1. Sean Lamarre
Erosion Control Devices on the Severn River
Abstract
Erosion and sediment transport from the Severn River to the Chesapeake Bay is
controlled by a variety of structural and non-structural techniques. This study examines
the techniques used by homeowners in Valentine Creek and adjacent Severn River
communities to manage their waterfront slope. Data was collected through riverside
observation, photographs and interviews with homeowners. The location of these erosion
mitigation devices is an important factor in their success and each is plotted using
Geographic Information System (GIS) ArcMap software. This study observes a wide
variety of structural and non-structural techniques to control riverside slopes such as;
wooden bulkheads, stone revetments and vegetation.
Introduction
From a homeowner’s point of view, protecting riverside property is necessary to
maintain aesthetic qualities and property values. From an ecological perspective, erosion
and sedimentation originating from the large number of riverside properties in the
Chesapeake Bay watershed can have negative impacts on the health of the Chesapeake
Bay and river ecosystems. The increased sedimentation can block boating channels,
increase turbidity and disrupt local habitat on land and the bottom of the river. Erosion is
impacted by multiple variables such as: shore orientation, fetch exposure, dominant wind
direction and topography of surrounding land. When the specific location of the
technique used is plotted on an interactive GIS map, the impacting variables should
2. coincide with the type of mitigation technique. Location and orientation are key factors in
examining the effectiveness of homeowner’s riverside slope management because of
seasonal wind variation and topographical elevation. By placing a coordinate location
that coincides with this data, a spatial dimension of information is acquired. The study
provides answers to two questions; what methods are used to mitigate erosion and where
these measures are located. The large area of riverside property on the Severn River
limits this study to the upper reaches of the Severn.
Literature Review
The Severn River watershed is populated with schools, parking lots, roads and
schools, but the most dominant use of land in the watershed is single-family residential
lots with a density of 38% (Frost, et al. 2006). It is necessary to introduce the different
types of erosion and sediment transport before examining the impacting variables. Rain
impact erosion occurs when precipitation breaks up soil into small particles; Sheet
erosion is caused by storm-water runoff peeling off a thin layer of topsoil where
vegetative nutrients are found, leading to algae blooms and anoxic waters; Rill and gully
erosion occurs when water carves out a path in the soil, leading to greater volumes of
runoff; Stream channel erosion is a result of gullies dumping large volumes of runoff into
a stream, which results in undercutting and erodes stream banks (Melonas and Maurer,
2004).
The degree and type of erosion is dependent upon many variables. Hydrodynamic
analysis studies show how the wave climate data incorporates fetch exposure, dominant
wind direction, storm surge frequencies, shoreline orientation, topography and soil types
3. (Hardaway et al. 2002). This data guides shoreline protection strategies but is dependent
upon the reach of the river [Segment of shoreline where the processes and responses of
erosion are mutually experienced] (Hardaway and Byrne 1999). Wave energy is
classified into low, medium and high-energy zones (Hardaway and Byrne 1999). Low-
energy shorelines have less then one mile of fetch exposure. The shorelines that are
exposed perpendicular to the dominant wind direction experience a higher average fetch
and thus a greater potential for erosion [In autumn and early spring the dominant wind
direction in the Chesapeake is north and northwest, in the spring and summer it switches
to the southwest] (Hardaway and Anderson 1980). The frequency and average storm
surge must also be accounted for when evaluating an appropriate mitigation technique.
Wave induced pressure fluctuations produced by storm waves superimposed on tidal and
wind driven currents contribute to erosion (Halka, et al., 1991). Storm force winds of 30
mph can create 5-7 ft waves in the Chesapeake Bay and 2-5 ft waves in its tributaries
such as the Severn River (Hardaway and Byrne, 1999). These waves contribute to the
undercutting of steep and unstable riverside slopes. Research suggests that the
topography of the shore and soil type are also important factors when addressing erosion.
For example, Shultz and Ashby (1967) conducted a study at Scientists Cliffs in Calvert
County, Maryland that analyzed the effectiveness and flaws of groin placement. Shultz
and Ashby concluded that without an adequate supply of coarse to medium sized sand
particles, groins do not accumulate enough sand to control cliff erosion. A common
characteristic of the Monmouth, Matawan and Magothy formations present in the Severn
River watershed is the presence of variable amounts of impermeable clay, which restricts
storm-water drainage and leads to a buildup in hydrostatic pressure that in turn
4. destabilizes the slope (Hardaway and Byrne, 1999; Severn River Master Plan, 2001).
Because of the richly interactive and mutually causal nature of the multiple variables that
impact erosion an integrated approach is necessary. The variables include erosion and
accretion as well as dynamic variables such as wave climate that is dependent on wind
and other factors.
There are four basic approaches to shoreline management: 1) no action; 2) defend
and erosional area with structures such as blockheads, seawalls or revetments;
3) maintain or enhance existing shoreline features such as beaches and dunes; or 4) create
a shore zone system of beaches, dunes and fringe marshes (Hardaway, et al., 2002).
Structural techniques such as vertical wooden blockheads and concrete seawalls
were installed from the 1950’s throughout the 1970’s as a result of the post WWII
increase in bay-shore second homes (Hardaway and Byrne 1999). However, Hardaway
and Byrne’s Shoreline Management in the Chesapeake Bay (1999) postulates that the
vertical faces of the blockheads reflect wave energy and cause currents to dig out the
substrate at the toe of the structure. Another popular structural technique is stone
revetments. These require stones of different sizes, layered on top of one another with
filter cloth separating the different layers of stone. The size of the stone is determined by
analyzing wave climate data and slope. Groins composed of wood or stone tied together
represent another structural technique. However, groins can disrupt the littoral drift of
sediment down river and cause the accretion of sediment within another segment of
shoreline (Hardaway et al., 2002).
Non-structural techniques tend to incorporate the surrounding habitat and
biodiversity of a particular reach into the mitigation process. The use of plants and
5. vegetation to stabilize sloping soil [Bio-structural engineering] dates back to the first
century A.D. (Andreu, et al., 2008). The seeding and planting of deep-rooted vegetation
helps to maintain a stable slope. The type of vegetation used is circumstantial and is
determined by on-site characteristics such as soil type, average precipitation and average
sunlight (Stokes, et al., 2008). The construction of tidal marshes on existing shorelines is
another form of bio-structural engineering. Depending on the width of a constructed
marsh, bank erosion rates are reduced due to the dissipation of wave energies passing
through the marsh (Garbisch and Garbisch, 1994).
A combination of both structural and non-structural techniques to mitigate erosion
is the hybrid model. Also called “Living Shorelines”, Burke (2005) and a team of
researchers from the University of Maryland conducted a comparative assessment of the
different erosion mitigation projects and found the hybrid model to be the most effective
at maintaining or improving the surrounding habitat while simultaneously decreasing
erosion rates.
The studies conducted by Hardaway and Byrne, Shultz and Ashby, Stokes and
Halka have all focused on erosion in a particular area. They have studied the structural
capabilities and the impacts on surrounding land and ecosystems. Others have studied the
ability of specific plants to stabilize slopes. This study shows where these devices are
located and will assist further research in determining if critical areas of attention are able
to be located through observation of a map of shoreline structures.
6. Methods
Thorough riverside analysis is conducted in this study to observe the multitude of
variables impacting certain shorelines. The field research consists of over 30 photographs
of the erosion mitigation device and riverside documentation. In ascertaining the
necessary data in a qualitative fashion, the study also focuses on individual homeowners
past experience with managing their slope. The interviews with homeowners were
structured open-ended because the homeowner is better acquainted with his/her property
than the researcher. The six interviews gathered data that was not readily apparent to the
researcher, such as, the age of the structure, maintenance, prior problems, and cost.
The subjects were chosen based on the technique used so that a variety of
techniques are analyzed. Several subjects have lived on the Severn River for 25+ years.
Prior problems associated with a mitigation technique are better obtained from these
residents.
Photography and mapping was conducted in a kayak starting in February. Two
mapping trips were cut short because of icy water and winds. A map constructed using
ArcMap GIS software displaying all the buildings and piers was used during riverside
documentation. While kayaking with a clipboard and several colored pencils, the wooden
bulkheads, stone revetments and tidal marshes were plotted and then digitized using
ArcMap. Native slopes in the area observed in addition to critical areas in need of
attention were digitized as well.
During data analysis, the maps made on the river were manipulated through
ArcMap to show where interviews and observations had taken place. Each method of
7. slope control consisted of a feature class. Combining these feature classes with base
images obtained from the Maryland Department of Natural Resources GIS data download
website, the maps in Appendices A and B were produced.
Findings
Interviews- On the dates of March 30 & 31 and April 6 & 7 a total of six interviews were
conducted with homeowners. The degree to which the interviewee was comfortable with
the researcher varied greatly. It was discovered through two interviews with homeowners
who requested anonymity that the permit process is very confusing, frustrating and
littered with bureaucratic red-tape. During riverside observation of a newly repaired
wooden bulkhead, the homeowner repeatedly asked, “Who will see the report?” and
“What is the purpose of the study?” alluding to the reluctance of homeowners to discuss
structures needing permits. During the interview, his wife was maintaining their garden
that sloped towards the wooden bulkhead shoreline. The wife planted, “what she believes
to look nice”, and was not concerned with the slope stabilizing qualities of her work. The
mulch bed garden with tall grasses and a rock border provides a stable slope but requires
more maintenance when compared to other techniques, such as ivy plantings.
Another interviewee, Ms. Edna has lived on Valentine Creek for over three
decades and was thrilled to see research being conducted to help the river. Her land does
not have a steep slope, but she did inform me of a sediment control issue with the beach
in her backyard. The beach once had over forty pine trees, however, they are dieing off
due to the earwig disease. She noted that these trees die and become uprooted in storms,
usually falling into the water. This decreases the soil stability of the beach and leaves the
beach more vulnerable to rain-impact erosion. This is a prime example of the eco-
8. systemic nature of the erosion control problem. Ms. Edna did point out that one of the
two groins on her beach had recently caused new accretion in the same area where the
pine trees are succumbing to earwig disease. Ms. Edna has also installed two rock drains
leading to a 60 year-old concrete bulkhead in good condition. These rock drains assist in
the flow and filter of excess runoff.
Unlike the previous homeowners whom have the ability to maintain their
riverfront slope, Mr. Tom Novotny of Sevarden Ln. has a different situation. His house
sits atop a steep hill with rampant native vegetation. His slope is too steep to terrace, and
having been a resident for a year and relocating soon, he has no interest in making any
changes. Mr. Novotny complained of the permit process as well, however, admitting that
it was a necessary evil. At the bottom of his native slope, there was evidence of a
concrete bulkhead, broken and buried under subsiding earth and fallen trees.
Just northeast of Cedar Point the circular inlet of Cedar Pond forms the backyard
of six houses. One of the homeowners is Mr. Shawn O’Brien, a resident of five years. He
said he has attempted to maintain the 2-3 ft of beach the community shares by planting
tall grasses on shore, in addition to his wooden retaining walls. In spots where he has not
planted or his neighbors have neglected their waterfront land, the water undercuts land
and exposes tree roots and bare sediment. The ivy that covers the community’s native
slope has been there for over ten years. Most of his neighbors cannot have a lawn nor
garden because of the steep slope to the water. Instead, they utilize ivy covered terraced
structures that support screened decks and porches.
Observations- The shoreline erosion management devices observed on Valentine Creek
and the Severn River incorporate both structural and non-structural means for sediment
9. control. The most common structural techniques observed were: stone revetments, stone-
walls, wooden bulkheads and wooden retaining walls. The ability of homeowners to
control their slope is dependent on the degree of the slope. The case with Mr. Novotny,
where his slope is too steep and filled with native vegetation, illustrates the problem
associated with steep slopes facing the water. Instead of mitigating erosion through a
riverside device, Mr. Novotny utilizes rain barrels and rock drains on his property, which
is elevated and removed from the shore. The homes within 100 yards of the water were
likely to have either a wooden bulkhead or stone revetment. These homes were not
elevated more than 10-20ft from the water level and did not face significant erosion
problems.
Mr. Novotny’s neighbors on Sevarden Ln. appeared to be visibly wealthy with
large homes and yachts. The three homes were given labels: House A, House B and
House C.
10. All three homes had similar slopes and were located next to each other. The first dock of
House A marked the start of a stone revetment running the length of the property,
followed by an artificial beach. Their sloping mulch bed runs about 100 yards by 25
yards and is filled with tall grasses that were cut back for winter. House B took a similar
approach with the mulch bed and stone revetment. House C however, did not have any
erosion management device and there was noticeable slope failure leading to the water’s
edge. The maintenance of the bio-structural techniques used by houses A & B assist in
the prevention of the slope failure observed in house C by stabilizing soil and limiting the
effects of rain impact erosion. The financial means to implement these measures is a
limiting factor in their widespread application. Homes that are located next to the water
with a lesser slope are more likely to have success in mitigating their sediment runoff.
The areas observed in this study varied in their elevation. There were two
instances of slope failure due in part to their elevation. The area directly east of the
entrance to Forked Creek is composed of a tidal marsh several hundred yards in length,
ending at a cliff. The cliff is about 15 ft tall by 100 ft long and is composed of sandy
11. white clay. Tree roots and bare sediment is exposed and fallen trees littered the coastline.
The closest property is located several hundred feet inland and the nearest dock was 100
yards away from the eroding area. Another example of elevation impacting erosion was
on the south shore of round bay, located about 1.5 miles south of Cedar Point. The cliff is
roughly 150 ft tall and about 600-1000 ft long. During examination of the soil located on
this cliff, the sandy topsoil, where one would attempt to gain footing, quickly gave way to
dark gray clay that is slippery when wet. There are multiple trees and native debris
located in the water for the entire length of the cliff. This area is particularly susceptible
to erosion due to its elevation and northwestern facing orientation [due to the dominant
summer southwestern winds in the area].
Cedar Point is located about 2200 ft due east of Valentine Creek and is exposed to
a higher average fetch than most of the areas observed. Cedar Point is composed of a
stone revetment with large flat armor stone. The waters are shallow here [visible bottom]
12. and the winds were strong. Observation in this area was limited to the northwestern face
of Cedar Point due to the strong winds. This research and experience suggests that the
southeastern face of Cedar Point will need repair prior to the northwestern face.
The banks of the Severn River are populated with a significant amount of single-
family homes. Wooden bulkheads have been in use for several decades and are subject to
decay over time. The repair of these bulkheads requires a permit from Anne Arundel
County. The permit process is complicated and time consuming, garnishing little support
from waterfront property owners. Properties with a greater slope to the river are more
likely to use a hybrid model of structural and non-structural techniques. The most
common hybrid model observed in this study is the use of wooden retaining walls
coupled with ivy. Waterfront properties sitting behind tidal marshes or stone revetments
have greater soil stability, but also a higher initial investment cost. The investments that
past and present homeowners have made are included in the cost of their homes, however
research was unable to affirm this with absolute certainty. The bio-structural techniques
are implemented by the homeowner, however, structural devices such as blockheads have
been in place prior to the present occupant of the home. With regards to the impact on
surrounding habitats, shoreline protection structures placed on an existing shoreline, at
best, maintain the present habitat situation but generally remove or isolate existing habitat
(Hardaway, et al., 2002).
13. Discussion
The causes of erosion are many and the effects are felt throughout the ecosystem.
The approaches taken to stabilize slopes are numerous and utilize many different
materials and techniques, some with more drawbacks than others. Unexpected
complications and consequences are bound to arise when so many variables and natural
externalities must be analyzed in order to produce a desired result. Calculated and desired
results are a result of a widening knowledge base within the scientific and engineering
community.
The permitting process compounds the problems associated with erosion because
it adds an element of environmental policy to the equation. Not only does it increase the
difficulty for the homeowner to get anything done, it increases the likelihood that the
homeowner will find a non-systemic approach to resolving their erosion problem. The
problem occurs when homeowners fix individual problems without considering the full
extent of their actions. Constructing anything on waterfront property requires a permit
that incorporates the environmental impacts of the structure. But what if the area is in
critical need of attention but either the homeowner fails to act and request a permit? Or
the shoreline is situated between two property lines, prompting county intervention. The
resulting impact on the river can be negative if the county fails to act as well. The burden
ultimately lies on the homeowner to maintain his/her slope. All of the subjects
interviewed in this study were in favor of state funding being provided to homeowners to
aid in the maintenance and construction of erosion mitigation devices. However,
homeowners are weary of county intervention when dealing with the permitting process.
14. This research suggests that homeowners are best suited to determine when and where
maintenance of their waterfront slope is needed. State funding to assist in these measures
could be incorporated into the permitting process. If homeowners knew when they filed
for a permit that funds to assist them would be appropriated, they would be more inclined
to do so. The health of the Severn River ecosystem has direct impacts on the Chesapeake
Bay, both of which are in the common interest of the state and surrounding communities
not situated on the water. Garnishing support for such a bill would be tricky because the
tax base for such a measure is not entirely situated on the river. Residents of surrounding
communities must be convinced that the health of the Severn River is in everyone’s best
interest.
Conclusion
This study adds to the broader knowledge base by surveying and mapping the
location of these structural and non-structural approaches to erosion control along a
particular reach of the Severn River. In particular, the survey and maps add a spatial
dimension to the data acquired. The location and type of approach used is important
because of the mutual impact erosion has on the adjacent shore segments. Anne Arundel
County is well aware of what erosion mitigation device is located on someone’s property
based on permit records. When these measures are mapped, pier-by-pier, a broader point
of view is established which paints a portrait of the shoreline. This portrait can be used to
show how areas of concern can develop in regions where there is no erosion mitigation
device. Also, this study shows how areas without bulkheads or stone revetments are
prone to slope failure.
15. Future research should focus on mapping the information contained in the permit
records. The county’s extensive permit database holds all the data necessary to plot the
information on a map. This map could be used to theoretically predict where slope failure
will occur and whom to notify of intended action on their land.
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