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Alternative Stormwater Management: Low Impact Development

Cory L. Horton, P.E.

Course Outline

This 10-hour course provides guidance for the application and design of the alternative stormwater management techniques of Low Impact Development (LID). The course content is based on the Prince George's County Maryland publication Low Impact Development Design Strategies: An Integrated Design Approach 1999 (150 pages). This publication introduces the goals of LID, presents the methodology of LID site planning, teaches how hydrologic methods can be used in LID design, and provides information to select and implement site specific integrated management practices.

This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.

Learning Objective

This course introduces the reader to alternative stormwater management techniques of Low impact Development (LID). This course is intended for practicing engineers, and others, who seek additional alternatives to conventional stormwater management practices.

At the conclusion of this course, the student will:

Course Introduction

Environmental Effects of Urbanization

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 Low Impact Development?

Low impact development is a relatively new site design strategy with the goal of creating a post development hydrologic landscape that mimics pre-developed conditions. 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 retention and detention areas, reduction of impervious surfaces, and the lengthening runoff time (Coffman, 2000). LID also incorporates non-structural site design goals such as the avoidance / minimization of impacts to sensitive site features such as permeable soils, steep slopes, wetlands, and flood plain areas.

How does LID 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. In many ways LID aims to treat the problems at hand, rather than merely dealing with the symptoms. Low impact development (LID) integrates ecological and environmental considerations into all phases of urban planning, design, and construction.

Why is LID gaining Popularity?

The public and stormwater professionals are becoming aware that conventional stormwater management is not addressing all of the impacts of urbanization. LID is merely another viewpoint on stormwater management, that presents tools to help minimize impacts to the environment.

Course Content

The purpose of this course is to provide guidance on the design and construction of LID. You will be directed to the U.S. Environmental Protection Agency website to study Low Impact Development: an Integrated Design Approach (1999 edition, 9MB 150 pages, PDF file format), which presents the methodology and design approach of LID site development. The link to the document is as follows:

Low Impact Development: an Integrated Design Approach

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.

Table of Content

Chapter 1 - Introduction

Chapter 2 - Low-Impact Development Site Planning

Chapter 3 - Low-Impact Development Hydrologic Analysis

Chapter 4 - Low-Impact Development Integrated Management

Chapter 5 - Erosion and Sediment Control Considerations for Low-Impact Development

Chapter 6 - Low-Impact Development Public Outreach Program

Course Summary

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

Related Reading

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

Low Impact Development Center
Center for Watershed Protection
Stormwater Manager's Resource Center
U.S. Environmental Protection Agency
Prince George's County, Maryland

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 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 professional engineer. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.