One of the hot topics in stormwater management is Low Impact Development (LID), an approach to land development that attempts to manage stormwater as close to its source as possible by imitating the natural hydrology of the project site.  For example, LID techniques like rain gardens, vegetated “green” roofs, and permeable pavements are all designed to retain more water on site and send less water into pipes or water bodies.  Some developers are starting to experiment with LID on a voluntary basis, and larger cities and counties are adopting new development code provisions requiring the use of LID “where feasible” – a result of a recent ruling by the State Pollution Control Hearings Board.

After hearing the story of failed rain gardens in Ballard, some have questioned whether it makes sense for local governments to require developers to use LID techniques. We should certainly try to find lessons in such failures. But the lesson here isn’t so much about whether LID should be required, but when and how it should be required.  The rain gardens in Ballard failed because the City took shortcuts in evaluating the feasibility of LID on that site.  As a result, the City overlooked conditions that made LID more problematic in that location, such as the presence of underground spring water and shallow groundwater.

Whether a particular LID technique is “feasible” depends on a number of factors, including site conditions such as soils, slopes, and groundwater levels, the type of land use, and operations and maintenance considerations.  These factors are likely to be addressed in preliminary draft permit language addressing the use of LID, scheduled for release by the State Department of Ecology on May 16.  By describing in more detail what it means for LID to be “feasible,” and when and how LID should be required, that permit language will provide guidance for development code requirements to be adopted by cities and counties that are subject to the LID requirement.