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Low Impact Development (LID) is an approach to land development (or re-development) that works with nature to manage stormwater as close to its source as possible. LID employs principles such as preserving and recreating natural landscape features, minimizing effective imperviousness to create functional and appealing site drainage that treat stormwater as a resource rather than a waste product. There are many practices that have been used to adhere to these principles such as bioretention facilities, rain gardens, vegetated rooftops, rain barrels, and permeable pavements. By implementing LID principles and practices, water can be managed in a way that reduces the impact of built areas and promotes the natural movement of water within an ecosystem or watershed. Employed on a broad scale, LID can help maintain or restore a watershed’s hydrologic and ecological functions.

Typical applications of LID include new development, redevelopment, and retrofits to existing development. LID has been adapted to a range of land uses from high density urban settings to low density development (EPA 2013), and has been demonstrated to work in arid and semi-arid regions such as eastern Washington.

The purpose of this Manual is to provide stormwater managers, site designers, and design reviewers with a common understanding of LID goals, objectives, design of individual practices, and flow reduction and water quality treatment that are applicable to eastern Washington. LID is a constantly evolving stormwater management approach. Over time, new technologies and best management practices (BMPs) will promote greater efficiency in managing stormwater runoff. This document will evolve as additional research becomes available, new and innovative practices become approved for general use, and professionals in the region gain more practical experience. The Washington Stormwater Center (WSC) will be cataloging LID research and new and emerging tools that are relevant to eastern Washington practitioners and publishing it on its website (www.wastormwatercenter.org/).

Unless adopted through a locally-enacted ordinance, the Manual is intended to provide guidance to assist professional designers and does not replace or supersede local design standards or requirements.

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