Adapted from the Southeast Michigan Low Impact Development Manual.
The LID site design process builds on the traditional approach to site design. It begins with analysis of the site, and incorporates steps to involve local decision makers early in the process. The process has been consolidated into nine basic steps:
Step 2: Inventory and evaluate the site
Step 3: Integrate municipal, county, state, and federal requirements
Step 4: Develop initial concept design using nonstructural BMPs
Step 5: Organize pre-submission meeting and site visit with local decision makers
Step 6: Incorporate revisions to development concept
Step 7: Apply structural BMP selection process
Step 8: Apply the LID calculation methodology
Step 9: Develop the preliminary site plan
Each designer may want or need to adjust the process to fit specific site circumstances.
The EPA defines a best management practice (BMP) as "a device, practice, or method for removing, reducing, retarding, or preventing targeted stormwater runoff constituents, pollutants, and contaminants from reaching receiving waters." Despite the widespread use of "best" to describe these practices, these practices are much more effective when used in conjunction with each other. There are over 200 BMPs that may or may not apply to a particular project. Different practices may be addressed during all or some of the project phases. For example, saving a tree requires careful site layout in the planning phase: a design that reduces cut and fill, shows tree protection, and is mindful of utility and other excavation cuts needed during construction; a general contractor who respects the tree protection zone outlined during the design phase and calls an arborist when roots must be cut; and maintenance practices that support the health of the tree through appropriate pruning, integrated pest management, and limiting compaction.
Best management practices can be divided into two overarching categories, non-structural and structural. Non-structural BMPs tend to be either good decisions that protect a site (i.e. limit compaction), restore a site (i.e. use a foundation system that won't impede subsurface flows) or temporary measures (i.e. employ sediment prevention and erosion control). These practices may also be associated with behavioral changes like using integrated pest management.
Structural BMPs, on the other hand, are engineered or highly designed facilities that mitigate the damage created by changing the land use from natural lands (pre-developed or pre-settlement) to any other use (post-developed). They tend to be expensive and not as effective for protecting water resources as non-structural practices.