Print this page Beneficial Use of Dredged Material – Habitat
John Poullain, P.E.
Course Outline
This four hour online course provides an overview for the planning, design and selection of dredged material as a manageable, beneficial resource as an alternative to normal methods of disposal. Land creation with dredged material often consists of filling, raising and protecting areas that are not normally, only periodically, or permanently submerged. The types of habitat considered in this course are upland, island, and aquatic. Guidelines for development of habitat suitable for nesting birds, fish and animals are discussed. Development of wetland habitats is also briefly discussed.
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:
- Be familiar with the guidelines for planning, designing and developing areas for feasible beneficial use;
- Understand the value of dredged material as a resource and its beneficial uses in order to be included in a project’s planning stages;
- Be familiar with the physical, engineering and chemical characteristics of dredged material which will make it suitable to use for habitats;
- Consider the basic economics and methods for dewatering, transporting, handling and storage of dredged materials;
- Be familiar with the ecological and biological considerations for dredged material disposal;
- Consider factors such as dredge material characteristics, shape and size of containment areas, which affect the containment storage capacity of dredged material;
- Be aware of the environmental concerns for dredging in rivers and open water areas and to avoid the impacts of adverse operations;
- Understand the basic guidelines for nesting birds, fish and animal habitats;
- Understand the basics for planning, management and maintenance to achieve successful island habitat sites;
- Be familiar with the guidelines, dredging and disposal operations and the engineering and ecological design of upland habitat sites;
- Have an understanding for the development of aquatic habitat and seagrass habitat;
- Gain insight for the processes that are used to develop habitats and to understand the development of projects from various case studies and other examples presented in the text; and
- Be aware of local, state and federal level regulatory and environmental restrictions.
Intended
Audience
This course is intended for civil and environmental engineers and planners.
Benefit to Attendees
The student will learn the value of dredged material as a resource and its uses for several beneficial purposes. Beneficial uses discussed in this course include upland habitats, island and aquatic habitats. Among the topics covered are the physical, chemical, and engineering characteristics of dredged material, and the logistical considerations including transport, handling and storage. The local, state and federal regulatory and environmental restrictions are also presented.
Course
Introduction
About 70% of dredged material in the US are placed in aquatic disposal areas, open water, such as river channels. This course discusses confined disposal areas, island, upland and aquatic habitats where the dredged material is used as a resource that can provide beneficial uses rather than solely as a disposal necessity. Typical uses are parks, recreation, forests, industrial, commercial, residential and for upland, island and aquatic habitat.
Approximately 350 million cu. yd. of material are dredged from the waterways and shipping channels in the US each year. Striving to achieve greater economy in shipping has led to larger container ships, which in turn require deeper drafts. The port of Los Angeles has excavated channels to provide 81 feet of draft for the larger ships. Some super large ships are called post Panamanian since they exceed the draft of the Panama Canal channel.
There are several methods of excavation, which include cutter head suction and hopper suction dredges and excavators. Cutterhead suction dredges have suction pipelines to pump the dredged material into disposal areas, barges or hopper barges for longer distance transportation. At least one cutterhead dredge in the US is electrically powered via power cables from shore side substations. The Air Quality Control Board of Los Angeles required stationary construction equipment be electrically powered. The all electric dredge has a 34-inch diameter suction pipeline and is powerful enough to pump very long distances without using booster pumps, one of the longest discharge distances was about 18,000 feet. Another type of dredge, the hopper suction dredge, drag suction heads along the ocean floor or marine area to be excavated. The dredge material is deposited in the hopper and transported to disposal areas, making them a good choice for long distanced disposal areas, which usually requires pumping assistance with booster pumps.
Channel excavation may require blasting to break rock masses into more readily excavatable strata. There are a few excavators which have enough power to breakup rock with out blasting with the biggest having perhaps 370,000 lbs. of breakout force. The bucket teeth are used to break into rock gaps in order to reduce a rock mass to smaller pieces for ease in removal and loading. They are similar to the land based excavators and have hydraulically controlled booms and 26 cu yd buckets.
An example of a recent beneficial use for dredged material is the Pier 400 of the port of Los Angeles, a 590-acre container terminal that required about 60 million cu yd of dredging for the harbor and ship channels. Cutterhead suction, clamshell and hopper dredges were used. Dredged material used for the port expansion was contained within breakwaters constructed with quarry run rock and 500 lb. to one-ton rock around the perimeter. Several areas were developed into shallow-water habitats to mitigate for the port expansion into bay areas. Some ship channels were dredged to provide 50 to 81 foot drafts. A cutter suction dredge with a 34-inch diameter discharge pipe was used to pump the materials into spill barges. The spill barges in turn placed the material for port landfill via cantilever booms to get the required port landfills.
Course or fine-grained materials may be used for land creation. The types of dredged materials will determine the suitability of how the land can be used. For instance, fine-grained material requires a long time to drain and consolidate but can be speeded up with planned dewatering operation. Development of such land may be limited to uses where any imposed load is low because of the resulting weak soil strengths. The time and availability of suitable dredged material often limit the type of land use. Sound and careful long term planning and design can overcome these constraints. Also it should be noted dredged material contaminants usually fall within acceptable limits. However, contaminated dredged material can be reused in several beneficial ways as fill material, topsoil, for construction and environmental projects and as raw material for manufacturing building products such as building blocks and tiles.
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 investigated 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. Factors to consider for economic and productive dredge disposal include:
- Adequate storage capacity.
- Containment weir location, size and shape and necessary cross dikes. Adjustments in the locations and arrangements are made as dredging continues.
- Disposal operations require monitoring during and after dredging is completed.
Dredging 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 some beaches, islands 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 and other devises such as long metal staples may be necessary in some cases to hold seed, soil and transplants 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 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 the US Army Corps of Engineers Manual, Chapters 3 and 4 and 6 through 8 of Beneficial Use of Dredged Material EM 1110-2-5026, 1987 Edition, 60 pages, PDF file.
The link to the document is as follows:
A brief list of "Glossary of Terms" shown in the text material has been included as a study aid for the course:
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Course Summary
Urban sprawl has reduced the availability of dredge disposal areas, which has increased the cost of dredging by increasing the distances to available disposal areas. Environmental restrictions have also increased costs of disposal. Dredged material can be a valuable commodity by placing in beneficial use areas while also increasing land available for many purposes including fish and wildlife habitats and for land developmental. Among the factors for the end user to consider are the target habitat, physical, engineering and chemical characteristics and the transport and handling of the dredged material.
Related Links
For additional technical information related to this subject, please visit the following websites or web pages:
http://www.dredgingcontractors.com
The site provides information, news and links for the dredging and construction of channels, harbors.
http://www.epa.gov/owow/oceans/regulatory/dumped/dredgemgmt.html
US EPA site has broad field of information, case studies, and management of dredging and dredged material disposal operations for environmental protection.
The Beneficial Reuse of Dredged Material prepared for the Port of Long Beach, Long Beach, California, 2000, by Harding Lawson Associates.
Quiz
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.
