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Protective Coastal Beaches and Dredging

John Poullain, P.E.


Course Outline

This three-hour 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.

Learning Objective

At the conclusion of this course, the student will:


Intended Audience

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.


Course Introduction

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 for environmental.

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:

a. Increase in Turbidity from Dredging

Impacts: Damage to coral reefs, fish (gill abrading and coating) and seagrass beds from resuspended sediments.
Preventative Measures: Use borrow material with low fines, avoid cutterhead dredging and avoid dredging and construction activities in sensitive resource areas.

b. Disturbance of Beach Habitat and Animals

Impacts: Beach 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.

c. Offshore Borrow Dredge Sites

Impacts: 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.

Vegetation protects 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.

Course Content

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 3

USACE "Beneficial Use of Dredged Material", Chapters 9

SACE &Environmental Engineering for Coastal Shore Protection", Chapters 4

You need to open or download above documents to study this course.


Course Summary

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.


Related Links

For additional technical information related to this subject, please refer to:

http://www.dep.state.fl.us/beaches/
Florida Department of Environmental Protection, Coastal planning and engineering, includes beach and inlet studies and management policies followed for shore protection.

http://www.dredgingcontractors.com/
The site provides information, news and links for the dredging construction of beaches and dunes.

http://www.wes.army.mil/
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".

Cornelia Dean, 1999, "Against the Tide", Anecdotes, experiences, successes and failures are presented to give an account of coastal erosion around the nation.
Quiz

Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.