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Design of Bioretention

Cory L. Horton, P.E.

Course Outline

This six hour online course provides an introduction the design and implementation of bioretention. This course is intended for practicing engineers, and others, who seek to gain knowledge to implement stormwater treatment using bioretention. After completing the course the student will have a greater understanding of when, where, and how to implement bioretention. The course content is based on the Prince George's County Maryland publication The Bioretention Manual Chapter 2 Rev. 2002 (60 pages). This publication provides a background on the siting, sizing, and design criteria for bioretention. This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of course materials.

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 understand the following concepts:

Intended Audience

This course is intended for practicing engineers, and others, who seek to gain knowledge to the design and implementation of bioretention.

Course Introduction

Urbanization causes drastic changes in the biological, ecological, and hydrologic makeup of the land. Construction inevitably causes some degree of compaction of the soil, the loss of vegetation density, the creation of impervious surfaces, and the loss of bio-diversity. This in turn changes a watershed's response to precipitation. The most common effects are decreased infiltration and evapotranspiration and decreased travel time, which often significantly increases peak flows and total runoff volume.

Water quality is also affected by urbanization. Increased flow during runoff events and decreased flow during dry weather periods and have an adverse impact on local surface waters. The loss of infiltration, and hence base flow, can result in increased temperature and decreased oxygen available for aquatic life in streams. Natural channels also undergo morphologic changes such as channel widening, downcutting, and accelerated erosion when accommodating additional runoff volumes.

What is Bioretention?

Bioretention is a water quality and quantity control practice designed to use the properties of plants, microbes, and soils to mimic the pre-developed hydrologic regime and to remove pollutants from storm water. Bioretention is a Low Impact Development (LID) Integrated Management Practice (IMP). Hydrologic functions of storage, infiltration, and ground water recharge, as well as the volume and frequency of discharges are maintained through the use of integrated and distributed micro-scale stormwater detention and treatment areas.

How does the LID bioretention IMP compare to conventional stormwater management?

Conventional stormwater management (CSM) arose from the need to prevent downstream flooding. CSM aims to limit peak flow rates by using macro-scale treatment measures. CSM does not attempt to mitigate for the increased runoff volume created by additional imperviousness. Bioretention integrates ecological and additional environmental considerations, such as water quality and water quantity into the design.

Why is bioretention gaining Popularity?

The public and stormwater professionals are becoming aware that conventional stormwater management is not addressing all of the impacts of urbanization. Bioretention is merely another tool to help minimize impacts to the environment.

Course Content

The purpose of this course is to provide guidance on the design of stormwater projects using bioretention. You will be directed to the Prince George's County Maryland website to study The Bioretention Manual Chapter 2 (2001Rev. 2002, 2.67 MB, 60 pages, PDF file format).

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

Course Summary

Bioretention has the potential to address impacts from urbanization that conventional stormwater management (CSM) is currently neglecting. The use of this microscale integrated management practices has the potential for improving water quality, reducing runoff volume, improving aesthetics, and mimicking the existing hydrologic conditions better than CSM.


For additional technical information related to this subject, please visit the following websites or web pages:

Low Impact Development Center
Center for Watershed Protection
U.S. Environmental Protection Agency
Prince George's County, Maryland
Wisconsin DNR


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

Take a 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.