John Poullain, P.E.
online course provides general guidelines and practices for the development
of wetland habitat areas by dredging and the construction of stormwater wetlands
for stormwater runoff and sediment control at construction sites and urban areas.
The course provides an overview for planning, design and utilization of dredged
material as an alternative method for beneficial dredge disposal. Wetland creation
with dredged material often consists of filling, raising and protecting areas
that are periodically or permanently submerged. Remedial actions and activities
performed at construction sites must comply with federal, state and local regulations
to protect water quality.
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 and developing feasible areas for wetlands and marches with dredged material, the benefits and disadvantages. Design factors including dredge material, weirs, shape and size and siting of dredged material wetlands are discussed. The student will also become familiar the techniques of constructed wetlands to manage stormwater drainage at construction sites and developed areas. The purpose is to reduce erosion, water ponding and runoff of sediments and pollutants onto down gradient land and downstream water or streams since groundwater and surface water may be contaminated with volatiles, soluble organics, corrosive acids and alkalis.
About 70% of the
dredged 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 wetlands rather than solely as
a disposal necessity. The course also covers the construction of stormwater
wetlands. Wetlands are used to manage the movement of storm water and sediments
at construction sites, improve water quality, and retain floodwater, recharge
groundwater and to protect commercial or residential areas from storm-driven
waves and tides. Hurricane protection is reduced as wetlands are lost and more
open water appears. Other benefits of wetlands are the creation of wildlife
and fish habitats for commercial and recreational purposes.
Wetlands have many names - freshwater and saltwater marches, bogs, sloughs, swamps, bottom lands. They are in-between places, which lie between large bodies of water, coastal areas, lakes and streams and dry land. They are defined as areas inundated by surface or ground water at frequencies and duration that support vegetation adapted to saturated soil conditions. Although all wetlands are not "wet" all year, drier wetlands have significant functions. The type of dredged material will determine the suitability for wetland creation. Course or fine-grained materials may be used for their creation and will determine the need for containment dikes. It should be noted dredged material contaminants usually fall within the acceptable limits, which will allow it to be used as fill material for wetland and environmental construction.
In addition to the above-mentioned methods for wetland development, there are also wetland restoration projects and environmental enhancement projects. The purpose of these projects is to maintain or revive former wetland areas by diverting stream flows and mimic spring floods. Levees are normally built for flood protection. In these cases however interior water levels are regulated with gated structures to provide conditions that naturally occurs. Gated gravity drainage structures are built into existing river levees to divert sediment-laden river water in a controlled manner and flood the landside marshes. The goal is to allow deposition of sediment load and nutrients as was performed naturally before levees were built. The technique is beneficial in restoring wetlands, which have settled or eroded.
The wind erosion occurring during the "dirty thirties" fostered early soil conservation efforts. These first measures were aimed at soil conservation but as land development increased, runoff erosion and sedimentation became issues also. Remedial actions include stormwater control like constructed wetlands to prevent off-site migration of surface water, sediments and pollutants which can contaminate the soil, groundwater, wells and nearby bodies of water unless properly managed. Land disturbed by construction activities causes soil erosion and downstream sedimentation. Sediment contains soil particles along with petroleum products, metals, chemicals, corrosive acids, pesticides, organics and other pollutants. A construction site must be investigated for a wide range of conditions, including ground water level, surface drainage and subsurface ground conditions.
Plans for erosion and sediment control (ESC) are necessary to protect property, waterways and wildlife habitat. An ESC plan establishes the specific control practices like wetlands to prevent erosion and off site sedimentation. Based on volume, sediment from erosion may be a larger pollutant of waterways and lakes than are toxic waste or chemicals. In cases where the National Pollutant Discharge Elimination System (NPDES) for stormwater permits applies, a Stormwater Pollution Prevention Plan (SPPP) is required for construction sites. State and local governments also have ESC regulations that require special precautions for land-disturbing activities.
Erosion occurs naturally but is accelerated by land development and land use changes. Increased urbanization, with increased roof areas, pavements and the clearing of woodland and grassland without proper conservation management create erodible land areas, speed up runoff and remove areas available for rainfall infiltration. Vegetation removal from land areas will further accelerate erosion and siltation. Using constructed wetlands attempts to keep the stormwater runoff rate from exceeding the predevelopment runoff rate. In order to develop an area and properly manage the stormwater, the predevelopment and post development runoff must be estimated and compared for the area.
The constructed wetlands described in this course are intended for the detention of runoff and the deposition or trapping of sediment. If the containment could retain all runoff the efficiency would be 100% but would not be impractical. Complete retention would be prohibitively expensive considering the required acquisition of land and the loss of future development. Detention practices serve to reduce the frequency of erosive downstream flooding and to trap the sediment and contaminants or nutrients carried by the runoff. Water is discharged at a controlled non-erosive rate and suspended particles are allowed to settle in the wetlands.
Vegetation - Site specific conditions must be considered to use vegetation. Success of vegetation depends on the climate characteristics, slope grades, site preparation, water and watertable elevation and compatibility of vegetation with these conditions. Vegetation is one of the most commonly used methods for stabilization of stormwater dikes and in some cases containment dikes. It is relatively easy to maintain and establish 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. Nurse crops are sometimes uses in the seeding mix. Annuals such as wheat or rye provide winter protection for the permanent grasses of stormwater wetland containment dikes to become established and help in controlling weeds.
Riprap - Riprap may be necessary for erosion protection from flowing streams, rivers or tidal and wave action at the proposed wetland 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 5 of the US Army
Corps of Engineers Manual, "Beneficial Use of Dredged Material", EM
1110-2-5026, (1987 Edition 31 pages), PDF file. The course is also based on
the Constructed Wetlands section from the Missouri Department of Natural Resources
Manual, "Protecting Water Quality", a guide to erosion, sediment and
stormwater best management practices (BMP) for development sites, (1998 Edition,
9 pages), PDF file and the Course Introduction paragraph.
The link to the above course materials are:
Item numbers indicated in the text (item 1, 2 etc) correspond to similarly numbered items in Appendix A, Bibliography of EM 1110-2-5026.
You need to open or download above documents to study this course.
Urban sprawl has reduced the availability of dredge disposal areas, increasing the distances for dredge disposal and the cost of dredging. Environmental restrictions have also added to the costs. Among the factors considered for wetland 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. This course also considers the construction of stormwater wetlands to control soil erosion and sediment at construction sites and to protect water quality. The design, installation, type of materials, advantage and the effects of the physical site condition is also considered.
technical information related to this subject, please refer to:
The Center for Watershed Protection provides technical tools to local governments and watershed organization watershed protection, restoration and research and stormwater management.
Case studies for EPA wetland development program (WPDG) considering 6 core elements and serves as a guide for state and federal agencies to evaluate their wetland programs.
Also consider US Army Corps of Engineers EM 1110-2-5025, dredging and Dredge Material Disposal", Chapter 4, Containment Area Design
Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.