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Stormwater Control Measures-Post Construction

John Poullain, P.E.


Course Outline

This four-hour online course provides general guidelines and practices for stabilizing post construction sites by controlling both the stormwater quantity and quality. The practices achieve these goals by slowing stormwater flow which allows suspended sediment to settle out and thus not leave the site. Some of the practices discussed include rooftop and surface runoff controls, green roofs, swales, ponds, stormwater wetlands, and stream bank protection. Remedial actions and activities performed at post construction sites must comply with federal, state and local regulations to protect water quantity and/or quality.

Following topics are covered in this course:

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 have covered these topics:

Intended Audience

This course is intended for engineers, planners, local governments, site developers, and others involved in SCMs at completed construction sites. 

Benefit to Attendees

The student will become familiar with practices used to manage stormwater drainage at post construction sites. The purpose is to reduce erosion and runoff of sediments and pollutants onto down slope land and downstream water or streams. Ground water and surface water can contain contaminants - volatiles, soluble organics, corrosive acids and alkalis. The student will better understand the application of interception or diversion methods such as listed above. Basic guidance in the selection of the most appropriate practice to use and cost considerations are discussed.  

Course Introduction

This course covers the practices commonly used to manage the movement of storm water and sediments at post construction sites with permanent devices. Early soil conservation efforts were driven by the wind erosion occurring during the “dirty thirties”. These first measures were aimed at soil conservation but as land development increased, runoff erosion and sedimentation became issues also. Land disturbed by construction activities requires permanent post construction stormwater control to stabilize the site after construction is complete. 

Sediments contain not only soil particles but pollutants like petroleum products, metals, chemicals, pesticides and organics. Measures for erosion and sediment control are necessary to protect property, waterways and wildlife habitat. Based on volume, sediment may be a larger pollutant of streams, rivers and lakes than toxic waste or chemicals. The amount of sediment could also be more from construction activities than would normally occur. State and local governments have ESC regulations that require special precautions for land-disturbing activities.  

Soil Erosion Causes

Land Development and Land Use Changes. Increased urbanization, more roofs, paving and 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 area further accelerates erosion and siltation.

Overbank Drainage and Groundwater Seepage. Overland stormwater drainage or runoff can severely erode unprotected slopes during runoff. Rainfall that does not runoff may seep downward through the soil resulting in a loss in shear strength. This condition may appear as wetness or piping flow down the slope. Clay soils swell and lose shear strength after absorbing surface and groundwater, resulting in creep or soil movement.

Management and Protection Practices

Management practices include overland flow diversion and perimeter protection of a site with earth berms and ditches, vegetation and by controlling development along fills. Structural methods include riprap, rock check dams, earth berms, sediment fences, compost blankets, straw bale traps and sediment basins.

Swales - Swales are used in a similar fashion, as ditches but do not block traffic as ditches due to their wider and shallower channel cross section. A wider and shallower cross section reduces the stormwater velocity and potential for erosion. A wider but shallower trapezoidal channel compared with a v-ditch of equal area for instance will be shown to have a lower velocity of flow. Grassed swales also promote infiltration and help to remove sediments.

Vegetation - Site specific conditions must be considered to use vegetation. Success of vegetation depends on the climate characteristics, slope grades, site preparation and compatibility of vegetation with these conditions. Vegetation is one of the most commonly used methods for stabilization. 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. Slopes flatter than 1V to 1 ½ H can accommodate vegetation but slopes flatter than 1V on 2H or 3H are preferable especially for ease and safety in maintenance.

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. Annual grasses provide winter protection for the permanent grasses to become established and help in controlling weeds.

Course Content

This course is based primarily on Chapter6 (Section 5) 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, (2011 Edition, 108 pages), PDF file. 

Missouri Department of Natural Resources Manual, “Protecting Water Quality”

Terms and Definitions

Please click on the above underlined hypertext to view, download or print the document for your study. Because of the large file size, we recommend that you first save the file to your computer by right clicking the mouse and choosing "Save Target As ...", and then open the file in Adobe Acrobat Reader. If you still experience any difficulty in downloading or opening this file, you may need to close some applications or reboot your computer to free up some memory.

Course Summary

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 considers the techniques and methods used to manage stormwater, the control of run-on and run-off and the control of soil erosion and sediment at construction sites after construction is completed. Among the practices considered are rooftop runoff control, bioretention, dry and wet swales, ponds and stormwater wetlands. The installation, advantage and disadvantages and the effects of the physical site condition are also considered. 

Related Links

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

http://www.errosioncontrol.com/ec.html
“Erosion control at Construction Sites” has information about erosion and sediment control and stormwater management from the journal “Erosion Control” published by the International Erosion Control Assc. 

http://cwp.com/store/free-downloads.html
The Center for Watershed Protection provides technical tools to local governments and watershed organization watershed protection, restoration and research and stormwater management.

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.