ERDC/CHL TR-20-14 

Regional Sediment Management (RSM) Program

Post-Project Monitoring of a Navigation 

Solution in a Dynamic Coastal Environment, 

Smith Island, Maryland 

Year One of Post-Project Monitoring 

Coastal and Hydraulics Laboratory 

Jacqueline A. Seiple, Christopher C. Spaur, Safra Altman, 

Matt T. Balazik, Luis E. Santiago, Daniel O. Mensah, 

Warunika G. Amarasingha, Steven M. Golder, and Andrew W. Payson

July 2020

Approved for public release; distribution is unlimited.
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Regional Sediment Management (RSM) Program ERDC/CHL TR-20-14 

July 2020 

Post-Project Monitoring of a Navigation 

Solution in a Dynamic Coastal Environment, 

Smith Island, Maryland

Year One of Post-Project Monitoring

Safra Altman, Matthew T. Balazik

Coastal and Hydraulics Laboratory

US Army Engineer Research and Development Center

3909 Halls Ferry Road

Vicksburg, MS 39180-6199

Jacqueline A. Seiple, Christopher C. Spaur, Luis E. Santiago, Daniel O. Mensah, 

Warunika G. Amarasingha, Steven M. Golder, and Andrew W. Payson

US Army Corps of Engineers, Baltimore District

2 Hopkins Plaza

Baltimore, MD 21201

Final report

Approved for public release; distribution is unlimited.

Prepared for US Army Corps of Engineers

Regional Sediment Management Program 

Vicksburg MS 39180

US Army Corps of Engineers, Baltimore District

Baltimore MD 21201

Under Project No. 484149, “RSM NAB Smith Island”
ERDC/CHL TR-20-14 ii

Abstract

In 2018, jetties and a sill were constructed by the US Army Corps of 

Engineers (USACE) adjacent to the Sheep Pen Gut Federal Channel at

Rhodes Point, Smith Island, Maryland. These navigation improvements 

were constructed under Section 107 of the Continuing Authorities 

Program. Material dredged for construction of the navigation structures 

and realignment of the channel were used to restore degraded marsh.

Following construction and dredging, 1 year of post-project monitoring 

was performed to evaluate the performance of navigation improvements 

with respect to the prevention of shoaling within the Sheep Pen Gut 

channel, shoreline changes, and impacts to submerged aquatic vegetation 

(SAV). Given the short period of record after the completion of the 

navigation improvements, it was difficult to draw conclusions regarding 

stability of the channel, structures, and shoreline. Therefore, this report 

documents methodology and baseline conditions for monitoring, except 

for SAV, which was found to be potentially impacted by construction.

A second year of monitoring was funded by the USACE Regional Sediment 

Management Program for fiscal year 2020. Findings can be used to inform 

plan formulation and design for USACE navigation projects by 

illuminating considerations for placement of structures to prevent 

shoaling and by informing SAV management decisions.

DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. 

Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. 

All product names and trademarks cited are the property of their respective owners. The findings of this report are not to 

be construed as an official Department of the Army position unless so designated by other authorized documents.

DESTROY THIS REPORT WHEN NO LONGER NEEDED. DO NOT RETURN IT TO THE ORIGINATOR.
ERDC/CHL TR-20-14 iii

Contents

Abstract.................................................................................................................................... ii

Figures and Tables..................................................................................................................iv

Preface......................................................................................................................................v

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

Background..................................................................................................................1

Objectives.....................................................................................................................3

Approach......................................................................................................................4

2 Data Collection and Monitoring.....................................................................................5

Bathymetric and topographic data.............................................................................5

Sediment sampling......................................................................................................7

Structural surveys......................................................................................................10

Submerged aquatic vegetation (SAV) monitoring....................................................11

3 Observations...................................................................................................................16

Channel stability ........................................................................................................16

Shoreline change...................................................................................................... 18

Sediment transport .................................................................................................. 20

SAV..............................................................................................................................21

4 Conclusions and Recommendations...........................................................................26

Conclusions............................................................................................................... 26

Recommendations ................................................................................................... 26

References.............................................................................................................................28

Unit Conversion Factors.......................................................................................................29

Acronyms and Abbreviations...............................................................................................30

Report Documentation Page
ERDC/CHL TR-20-14 iv

Figures and Tables

Figures

Figure 1. Location of Rhodes Point Navigation Project (preconstruction channel 

is shown).........................................................................................................................................2

Figure 2. Aerial view of the completed jetties and sill at the Rhodes Point 

Navigation Project in June 2018, prior to dredging of the channel (photo credit: 

Coastal Design & Construction, Inc)............................................................................................3

Figure 3. February 2019 grab sample locations.......................................................................9

Figure 4. June 2019 grab sample locations. ...........................................................................10

Figure 5. Crew setting up transects for future analysis of structural stability. ....................11

Figure 6. Top: SAV sampling quadrat. Bottom: Example of quadrat with 15

squares having vegetation present, resulting in 60% coverage. ..........................................13

Figure 7. SAV monitoring locations: North Area (black rectangles), South Area (red 

rectangle), MDDNR survey area (blue rectangle), and reference area (green 

rectangle)......................................................................................................................................14

Figure 8. Changes in channel elevation for pre-dredge conditions (comparison of 

November 2017 to June 2018) and post-dredge conditions (comparison of 

February 2019 to July 2019)......................................................................................................17

Figure 9. Shoreline changes from 1849 to present. ..............................................................19

Figure 10. Shoreline elevation differences between 2015 and 2019.................................20

Figure 11. Locations of Areas X, Y, and Z described in the text.............................................21

Figure 12. SAV survey results within the South Area in June 2019. The 

yellow-shaded polygon is the 2016 SAV coverage; the grey-shaded polygon is the 

2017 coverage, and the blue-shaded polygon is the where SAV occurred in both 

2016 and 2017. ...........................................................................................................................24

Figure 13. SAV survey results within the reference area. The yellow-shaded 

polygon is the 2016 SAV coverage, the grey-shaded polygon is the 2017

coverage, and the blue-shaded polygon is where SAV occurred in both 2016 and 

2017...............................................................................................................................................25

Tables

Table 1. Dates and sources of bathymetric survey data used for comparisons. ..................6

Table 2. Maps generated to compare bathymetric conditions of the channel and 

adjacent areas. ..............................................................................................................................7

Table 3. Sediment volume in the Sheep Pen Gut channel above 1.8 m. ............................18
ERDC/CHL TR-20-14 v

Preface

This study was conducted for the US Army Corps of Engineers (USACE),

Regional Sediment Management (RSM) Program, and the USACE 

Baltimore District (NAB), under Project No. 48419, “RSM NAB Smith 

Island.” The USACE National RSM program manager at the time of 

publication of this report was Dr. Katherine Brutsché. 

The work was performed by the Planning, Engineering, and Operations

Divisions of the USACE NAB and the US Army Engineer Research and 

Development Center, Coastal and Hydraulics Laboratory (ERDC-CHL)

and Environmental Lab (ERDC-EL) Wetlands and Coastal Ecology 

Branch. Ms. Patricia M. Tolley was Chief, Wetlands and Coastal Ecology 

Branch, and Mr. Mark Farr was Chief, Environmental Laboratory 

Division. At the time of publication of this report, COL John T. Litz was 

the NAB Engineer. The Deputy Director of ERDC-CHL was Mr. Jeffrey R. 

Eckstein, and the Director was Dr. Ty V. Wamsley.

The Commander of ERDC was COL Teresa A. Schlosser, and the Director 

was Dr. David W. Pittman. 
ERDC/CHL TR-20-14 1

1 Introduction

Background

Smith Island is a historically significant group of small islands in the 

Chesapeake Bay, primarily in Maryland. Located in Somerset County, 

Maryland, Smith Island is home to three small villages, Rhodes Point, 

Tylerton, and Ewell. Many of the residents of the island rely on the use of 

the Sheep Pen Gut federal navigation channel for their livelihoods related 

to fishing or tourism, due to easy access to the Bay. Sheep Pen Gut is a 

natural waterway, modified by decades of dredging. Prior to construction 

of the navigation improvements at the channel near Rhodes Point, the 

channel in-filled at rates of up to 1 m/yr* due to the energy of the open Bay 

and substantial littoral drift along the shoreline of the island. In addition, 

given exposure to the Bay, erosion of the shoreline was occurring at a rate 

of up to 2.5 m/yr. In 2017, Somerset County constructed segmented 

breakwaters along the Bay shoreline to reduce erosion.

In June 2018, the US Army Corps of Engineers (USACE) in cooperation 

with the Maryland Department of Natural Resources (MDDNR), Somerset 

County, and the Maryland Department of Housing and Community 

Development completed construction of navigation improvements 

adjacent to the Sheep Pen Gut Federal channel at Rhodes Point (Figure 1).

This project was completed under Section 107 of the Continuing 

Authorities Program. The navigation improvements included the

construction of two jetties adjacent to the Sheep Pen Gut channel to 

prevent shoaling within the channel and a segmented stone 

breakwater/sill constructed along the shoreline south of the jetties 

(Figure 2). The sill was constructed to protect the shoreline and provide

containment for sediment excavated during construction of the structures 

and dredged from the Sheep Pen Gut channel.

 

* For a full list of the spelled-out forms of the units of measure used in this document, please refer to US 

Government Publishing Office Style Manual, 31st ed. (Washington, DC: US Government Publishing 

Office 2016), 248-52, https://www.govinfo.gov/content/pkg/GPO-STYLEMANUAL-2016/pdf/GPOSTYLEMANUAL-2016.pdf.
ERDC/CHL TR-20-14 2

Dredging of the Sheep Pen Gut channel occurred in November 2018. The

dredged and excavated material was placed to beneficially restore 

previously existing wetlands behind the newly constructed stone sill.

Project structures were placed to avoid impacts to existing submerged 

aquatic vegetation (SAV) as SAV is a vital living resource in the 

Chesapeake Bay. Marsh vegetation was planted at the placement site in 

June 2019, with planting of the higher elevation hummock area scheduled 

for fall 2019.

Figure 1. Location of Rhodes Point Navigation Project 

(preconstruction channel is shown). 
ERDC/CHL TR-20-14 3 

Figure 2. Aerial view of the completed jetties and sill at the Rhodes Point Navigation 

Project in June 2018, prior to dredging of the channel (photo credit: Coastal Design & 

Construction, Inc). 

Objectives 

This technical report provides the results of 1 year of post-project 

monitoring of these recently constructed navigation structures. The 

primary purpose of this monitoring was to evaluate the performance of the 

navigation improvements, including jetties and a segmented sill, with 

respect to the prevention of shoaling within the Sheep Pen Gut federal 

navigation channel, shoreline changes, and impacts to SAV. Shoreline 

response to coastal structures, including scour and deposition, will be 

evaluated to improve design criteria and methodology for the placement of 

navigation structures in dynamic coastal environments. Findings from the

monitoring will inform future plan formulation and design for USACE

navigation projects by illuminating potential considerations for placement 

of structures to prevent shoaling, as well as by informing SAV 

management decisions and the consideration of indirect impacts of 

projects on SAV. 
ERDC/CHL TR-20-14 4

Approach

The following data were collected in support of this project. Methodology 

and observations are described in Section 2.

• Bathymetric surveys

• Topographic and shoreline surveys

• Structural surveys

• Sediment grain size analyses

• SAV occurrence data
ERDC/CHL TR-20-14 5

2 Data Collection and Monitoring

Bathymetric and topographic data

Bathymetric survey data were collected for two sampling events in February 

and July 2019. In addition, pre-construction survey data were compiled, 

which included data collected since 1996. The survey data were evaluated to 

discern whether the structures are acting as intended to reduce 

sedimentation within the Sheep Pen Gut channel and also to determine if 

the jetties or sill are inducing sedimentation or scouring within the channel 

or adjacent to the structures. The extent of the surveyed area is consistent 

with the surveyed and modeled area for the Rhodes Point Section 107 

Navigation Project. Topographic data were collected in February and July 

2019 along the shoreline. These data were compared to pre-construction 

survey data to evaluate changes to the shoreline.

Topographic survey data were processed into geographic information 

systems (GIS) format to assist in the evaluation of bathymetric and 

topographic data. Points were converted using the Display XY tool and 

exported to an ArcGIS shapefile as a point dataset. The source datum for 

the survey data is Maryland State Plane, NAD 1983 (US feet), for the 

horizontal units and the North American Vertical Datum of 1988 (feet) for 

the vertical datum. The survey data were converted into a triangulated 

irregular network (TIN) dataset using the Create TIN tool in ArcGIS Pro.

Standard settings are used (No Constrained Delaunay). To avoid 

interpolation in areas with no data, an outer boundary is created by using 

the TIN Edge tool to create a shapefile of the structure of the triangles.

Lines interpolated between data points were determined by identifying the 

maximum distance between points using the Near tool. Lines in triangles 

exceeding 30 m were deleted from the TIN Edge resulting in an area 

approximately representative of the survey data. A polygon with a 1.5 m

buffer was created around the network to constrain the TIN.

The Edit TIN tool is used to create the outer boundary of the TIN surface 

using the polygon shapefile as an outer boundary and using the “Hard 

Line” type. This limits interpolation outside of the polygon area. TIN 

surfaces were converted into raster using the TIN to Raster tool to allow 

for the use of mathematical functions in the Raster Calculator when 

appropriate. The March 2018 survey data and the April–June 2015 

topographic survey data were both converted using this tool. 
ERDC/CHL TR-20-14 6

Some topographic survey elevations were collected in the vertical datum 

NAVD 88, whereas all project data is in Mean Lower Low Water (MLLW) 

referencing the tidal epoch 1983–2001 at Ewell, Maryland, which is also 

the project construction datum. These data were converted by using the 

Raster Calculator to adjust elevations to MLLW. The following function is 

applied in the Raster Calculator, using the datum diagram on the Rhodes 

Point Section 107 Navigation Project as-builts below:

NAVD88 + 1.04’ = MLLW.

The March 2019 survey was compared against baseline conditions in the 

topographic survey completed in April–June 2015 using the Raster 

Calculator. Topographic elevation differences between the surfaces were 

calculated, and maps were generated showing the elevation differences 

between the raster layers (e.g., Figure 10).

Bathymetric surveys were collected by USACE, the MDDNR, and by the 

subcontractor Waterways Surveys & Engineering Ltd. on behalf of Coastal 

Design & Construction, Inc. (Table 1). The available bathymetric survey 

data are summarized below. 

Table 1. Dates and sources of bathymetric survey data used for comparisons. 

Date Source Project Phase Description 

19 May 2015 & 

11 June 2015 USACE

Planning Phase (baseline 

conditions) Full bay and channel

02 November 

2017 Maryland DNR Pre-Construction Survey Partial bay and channel

07 June 2018 Maryland DNR Post-Construction of Jetties Channel only

25 September 

2018

Waterway Surveys & 

Engineering Ltd. Pre-Dredge Survey Partial bay and channel

14 November 

2018

Waterway Surveys & 

Engineering Ltd. Post-Dredge Survey Partial bay and channel

26 February 

2019 USACE Monitoring (+3 months) Full bay and channel

10 July 2019 USACE Monitoring (+7 months) Full bay and channel

Bathymetric survey data were available as multipoints in XYZ, txt, and 

drawings files and were imported into ArcGIS Pro. The datasets were then 

processed into TIN surfaces following the procedures detailed for the 

topographic survey data. Bathymetric surveys were compared in TIN 
ERDC/CHL TR-20-14 7

format using the Surface Difference tool in ArcGIS Pro. Table 2 shows the 

comparisons that were completed using the existing bathymetric surveys 

to assess the change in depth in the surveyed channel and near-shore 

areas adjacent to the completed project. Two outputs are specified in this 

tool: a vector shapefile that illustrates areas above, below, and the same as 

the previous elevation (i.e., the difference between the input and the 

reference surface) and an elevation difference TIN. The vector shapefile 

also includes volumetric differences between the two bathymetric surveys 

for areas where both surveys intersect. Maps were generated showing the 

elevation differences between the bathymetric surveys and the vector 

surface difference layer for a simplified display (see Figure 8 for an 

example of these comparisons).

Table 2. Maps generated to compare bathymetric conditions of the channel and adjacent areas. 

Input Surface Reference Surface Description of Comparison 

June 2018 November 2017 Post-construction of jetties to pre-construction of jetties

September 2018 May-June 2015 Pre-dredge conditions to baseline conditions

July 2019 May-June 2015 Monitoring survey to baseline conditions

July 2019 June 2018 Monitoring survey to post-construction of jetties

July 2019 September 2018 Monitoring survey to pre-dredge conditions

July 2019 February 2019 Monitoring surveys (7 months to 3 months post-dredging)

Sediment sampling

Sediment samples were collected prior to this study for the design of the 

Rhodes Point Section 107 Navigation Project. These pre-construction data 

were considered for this evaluation and included data from samples 

collected in October 2001, August 2008, and June 2015, before the 

navigation improvements were constructed. Data collected as a part of this 

monitoring program are referred to as post-construction samples and were 

collected in February 2019 and June 2019. Sample locations and soil 

characteristics for pre and post-construction samples are stored in a 

project database and are available upon request.

Pre-construction data. A field investigation was conducted in October 

2001. Drill holes were accomplished by the Standard Penetration Test 

procedure. Eight borings were completed, and all the borings were 

completed to a depth of 8 m below Bay bottom. However, only the surficial 

sediment type was analyzed for the 2019 RSM study and are included in 

this technical report.
ERDC/CHL TR-20-14 8

August 2008 data: Drill holes were accomplished by the Standard 

Penetration Test procedure. Fourteen borings were completed, and the 

depths of the borings varied from 1.8 m to 7.6 m below Bay bottom. 

However, only the surface soil type was analyzed for the RSM study and 

included in this technical note.

June 2015 data: Sixteen grab samples were collected in June 2015. The 

samples were visually examined and were analyzed using mechanical sieve 

tests for each sample. Material was classified using ASTM D 2487.

Post-construction data. In February 2019, 29 grab samples were 

collected. All 29 samples were visually inspected, and 25 samples were 

analyzed using mechanical sieve tests. Material was classified by ASTM D 

2487. Figure 3 shows sample locations for February 2019. 

In June 2019, 40 grab samples were collected. All samples were visually 

inspected, and 25 samples were analyzed using mechanical sieve tests for 

each sample. Material was classified by ASTM D 2487. Figure 4 shows 

sample locations or June 2019.
ERDC/CHL TR-20-14 9

Figure 3. February 2019 grab sample locations. 
ERDC/CHL TR-20-14 10

Figure 4. June 2019 grab sample locations. 

Structural surveys

Two civil surveys of the jetty and sill structures were originally planned for 

February and July 2019 to assess the stability of the navigation project 

structures. However, due to extreme weather conditions and safety 

concerns in the winter of 2019, it was not possible to access the structures 

in early 2019. In June 2019, a three-man team set up transects measuring 

at stations every 61 m along the centerline of the north and south jetty and 

along a portion of the sill (Figure 5). Points were not taken on a portion of 

the sill because those segments were unreachable due to the tide, and 

other parts were submerged. 
ERDC/CHL TR-20-14 11

Points were taken near the waterline, at approximately mid slope, at the 

top of slope, on the left and right sides, and on the jetty centerline. Large 

sturdy rocks were selected for the point locations, and most points (except 

those that were near or in the water or had algae on top of them) were 

spray marked. Photos of each marked point was taken. For each point, the 

following were recorded: station, point location along the transect, point 

elevations, photo number, and the approximate latitude and longitude of 

the photos.

Figure 5. Crew setting up transects for future analysis of structural stability. 

Submerged aquatic vegetation (SAV) monitoring

SAV habitat occurrence in the Chesapeake Bay is largely governed by the 

amount of light that reaches the plants. This is related to water depth and 

clarity, with occurrence also influenced by bottom sediment character 

(sand versus mud or peat). SAV is monitored annually by the Virginia 

Institute of Marine Science (VIMS) in the Chesapeake Bay, which 

constitutes perhaps the best long-term annual record of SAV monitoring 

in the world. VIMS mapping is based on aerial surveys supplemented by 

ground-truthing. In addition to this record, MDDNR independently 

sampled the project area in 2015. SAV beds in the Rhodes Point area 

contain two species: Ruppia maritima and Zostera marina.
ERDC/CHL TR-20-14 12

The placement of the structures at Rhodes Point navigation improvement 

project avoided direct SAV habitat impacts by positioning the jetties and 

channel improvements out of mapped SAV areas. Because it was believed 

that the jetties and channel could alter patterns of bottom sedimentation 

and erosion, and consequently water depths, monitoring of changes to 

SAV occurrence was desirable. Changes in water depths could also be 

affected by escape of placed dredged material and/or reduced erosion 

through placement of the sill. Barge impacts to the bottom during 

construction could also impact SAV.

SAV monitoring was conducted in June 2019 to understand whether the 

channel alignment had any impacts on Ruppia maritima and Zostera 

marina coverage in the project area. Some potential natural factors and 

anthropogenic stressors that could impact SAV within the project area 

include precipitation and nutrient input, predation and biological 

disturbance (e.g., due to cownose rays or mute swans), physical 

disturbance or displacement due to barge bottom impacts or outwelling of 

placed material, and alteration of sedimentation, erosion, and turbidity 

patterns due to project implementation. 

Sampling was conducted during the growing season of both SAV species 

on June 24–25, 2019. SAV abundance was measured using a 0.5 m2

quadrat divided into twenty-five 10 × 10 cm squares (Figure 6). A grid cell 

was considered covered when at least one SAV shoot was located within 

the grid cell. Species coverage for each species and total coverage within a 

quadrat were determined by the number of cells each species occupied 

within the quadrat. Quadrat samples were taken at odd intervals of 

quadrat flips from the starting point. A global positioning system

coordinate was taken for each quadrat sample. In areas of completely 

uniform coverage along transects, quick visual scans were conducted to 

save time.
ERDC/CHL TR-20-14 13

Figure 6. Top: SAV sampling quadrat. Bottom: Example 

of quadrat with 15 squares having vegetation present, 

resulting in 60% coverage. 

Five stratified randomly selected transects perpendicular from shore were 

measured for SAV coverage within the project footprint: one north of the 

northern rock jetty, one south of the northern rock jetty, and three south 

of the southern rock jetty (Figure 7). The project footprint is considered to 

encompass the area where material was dredged, construction was carried 

out, and dredged material was placed for beneficial use. A transect 500 m 

south of the south jetty and outside of the project footprint was sampled as 

a reference location as it was assumed that it will be minimally impacted 

by the project. Each transect started at the shore edge and continued 

perpendicular from shore until water depth reached 1.5 m. SAV rarely 

grows at depths >1.1 m mean low water in this area of the Chesapeake Bay,

so sampling to a depth of 1.5 m should account for all SAV in the area.

0.5m
ERDC/CHL TR-20-14 14

Figure 7. SAV monitoring locations: North Area (black rectangles), South Area (red 

rectangle), MDDNR survey area (blue rectangle), and reference area (green 

rectangle). 

During the period of time in which surveys were conducted, daily tidal 

range did not exceed 0.37 m, and tidal ranges during sampling did not 

exceed 0.34 m referenced to MLLW. In addition to transect surveys, 50 

randomly selected points were sampled where SAV has occurred in the 

past based on previous aerial surveys conducted by the VIMS SAV survey.

These random points help account for sparse SAV coverage and provide a 

better estimate of coverage throughout the entire study area. Points 

sampled by MDDNR taken in August 2015, prior to project construction, 
ERDC/CHL TR-20-14 15

were resampled. These provide a previously sampled point within the area 

of likely project effects.

In addition to field sampling in the project vicinity, VIMS SAV mapping 

are used as an additional means to characterize the Rhodes Point beds, as 

well as to evaluate SAV performance regionally. The years 2017 and 2018 

were particularly wet years for the region. Fresh water inflow and nutrient 

loading may have driven heightened algal growth that could contribute to 

or even overshadow local factors. VIMS SAV mapping for 2019 was not 

available at the time this report was prepared.
ERDC/CHL TR-20-14 16

3 Observations

To evaluate change in conditions of the study area, the data must be put 

into the context of pre- and post-construction of the navigation 

improvements. The following timeline is provided for project construction: 

• Construction of the jetties and sill: January to June 2018

• Dredging of the Sheep Pen Gut Navigation Channel (to 6 ft depth):

November 2018

• Planting of the placement site low and high marsh elevations: June 

2019

• Planting of the placement site hammock elevations: September 2019 

(incomplete at time of study).

Channel stability

The following comparisons were completed using the existing bathymetric 

surveys to assess the change in depth in the channel and the surveyed 

near-shore areas adjacent to the completed project. Based on the timing of 

the surveys relative to construction, dredging, and post-project 

monitoring, the November 2017 to June 2018 comparison (pre-dredge) 

and the February 2019 to July 2019 (post-dredge) comparisons were 

determined to be the most useful.

Figure 8 shows comparison of the channel condition for two different 

time periods. The pre-dredge condition (top) is a comparison of the 

change in channel elevation for a time period prior to dredging 

(November 2017–June 2018). Although dredging had not yet occurred, 

the structures were completed in June 2018. For that period, most of the 

channel experienced a small amount of scouring, although within the 

interior of the channel, accretion is evident moving inland. The channel 

was dredged in November 2018. The bottom section of Figure 8 shows a 

post-dredge comparison of changes in channel condition, between 

February 2019 and July 2019. During this time, most of the channel is 

below the previous elevation, including the interior where scouring 

appears to have occurred. Some sediment build up appears present at the 

mouth of the channel. When evaluating the survey point data more 

closely, the change in elevation between February and July 2019 is a 

matter of a few inches at the most; therefore, additional time is needed to 

determine the post-construction change.
ERDC/CHL TR-20-14 17

Using a different methodology, evaluation of sediment volume within the 

channel (above 1.8 m depth) from channel cross-sections, indicates a 

similar trend (Table 3). As observed prior to the project and also during 

construction, sedimentation occurred in the channel in the years leading up 

to construction of the project (1998–2017). A survey done by MDDNR in 

June 2018 following completion of construction of the jetties, indicates a 

significant reduction of sediment in the channel. Note that surveys 

performed by MDDNR do not use the same methodology as bathymetric 

surveys conducted by USACE. However, the reduction in sediment is also 

evident in the survey done by the dredging contractor (Waterways) 

immediately before dredging (IBD). It is possible that bottom disturbance 

during construction, excavation of material to build the jetties, and/or selfscouring of the channel upon completion of the structures contributed to 

removal of sediment within the channel. This trend appears to continue 

following dredging completed in November 2018. From the volumes 

calculated, there is a substantial reduction of sediment within the channel 

following the after-dredge (AD) survey performed by the contractor, up to 

the first monitoring event in February 2019. Since February, conditions

within the channel above 1.8 m have been stable. 

Figure 8. Changes in channel elevation for pre-dredge conditions (comparison of 

November 2017 to June 2018) and post-dredge conditions (comparison of February 

2019 to July 2019). 
ERDC/CHL TR-20-14 18

Table 3. Sediment volume in the Sheep Pen Gut channel above 1.8 m. 

Agency (Survey Type) Month Year Volume (yd3) Volume (m3) 

USACE July 1998 5236.7 4003.7

USACE March 2008 7829.2 5985.9

USCAE June 2015 7564.5 5783.5

USACE (IBD*) November 2017 8793.5 6823.1

MDDNR June 2018 4016.4 3070.8

Waterways (IBD) September 2018 5780.8 4419.7

Waterways (AD**) November 2018 1926.0 1472.5

USACE (AD) February 2019 573.0 438.1

USACE July 2019 579.9 443.4

*IBD - Immediately before dredging

**AD - After dredge

Shoreline change

Existing and historical shoreline data were used to map shoreline change 

over time. The historical shoreline layers were already available in the 

Maryland State Plane, NAD 83, coordinate system from previous analyses 

completed from the project and from the Maryland Geological Survey 

(MGS 2000). The waterline points from the 2019 survey were extracted 

from the GIS data using the information in the attribute table populated 

by the field surveyors. A polyline shapefile and a new feature were created 

in an EDIT environment that links the points along the shoreline. Gaps in 

the survey data were kept in the waterline shapefile for consistency. A map 

was generated from the historical shoreline and the waterline shapefiles 

from the 2019 and 2015 surveys. This is shown in Figure 9, along with 

shoreline change over time using other available data. Note that tidal 

variation in this area may have an influence on the waterline at the time of 

survey, so observed variations likely reflect changes in geomorphology 

plus differing water levels.

As can be seen from the evaluation (Figure 9), shoreline has significantly 

changed in the study area from 1849 to the present. The length of the 

Sheep Pen Gut channel has shortened significantly due to shoreline 

erosion and its location has shifted to the southeast. Prior to the 

emplacement of the jetties, the federal navigation channel extended out of 

Sheep Pen Gut at the location of the jetties, but then took a sharp turn to 

the southwest, to reach deeper water in the Bay. A darker area can be seen 

in Figure 9, extending perpendicular from the end of the south jetty, which 
ERDC/CHL TR-20-14 19

is the former federal channel. Given the shoreline changes, that turn in the 

channel was no longer necessary to reach deep water when the Rhodes 

Point Section 107 Navigation Project was constructed.

Figure 9. Shoreline changes from 1849 to present. 

Topographic shoreline changes are shown in Figure 10, which compares 

the preconstruction shoreline (2015) to the shoreline post-dredge material 

placement (2019). Changes in elevation seen in the figure are largely due 

to the placement of dredged material behind the sill. In addition to the sill 

emplaced for the Rhodes Point Section 107 Navigation Project conducted 

by USACE, breakwaters were also constructed by Somerset County in 2017 

along the shoreline to the north and south of the USACE project, with 

material potentially placed behind those breakwaters.
ERDC/CHL TR-20-14 20

Figure 10. Shoreline elevation differences between 2015 and 2019. 

Sediment transport

The following observations were gained from the evaluation of the 

characteristics of the surface sediment samples pre and post-construction; 

however, with such a short period of record since dredging, it is difficult to 

draw conclusions based upon the data.

• Prior to construction, surface sediment outside of the channel was 

categorized as silt and clay; however, post-construction (after 

dredging) sediment is characterized as poorly graded sand (i.e., wellsorted) (Figure 11, Area Y and Z).

• Post-construction, material on the interior of the channel has become 

more silty, transitioning from poorly graded (i.e., well-sorted) sand 

during February 2019 to sandy silt in June 2019 (Figure 11, Area X).

• Based on the post-dredge bathymetric survey data comparison, the 

north side of the channel has gained material from February 2019 to 

July 2019 (Figure 8, post-dredge).

• Material has accumulated outside of the channel/jetty mouth from 

February 2019 to July 2019 (Figure 8, post-dredge).
ERDC/CHL TR-20-14 21

With such a short period of record and the dynamic nature of this 

environment, it is difficult to draw any conclusions from grain size 

analyses as the observed changes in grain size could be related to material 

accumulation or erosion. 

Figure 11. Locations of Areas X, Y, and Z described in the text. 

SAV

During the 2-day field survey, 376 quadrat points were sampled along with 

six quick visual scans covering approximately 200 m2 (Figure 7). Both 

Ruppia maritima and Zostera marina were observed during the survey.

Based on the VIMS aerial surveys, 290 of the 332 quadrat points 

overlapped where SAV had been recorded in 2016, 2017, or both years in 
ERDC/CHL TR-20-14 22

the project footprint. Of the 290 quadrats points that had SAV in previous 

years, only 20 had SAV coverage during this survey.

No SAV was observed during the survey of the North Area. Maps prepared 

by VIMS in 2016 and 2017, showed SAV density of 10%–40%. Even 

though SAV had not occurred behind the sill prior to being constructed, 

the post-construction area had conditions where SAV could colonize.

Accordingly, a visual scan was conducted behind a stone sill inside of the 

two jetties, but no SAV was present. Based on touch, the area south of the 

jetty had significant undulation with organic sediments and was different 

from the area north of the jetty, south of the southern jetty, and the 

reference transect 500 m south of the project, which had a smoother 

bottom and less organic material. 

The 19 points previously surveyed by MDDNR were within the project 

impact area <70 m from the southern jetty (Figure 7). Eight of the 19

previously sampled points had SAV coverage in 2015, and the distribution 

overlapped almost exactly with the 2016 VIMS mapping. No SAV was

found at these MDDNR points during the June 2019 survey. The only 

difference in sampling method was that the survey in 2015 used a 0.25 m2

quadrat as opposed to a 0.5 m2 quadrat (current study), meaning that the 

June 2019 survey covered four times the bottom area of the 2015 MD DNR 

survey and thus was more likely to encounter SAV if it were in the area.

A total of 239 quadrat points were sampled in the South Area (Figure 12), 

214 of which were mapped as having SAV density of 40%–70% (2016) and 

10%–40% (2017) by VIMS. Of these, only 21 (10%) had SAV during 

sampling in June 2019. All 21 points were in areas that were mapped as 

having SAV in both 2016 and 2017. Most of the quadrats that did have SAV 

coverage (18, 86%) were on the most southern transect at the very edge of 

the project footprint. No SAV was observed during two quick visual scans. 

The reference transect consisted of 44 quadrat samples and a 45 m visual 

scan (Figure 13). All the points and visual scan had SAV mapped in 2016 

and 2017. There was no SAV in the portion close to shore where SAV was 

mapped in 2016 (equivalent to 13 quadrat samples on the transect); 

however, 30 of 31 quadrat samples overlapping the area where SAV was 

mapped in both 2016 and 2017 had SAV present with 93% having 

complete SAV bottom coverage. Based on small leaf size, it appeared that 

Ruppia maritima was spreading in a shoreward direction to where SAV 
ERDC/CHL TR-20-14 23

was delineated only in 2016 and not in 2017. The entire 45 m visual scan 

area had complete bottom coverage by SAV. SAV continued offshore of the 

visual scan endpoint, but due to strong waves and incoming tide, sampling 

could not go out to 1.5 m deep at low water. Based on the visual survey and 

very dense growth, it is hypothesized that SAV coverage continued to at 

least to where SAV was mapped in 2016 and 2017.

Where SAV was present, both species were found in close proximity, with 

Ruppia maritima occurring a bit closer to shore. However, as the observed 

SAV coverage was low overall, it is difficult to make any conclusive 

statements about potential differences in species zonation patterns. 

The survey results indicate that SAV is largely absent adjacent to the 

placement area (and potential area of effect) except in the most southern 

extent of the project footprint where it is present, but sparse. It is too early 

in the study to determine why the SAV beds are not present as there are 

many variables that could be effecting SAV within the project footprint.

These variables could include precipitation and nutrient input, biological 

disturbance, physical disturbance or displacement, alteration of 

sedimentation, and erosion and turbidity patterns due to project 

implementation. The reduction of SAV in the project footprint may also be 

due to the extremely wet winter and spring in the Chesapeake Bay region.

At the time of this report preparation, regional SAV data from VIMS for 

2019 was not yet available to characterize regional SAV health. However,

numerous rafts of Ruppia maritima and Zostera marina were observed

while traveling to the study location and both species were scattered along 

rack lines so SAV is growing in this region of the Bay. Erosion of the 

backfill area exposed to direct wave energy caused by the great fetch across 

the open Bay was observed. It is possible that the southern jetty is holding 

suspended sediments in the area, exacerbating effects of sediment lost 

from the placement site. Based on dense SAV beds used as a reference just 

outside of the project footprint and observations in the Southern Area, it 

would appear that erosion of the placed material and/or disturbance 

during construction has negatively impacted SAV within the project area.

The Northern Area did not seem to be suffering from wave exposure like 

the Southern Area, but the bottom seemed highly disturbed, possibly due 

to construction. This recent disturbance may be a factor contributing to 

the absence of SAV in the Northern Area. Considering the dense SAV beds 
ERDC/CHL TR-20-14 24

within close proximity to the project footprint, there is the potential these 

beds will recolonize the area adjacent to the project structures.

Additional observations were made shoreward of the stone sill in the 

Southern Area of the project footprint. The placed dredged material had 

recently been planted within 3 weeks of the SAV monitoring. The areas 

where waves from the bay had a straight line path to the backfill was

experiencing significant erosion, including erosion of recently planted 

Spartina alterniflora plugs, which were likely uprooted by waves prior to 

the roots being able to establish in the soil. The higher elevation Spartina 

patens appeared very healthy and stable.

Figure 12. SAV survey results within the South Area in June 2019. The 

yellow-shaded polygon is the 2016 SAV coverage; the grey-shaded polygon is the 

2017 coverage, and the blue-shaded polygon is the where SAV occurred 

in both 2016 and 2017. 
ERDC/CHL TR-20-14 25

Figure 13. SAV survey results within the reference area. The yellow-shaded polygon is 

the 2016 SAV coverage, the grey-shaded polygon is the 2017 coverage, and the 

blue-shaded polygon is where SAV occurred in both 2016 and 2017. 
ERDC/CHL TR-20-14 26

4 Conclusions and Recommendations

Conclusions

Given the short period of record following the completion of the 

navigation improvements, it is difficult to draw any conclusions regarding 

the stability of the channel, structures, and shoreline. The structures were 

completed in June 2018, and the dredging was performed in November 

2018; therefore, the monitoring data collected under this study represent a 

good baseline for base-year conditions. Planting of the placement site is 

still ongoing and scheduled to be completed in October 2019, which has 

had implications for shoreline and SAV stability.

With respect to SAV, disturbance and erosion of the placement site has 

had a potential impact. When originally planned, the shoreline sill was 

intended to be built as a continuous sill to contain the placed dredge 

material, with notches cut into the sill later to allow water to access the 

marsh. However, upon the start of construction, conditions in the Bay 

were unexpectedly shallow, such that the sill had to be built as a 

segmented breakwater due to construction feasibility. This has led to 

erosion of the placement site due to the strong waves through the 

segmented breakwaters. In retrospect, a staggered breakwater might have 

been able to reduce the wave energy and better contain the placed 

material. Note that prior to mid-June 2018, the placement site was bare 

(not yet planted). Therefore, it is anticipated that once the site becomes 

stabilized by the planted vegetation, erosion will be significantly reduced. 

Recommendations

It is recommended that the monitoring activities conducted this year be 

extended for an additional year to better evaluate post-construction 

conditions. For future monitoring of the navigation structures, the 

transects that were established on the structures should be used to 

evaluate changes in jetty profile, relative movement of stones, settlement 

of the jetties, and overall structural stability of jetties and sill, which could 

provide an assessment of the impacts of wave action. Continued collection 

of bathymetric surveys and grain size data should occur to evaluate 

channel conditions with respect to shoaling. Additionally, SAV monitoring 

next growing season is recommended to evaluate the recovery of SAV in 

the project area. There are abundant SAV propagules in Bay waters, and 
ERDC/CHL TR-20-14 27

natural recolonization of disturbed areas that become suitable for SAV 

growth are anticipated. It is also suggested that water quality monitoring 

occur within the project footprint and the reference location to better 

understand differences between the two sites. Two continuous-sampling 

water quality sondes could be deployed to create long-term datasets 

describing water quality within the footprint area where SAV has been 

impacted and the reference area where SAV is flourishing.
ERDC/CHL TR-20-14 28

References

MGS (Maryland Geological Survey). 2000. Historical Shorelines, 1841-1976; Chesapeake 

Bay Region of Maryland, Edition 1.
ERDC/CHL TR-20-14 29

Unit Conversion Factors

Multiply By To Obtain 

acres 4,046.873 square meters

cubic feet 0.02831685 cubic meters

cubic inches 1.6387064 E-05 cubic meters

cubic yards 0.7645549 cubic meters

feet 0.3048 meters

inches 0.0254 meters

miles (US statute) 1,609.347 meters

square feet 0.09290304 square meters

square inches 6.4516 E-04 square meters

square miles 2.589998 E+06 square meters

square yards 0.8361274 square meters

yards 0.9144 meters
ERDC/CHL TR-20-14 30

Acronyms and Abbreviations

GIS geographic information systems

IBD immediately before dredging 

MDDNR Maryland Department of Natural Resources 

MLLW Mean Lower Low Water 

RSM Regional Sediment Management 

SAV submerged aquatic vegetation

TIN triangulated irregular network

USACE US Army Corps of Engineers 

VIMS Virginia Institute of Marine Science
REPORT DOCUMENTATION PAGE Form Approved

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PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS.

1. REPORT DATE

July 2020

2. REPORT TYPE

Final Report

3. DATES COVERED (From - To)

4. TITLE AND SUBTITLE

Post-Project Monitoring of a Navigation Solution in a Dynamic Coastal Environment, Smith 

Island, Maryland: 

Year One of Post-Project Monitoring

5a. CONTRACT NUMBER

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

Jacqueline A. Seiple, Christopher C. Spaur, Safra Altman, Matt T. Balazik, Luis E. Santiago, 

Daniel O. Mensah, Warunika G. Amarasingha, Steven M. Golder, and Andrew W. Payson

5d. PROJECT NUMBER

484149

5e. TASK NUMBER

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND 

ADDRESS(ES)

Coastal and Hydraulics Laboratory

US Army Engineer Research and 

Development Center

3909 Halls Ferry Road

Vicksburg, MS 39180-6199

US Army Corps of Engineers, Baltimore 

District

2 Hopkins Plaza

Baltimore, MD 21201

8. PERFORMING

ORGANIZATION REPORT

NUMBER

ERDC/CHL TR-20-14

9. SPONSORING/MONITORING AGENCY

NAME(S) AND ADDRESS(ES)

US Army Corps of Engineers

Regional Sediment Management Program 

Vicksburg MS 39180

US Army Corps of Engineers, Baltimore 

District

Baltimore MD 21201

10. SPONSOR/MONITOR'S ACRONYM(S)

USACE RSM NAB

11. SPONSOR/MONITOR'S

REPORT NUMBER(S)

12. DISTRIBUTION/AVAILABILITY STATEMENT

Approved for public release; distribution is unlimited.

13. SUPPLEMENTARY NOTES

14. ABSTRACT

In 2018, jetties and a sill were constructed by the US Army Corps of Engineers (USACE) adjacent to the Sheep Pen Gut Federal Channel 

at Rhodes Point, Smith Island, Maryland. These navigation improvements were constructed under Section 107 of the Continuing

Authorities Program. Material dredged for construction of the navigation structures and realignment of the channel were used to restore 

degraded marsh. Following construction and dredging, 1 year of post-project monitoring was performed to evaluate the performance of 

navigation improvements with respect to the prevention of shoaling within the Sheep Pen Gut channel, shoreline changes, and impacts to 

submerged aquatic vegetation (SAV). Given the short period of record after the completion of the navigation improvements, it was 

difficult to draw conclusions regarding stability of the channel, structures, and shoreline. Therefore, this report documents methodology 

and baseline conditions for monitoring, except for SAV, which was found to be potentially impacted by construction. 

A second year of monitoring was funded by the USACE Regional Sediment Management Program for fiscal year 2020. Findings can be 

used to inform plan formulation and design for USACE navigation projects by illuminating considerations for placement of structures to 

prevent shoaling and by informing SAV management decisions.

15. SUBJECT TERMS

Aquatic plants, Channels (Hydraulic engineering), Chesapeake Bay (Md. And Va.), Coastal engineering, Dredging spoil, Jetties, Rhodes 

Point (Md.), Salt marshes

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF

ABSTRACT

SAR

18. NUMBER

OF

PAGES

38

19a. NAME OF RESPONSIBLE PERSON

Jacqueline A. Seiple a. REPORT

Unclassified

b. ABSTRACT

Unclassified

c. THIS PAGE

Unclassified 19b. TELEPHONE NUMBER (Include area code)

410-962-4398

Standard Form 298 (Rev. 8/98)

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