State of Yorktown

STATE OF YORKTOWN BEACH

November 2006

State of Yorktown Beach2006

Donna A. MilliganC. Scott Hardaway, Jr.

Kevin O’BrienChristine A. Wilcox

A report obtained under contract with York County, Virginia

Shoreline Studies ProgramVirginia Institute of Marine Science

School of Marine ScienceCollege of William & MaryGloucester Point, Virginia

November 2006

ShorelineStudies

ProgramVIMS

i

Table of Contents

Table of Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i

List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i

1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2 METHODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.1 Site Surveying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.2 Aerial Photo Geo-Referencing and Mosaicking . . . . . . . . . . . . . . . . . . . . . . . . . . 2

3 RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

4 CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

5 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

APPENDIX AGround photos taken in April and May 2006

APPENDIX BYorktown Beach Planform Survey Plots Spring 2006

APPENDIX CYorktown Beach Cross-Sectional Profile Plots 2003-2006

List of Figures

Figure 1. Location of Yorktown Public Beach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Figure 2. The survey baseline for Yorktown’s main recreational beach . . . . . . . . . . . . . . . 6Figure 3. The survey baseline for the breakwaters near Yorktown Creek . . . . . . . . . . . . . . 7Figure 4. Distance to MHW from the baseline between profiles 5 and 22 . . . . . . . . . . . . . . 8Figure 5. Georectified 2005 aerial photos and digitized mean high water along Yorktown’s

main recreational beach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Figure 6. Georectified 2005 aerial photos and digitized mean high water along Yorktown’s

entire shore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

1

1 INTRODUCTION

The Yorktown Public Beach is located on the south side of the York River at Yorktown,Virginia (Figure 1). Recently, it has undergone dramatic transformation with the construction offloating piers, upscale restaurants and shops, parking garage, and additional shore managementstructures. The main recreational beach is now about 1,600 feet in length. A new section ofbeach and breakwaters is located upstream of the main recreational shore; this project area is1,500 ft long which includes property owned by the Waterman’s Museum. The middle sectionof the shoreline downriver of the Route 17 Coleman Bridge, where the floating piers are located,was surveyed but is not part of the analysis since little sand occurs in that area.

Historically, the beach was a product of erosion of nearby sandy upland banks and thelittoral transport system. Over the years, the beaches along the waterfront began to narrow as thenatural sediment supply was depleted by hardening of the updrift shorelines and were easilyoverwashed in storms and had continually eroded. Since 1978, various projects have taken placealong Yorktown’s shoreline in order to abate erosion, provide a recreational beach, and minimizedamage to the upland during storms. Between 1994 and 2004, seven breakwaters with beach fillwere installed along the shoreline. These structures have created a stable beach planform alongthe main recreational beach that was designed to withstand a 50-yr storm event. The shops andpiers were begun in 2004 which required modification to the structures along that section ofshore. The additional breakwaters upriver of the Coleman Bridge were constructed in early 2005as was a structure downriver of the pier at the end of Comte de Grasse Street. These structuresare shown in ground photos taken in April and May 2006 which are shown in Appendix A. Anadditional breakwater with pipes to stabilize the flow of Yorktown Creek was constructed inJune 2006.

2 METHODS

2.1 Site Surveying

Shoreline Studies personnel from VIMS began monitoring the beach at Yorktown in thespring of 1985. Through various phases of project installation, the baseline and methodolgy ofdata collection and reduction have changed. For additional information, see Milligan et al.(1996 and 2005). Beginning in 2003, new methodologies were established for surveying thebeach. The Trimble 4700 Real-Time Kinematic Global Positioning System (RTK-GPS) wasused to set site control and acquire beach and shore data. The 4700 receiver utilizesdual-frequency, real-time technology to obtain centimeter accuracy in surveying applications. Inaddition, a Trimble 5600 Robotic Total Station was used to acquire data in the nearshore. Thecombination of these new instruments allows for a more detailed mapping of the beach andnearshore in a shorter amount of time.

One shoreline and nearshore survey was performed at Yorktown in the spring of 2006(April/May). In addition, a small section of shore (profiles 32-35) was surveyed in July 2006 tocapture the installation of the new breakwater at Yorktown Creek. The planform surveys areshown in Appendix B.

2

The RTK-GPS base station benchmark was pre-set with a 2-hour occupation. These datawere processed through the National Geodetic Survey’s On-line Positioning User Service(OPUS). All the survey data were based on this benchmark. In addition, 3-minute occupationswere taken at previously- established benchmarks in order to tie newer data to the older data aswell as determine survey error. The data is presented with a horizontal datum of State PlaneVirginia South, NAD83, international feet. The vertical datum is feet mean lower low water(MLLW), geoid99, as determined from nearby benchmarks publishing both NAVD88 andMLLW for the 1983-2001 tidal epoch.

Generally, the surveys included the following elements:1. Dimensions of the project structures including breakwaters and revetments;2. Mean High Water (MHW) and MLLW; survey extends to approx. the -4 ft

MLLW contour (Tidal Epoch 1983-2001).

2.2 Aerial Photo Geo-Referencing and Mosaicking

Recent color aerial photography was acquired by Shoreline Studies Program on 1September 2005. The images were scanned as tiff files at 600 dpi. ESRI ArcMap GIS(www.esri.com) software was used to georeference the images for Yorktown. The referencemosaic, the 2002 Digital Orthophotos from the Virginia Base Mapping Program (VBMP), isdivided into a series of orthophoto tiles and is stored in a Virginia south, state plane projection,in feet. The aerial photo tiles from VBMP for each site were mosaicked and re-projected to aUTM zone 18 North, NAD83 projection, in meters.

Rectifying requires the use of ground control points to register the aerial photography tothe reference images. Ground control points are points that mark features found in common onboth the reference images and on the aerial photographs that are being georeferenced. Controlpoints were distributed evenly to maintain an accurate registration without excessive amounts ofwarp and twist in the images. In addition, where possible, enough control points were placedwithin the area of interest, the shoreline and the breakwaters, to ensure accurate registration inthese key areas. Good examples of control points are permanent features such as manmadeobjects and stable natural landmarks. The standard in this project was to achieve a root meansquare (RMS) error under six for each aerial photo.

Georeferencing was done by using the Georeferencing Tool in ArcMap. First thereference image and the scanned aerial photograph are roughly aligned so that common pointscan be identified. Then, with the aid of the Georeferencing tool, ground control points are addeduntil the overall RMS error is less than six and the location of the aerial photograph closelymatches the location of the reference image. When an acceptable correspondence is achieved,the aerial photograph is saved as a rectified image. All the rectified images were then mosaickedusing the mosaic tool in ERDAS Imagine(http://www.gis.leica-geosystems.com/Products/Imagine/).

3

3 RESULTS

Figure 2 and 3 show the baseline and cross-sectional profiles used in this analysis forboth the main recreational area and the Yorktown Creek breakwaters. The plots of each profileare shown in Appendix C. Relatively small changes occurred in the cross-sectional profilesalong the main recreational shore. On the downriver end where the construction of the newbreakwater took place, an increase in sand in the nearshore is shown by the cross-sectionalprofiles. Volume change analysis between January 2005 and May 2006 agrees. Betweenprofiles 6 and 22, the beach above MLLW gained about 530 cy, while the nearshore gainedabout 220 cy mostly in the downriver section.

Distance to MHW (defined as +2.5 ft MLLW) from the baseline is commonly plotted toshow the movement of the subaerial beach (Figure 4). In general, the position of MHWremained relatively stable between January 2005 and May 2006. Small increases riverwardoccurred along much of the beach except directly behind breakwater 5. Figure 5 shows theposition of MHW on geo-rectified aerial photos taken on 1 September 2005. As shown in theprofile analysis, MHW is relatively stable with small increases over time. Figure 5 also showsthe change in shoreline due to the construction of the downriver breakwater (number 7). Prior toit’s construction, MHW was close to the Colonial National Historical Park’s road.

Figure 6 shows the entire project area on a geo-rectified aerial photo. One of the originalseven breakwaters on the downriver section of shore is not labeled since it does not function as abreakwater because one of the floating piers goes through it. The breakwater at YorktownCreek had not been constructed at the time of the photo and is shown in it’s approximatelocation. Profiles 32-35 (Appendix B) show the impact of it’s construction on the shore. Profiles 32 and 35 lost sand in the nearshore where the Creek’s ebb tidal delta had existed priorto construction of the breakwater and piping of the Creek. Appendix A shows ground photos ofthe delta.

4 CONCLUSIONS

Yorktown’s waterfront has been enhanced with many shore protection structuresenhancing the recreational opportunities along this stretch of shore. These structures havecreated a stable environment by maintaining a protective beach. Little natural change occurredto the site between January 2005 and May 2006.

4

5 REFERENCES

Milligan, D.A., C.S. Hardaway, Jr., and G.R. Thomas, 1996. Public Beach Assessment Report,Yorktown Public Beach, Yorktown, Virginia. Technical Report. Virginia Institute ofMarine Science, College of William & Mary, Gloucester Point, Virginia.

Milligan, D.A., C.S. Hardaway, Jr., Linda M. Meneghini, George R. Thomas, Christine A.Wilcox, 2005. Yorktown Beach 2003-2005 with Hurricane Isabel Impacts. TechnicalReport to York County. Virginia Institute of Marine Science, College of William &Mary, Gloucester Point, Virginia.

YorkRiverR

t.17

Colonial

National

Historical

ParkWay

Rt. 238

N

1”=4000’

Figure 1. Location of Yorktown Public Beach.

Photo Date

26 Aug 2004

Photo Date:1 September 2005 Photo Date:

1 September 2005

76 30’00”o2,580,000 ft

Cole

man

Bri

dge

Atlant

icO

ce

an

Ce

hsa

pea

ke

Bay

Potomac

Rappahannock

York

James

Site

Yorktown Creek ReachMain Recreational Beach Reach

5

Figure 2. The survey baseline for Yorktown’s main recreational beach (survey date is May 2006).

Bw

3

Bw

4

Bw

5

Bw

6

Bw

7

6

Yorktown Creek Waterman’s Museum

Rt. 17

Coleman

Bridge

Figure 3. The survey baseline for the breakwaters near Yorktown Creek (survey date is May 2006).

Bw8Approximate

Bw9

Bw10

Bw11

Bw12

7

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600

20

40

60

80

100

120

140

160

Figure 4. Distance to MHW from the baseline between profiles 5 and 22.

5 6 7 86.5 9 10 11 12 13 14 15 16 17 18 19Bw3

Bw4 Bw5

Bw6

Bay C

Bay D

Bay E

21 22

Bw7

Jul 2004

Jan 2005

yMa 2006

Bay F

Dis

tance

toM

HW

from

the

baselin

e(f

t)

Distance alongshore from Profile 5 (ft)

milligan

Text Box

8

26 August 2004

1 September 2005

Figure 5. Georectified 2005 aerial photos and digitized mean high water along Yorktown’s main recreational beach.

Bw2

Bw3

Bw4

Bw5

Bw6

Bw7

Bay B

Bay C

Bay D

Bay E

Bay F

York River

Water St.

Photo Date: 1 Sep 2005

COLO Picnic Area Road

Floating Pier

9

26 August 2004

1 September 2005

Figure 6. Georectified 2005 aerial photos and digitized mean high water along Yorktown’s entire shore.

Bw2Bw3

Bw4Bw5

Bw6

Bw7

York River

Photo Date: 1 Sep 2005

York River

Bw8

Bw10

ApproximateBw9

Bw11

Bw12

Rt. 17ColemanBridge

Floating piers

Yorktown Creek Mouth

Watermans

Museum

Water St.

Bw1

10

APPENDIX AGround Photos taken in April and May 2006

Looking upriver from the Yorktown pier

A1

Looking upriver from the Yorktown pier

Looking downriver from the Yorktown pier at the new breakwater

A2

Looking downriver at the revetment and floating piers

Under the Rt. 17 Coleman Bridge

A3

Backshore plantings in front of the Watermans Museum

Backshore plantings on the upriver section of beach

A4

Backshore from Breakwater 10

Yorktown Creek section of shore

A5

Yorktown Creek tidal delta

Yorktown Creek tidal delta

A6

APPENDIX BYorktown Beach Planform Survey Plots

2006

milligan

Text Box

B1

milligan

Text Box

B2

APPENDIX CYorktown Beach Cross-Sectional Profile Plots

2003-2006

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6_2003Jun30 6_2003Sep25_PI 6_2003Dec18

6_2004Jul27 6_2005Jan5 6_2006May24

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6.5_2004Jul27 6.5_2005Jan5 6.5_2006May24

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Profile 6

Profile 6.5

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8_2004Jul27 8_2005Jan5 8_2006May24

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Profile 7

Profile 8

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10_2004Jul27 10_2005Jan5 10_2006May24

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Profile 9

Profile 10

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11_2003Jun30 11_2003Sep25_PI 11_2003Dec18

11_2004Jul27 11_2005Jan5 11_2006May24

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12_2003Jun30 12_2003Sep25_PI 12_2003Dec18

12_2004Jul27 12_2005Jan5 12_2006May24

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MHW

MLLW

Profile 11

Profile 12

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13_2003Jun30 13_2003Sep25_PI 13_2003Dec18

13_2004Jul27 13_2005Jan5 13_206May24

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14_2003Jun30 14_2003Sep25_PI 14_2003Dec18

14_2004Jul27 14_2005Jan5 14_2006May24

MHW

MLLW

MHW

MLLW

Profile 13

Profile 14

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15_2003Jun30 15_2003Sep25_PI 15_2003Dec18

15_2004Jul27 15_2005Jan5 15_2006May24

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16_2003Jun30 16_2003Sep25_PI 16_2003Dec18

16_2004Jul27 16_2004Jan5 16_2006May24

MHW

MLLW

MHW

MLLW

Profile 15

Profile 16

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17_2003Jun30 17_2003Sep25_PI 17_2003Dec18

17_2004Jul27 17_2005Jan5 17_2006May24

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18_2003Jun30 18_2003Sep25_PI 18_2003Dec18

18_2004Jul27 18_2005Jan5 18_2006May24

MHW

MLLW

MHW

MLLW

Profile 17

Profile 18

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19_2003Jun30 19_2003Sep25_PI 19_2003Dec18

19_2004Jul27 19_2005Jan5 19_2006May24

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21_2006May24

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MLLW

Profile 19

Profile 21

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22_2006May24

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Yorktown Upriver Section

30_2006May24

MHW

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Profile 22

Profile 30

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31_2006May

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32_2006May 32_2006Jul10

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Profile 31

Profile 32

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34_2006May 34_2006Jul1-

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Profile 33

Profile 34

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36_2006May

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35_2006May

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Profile 35

Profile 36

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37_2006May

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38_2006May

Profile 37

Profile 38

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40_2006May24

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39_2006May24

Profile 39

Profile 40

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Documents

State of Yorktown