Appendix 5 - Chesapeake Bay Site
Address:
Terrapin Nature Area
Stevensville, MD (see Maps 1,2)
General Location Description: The site is located on Kent Island on Chesapeake Bay
approximately .3 miles north of the Bay Bridge. The area is part of Terrapin Nature Area.
The general area is used for recreation with no upland structures. Landward of the project
site is a un-improved dirt road (see Maps 1 and 2 for vicinity and project site locations).
As depicted in Exhibits 1, and 1a the riparian land uses both upstream and downstream of
the site are Forested / Scrub, Shrub and Grass, respectively.
Erosion Potential: As reflected in Exhibit 5 (Historical Shorelines) the project site has
historically experienced accretion over the two most recent time periods. However, as
reflected in Exhibit 5a is the significant erosion losses indicated between the two
previous time periods extending back to early 1900’s. This depicts a dramatic reversal in
factors affecting shoreline change over time. Exhibit 7 depicts historical littoral currents
prior to the construction of the Bay Bridges, showing net drift to the south. However,
with the construction of the approaches to the bridges the post-littoral currents were
altered affecting the erosion and accretion patterns. The approaches act as a groin in the
retention of materials that have accumulated since its construction. This is indirectly
suggested by bottom patterns as reflected in Exhibit 1a. To this extent historical
shoreline changes are not a good indicator of present day erosion.
However, strong wave action as suggested by a fetch length of over 10 miles to the north,
northwest (see Exhibit 9) in the direction of prevailing winter winds (see Exhibit 10)
establish a high-energy environment and resultant potential erosion.
A second factor determining the erosion potential is the soil characteristics landward of
the MHW line. The soil composition landward of the shoreline within the riparian area of
the project site consists of a peat(see Exhibit 8, 8a). This material has a moderate
susceptibility to being eroded as expressed in Exhibit 8a.
Description of Erosion Control Project: The Beach Prisms span a distance of 788 feet
consisting of 57 Beach Prisms 4 foot high x 4 foot wide x 10 feet long. Spacing between
units ranged from 3 feet at the northern portion of the structure to 5 feet at its southern
terminus. Terrapin Nature Area was used as a “test site” for determining optimum
spacing between Beach Prisms. As such the Beach Prisms were set in three distinct
groups based on spacing as follows; a southern grouping covering 265 feet containing 18
Beach Prisms spaced at 5 feet, a middle grouping covering 266 feet containing 19 Beach
Prisms spaced at 4 feet, and a northern grouping covering 257 feet containing 20 Beach
Prisms spaced at 3 feet with last two Beach Prisms angled at 45 degrees to the shoreline.
Over the last 20 years the Beach Prisms have maintained alignment for the exception of
three units that were located in the southern grouping. Pictures 1 through 3 view the
beach prisms from north to south. Exhibits 3 and 3a are consistent with field observations
of adjoining sites depicting a bulkhead to the north and riprap to the south.
Assessment: Performance of the Beach Prisms is based on the bank and buffer
conditions behind the structure and adjacent properties both upstream and downstream of
the structure. The bank conditions (see Picture 2) indicate a highly stabilized and
vegetated bank with a fringing beach which is consistent with characterizations in Exhibit
2 and 2a. However, Exhibits 2 and 2a characterize the beach as suffering high erosion.
This characterization is in conflict with the co-occurrence of a stabilized bank.
Potentially, this was an error based on visual observation of different offsets from the
shoreline of the structure at its northern and southern ends. As based upon these
observations and archival information, the Beach Prisms used in this context have
demonstrated protection against wave action. However, the five-foot spacing at the
southern end where Hurricane Isabel moved three units out of alignment has created
“alignment issues” that could cause future errors.
APPENDIX 1
Onsite Survey
1) Date and Conditions The site was surveyed on August 24, 2009 at approximately
11:40am. There was a one foot water chop. Winds were light out the NW. Skies were
mostly sunny. High tide occurred at 8:35am.
2) Project Description The Beach Prisms span a distance of 788 feet consisting of 57
Beach Prisms 4 foot high x 4 foot wide x 10 feet long. Spacing between units ranged
from 3 feet at the northern portion of the structure to 5 feet at its southern terminus.
The alignment of the structure is north, northeast to south, southwest at slight angle to
the shoreline. In addition, at the northern end 2 Beach Prisms were angled 45 degree
landward (see Picture 1). At the angle point a distance of 35 feet was measured to the
shoreline at time of the survey. The southern end of the Beam Prisms terminated at
the shoreline. Pictures 1 through 3 view the Beach Prisms from north to south.
3) Site Description
a) The beach is located at the southern portion of the Terrapin Nature Area.
b) Vegetated bank in the near shore area ranged in height to 5 feet (see Picture 2)
c) A fringing beach ranged in width of 15 feet to north to 5 feet in the south at the
time of the survey.
d) Depths ranged from 2 feet at the Beach Prism to 3.0 feet at a distance of 100 feet
channelward of the Beach Prism.
e) A soil profile taken at the base of the Beach Prism was homogenous to depth of
12 inches and consisted of hard packed sand.
APPENDIX 2
Archival Information
1) Riparian Land Use
a) At Site: Forested / Scrub, Shrub
b) Upstream: Forested
c) Downstream: Grass
2) Bank and Buffer Conditions
a) At Site:
i) 0 - 5 bank / low erosion, total bank coverage
ii) beach / high erosion
iii) Phragmites australis
b) Upstream:
i) 0 - 5 ft bank / low erosion, total bank coverage
ii) beach / high erosion
iii) Phragmites australis
c) Downstream:
i) 0 - 5 ft bank / low erosion, total bank coverage
3) Shoreline Features
a) At Site: Breakwater
b) Upstream: Bulkhead
c) Downstream: Riprap
4) Submerged Aquatic Vegetation
a) At Site: 0%
b) Upstream: 0%
c) Downstream: 0%
5) Historical Shorelines
a) At Site: accretion (as based two most recent time periods)
b) Upstream: accretion
c) Downstream: none detect
6) Bathymetry
7) Littoral Drift
8) Soils
9) Fetch Length
10) Wind
Exhibits
1, 1a
2, 2a
3, 3a
4
5, 5a
6
7
8, 8a
9
10