Protective Coastal Beaches and Dredging
John Poullain, P.E.
online course provides general guidelines and practices for the development
and construction of beaches and dunes for the protection of coastal lowlands
and restoration of eroded beaches. The course provides an overview for planning
and utilization of dredged material as an alternative method for beneficial
dredge disposal. Beach and dune creation with dredged material consists of filling,
raising and protecting areas that are subject to wave attack and periodically
or permanently submerged. Remedial actions and activities performed at the construction
sites must comply with federal, state and local regulations to protect water
quality, fish and animal habitat.
This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.
At the conclusion of this course, the student will:
This course is intended for civil engineers and planners.
Benefit to Attendees
The student will understand the procedures for planning, developing and restoring beaches and dunes with dredged material and the benefits and disadvantages. Design factors including types of dredge material and equipment selection, timing of material placement and methods for placement are discussed. The student will also become familiar with the techniques used to construct beaches for wildlife habitat and measures to avoid adverse results.
About 70% of the
dredge material in the US are placed in aquatic disposal areas and open water
such as river channels and coastal waters. This course discusses the beneficial
use of dredged material for the development of beaches and dunes as an alternative
method for dredge disposal in place of using offshore or contained disposal
areas. In many coastal states beach erosion threatens developed areas, recreational,
cultural and environmental interests. Beaches, dunes and barrier islands are
built to protect commercial and residential areas from storm-driven waves and
tides and attempt to mimic natural beach and dune creation. Such non-rigid structure
construction is an alternative to hard structures like bulkheads, breakwaters
and sea walls. As coastal area is lost more open water appears and protection
from storms and hurricanes is reduced. Other benefits of beaches and dunes are
the creation of wildlife habitats for commercial and recreational purposes and
It has been estimated that over half of the US population is located within an hour's drive of the seashore, which makes beaches significant economic, recreational, and natural resources. Increased tropical storm activity, rising sea levels and development along the shorelines has been a concern. Developed beaches require maintenance and beach nourishment because of erosion caused by hurricanes, tropical storms and tides. The state of Florida estimates about 50 % of the state's beaches have some degree of erosion. Coastal states have developed beach management programs to evaluate beach erosion problems in a manner similar to the erosion, sediment and stormwater control programs employed by other states. They work with other governmental entities: local, state and federal, to protect, preserve and restore eroded beaches and coastal lowlands of the state. Beaches, dunes, boat inlets and inlet sand transfer are included in their studies, monitoring and construction activities.
Another cause, which causes a significant amount of damages, is the construction of navigation inlets for commercial and recreational boats. In order to reduce maintenance dredging of the boat inlet channels, jetties similar to river dikes are often built out from the boat inlet into the water to retard sediment from filling in the channel. The jetties often interrupt normal deposition of sand along the beach, which often results in accretion of sand on one side of the jetty and sand losses on the other side of the inlet.
The type of dredged material will determine its suitability for beach creation. Course or fine-grained materials may be available for beach creation and will determine the need for containment dikes. Beach restoration is typically done by dredging beach quality sand, preferably without any fine sediment and pumping it onto the site. The slurry of water and sand discharged from the dredge pipelines is dewatered as the water drains away. The remaining sand may then be moved about the beach to meet the design grades and profile, or in some cases to form dunes or sand stockpiles. It should be noted dredged material contaminants usually fall within the acceptable limits, which will allow the material to be used as fill for beaches and dunes and for environmental construction such as wetlands and marshes.
Land disturbed by construction activities causes soil erosion and possible migration of sediments. Sediment contains soil particles and possible petroleum products, metals, chemicals, corrosive acids, pesticides, organics or other pollutants. Onshore and offshore borrow sources must be investigate for contaminants. A construction site must be investigated for a wide range of conditions, including ground water level, surface drainage, subsurface ground conditions and existing animal habitat.
Dredging for beach and shore restoration may have adverse physical effects on the habitat when not properly planned. Certain precautions can be taken to minimize the impact of dredging activities especially from offshore borrow dredging. Some of these are:
in Turbidity from Dredging
Damage to coral reefs, fish (gill abrading and coating) and seagrass beds from
Preventative Measures: Use borrow material with low fines, avoid cutterhead dredging and avoid dredging and construction activities in sensitive resource areas.
of Beach Habitat and Animals
animal nesting areas and coral reefs are damaged by dredge anchors, cables,
pipelines and dredging operations.
Preventative measures: Schedule operations based on time of year, locate and avoid sensitive areas, avoid cutterhead dredging and use sedimentation basins to dewater pumped slurry as necessary.
Borrow Dredge Sites
Beach animals are removed or destroyed by dredging activities. Organic material
may accumulate; the effect on animal species will vary by species.
Preventative Measures: Selection of borrow areas, locate sensitive areas, avoid cutterhead dredging, perform shallow versus deep borrow dredging.
Vegetation is one
of the most commonly used methods for stabilization of dunes, beaches and any
necessary containment dikes. Site specific conditions must be considered to
use vegetation. Success of vegetation depends on the climate characteristics,
time of year, slope grades, site preparation, tide changes, water and watertable
elevation and compatibility of vegetation with these conditions. It is relatively
easy to maintain and establish vegetation and properly selected plants and grasses
are self-maintaining. Erosion control matting may be necessary to hold the seed
and soil in place until the vegetation is established.
a slope with the roots and exposed branches, stems. Surface flow velocity is
reduced and the capacity for infiltration and water withdrawal from the soils
is increased. Seedbed preparation, fertilizers, planting dates, rates of application
and type of grasses will depend on the region, specific area for planting, time
of year and as specified in the design plans. Also there are temporary and permanent
plantings. Permanent seeding is typically for periods longer than 12 months
with perennial grasses.
Riprap may be necessary
for erosion protection from flowing streams, rivers or tidal and wave action
at the proposed beach site. There are several ways to place riprap. It can be
mechanically placed along the slope or in wire baskets as a blanket over the
slope. Riprap mattresses are relatively flexible and can adjust as changes from
settlement or erosion occur. Minor damage can be easily repaired with additional
stone to fill settlement or voids from erosion. A rule of thumb for mattress
thickness is 1.5 times the thickness of the largest stone being used. Filter
fabric or a drainage material is usually placed as an underlayment to protect
from loss of fine soils and to allow for water seepage under the riprap.
This course is based primarily on Chapters 3 and 9 of the US Army
Corps of Engineers Manual, "Beneficial Use of Dredged Material", EM
1110-2-5026, (1987 Edition 20 pages), PDF file. The course is also based on
selected paragraphs from Chapter 4 of the US Army Corps of Engineers Manual,
"Environmental Engineering for Coastal Shore Protection", EM 11110-2-1204,
(1989 Edition, 20 pages), PDF file.
The link to the above course materials are:USACE "Beneficial Use of Dredged Material", Chapters 9
You need to open or download above documents to study this course.
Urban sprawl has reduced the availability and acceptability of dredge disposal areas, increasing the transport distances for dredge disposal and the cost of dredging. Environmental restrictions have also added to the costs. Among the factors considered for protective beach dredge creation is physical, engineering and chemical characteristics and the transport and handling of the material. State and federal regulations have to be complied with at construction sites in order to remove any threat to public health or the environment. The installation, type of materials, time of placement, sources of borrow material, advantages and the effects on the physical site conditions are also considered.
technical information related to this subject, please refer to:
Florida Department of Environmental Protection, Coastal planning and engineering, includes beach and inlet studies and management policies followed for shore protection.
The site provides information, news and links for the dredging construction of beaches and dunes.
Beach nourishment, dredging techniques, coastal beach protection, publications and research by the US Army Corps of Engr. Waterways Experiment Station.
Also consider US Army Corps of Engineers EM 1110-2-5025, "Dredging and Dredge Material Disposal", Chapter 4, "Containment Area Design".
1999, "Against the Tide", Anecdotes, experiences, successes and failures
are presented to give an account of coastal erosion around the nation.