Engineered Approaches for Limiting Erosion along Sheltered

104 Pages·2012·3.1 MB·English

Engineered Approaches for Limiting
Erosion along Sheltered Shorelines:
A Review of Existing Methods

Prepared for:
Hudson River Valley Greenway
Hudson River National Estuarine
Research Reserve

As a part of:
The Hudson River
Sustainable Shorelines Project

Prepared by:
Andrew J. Rella, &
Jon K. Miller, Ph.D.

September 2012
Acknowledgements Water levels are also determined chiefly by
tides, but can be strongly affected by high
This report was prepared by Andrew Rella
flows from upriver and tributaries, and by
and Jon Miller of Stevens Institute of
storm surges. The transition from fresh to
Technology in the course of performing
saltwater occurs in the lower half of the
work contracted for the Hudson River
river, depending on freshwater flows and
Sustainable Shorelines Project.
tides.
The authors would like to acknowledge the
Forces impinging on the Hudson’s shores
Sustainable Shorelines coordinating team,
include wind-driven waves, wakes from
especially Emilie Hauser, Dave Strayer, and
commercial and recreational vessels,
Kristin Marcell for their assistance.
currents from tides and downriver flow, and
floating debris and ice driven onshore by
About the Hudson River Estuary
these forces. Depending on their exposure
The Hudson River Estuary is a narrow, 152 to wind, currents, wakes, and ice, and their
mile arm of the sea that extends from the position relative to the navigation channel
southern tip of Manhattan north to the and protective shallows, different parts of
Troy Dam. The maximum width of the river the Hudson’s shores receive very different
is 3 miles in the Tappan Zee, but most of inputs of physical energy. Likewise, land
the river is 0.5-1 mile wide, and the upper uses on the landward side of the shore and
section near Albany is less than 0.5 miles water-dependent uses on the riverward
wide. Much of the river is 20-50 feet deep, side of the shore are highly variable along
and a 32 foot deep navigation channel the Hudson. As a result, different parts of
extends all the way to Albany. However, the the Hudson place very different demands
river also contains extensive shallow-water on engineered structures along the shore.
areas that are less than 5 feet deep at low
The shoreline has been dramatically altered
tide, many of which support wetlands or
over the last 150 years to support industry
beds of submersed vegetation. Much of the
and other development, contain channel
river bottom is sand or mud, although
dredge spoils, and withstand erosion. About
patches of gravel, cobble, relict oyster reefs,
half of the shoreline has been conspicuously
and debris do exist. The average tidal range
engineered with revetment, bulkhead,
along the Hudson River is about 4 feet,
cribbing or reinforced with riprap. Many
peaking at 5 feet at either end of the
additional shorelines contain remnant
estuary. In periods of normal freshwater
engineered structures from previous human
flows, strong tidal flows (often greater than
activities. The remaining “natural”
2 feet/second) reverse the direction of
shorelines (which, however, have been
water flow every 6 hours throughout the
affected by human activities such as
entire estuary, and are roughly 10 times as
disposal of dredge spoil, invasive species,
large as downriver flow of fresh water.
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and contaminants) include a mix of Science Collaborative puts Reserve-based
wooded, grassy, and unvegetated science to work for coastal communities
communities on mud, sand, cobbles, and coping with the impacts of land use change,
bedrock. Miller et al. (2006) performed an pollution, and habitat degradation in the
inventory of Hudson River shorelines context of a changing climate.
between the Tappan Zee Bridge and the
Disclaimer
head of tide at the federal dam at Troy and
proposed a 5 level classification scheme. Of
The opinions expressed in this report are
the 250 miles of shorelines inventoried,
those of the authors and do not necessarily
42% were hard engineered, 47% were
reflect those of the New York State
natural, and 11% were natural with
Department of Environmental Conservation
remnants of engineering structures. The
and the Greenway Conservancy for the
most common shoreline structure was rip-
Hudson River Valley or our funders.
rap (32%), followed by woody (29%) and
Reference to any specific product, service,
unvegetated (16%) slopes. The dominant
process, or method does not constitute an
substrate found within the region was
implied or expressed recommendation or
unconsolidated rock (52%), mud/sand (16%)
endorsement of it.
and mixed soil/rock (12%).
Terminology
About the Sustainable Shorelines
Project There are many ways to describe both
standard and innovative engineering
The Hudson River Sustainable Shorelines
methods to protect shoreline. The Hudson
Project is a multi-year effort lead by the
River Sustainable Shorelines Project uses
New York State Department of
the term ecologically enhanced engineered
Environmental Conservation Hudson River
shoreline to denote innovative techniques
National Estuarine Research Reserve in
that incorporate measures to enhance the
cooperation with the Greenway
attractiveness of the approach to both
Conservancy for the Hudson River Valley.
terrestrial and aquatic biota. Some
Partners in the project include Cary
documents and reports of the Hudson River
Institute for Ecosystem Studies, NYSDEC
Sustainable Shorelines Project may use
Hudson River Estuary Program and Stevens
other terms to convey this meaning,
Institute of Technology. The Consensus
including: alternatives to hardening, bio-
Building Institute facilitates the project.
engineered, eco-alternatives, green,
habitat-friendly, living, soft shorelines, or
The project is supported by the National
soft engineered shoreline.
Estuarine Research Reserve System Science
Collaborative, a partnership of the National
Suggested Citation: Rella, Andrew, and Jon
Oceanic and Atmospheric Administration
Miller, 2012. Engineered Approaches for
and the University of New Hampshire. The
ii
Limiting Erosion along Sheltered Shorelines:
A Review of Existing Methods. In association
with and published by the Hudson River
Sustainable Shorelines Project, Staatsburg,
NY 12580, http://hrnerr.org.
Hudson River Sustainable Shorelines Project
NYSDEC Hudson River National Estuarine
Research Reserve
Norrie Point Environmental Center
Staatsburg, NY 12580
845-889-4745 hrnerr @gw.dec.state.ny.us
http://hrnerr.org

Authors contact: [email protected]
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Contents
Contents .......................................................................................................................................... iv
Introduction ...................................................................................................................................... 1
Bulkheads ......................................................................................................................................... 5
Gabions ............................................................................................................................................. 9
Revetments .................................................................................................................................... 13
Rootwad Revetments ..................................................................................................................... 17
Tree Revetments ............................................................................................................................ 20
Rip-rap ............................................................................................................................................ 23
Jack Fields ....................................................................................................................................... 26
Green (Bio) Walls ............................................................................................................................ 28
Timber Cribbing .............................................................................................................................. 30
Live Crib Wall .................................................................................................................................. 33
Levees (Dikes) ................................................................................................................................. 36
Geotextile Roll ................................................................................................................................ 38
Vegetated Geogrids ........................................................................................................................ 41
Live Stakes / Joint Planting ............................................................................................................. 44
Brush Mattress ............................................................................................................................... 46
Branch Packing ............................................................................................................................... 49
Live Fascines ................................................................................................................................... 51
Coconut Fiber Rolls ......................................................................................................................... 54
Reed Clumps ................................................................................................................................... 56
Dormant Post Planting ................................................................................................................... 58
Groins ............................................................................................................................................. 60
Stream Barbs .................................................................................................................................. 63
Wave Screens ................................................................................................................................. 65
Breakwater ..................................................................................................................................... 68
Floating Breakwater ....................................................................................................................... 70
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Living Reef Breakwater ................................................................................................................... 72
Sills .................................................................................................................................................. 74
Artificial Vegetation ........................................................................................................................ 76
Summary......................................................................................................................................... 78
Glossary of Terms ........................................................................................................................... 80
References ...................................................................................................................................... 84

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Introduction available. Historically in the Hudson River
Estuary, as elsewhere, ecological impact
The purpose of this document is to provide
was rarely considered during the design of
an overview of the engineered approaches
shore protection works; however the
currently being utilized to manage erosion
modern trend is to place significantly more
along sheltered shorelines. In their natural
emphasis on such considerations. Many of
state, shorelines tend to be dynamic,
the approaches discussed in this document
cycling through periods of erosion and
were developed in an attempt to try to
accretion in response to changes in weather
balance the need for structural stabilization
patterns and sediment supply. Along
with ecological considerations. Such
developed shorelines, such as those of the
approaches fall into a category of
Hudson River Estuary, the dynamic nature
techniques collectively referred to by the
of shorelines often conflicts with
Sustainable Shorelines team as “ecologically
requirements to protect private property
enhanced shore protection alternatives”.
and infrastructure. In these areas a variety
of engineered erosion control approaches
This document is intended to help make
are employed as a way of reducing or
decision makers aware of the variety of
eliminating further land loss. Designing an
different alternatives that have been
appropriate shore protection measure for a
utilized elsewhere, and is not intended to
particular location reflects a delicate
be specific to the Hudson River Estuary.
balance between the required protection
Future work to be conducted under the
level and factors such as cost, aesthetics,
Sustainable Shorelines Project will focus on
and environmental impact.
a subset of the techniques presented here
that are most appropriate for the Hudson
In general, the lower energy along sheltered
River Estuary.
coastlines allows for greater creativity in
designing shore protection projects;
Engineering Terminology
therefore a variety of different engineering
In order to facilitate the understanding of
approaches have been developed. These
the sections that follow, it is useful to set
approaches range from shoreline armoring
forth a few basic definitions commonly used
or hardening via bulkheads, revetments,
by the engineering community. Figure 1
gabions and other structures, to softer
defines several terms frequently used to
more natural methods such as vegetative
describe the geometry of the shoreline and
plantings. In 2007, the National Academies
any structures. In particular, crest refers to
Press released the report, Mitigating Shore
the top elevation of the structure, while toe
Erosion along Sheltered Coasts, which
refers to the base of the structure, typically
advocated the development of a new
on the side facing the water. The area
management framework within which
between high and low tide is referred to as
decision makers would be encouraged to
the intertidal zone, while the bottom and
consider the full spectrum of options
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upland slopes are referred to as the bed among these. Traditionally, hard was used
and bank slopes, respectively. Figure 2 to refer to shoreline stabilization
defines some additional terms that apply to approaches that incorporated some sort of
the plan, or overhead view of a project. In structural element, whether it be steel,
the plan view, flank refers to the area concrete or rock. Conversely, soft was used
immediately adjacent to the ends of the almost exclusively to refer to approaches
project, while upland and nearshore are that did not incorporate a structural
used to refer to the areas immediately element, such as beach fills and/or
landward and seaward, respectively. plantings. Here we utilize the terms, but
recognize there is a continuum between
hard and soft (see below for more
information).
Living shorelines is a term that has become
popularized recently; however there is
frequently a considerable amount of debate
over what constitutes a living shoreline.
The term is often used broadly to represent
a system of protection that incorporates
many of the individual approaches
Figure 1: Engineering terminology profile view.
identified elsewhere in this document.
Living shorelines can include both bank
stabilization as well as methods to reduce
the wave and/or current energy along the
bank. Living shorelines are typically
considered a “soft” approach to shoreline
protection, because of the use of natural
and often biodegradable techniques. The
use of vegetation often plays a significant
role in developing a living shoreline where
the vegetation is used to help anchor the
soil and prevent erosion, while at the same
time trap new sediment. The vegetation
Figure 2: Engineering terminology plan view.
also provides shelter and habitat for wildlife
In addition to these terms, there are a host living along the shoreline and can act as a
of terms which are frequently used to natural filter for removing pesticides and
describe engineering projects that often fertilizers. Natural buffers such as oyster
have conflicting, or at least unclear and/or mussel reefs are also frequently
definitions. The terms hard and soft, are used to dissipate energy, and create
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submerged habitats. Along some higher inadequacy of traditional terms as more
energy shorelines, a hybrid of solutions may and more hybrid approaches are being
be implemented, where low-profile in- developed, the sustainable shorelines team
water rock structures may be used to decided to adopt the phrase ecologically
dissipate energy. Other materials enhanced to refer to innovative techniques
frequently used along living shorelines that incorporate measures to enhance the
include sand fill, and biodegradable attractiveness of stabilization methods to
materials such as natural fiber logs or rolls both terrestrial and marine biota.
and organic matting. Some of the
Methodology
techniques which are discussed later in the
The objective of this document is to provide
document that incorporate many of the
a general overview of the variety of shore
living shorelines principles are: living
protection alternatives currently being used
breakwaters, sills, live fascines, dormant
along sheltered shorelines, and is not
posts, live stakes, reed clumps, coconut
intended to be specific to the Hudson River
fiber rolls and brush mattresses.
Estuary. A systematic approach is used to
Soil bioengineering is another generic term facilitate comparison of the alternatives,
that can be used to refer to a variety of which are generally presented in the
shoreline stabilization approaches, following order: shore face, shore parallel
including some that can be classified as treatments; shore face, shore perpendicular
living shorelines. Soil bioengineering refers treatments; and shore detached, shore
to the concept of utilizing vegetation to parallel treatments. Each shoreline
stabilize the soil along eroding banks. The stabilization technique is qualitatively
vegetation provides immediate protection, evaluated in 4 categories: Approach,
and as the root systems develop, they bind Construction Cost, Maintenance Cost, and
the soil more tightly creating a resistance to Adaptability. Approach refers to the type of
sliding or shear. Soil bioengineering shore protection strategy being employed
projects can also include structural and ranges from what has traditionally been
components if additional bank protection is referred to as “hard” by the engineering
required. Examples of soil bioengineering community (bulkheads for example), to
approaches discussed in more detail later in more natural or “soft” approaches such as
this document include: brush mattresses, vegetative planting. Construction Cost
live stakes, joint plantings, vegetated takes into account the typical costs
geogrids, branch packing, dormant posts, associated with initial construction, while
and live fascines. Maintenance Cost refers to the cost of
maintaining the system over its lifetime.
In part because of the confusion
Adaptability considers the effort required to
surrounding some of the existing
modify in-place projects to handle new
terminology, and in part because of the
conditions brought on by climate change or
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other factors. A table summarizing these Advantages and Disadvantages sections,
qualitative evaluations is presented at the bulleted lists summarizing the positive and
end of the document. negative attributes of a given method are
provided. Similar Techniques lists the
More detailed information is presented in
alternative approaches or methods which
the descriptions which follow each
are most similar to the one being discussed
evaluation. These descriptions vary in
in the way that they interact with the
length depending on how well documented
physical forces at a site to reduce erosion at
the technique is. Wherever possible,
the shoreline. A glossary containing concise
pictures and figures showing cross-sections
(1 or 2 sentence) descriptions of each
and/or typical installations are provided.
approach is presented at the end of the
The descriptions are broken down into the
document.
following 6 categories: Description, Design
and Construction, Adaptability, Advantages, It should be noted, that each technique
Disadvantages, and Similar Techniques. The must address a variety of often competing
Description section provides a short concerns. The information presented
discussion of the specified approach. The within this document primarily relates to
Design and Construction section contains the engineering aspects of each approach.
information on some of the basic design As a part of the design process, a
and construction considerations associated responsible engineer needs to consider
with each approach. It should be noted numerous factors beyond the scope of this
that the information presented in this document.
section is intended only to relay the basic
design principles and that detailed designs
require much more information than
provided in this document. When available,
cost information as well as information
about operation and maintenance
considerations are also presented in this
section. Costs have been taken directly
from the references cited and no inflation
adjustment has been applied. The
Adaptability section contains information
related to the ability of the selected
treatment to adapt to changing conditions
either naturally or through anthropogenic
intervention. Factors such as expected
lifespan, durability, and the ease of
modification are considered. In the
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