lake Sperry –

Alternative Analysis Report

December 2013

D R A F T

Taylor Engineering, Inc.

10151 Deerwood Park Blvd.

Bldg. 300, Suite 300

Jacksonville, FL 32256

(904) 731-7040

www.taylorengineering.com

City of Dunedin Dredging Feasibility:

Cedar Creek and Lake Sperry –

Alternative Analysis Report

D R A F T

Prepared for

City of Dunedin

By

Taylor Engineering, Inc.

10151 Deerwood Park Blvd., Bldg. 300, Suite 300

Jacksonville, FL 32256

(904) 731-7040

December 2013

C2012-060

i

Table of Contents

Introduction ................................................................................................................................................. 1

A. West Cedar Creek .......................................................................................................................... 1

A.1 Stormwater Conveyance/Sediment Transport Improvements ............................... 1

A.2 Maintenance Dredging ........................................................................................... 1

A.3 Environmental Restoration or “Cleanup” ............................................................. 4

A.4 Navigation................................................................................................................ 5

A.5 No Action ................................................................................................................. 7

B. East Cedar Creek ........................................................................................................................... 7

B.1 Stormwater Conveyance/Sediment Transport Improvements ............................... 7

B.2 Maintenance Dredging and Related Activities ....................................................... 8

B.3 Environmental Restoration or “Cleanup” ............................................................. 9

B.4 Navigation................................................................................................................ 9

B.5 No Action ............................................................................................................... 10

C. Lake Sperry .................................................................................................................................. 10

C.1 Stormwater Storage/Sediment Transport Improvements ..................................... 11

C.2 Maintenance Improvements thru Biodiversity ..................................................... 13

C.3 Navigation.............................................................................................................. 13

C.4 Environmental Restoration or “Cleanup” ........................................................... 13

C.5 No Action ............................................................................................................... 14

References ................................................................................................................................................ 155

1

Introduction

This document assesses alternatives for removing accumulated sediments in West Cedar Creek, East

Cedar Creek, and Lake Sperry. Dredging would provide the means for sediment removal and would be

subject to permitting in accordance with regulations primarily administered by the US Army Corps of

Engineers (USACE), the Pinellas County Water & Navigation Control Authority, and the Southwest

Florida Water Management District (SWFWMD). USACE staff requires that project permit applications

identify a clearly defined purpose – an objective or goal. A clearly defined purpose is necessary to justify

the project and its potential environmental impacts in terms of applicable state and federal regulations.

The sections below provide brief discussions regarding each of the subject water bodies to identify the

variously considered purposes for dredging and to assist the City in selecting its preferred alternative(s).

A. West Cedar Creek

A.1 Stormwater Conveyance/Sediment Transport Improvements

Portions of the City stormwater systems discharge into Cedar Creek, and some citizens have questioned

whether dredging might not improve stormwater conveyance. However, because Cedar Creek is a tidally

influenced water body; tidal elevations form the tailwater control for the stormwater system. Dredging

work would occur predominantly below the mean low water tidal elevation. The City has pointed out that

its Master Drainage Plans developed in 1981, 1993 and 2003, indicate that modifications to Cedar Creek

would provide limited opportunity for stormwater improvements. It may be possible to achieve some

modifications to stormwater conveyance and associated sediment transport patterns within the creek.

Evaluating such modifications would require a significant engineering analysis linking coastal

engineering, sediment transport, and stormwater modeling tools.

If modeling proves a successful stormwater conveyance/sediment transport solution, the City may be able

to optimize the dredging project to reduce costs. While, without modeling, we cannot predict the

geometry of such a dredging project, it is reasonable to expect that such a project would cover a smaller,

more targeted footprint than a project aiming to provide wide-area navigation or maintenance.

CONCLUSION: Taylor Engineering considers that a West Cedar Creek dredging project would likely

provide limited, if any, improvement to stormwater conveyance through the upstream stormwater system.

A.2 Maintenance Dredging

Anecdotal information and aerial photographs indicate that in the 1960’s, West Cedar Creek was

apparently dredged to remove the established mud flats, to accommodate adjacent development, and to

provide for recreational boating from the seawalls constructed on either side of the creek between the US

Alternate 19 bridge and St Joseph Sound. There are no available data to indicate any maintenance

dredging between the 1960’s original dredging and subsequent permitted dredging that occurred in 1996.

Based on review of aerial photographs, West Cedar Creek has largely reverted to its pre-development

condition as a coastal mudflat.

The term Maintenance Dredging is defined in the Florida Statutes, Section 403.813(1)(f), as follows:

2

"The performance of maintenance dredging of existing manmade canals, channels, intake and

discharge structures, and previously dredged portions of natural water bodies within drainage

rights-of-way or drainage easements which have been recorded in the public records of the

county, where the spoil material is to be removed and deposited on a self-contained, upland spoil

site which will prevent the escape of the spoil material into the waters of the state, provided that

no more dredging is to be performed than is necessary to restore the canals, channels, and intake

and discharge structures, and previously dredged portions of natural water bodies, to original

design specifications or configurations, provided that the work is conducted in compliance with s.

379.2431(2)(d), provided that no significant impacts occur to previously undisturbed natural

areas, and provided that control devices for return flow and best management practices for

erosion and sedimentation control are utilized to prevent bank erosion and scouring and to

prevent turbidity, dredged material, and toxic or deleterious substances from discharging into

adjacent waters during maintenance dredging. Further, for maintenance dredging of previously

dredged portions of natural water bodies within recorded drainage rights-of-way or drainage

easements, an entity that seeks an exemption must notify the department or water management

district, as applicable at least 30 days prior to dredging and provide documentation of original

design specifications or configurations where such exist. This exemption applies to all canals and

previously dredged portions of natural water bodies within recorded drainage rights-of-way or

drainage easements constructed prior to April 3, 1970, and to those canals and previously dredged

portions of natural water bodies constructed on or after April 3, 1970, pursuant to all necessary

state permits. This exemption does not apply to the removal of a natural or manmade barrier

separating a canal or canal system from adjacent waters. When no previous permit has been

issued by the Board of Trustees of the Internal Improvement Trust Fund or the United States

Army Corps of Engineers for construction or maintenance dredging of the existing manmade

canal or intake or discharge structure, such maintenance dredging shall be limited to a depth of no

more than 5 feet below mean low water. The Board of Trustees of the Internal Improvement Trust

Fund may fix and recover from the permittee an amount equal to the difference between the fair

market value and the actual cost of the maintenance dredging for material removed during such

maintenance dredging. However, no charge shall be exacted by the state for material removed

during such maintenance dredging by a public port authority. The removing party may

subsequently sell such material; however, proceeds from such sale that exceed the costs of

maintenance dredging shall be remitted to the state and deposited in the Internal Improvement

Trust Fund."

Conditions for Maintenance Dredging are further discussed in the following rules of the Water

Management District (adopted for use by DEP in Rule 62-330, F.A.C., Rules 40D-4.051(8)(d), F.A.C.

and Rule 62-346.051(7)(a), F.A.C.) The State of Florida also provides the following critical guidelines on

its website:

(http://publicfiles.dep.state.fl.us/dwrm/slerp/erphelp/mergedProjects/erphelp/Subject_Discussions/Mainte

nance_Dredging.htm).

“Dredging that exceeds any of the following thresholds generally will not be considered maintenance

dredging:

The area to be dredged has not been dredged in the past;

3

The area to be dredged has been allowed to shoal in to such an extent as to render the area to

be dredged non-functional for a prolonged period of time;

The proposed dredging will expand (deepen, widen, or lengthen) the dredge area from

original design specifications;

Generally, dredging proposed more than 2 years after a storm event that caused sudden

shoaling is no longer considered maintenance dredging.

In all cases, maintenance dredging cannot exceed the depths, widths, and configurations that were

previously achieved by previous dredging.

In the following cases, the maintenance dredging exemption may not be applicable until a permit is

first obtained that establishes or re-establishes the area that will be subject to future maintenance:

Original design specifications cannot be documented, either through a previous authorization,

previous engineering specifications, or evidence of the prior dredging that still exists (such as

aerial photography, the presence of spoil piles that still contain the material from the original

dredging, or core borings);

The area subject to the dredging was never dredged;

The area subject to the dredging was not dredged to the full extent of the original design

specifications or to the extent being proposed.

Before assuming that dredging does or does not qualify for the maintenance dredging exemption, it is

recommended that you consult with the local DEP staff.”

CONCLUSION 1: As stated in the statute, for a project to qualify for the maintenance dredging

exemption, a previously permitted and constructed dredging project must exist and/or the dredging must

occur within drainage rights-of-way or drainage easements that have been recorded in the public records

of the county. Therefore, the City may leverage any previously permitted dredging projects to acquire

authorizations for maintenance. Specifically, in 1994 and 1995 the City acquired two permits — one to

dredge a channel in east and west Cedar Creek, and one to create a sediment trap in east Cedar Creek. The

City constructed these improvements in 1996. If the City determines that the goals and purpose of the

currently considered project match those outlined in the 1996 authorizations, requesting a maintenance

dredging exemption may provide the most direct path to regulatory authorization. However, re-applying

the 1996 dredging template and sediment trap template comes with the disadvantage that the City must

maintain strict compliance with the original design. Therefore, the project would restore a limited

navigation route and provide minimal benefit for sediment trapping.

The project discussions have included consideration of potentially applying the maintenance dredging

exemption to develop a new dredging scenario that expands on the 1996 dredging. Here, the goal would

be to restore the creek to its 1960’s condition. A few issues complicate this approach.

1. The City would have to show the project occurs “within drainage rights-of-way or drainage

easements which have been recorded in the public records of the county.”

2. The project would have to overcome the potential agency argument that “the area to be dredged

has been allowed to shoal to such an extent as to render the area to be dredged non-functional for

a prolonged period of time.”

4

3. The permit applications cannot present original design specifications through self-evident

documentation in the form of either previous permit authorization or previous engineering

specifications. Instead, the project would have to rely on other evidence of the prior dredging that

still exists such as aerial photography or interpretation of soil core borings.

CONCLUSION 2: If the project’s goals require dredging in areas beyond the 1996 template, Taylor

Engineering expects the project would not qualify for a maintenance dredging exemption. Instead,

dredging of West Cedar Creek would likely require a new Southwest Florida Water Management District

(SWFWMD) Environmental Resource Permit (ERP) and a USACE Dredge and Fill Permit.

A.3 Environmental Restoration or “Cleanup”

Dredging projects to provide environmental restoration or “cleanup have been justified through the ERP

process” Project discussions have included consideration that water quality improvements might be

attainable through removal of contaminated sediments. However, prior data collected by the City

associated with the 1996 project as well as the data recently collected by Taylor Engineering shows

sediments in both East and West Cedar Creek exhibit no significant chemical contamination. The Taylor

Engineering team tested and sampled for sediment concentration of the contaminants most likely to occur

in these sediments — arsenic, cadmium, chromium, copper, lead, mercury, zinc, nickel, and silver.

Laboratory results show no samples exceeding the commercial/industrial standard. With the exception of

arsenic, all samples met the residential cleanup standards. Three samples had arsenic concentrations (3.0

– 3.7 mg/kg sediment) slightly above the residential standard (2.1 mg/kg). The levels of arsenic found in

those three samples are common in naturally occurring base limestone that contributes arsenic to surficial

sediments in Pinellas County (e.g. see Karlen et al 2009, PBS&J 2006) and elsewhere in Florida (e.g. see

Jones and Pichler 2007). Plants naturally accumulate arsenic, and as organic material decomposes and

creates sediment, the arsenic in that plant material concentrates to some extent. The cleanup target values

promulgated by the state do not consider this natural process; thus, the fact that the concentrations fall

above the regulatory limit does not mean that these levels present a human or environmental health

concern. Note that the threshold effects level (TEL) for arsenic (7.24 mg/kg) represents the upper limit of

the range of sediment contaminant concentrations thought to have no measurable effects on associated

organism (PBS&J 2006). All measured arsenic concentrations were below the TEL. Therefore, the

chemical composition of the sediment would not limit its reuse for commercial or industrial applications,

and some of the sediments meet all residential standards. Depending on the physical characteristics

required, dredged material may have application in a range of construction projects. Notably, if the City

can find a public use for the dredged material — roadway construction, landfill cover, of fill for a grading

project, for example — the state would waive requirements for severance fees.

Sediment testing did show elevated fecal coliform content. However, sediment likely is not the primary

source of fecal coliform within the water body; rather, elevated fecal coliform content suggests animal or

human waste entering the water through upstream sources, often related to stormwater runoff or faulty

septic systems. Therefore, sediment removal through dredging does not present a viable approach to cause

a long-term reduction of fecal coliform for water quality improvement. To the contrary, removal of

existing sediments may temporarily reduce fecal coliform measurements, but without elimination of the

upstream sources, fecal coliform concentrations will quickly return to pre-dredging levels.

5

CONCLUSION 1: Because sediment sampling identified no significant chemical contamination and

dredging does not provide an effective means to permanently reduce fecal coliform concentrations,

justification for a dredging project to improve sediment or water quality is eliminated. There is no

pollutant-related “Cleanup” need for dredging West Cedar Creek. Further, a dredging project will not

prevent the accumulations of floatables (floating trash and refuse).

A.4 Navigation

One of the most commonly identified purposes for dredging is to provide navigation access. Here, the

project’s goal would be to provide deeper water to support access for local boating activities. In this case,

the type of navigation access required — the size of the boat and the locations being accessed — define

the project parameters. For example, the 1996 dredging project was presented as a navigation project with

the primary purpose to provide limited access to very small boats and personal watercraft (kayaks and

canoes). The dredging encompassed a relatively shallow channel, to a depth of -3 ft NGVD 29, and

provided a narrow channel (varying bottom width of up to about 20 feet) with access to the mobile home

boat ramp area and the City canoe launch area. Repeating such a project would restore this limited

navigation route but provide no additional navigational access.

The shoreline of West Cedar Creek includes residential docks, and some citizens would support dredging

to improve navigation access. However, to successfully achieve this purpose, the project would require a

significant expansion beyond the 1996 project. The dredging template would have to provide access to the

docks and include a wider area of dredging. Also – dredging depths should extend to a minimum depth of

-6 MLW.

A navigation-dredging project presents several challenges to be addressed during feasibility analysis and

final engineering. First, the shoreline of West Cedar Creek includes seawalls as well as residential dock

structures. Dredging immediately adjacent to these structures comes with risk of structural damage. To

mitigate the risk, the dredging specifications should include a minimum setback between 5 and 20 feet

from the structure. Greater setbacks lower the risks of structural damage. However, large setbacks may

decrease the effectiveness of dredging. For example, if the design specifications allow no dredging within

20 feet of all structures, then the project would not effectively improve navigation to the existing

waterway docks. To maximize the benefit of dredging while minimizing the risk to the City, Taylor

Engineering would recommend the City discuss with its legal staff the feasibility of requesting that

individual waterfront owners authorize a “release of claims agreement” with the City. This legal

document would inform the owners of both benefits and the risks of dredging and require that any

authorizing homeowner waive any claims against the City that might arise related to the dredging project.

For those owners who are willing to authorize such an agreement, dredging setback may be minimized;

for those who refuse the agreement, the City’s project should maintain the maximum setbacks.

The need for maintenance dredging represents another challenge associated with all dredging project;

however, the question of maintenance interval is of particular importance for navigation projects where

maintenance of minimum water depth defines the entire project function. Once the project identifies a

preferred dredging template, engineers can provide an initial estimate of expected sedimentation rates and

maintenance interval. At the feasibility stage, engineers attempt to evaluate maintenance dredging

intervals through evaluation of likely sediment sources which would contribute to the need for

maintenance. For West Cedar Creek, there are three potential sources of sedimentation. Sediments may

6

possibly enter the creek from St. Joseph Sound on tidal flood current, from flows carrying sediments

downstream from areas east of Bayshore Blvd, or from overland sheet flow or windblown sources.

Based on field observations, Taylor Engineering expects that upland sources (sheet flow or windblown

sources) are minimal. Observations can provide insight regarding which of the other two sources (tidal

flood currents or downstream flow) likely dominate sedimentation. Review of the survey shows that

contours generally slope from the creek toward the sound. No significant shoal has formed in the sound at

the mouth of the creek; in fact, a possible scour hole lies in the sound just off the mouth of the creek.

Athena Technologies geotechnical exploration shows (1) slightly decreasing sediment depth from the

Bayshore Drive Bridge to the sound; (2) unusually low sediment deposition and low bed elevation levels

immediately on the east side of Bayshore Drive Bridge; (3) higher deposition 500 – 1,000 ft east of the

Bayshore Drive Bridge (similar to levels immediately west of the bridge). These survey and geotechnical

observations do not suggest sediment transport from the sound to the creek. Observations of decreasing

sediment deposition on the approach to the sound from the east, the absence of a shoal, and the presence

of a possible scour hole in the sound suggest that the sound sweeps away sediment discharged from the

creek. The unusually low sediment deposition and low bed elevation levels immediately on the east side

of Bayshore Drive Bridge suggest some influence of the bridge constriction to speed east-to-west flows at

the bridge approach – possibly scouring sediment or at least preventing sediment deposition until flows

slow west of the bridge.

While engineers can provide qualitative assessments of sedimentation rates based on basic observations,

the City should recognize that the complexity of the system makes it impossible to definitively

characterize sedimentation sources or rates. To advance initial assessments to more definitive evaluations,

additional studies including dye studies, hydrodynamic modeling, sediment transport modeling, and

sediment trap field studies may be necessary.

Dredging will not reduce the sources of sediment inflow. In fact, dredging may actually increase

sedimentation rates. Flow velocities decrease when flow areas transition from shallow and narrow flow

channels to deeper and wider channels with an increased opportunity for increased sedimentation. During

final engineering design, a dredging project should consider and accommodate projected sedimentation

rates. Applications of some of the modeling and field analysis tools noted above may allow for

optimization of the design to decrease sedimentation rates as much as practical. Regardless of the detail

level of analysis and design, the City must view predictions of sedimentation rates and maintenance

dredging requirements in the appropriate context — as estimates of future conditions within a complex

natural system. For example, a major coastal storm event may invalidate any estimate of average

sedimentation rates and cause a significant increase in maintenance dredging requirements. The City must

evaluate the costs and risks of maintenance dredging when considering the development of a navigation

dredging project.

CONCLUSION 1: Dredging of West Cedar Creek as was permitted and completed in 1996 is likely to be

permitted for maintenance dredging purposes. Such dredging would likely result in an ability to operate

small watercraft (canoes and kayaks) under lower tide conditions between East Cedar Creek and St

Joseph Sound. Operation of watercraft from the adjacent fourteen seawalled properties along West Cedar

Creek would not be practical except under higher tide conditions. Conditions for such dredging can be

evaluated and considered relative to probable costs and schedules for implementation. Assuming

7

avoidance of seagrass impacts, securing a maintenance dredging permit would likely entail a six month or

longer permitting period at a relatively low cost. Impacts to seagrass, if unavoidable, could extend the

permit application schedule and increase the cost of such a project.

Conclusion 2: Dredging of West Cedar Creek for navigation as was once available to the adjacent,

seawalled properties following development in the 1960’s, appears to be permittable under USACE and

SWFWMD regulations.. Operation of watercraft from the fourteen seawalled properties along West Cedar

Creek would likely be practical under most tide conditions, at least until sediment accumulation again

restricts their operation. There is no practical method to define with complete certainty the rate of

sediment accumulation. The length of time prior to the first or subsequent maintenance dredging events

could be very short under severe storm conditions; or the channel could remain at useable elevations for

relatively long periods if normal or mild weather conditions persist. Necessary steps to design and permit

such expanded navigation dredging can be evaluated and considered relative to probable costs and

schedules for implementation. Securing a navigation dredging permit for an expanded channel design

could entail a 12+ month permitting period. This extended schedule results from a need to mitigate for

seagrass impacts and to establish the basis for subsequent maintenance dredging conditions.

A.5 No Action

A “No Action” plan adopted by the City of Dunedin would provide no changes to current West Cedar

Creek conditions.

CONCLUSION: Under a No Action plan, during mild weather conditions, West Cedar Creek would

likely continue to accumulate sediment in some areas. Sedimentation could result in increases or

decreases of benthic flora and fauna. West Cedar Creek would lose its ability to accommodate watercraft

operation, except canoes and kayaks, under most tidal conditions. In the event that accumulated sediments

eventually affected up gradient drainage, there might develop a need for limited dredging such as that

performed in 1996.

B. East Cedar Creek

Based on a few aerial photographs, in the 1960’s, East Cedar Creek was apparently dredged to provide fill

material for the adjacent mobile home park. As a result, the creek took the appearance of an open water

body suitable for small boats including canoes and kayaks. With the exception of the very limited

dredging performed in 1996, there are not data to indicate that East Cedar Creek has had any maintenance

dredging since its original dredging in the 1960’s. East Cedar Creek has been reverting to its apparent

pre-development tidal stream and mudflat conditions..

B.1 Stormwater Conveyance/Sediment Transport Improvements

As noted above within the West Cedar Creek discussion, portions of the City’s stormwater systems

discharges into East Cedar Creek. Again, potential dredging work would occur predominantly below the

mean low water tidal elevation. Flooding in this area is more closely associated with high tides and storm

surge events. As such, dredging will not reduce the potential for localized flooding of areas immediately

adjacent to East Cedar Creek. Dredging could potentially improve stormwater conveyance and associated

sediment transport patterns within the creek. However, evaluating such modifications would require a

8

significant engineering analysis linking coastal engineering, sediment transport, and stormwater modeling

analyses. Because tides control the water elevations, potential improvements are most likely minor or

insignificant, If the City wishes to perform such modeling analyses and if modeling provides a reasonable

stormwater conveyance/sediment transport solution, the city may be able to optimize the dredging project

to reduce costs. Notably, dredging for stormwater conveyance / sediment transport improvements could

result in impacts to mangroves.

CONCLUSION: A dredging project would likely provide little or no improvement to tidally influenced

localized flooding immediately adjacent to East Cedar Creek or to the upstream stormwater conveyance.

Expanded dredging of East Cedar Creek could incur additional costs associated with mangrove impact

and mitigation.

B.2 Maintenance Dredging and Related Activities

As noted within the West Cedar Creek discussion above, a maintenance dredging exemption for dredging

in East Cedar Creek cannot exceed the depths, widths, and configurations achieved by a previously

permitted dredging project. 403.813(1)(f), F.S. indicates that for a project to qualify for the maintenance

dredging exemption, a previously constructed dredging project must exist and/or the dredging must occur

within drainage rights-of-way or drainage easements which have been recorded in the public records of

the county. The City may leverage any previously permitted dredging project to acquire authorizations for

maintenance. Specifically, the City acquired permits and dredged Cedar Creek in 1996. If the City

determines that the goals and purpose of the currently considered project match those outlined in the 1996

authorization, requesting a maintenance dredging exemption may provide the most direct path to

regulatory authorization. However, re-applying the 1996 dredging template limits Dunedin to strict

compliance with the original design. Therefore, the project would provide minimal added benefit or

improvement.

The project discussions have included consideration of potentially applying the maintenance dredging

exemption to develop a new dredging scenario that expands on the 1996 dredging. The same issues noted

under West Cedar Creek complicate this approach for East Cedar Creek. Such a project would not meet

the standards for a maintenance dredging permit exemption.. Beyond the strict limits of a maintenance

dredging exemption, a dredging project might be justified through the ERP process to provide

environmental restoration or “cleanup” Project discussions have included consideration that water quality

improvements might be attainable through removal of contaminated sediments. However, data from East

Cedar Creek sediments indicate no significant sediment contamination.

Project discussions have also included consideration of a project with dual purposes to provide water

quality improvements combined with “preventative maintenance” aimed at keeping East Cedar Creek

open for stormwater conveyance. Widening and deepening East Cedar Creek to the furthest permitable

extents may be a means to address residence concerns regarding upstream drainage but might be difficult

because of impacts to mangroves. A project that deepens and maintains the creek could prevent further

incursion of mangroves within the waterway. Some beneficial mangrove trimming may be performed

without a permit, assuming the work is performed by a professional mangrove trimmer as defined by the

State.

9

On East Cedar Creek, mangroves have grown into the original open water footprint, and two mangrove

islands have formed in the remaining open area. Without regular maintenance, mangroves may,

ultimately, fill in additional areas of remaining open water. The consequences of that filled-in condition

include increased resident concerns for stormwater related impacts around the mobile home park.

Homeowner trimming of mangroves adjacent to the existing channel has helped to maintain that channel.

However, this trimming does not appear to have been done regularly enough to provide much control

over mangrove intrusion into the conveyance channel. Trimming likely will not greatly reduce (but may

slow) the expansion of the mangroves. Trimming could (but would not completely) control growth at the

edges of the large open water area. Mangrove trimming rules do not allow root trimming, and mangrove

roots extend into the open water area outside the lateral extent of the branches. Dredging provides a viable

means to maintain the open water area and prevent future intrusion of mangroves. However, dredging

would require mitigation for unavoidable impacts to mangroves. Once those impacts are mitigated, and

should mangroves regrow into the permitted project template, additional maintenance dredging within the

project footprint that included impacts to mangroves would be exempt from further mitigation

requirements.

CONCLUSION 1: If the projects goals require dredging in areas beyond the 1996 template, Taylor

Engineering expects that such a project would not qualify for a maintenance dredging exemption and

would likely require a new a State of Florida ERP and a USACE Dredge and Fill Permit.

CONCLUSION 2: If the project goals limit dredging to that permitted in the 1996 project, the goals

should be expanded to include routine maintenance and trimming of mangroves to maintain the

established channel and to avoid restrictions to stormwater transport. The city could have some beneficial

mangrove trimming performed without a permit by a professional mangrove trimmer.

B.3 Environmental Restoration or “Cleanup”

Beyond the strict limits of a maintenance dredging exemption, a dredging project might be justified

through the ERP process to provide environmental restoration or “cleanup.” Project discussions have

included consideration that water quality improvements might be attainable through removal of

contaminated sediments.

CONCLUSION: As noted above within the West Cedar Creek discussion (Section A3, above), prior data

collected by the City associated with the 1996 project as well as the data recently collected by Taylor

Engineering shows that sediments in both East and West Cedar Creek exhibit no significant chemical

contamination, and dredging does not provide an effective means to permanently reduce fecal coliform

concentrations. There is no “Cleanup” need for dredging East Cedar Creek.

B.4 Navigation

As noted above under West Cedar Creek, the 1996 dredging project presented itself as a limited

navigation project with the primary purpose to provide limited access to very small boats and personal

watercraft. The dredging encompassed a relatively shallow channel, to a depth of -3 ft NGVD 29, and

provided a narrow channel (varying bottom width of up to about 20 feet) with access to the mobile home

boat ramp area and the City canoe launch area. Repeating such a project would restore this limited

navigation route but provide no additional navigational access.

10

Some citizens would support dredging East Cedar Creek to improve navigation access. As noted above,

the shoreline of East Cedar Creek includes residential docks associated with the mobile home park and a

floating dock for canoe and kayak launching at the edge of Hammock Park. To achieve a broader

navigation purpose, the project would require a significant expansion beyond the 1996 project. The East

Cedar Creek potential dredging area lies east of the US Alt 19 and the Pinellas Trail bridges. Tidal

exchange completely drains the area on a regular basis. Access by motorized vessels would be difficult

under normal and high tide conditions. Dredging beyond the 1996 limits would disturb both re-

established mud flats as well as the two mangrove islands now growing in the remaining open area of the

creek beside the mobile home park.

All mangrove impacts would require mitigation. The agencies much prefer on-site, in-kind mitigation. An

investigation of Hammock Park to assess the potential of suitable mitigation would be a first step in

determining what mitigation opportunities the City could identify to account for the unavoidable impacts

to mangroves.

CONCLUSION 1: Dredging of the East Cedar Creek area for the limited navigation resulting from the

1996 permit would likely be readily (+6 month) authorized as a maintenance-dredging permit without

substantial additional investigations. Dredging of East Cedar Creek requires a substantive and continuing

commitment to mangrove trimming and related channel maintenance.

CONCLUSION 2: The US Alt 19 and Pinellas Trail bridges form substantial barriers to the navigation of

watercraft, other than canoes and kayaks, between the East Cedar Creek and the West Cedar Creek areas.

Dredging of areas greater than that permitted in 1996 would require substantial effort to determine

whether such expansion is permittable and affordable. Considering these challenges and the limited

navigation benefits, area-wide navigation dredging of East Cedar Creek may be infeasible.

B.5 No Action

A No Action plan adopted by the City of Dunedin would provide no changes to current East Cedar Creek

conditions and actions available to the city.

CONCLUSION: Under a No Action plan, East Cedar Creek would likely continue to accumulate

sediment in some areas and likely experience expanding-growth of mangroves and other native flora and

fauna. Some mangrove trimming would be allowed if performed by a professional mangrove trimmer.

East Cedar Creek would eventually lose its ability to accommodate canoe and kayak water operation

under most tidal conditions. In the event that accumulated sediments and mangroves eventually impact up

gradient drainage, there would develop a need for limited dredging and vegetation management to reduce

impacts of stormwater drainage from locations upstream. .

C. Lake Sperry

Lake Sperry is a privately owned, 4.5-acre waterbody apparently constructed in the 1960’s to provide a

source of fill to accommodate the adjacent development. The lake was constructed in a natural low area

thru which area drainage flowed. A low bulkhead stabilizes much of the lake edge. No formal as-built

survey of the lake and bulkhead structure is available. In some locations, this structure now exhibits signs

of structural distress. Stormwater drains into the lake from City stormwater pipes and drains out of the

11

lake in a similar fashion. An easement around the edge of the lake and at inflow and outflow stormwater

drain locations allows the City access for management activities. The lake includes no emergent

vegetation. This lack of vegetation may in part result from the efforts of the residents / lake owners and a

contractor hired by the residents to manage conditions in the lake.

The homeowners use canoes, kayaks and other small pleasure boats on the lake. Some have claimed that

there are areas of the lake where such craft scrape the bottom. There is no indication that motorized water

craft operate on the lake.

Based on the bathymetric survey collected April 26, 2013, the lake has an average bottom elevation of

8.00 ft NAVD 88. Assuming that the invert of the outflow stormwater discharge pipes (average invert

elevation of 11.1 ft NAVD 88) controls the lake level, when at equilibrium, lake depths average about 3.0

ft and vary from approximately 0.5 ft to 4.50 ft. The bathymetric survey indicates that water depths less

than about 4 feet primarily occur near the center of the lake as well as at some locations near the shore. A

review of project data, obtained from lake-bottom sediment borings, suggests the maximum original pond

depths averaged 5.7 ft.

Lakeside residents claim that the lake was once much deeper, that it has become shallow enough to

sometimes see a sandbar at the water surface, as well as observe other indications that the lake is filling

with sediments. The survey suggests that there are some areas that are quite shallow. It is also possible

that stormwater flowing into the lake moves sediment around. Such movement could result in shallow

sandbars.

Primary sources of sediment to the pond may include stormwater and erosion from behind the existing

bulkheads (part of each lakeside property) that are in various stages of deterioration. Other minor

sediment sources may include that blown in by the wind and vegetation deposited on the bottom from

aquatic vegetation management by homeowners and their contractors.. In addition, organic debris (grass

cutting, fallen leaves, etc.) that come in from lakeside lawns and with stormwater flows could also

contribute to the sediment and hence changes in lake depth.

C.1 Stormwater Storage/Sediment Transport Improvements

Stormwater flows into Lake Sperry through stormwater drainage pipes that collect stormwater from

surrounding residential streets. In 2012, the City installed a “Suntree” stormwater filtration unit that

captures large organic matter, floatables, and coarse sediments from at least some of the stormwater pipes

entering Lake Sperry through the City stormwater system. Appropriate construction and maintenance of

the filtration unit, should result in a reduction in sediment load flowing into the lake.

Because Lake Sperry is a “wet pond,” its capacity to store incoming water is defined by the volume above

the lake’s existing water level. Dredging would occur below the ponds existing water level and therefore

would provide no additional storage volume to accommodate stormwater.

Lake Sperry may receive sediments primarily because of erosion at the lake edge and stormwater flowing

in through the stormwater drainage system. Sediments exit the lake through the stormwater drainage

12

outflow on the lake. Shoreline erosion management by property owners would reduce or eliminate one

significant source of sediment.

Even with the Suntree filtration unit, it is likely that stormwater entering the lake carries some sediment

and solids; the filtration unit does cannot capture all particulate material. In addition, it is likely that some

of the material transported into the lake remains there. Finally, some of this stormwater-transported

material likely leaves the lake with the outflowing stormwater. The material remaining in the lake would,

over time, increase the amount of sediment covering the lake bottom and correspondingly decrease the

water depths in the lake. Assuming that this deposition process has occurred to a sufficient degree to

decrease lake depth, one alternative management plan would include dredging the lake to remove those

accumulated sediments.

Increasing the lake depth would not increase stormwater storage volume but would have the effect of

increasing the lake’s total water volume. An increased volume could increase the lake’s efficiency, or

capacity to capture sediment, compared to the lake’s current condition. An estimate of the amount and

extent of sediment removal provided by any particular depth increase would require measurement of

inflow and outflow quantities of water and sediment and lake level fluctuations associated with storm

events. However, as far as Taylor Engineering is aware, these measurements are not currently available.

A combination of dredging, construction of in-lake structures and development of some emergent wetland

vegetation might also improve sediment capture efficiency. However, as with increasing the water depths,

effective design would require better data on the stormwater flows and modeling in order to estimate

potential benefits and whether such benefits would be cost-effective.

Based on the limited available data regarding the original lake depths (and consequent volume), the

original depths were apparently not greatly different (many feet deeper) than current conditions. It is

reasonable to assume that 30 years of stormwater flows through the lake have resulted in perhaps a few

feet of sediment accrual. Since the inflowing stormwater is now at least partially treated by the Suntree

filtration unit, the City expects a reduction in floatables and sediment load, and therefore, reduced

sediment bypassing through Lake Sperry. Deepening the lake by dredging could accomplish some

increase in the retention of solids entering the lake. However, evaluating the efficacy of such a dredging

design would require additional field data.

CONCLUSION 1: Lake Sperry has been subject to two main sources of sediment – stormwater runoff

and lakeside bank erosion. Sediment from stormwater runoff is reduced with the City’s up gradient

treatment system. Lakeside bank erosion requires action by some of the lake owners.

CONCLUSION 2: Dredging does not increase the stormwater storage volume of Lake Sperry and hence,

provide no reduction in flood potential.

CONCLUSION 3: Dredging could reduce the concentration of suspended solids in water discharged from

Lake Sperry.

CONCLUSION 4: Dredging to increase water volume available for solids retention would likely be

limited to the center of the lake.

13

C.2 Maintenance Improvements thru Biodiversity

Lake Sperry currently has no emergent (wetland), floating leaves, or submersed vegetation. Such

vegetation is the basis for a diverse, healthy aquatic ecosystem. The simplified biological system in Lake

Sperry supports water column algal growth, which in turn supports a relatively limited animal

community.

A natural lake in Florida typically includes shallow depths where emergent vegetation grows and deeper

water that creates some open water areas too deep for emergent vegetation. These areas may support

submersed vegetation (not likely in Lake Sperry due to low water clarity) and /or plants that include

floating leaves attached to a root system by a long stem (e.g. water lilies). The vegetation provides a

habitat and food source for fishes that feed on plants, algae growing on the plants, small invertebrates

(insects, snails, etc.) and small vertebrates (e.g. frogs) that also use the plant community for their life

functions. Typically, depths less than three feet support emergent vegetation. Depths between about 3 and

6 ft support floating-leaved vegetation. Beyond that depth, submersed vegetation will grow in systems

with sufficient water clarity and quality.

Reconfiguring the bottom elevations (dredging the middle of the lake and relocating sediment to the

edges) to produce a more consistent littoral shelf around the edge of the lake and planting emergent

vegetation on that shelf would provide the basis for a more complex and probably healthier lake system.

The Florida Fish and Wildlife Commission could be contacted to determine the benefits of stocking the

lake with some native fish species. The small size of the lake probably makes active management to

produce and maintain a diverse system a necessary long-term activity. The current owners have indicated

that they are managing the lake to keep aquatic vegetation out. The planting and maintenance of

vegetation in the lake represents is a completely different approach to lake management than historically

applied here.

CONCLUSION: Lake Sperry is maintained by the adjacent property owners. If the lake is to be dredged,

lake biodiversity could be improved by re-configuring its bottom and allowing the growth of some

aquatic vegetation.

C.3 Navigation

The USACE does not consider the lake as a navigable water body for their regulation purposes and has

stated that they have no regulatory interest in the lake for the activities currently under consideration.

Therefore, there is no regulation-based “navigation” alternative to consider for this project. Lakeside

property owners have expressed that they would like the lake made deeper for general recreational

purposes, which include the use of small non-motorized boats such as kayaks and canoes.

CONCLUSION: Dredging the lake could improve the operation of canoes and kayaks across the water

surface.

C.4 Environmental Restoration or “Cleanup”

As discussed with West and East Cedar Creek, a dredging project might be justified through the ERP

process to provide environmental restoration or “cleanup.” Such cleanup considerations are related to

14

potential water quality improvements that might be attainable through removal of contaminated

sediments.

CONCLUSION: As noted above within the Cedar Creek discussion, prior data collected by the City as

well as the data recently collected by Taylor Engineering shows that sediments in Lake Sperry exhibit no

significant chemical contamination, and dredging does not provide an effective means to permanently

reduce fecal coliform concentrations. As such, there is no pollutant-related need for dredging Lake

Sperry.

C.5 No Action

A No Action plan adopted by the City of Dunedin would provide no changes to current Lake Sperry

conditions or management. As the lake is privately owned, this approach would allow the lake owners to

continue managing the lake as they desire.

CONCLUSION: Under a No Action plan, Lake Sperry would likely continue to accumulate sediment in

some areas, and residents would continue to manage the lake. The No Action conditions would afford

limited opportunity for the lake to develop the biodiversity of a healthy waterbody. Whether increased

sediment becomes an apparent issue would depend on storm conditions that could increase the discharge

of sediments from the lake rather than result in continued accumulation of sediment in the lake. An

increase in accumulated sediment, related to generally mild storm conditions, could impact the Lake’s

ability to accommodate canoe and kayak water operation in all directions.

15

References

Jones, Gregg W. and Thomas Pichler, 2007. Relationship between Pyrite Stability and Arsenic Mobility

During Aquifer Storage and Recovery in Southwest Central Florida Environ. Sci. Technol. 2007,

41, 723-730

Karlen, David J., Thomas L. Dix, Barbara K. Goetting and Sara E. Markham, 2009. The Benthic

Macrofaunal Community and Sediment Quality Conditions in Clam Bayou, Pinellas County,

Florida Environmental Protection Commission of Hillsborough County Data Report prepared for:

Tampa Bay Estuary Program March 2009.

PBS&J, 2006. Lake Seminole Sediment Removal Feasibility Study. Final Report, January 2006. Prepared

for Pinellas County by PBS&J in Association with Hayes-Bosworth, Inc.