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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 land.

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 and gutters?

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 approaches?

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 costs.

Question: Does LID involve expensive and complicated maintenance?

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.

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