DOCTORS PASS 2013

4-YEAR POST CONSTRUCTION

ENGINEERING MONITORING REPORT

Prepared For:

Collier County – Coastal Zone Management Department

2800 N. Horseshoe Drive

Naples, FL 34104

Prepared By:

Atkins

4030 West Boy Scout Boulevard, Suite 700

Tampa, FL

April 2013

i

DOCTORS PASS

2013 ENGINEERING MONITORING REPORT

EXECUTIVE SUMMARY

This report evaluates the performance of the 2009 maintenance dredging at Doctors Pass. Dredging for

Doctors Pass occurred in March to April of 2009. The current survey was taken on March 28, 2013. Since

the May 2012 survey provided by Humiston & Moore, the Doctors Pass survey area has experienced an

overall net volume gain of approximately 7,422 cubic yards. The total amount of material that would be

available if dredged at this time would be 36,872 and therefore the pass does require maintenance

dredging at this time.

Table 1: Volume Summary Within Limits of Permitted Dredge Template

Volume Summary

2013

Volume

Above DT

(cy)

2012

Volume

Above DT

(cy)

2012-

2013

Delta

2005 Post-

Con vs 2013

(cy)

Non-

Dredge

Probable

Rock (cy)

Total Volume Above

Dredge Template: 59,691 52,269 7,422 36,872 22,819

ii

DOCTORS PASS

2013 ENGINEERING MONITORING REPORT

TABLE OF CONTENTS

I. INTRODUCTION ............................................................................................................................... 1

II. HYDROGRAPHIC SURVEYS ......................................................................................................... 1

III. VOLUMETRIC CHANGE ................................................................................................................ 3

IV. CONCLUSIONS & RECOMMENDATIONS ............................................................................... 10

V. REFERENCES .................................................................................................................................. 13

LIST OF TABLES

Table 1. 2013 Morgan and Eklund Control Points ....................................................................................... 2

LIST OF APPENDICES

Appendix A. Doctors Pass Survey Map and Cross Sections

1

DOCTORS PASS

2013 ENGINEERING MONITORING REPORT

I. INTRODUCTION

This report describes the performance and volumetric changes for Doctors Pass, which is located between

Florida Department of Environmental Protection (FDEP) monuments T-57 and R-58A, from May 2012

through April 2013. This annual monitoring is required by FDEP JCP Permit No. 0235740-001-JC.

In March through April of 2009, a maintenance dredging event designed to remove 36,000 cubic yards of

sand occurred. After dredging took place, approximately 32,550 cubic yards of material was excavated.

The project’s remaining effectiveness from the 2009 dredging activities is assessed in terms of volumetric

changes from May of 2012 through March of 2013. A location map of the monitoring area can be found

in Appendix A.

Project area events since last dredge project:

February-April 2009: 32,500 cubic yards of sand was dredged and placed in the nearshore

between DEP reference monuments R-60 and R-62.

February-April 2011: Over 3,000 tons of armor stone were added to the north jetty to widen the

landward 160 feet by 5 feet, increase the height of the seaward 240 feet to +6.0 feet NAVD,

create a 2:1 slope along the south side, and increase the footprint by 4 feet on the seaward end.

February-April 2011: The beach immediately south of the pass from reference monument R-58

north to the south jetty was nourished with over 22,000 cubic yards of truck hauled sand.

June 21 – June 25, 2012: Tropical Storm Debby impacts Collier County coastline with four days

of rain, high tides, waves and winds.

II. HYDROGRAPHIC SURVEYS

The annual monitoring of Doctors Pass requires a bathymetric survey performed along previously

established survey track lines. This data allows Collier County and the Florida Department of

Environmental Protection (FDEP) to continually observe and assess the performance of the maintenance

dredging at Doctors Pass. The annual monitoring surveys are needed to observe the performance of the

maintenance dredging and assess these projects’ affects on adjacent shorelines. The scientific monitoring

process also provides information necessary to plan, design and optimize future projects.

Surveyors from Morgan & Eklund, Inc. (M&E) conducted the bathymetric survey for the borrow area on

March 28, 2013. All vertical elevations from the 2013 survey are referenced to the North American

Vertical Datum of 1988 (NAVD 88) and all horizontal data is referenced to the Florida State Plane

Coordinate System, East Zone, North American Datum of 1983/90 (NAD 83/90).

The horizontal positioning for the ebb shoal bathymetric survey relied upon Real-time Kinematic GPS,

with the GPS base station receiver set on Point #409, provided in Table 1 below.

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Table 1. 2013 Morgan and Eklund Control Points

Point Northing Easting Elevation Stamping Description

409 669925.74 389034.90 8.95 409 M&E IRC

410 669991.91 389035.15 6.13 410 M&E IRC

411 677948.90 390299.26 19.78 411 M&E IRC

412 677948.96 390336.02 19.56 412 M&E IRC

U-55 672131.10 388974.60 7.13 U-55 Coll. Co. 1979 DNR Disc in Concrete

A-11 676453.59 388667.14 5.77 64-78-A11 DNR Disc in Concrete

Offshore data collection performed to FDEP specifications by Morgan & Eklund, Inc. utilized a 26’

Parker survey vessel, Trimble SPS 852 Real-Time Kinematic GPS, Hypack Navigation Software, an

Odom CVM Digital Echosounder and a TSS Motion Compensator for data collection. Calibration of the

fathometer (depth sounder) involved adjusting for vessel squat and settlement while underway, vessel

draft, and the speed of sound in water (bar check). Both analog and digital fathomer readings were

calibrated at the beginning and end of each survey day and after replacing paper charts.

Elevations for the ebb shoal bathymetric survey relied on Real-time Kinematic tide files and were verified

with a tide staff and tide gauge set near Point #409 with an elevation of 8.95 feet NAVD 88 on March 28,

2013. The survey boat navigated along each transect using the steering indicator in Hypack and the

coordinates and depth soundings were simultaneously collected every 20 feet along the profile line. The

digital fathometer collected readings to the nearest 0.1 foot. The resultant accuracy of the bottom

elevations, from leveling to staff, staff accuracy, positional accuracy and sounding accuracy, are within

±0.5 feet, as stipulated in the FDEP specifications.

The 2013 survey recorded elevations in reference to the North American Vertical Datum of 1988 (NAVD

88), as requested by the FDEP. In order to convert to the National Geodetic Vertical Datum of 1929

(NGVD 29, datum previously used in permits and construction drawings) or to Mean Lower Low Water

(MLLW, Datum commonly used on navigation charts) one must refer to the nearest tidal benchmark. For

Doctors Pass the closest tidal benchmark is Tide Station 872-5110 Naples Gulf of Mexico. The second

table under NAVD 88 Feet shows the conversion between MLLW and NGVD88 of 2.3 feet. Therefore if

you have and elevation shown on the survey of -5.3 feet NAVD 88 and you subtract a -2.3, one would get

-3.0 feet MLLW. MLLW will show a shallower number than NGVD 29 which is shallower than NAVD

88. Figure 1 shows the conversion from NAVD 88 to NGVD 29 and to MLLW.

3

Figure 1: Datum Conversions

III. VOLUMETRIC CHANGE

In 2009 the maintenance dredging project excavated approximately 32,550 cubic yards of material from

Doctors Pass. In March of 2013 a bathymetric survey of Doctors Pass was performed and the resulting

color-banded elevation map is given in Appendix A. A volumetric comparison was made between the

March 2013 survey and the survey performed in May 2012 by Humiston and Moore. Based on total

extents of these two surveys, the analysis shows that the pass has an overall net gain in volume of

approximately 9,192 cubic yards over the past year. There was a net gain of 7,422 cubic yards within the

limits of the 2005 permitted dredge template. Further dissecting this volume into the 2005 permitted

dredge template sections, we can take a closer look at the areas that have gained and lost material over the

past 11 months. The volume shown are the net volumes for the segments, there is the potential for

isolated hotspots that are needed for navigation within the segments that may not show as appreciable net

volume accumulation. Appendix A contains the plan view survey differential contours in NAVD 88

which delineate the spots that have gained or lost material.

The 2005 permit divided the dredge template into eight segments. These segments and the associated

stationing are shown in Figure 2.

4

Figure 2: Doctors Pass Dredge Template Segments

5

A. Doctors Pass Dredge Segments (Settling Basin, Entrance Channel West, Entrance Channel

East)

i. Settling Basin:

The Doctors Pass Settling Basin is located just outside of Doctors Pass and includes the ebb shoal.

This dredge segment is permitted to a cut elevation of -15.3 feet NAVD 88 (-14.0 ft NGVD 29). This

segment has seen the largest increase in volume of all the dredge template sections with 5,207 cubic

yard increase from the 2012 survey and the total volume above the dredge template of 48,524 cubic

yards. It should be noted that during the 2005 dredge event the total amount of material in the dredge

template was not achieved in this section because the dredge encountered hard bottom substrate.

(CPE 2010) Therefore the entire 48,524 cubic yards will not be realized if a maintenance dredge

project was commissioned at present date. The volume of sediment closer to the amount that can

physically be removed would be 26,665 cubic yards, based on the comparison from the 2005 post-

dredge survey to the current 2013 survey.

Table 2: Doctors Pass Volumes

Segment Stations

Dredge

Cut

NGVD29

Dredge

Cut

NAVD88

2013

Volume

Above

DT (cy)

2012

Volume

Above

DT (cy)

2012-

2013

Delta

2005

Post-Con

vs 2013

(cy)

Non-

Dredge

Probable

Rock

(cy)

Settling

Basin

0+00 to

6+34 -14.0 -15.3 48,524 43,317 5,207 26,665 21,859

Entrance

Channel

West

6+34 to

12+00 -9.0 -10.3 3,195 2,636 559 3,195 0

Entrance

Channel

East

12+00 to

15+70 -8.0 -9.3 439 142 297 439 0

Subtotal: 52,158 46,095 6,063 30,299 21,859

Figure 3 below depicts the amount of material that has accumulated at the mouth of the pass at

Station 2+50 in the settling basin.

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Figure 3: Settling Basin typical cross section

ii. West Entrance Channel:

The West Entrance Channel begins at the west end of the south jetty and extends into the pass proper.

The dredge cut elevation is -10.3 ft NAVD 88 (-9.0 ft NGVD 29). The West Entrance channel runs

roughly the length of the rubble rip rap along the south jetty in the aerial photo. This area has gained

559 cubic yards of sediment since the 2012 survey, and has approximately 3,195 cubic yards

available above the dredge template. There is a shallow shoal developing just inside the south jetty

shown in Figure 4. The 2005 and 2009 dredge projects also encountered rock substrate in this section

so the full 3,195 cubic yards will likely not be captured in the next dredging project.

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Figure 4: West Entrance Channel cross section at shoaled area

iii. East Entrance Channel:

The East Entrance Channel starts approximately at the west terminus of the concrete seawall cap on

the south side of the pass and extends east to where the pass proper opens into the Turning Basin. The

dredge cut elevation for this segment is -9.3 ft NAVD 88 (-8.0 ft NGVD 29). This area accumulated

297 cubic yards of sediment in the past 11 months, but as Figure 5 shows and according to Table 2,

there is only 439 cubic yards in this segment currently above the dredge template.

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Figure 5: East Entrance Channel Typical Section

B. Turning Basin Dredge Segment

The Doctors Pass Turning Basin is the location where the backbay channels and the pass proper come

together. This confluence of channels from the Gulf and Moorings Bay is a wider area where currents

slow and sediment can begin to fall out of suspension. The Turning Basin leads from the pass to the start

of the flood shoal and the location where the main channel trifurcates into the east, west and south

channels in Moorings Bay. The permitted dredge cut elevation is -9.3 ft NAVD 88 (-8.0 ft NGVD 29).

The Turning Basin accumulated 1,182 cubic yards from 2012 to 2013 (Table 3) and currently holds 5,698

cubic yards of sediment in the dredge template.

Table 3: Turning Basin Volumes

Segment Stations

Dredge

Cut

NGVD29

Dredge

Cut

NAVD88

2013

Volume

Above

DT (cy)

2012

Volume

Above

DT (cy)

2012-

2013

Delta

2005

Post-Con

vs 2013

(cy)

Non-

Dredge

Probable

Rock

(cy)

Turning

Basin N/A -8.0 -9.27 5,698 4,516 1,182 4,738 960

Subtotal: 5,698 4,516 1,182 4,738 960

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C. Moorings Bay West Channel Dredge Segment

The West Channel in Moorings Bay is one of two routes for boaters to access Moorings Bay to the north.

The West Channel is divided into three segments. The north section is not permitted for dredging

currently. The South segment (Sta. 0+00 to Sta. 3+56) has a permitted dredge elevation of -9.3 ft NAVD

88 (-8.0 ft NGVD 29) and the Middle segment (Sta. 3+56 to Sta. 8+12) is permitted to -8.3 ft NAVD 88

(-7.0 ft NGVD 29). This section is bounded on the west by private docks and on the east by the Moorings

Bay flood shoal. As Figure 6 shows the flood shoal typically grows into the channel form the east

boundary (right side of the cross-section) requiring maintenance dredging.

Figure 6: West Channel Typical Cross-Section.

The South segment has accumulated 117 cubic yards from 2012 to 2013 (Table 4) and currently holds

1346 cubic yards of sediment in the dredge template while the Middle segment has gained only 14 cubic

yards and from 2012 to 2013 (Table 4) and currently holds 122 cubic yards of sediment within the dredge

template.

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Table 4: Moorings Bay West Channel Volumes

Segment Stations

Dredge

Cut

NGVD29

Dredge

Cut

NAVD88

2013

Volume

Above

DT (cy)

2012

Volume

Above

DT (cy)

2012-

2013

Delta

2005

Post-

Con vs

2013 (cy)

Non-

Dredge

Probable

Rock (cy)

South

0+00 to

3+56 -8.0 -9.3 1,346 1,229 117 1,346 0

Middle

3+56 to

8+12 -7.0 -8.3 122 108 14 122 0

Subtotal: 1,468 1,337 131 1,468 0

North (not

permitted)

8+12 to

19+00 N/A N/A N/A N/A 1,163 N/A N/A

D. Moorings Bay East Channel Dredge Segment

The East Channel in Moorings Bay is divided into two segments. The South Channel segment (Sta. 4+85

to Sta. 6+78) has a permitted dredge elevation of -8.3 ft NAVD 88 (-7.0 ft NGVD 29) and the East

Channel segment (Sta. 11+35 to Sta. 17+51) is also permitted to -8.3 ft NAVD 88 (-7.0 ft NGVD 29).

This section is bounded on the west by the Moorings Bay flood shoal and on the east by private docks. As

Table 5 shows there is typically only a small volume contained in these segments with the South Channel

accumulating 50 cubic yards in the past 11 months and with only 197 cubic yards available for dredge

above the template. The east channel has even less volume above the template with 170 cubic yards and

actually had a net loss of material this year.

Table 5: Moorings Bay East Channel Volumes

Segment Stations

Dredge

Cut

NGVD29

Dredge

Cut

NAVD88

2013

Volume

Above

DT (cy)

2012

Volume

Above

DT (cy)

2012-

2013

Delta

2005

Post-Con

vs 2013

(cy)

Non-

Dredge

Probable

Rock

(cy)

South

Channel

4+85 to

6+78 -7.0 -8.3 197 149 48 197 0

East

Channel

11+35 to

17+51 -7.0 -8.3 170 172 -2 170 0

Subtotal: 367 321 46 367 0

IV. CONCLUSIONS & RECOMMENDATIONS

Doctors Pass has a typically been dredged on a 3-4 year rotation with the last dredge event occurring in

2009. This would be the year for another maintenance dredge project based on that cycle and the volume

available within the dredge template (Table 6). Table 6 indicates there is approximately 36,872 cubic

11

yards of sediment that can be dredged and placed on the beach in the permitted area south of Doctors Pass

from R-58A to R-62 (permit pending).

Table 6: Volume Summary Within the Dredge Template

Volume Summary

2013

Volume

Above DT

(cy)

2012

Volume

Above DT

(cy)

2012-

2013

Delta

2005 Post-

Con vs 2013

(cy)

Non-

Dredge

Probable

Rock (cy)

Total Volume Above

Dredge Template: 59,691 52,269 7,422 36,872 22,819

Figures 3, 4 & 6 also show that shoaling at Station 2+50 in the Settling Basin, Station 8+00 in the West

Entrance Channel and Station 1+00 in the Moorings Bay West Channel are affecting navigation. As noted

in the hydrographic survey section, MLLW is 2.3 feet above NAVD88 therefore these figures show that

at low tide some shoaled areas may have less than three feet of water. The entire segment may not require

dredging and Figure 7 shows the areas where sediment has accumulated over 1 foot above the template.

Figure 7: Differential Contour Map

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Atkins recommends completing a maintenance dredge project for the Settling Basin, West Entrance

Channel, Turning Basin and West Channel in Moorings Bay. Also it is recommended to continue the

annual monitoring of the Settling Basin, Entrance Channel, Turning Basin and Moorings Bay Channels

should be continued in the future to determine a rate of infill for future use and permit compliance.

13

V. REFERENCES

Atkins, Doctors Pass – 2011 Engineering Monitoring Report, August 2011.

Coastal Planning & Engineering, Inc., Wiggins and Doctors Passes 2009 Maintenance Dredging Post-

Construction Report, July 2009.

Coastal Planning & Engineering, Inc., North County Passes: Wiggins, Doctors, and Clam Passes 2010

Engineering Monitoring Report, October 2010.

Humiston & Moore, Inc., Doctors Pass Maintenance Dredging 2012 Three-Year Post Construction

Monitoring Summary, August 2012.