Frequently Asked Questions
Question: What is Low Impact Development?
Answer: "LID is a storm-water management and land
development strategy applied at the parcel and subdivision scale that
emphasizes conservation and use of on-site natural features integrated with
engineered, small-scale hydrologic controls to more closely mimic
predevelopment hydrologic functions." (LID Technical Guidance Manual, Puget
Sound Action Team, 2005)
Question: Do LID techniques take up a lot of land?
Answer: In most cases, Low Impact Development
techniques can actually reduce the amount of land devoted to stormwater
management, because LID lessens the need for large detention ponds. Green roofs
take up no extra space at all, while techniques such as bioretention areas,
grass filter strips, and swales help to fulfill site landscaping/open space
requirements. Also, narrower roadways and smaller parking lots help to conserve
Question: Won't narrower roadways impede large
emergency and utility vehicles?
Answer: Narrow streets in low-traffic residential
areas are generally not a problem for emergency access; especially since
on-street parking is rare (most new homes have off-street parking.)
Conventional street widths are based on a scenario in which two fire trucks
going in opposite directions need to pass each other at full speed with cars
parked on both sides of the street. Alternative roadway cross-sections can
provide sufficient room for passage of emergency vehicles, with the recognition
that oncoming traffic may need to pull into a parking lane.
Question: Won't flooding be a problem without curbs
Answer: Properly designed Low Impact Development
techniques will convey water away from buildings and paved areas as quickly as
conventional stormwater systems. Because LID emphasizes infiltration and
reduction of impervious surfaces, there will actually be less runoff and a
lower potential for flooding downstream. With a decentralized approach, one
component (such as one bioretention cell) might fail without compromising the
integrity of the entire system.
Question: What about standing water?
Answer: All Low Impact Development techniques are
designed to prevent standing water and pest problems. Bioretention areas should
drain within 72 hours after a rainstorm, and should be designed with an
overflow outlet to prevent flooding. On sites with tight soils, bioretention
and infiltration areas can be designed with perforated underdrains to allow
rapid drainage. Cisterns and rain barrels should all be fitted with screens to
prevent mosquito breeding.
Question: Does LID cost more than conventional
Answer: Some Low Impact Development techniques can
cost more than conventional approaches, but overall LID is cost-competitive
because it can reduce the size of stormwater pipes and detention ponds, reduce
the amount spent on paving all while enhancing the site's aesthetics and value.
The life-cycle cost of green roofs is lower than conventional roofs due to a
much longer life span and considerable savings on heating and cooling
Question: Does LID involve expensive and complicated
Answer: All stormwater management structures
require some sort of ongoing maintenance, and LID techniques are no different.
However, many of the maintenance activities associated with LID strategies are
quite simple and can be conducted by property owners or landscaping crews, with
proper direction. Pervious concrete needs only minimal maintenance. Parking
areas and sidewalks properly designed and constructed will last 20-40 years
with little or no maintenance. Periodic sweeping, vacuuming, or power-washing
are all that's needed. Maintenance actions for other LID features can include
mulching bioretention areas, reseeding or re-vegetating swales and rain
gardens, picking up trash, removing accumulated sediment and dead vegetation,
and monitoring performance of the system.
Do you have other questions
about LID? If so, email firstname.lastname@example.org.