Storm Water Low Impact Development (LID) Part 1 – LID Concepts

In Storm Water Low Impact Development (LID) Part 1 – LID Concepts, you'll learn ...

• Impact of urbanization on runoff
• Advantages of LID
• Water quality improvements with LID
• 90% rainfall analysis

Overview

Credit: 2 PDH

Length: 24 pages

Low Impact Development (LID) is a relatively new concept for storm water management that can provide numerous benefits to a community that are different than the benefits provided by conventional storm water management approaches. When rain falls onto the hard surfaces in an urban landscape, the water cannot infiltrate into the soils in the same way that it does in a rural landscape, so the runoff volume and peak flows are significantly increased. Most LID techniques are designed to reduce and treat storm water near its source. Use of LID (also called green infrastructure in some areas) can help to mitigate the impacts of urbanization.

Part 1 of this two-part course series will provide engineers and public works officials with the basic concepts of LID design. Part 2 will cover the detailed hydrologic and hydraulic analysis of LID features using the EPA SWMM software.

This course, Part 1, will cover the basis of the 90% rainfall event, including an explanation and example of how this value should be calculated. It will include a discussion of the different LID features that can be used. The importance of field testing of infiltration for these features will be discussed along with a description of several common testing methods. A discussion of how to ensure the design flows are conveyed to the feature will be provided. A description of the process to determine the impact of a LID feature on runoff will also be provided.

It will include examples of several common features and include analysis of conveyance into the LID, storage, infiltration and bypass flows. The examples will be used to illustrate the effectiveness of LID features on total runoff volume and on reduction of peak flows.

In an attempt to mitigate the impacts of urbanization, LID techniques promote substantially more infiltration into the soils than normal storm water management techniques. There are many different LID techniques, but from an engineering standpoint, they can all be broken down into simple hydraulic functions.