Low Impact Development
Low Impact Development (LID)
is a stormwater management approach that works with nature to manage rainwater as close to where it falls as possible.
What is Stormwater runoff?
Stormwater runoff is rain or snowmelt when it flows over land or paved surfaces and is not absorbed into the ground.
The Problem with Runoff
As water runoff flows across the ground's surfaces, it picks up what it touches. The further over land runoff travels, the more polluted it becomes.
Unless something intercepts it, the runoff carries dirt, chemicals, and other pollutants directly to our streams and waterways.
Skagit County is subject to a National Pollutant Discharge Elimination System (NPDES) permit that can result in significant penalties upon the County and property owners if polluted water is discharged to ditches or streams. Stormwater management is governed by Skagit County Code Chapter 14.32, which received major revisions effective January 1, 2016. All land disturbing activity (except when vested before that date) must manage stormwater consistent with this chapter.
Stormwater Management Requirements
Stormwater Site Plan Requirements
The other Problem; there's too much runoff
As we build more roads, houses, and other hard surfaces, the less water is able to be absorbed into the soil and underground aquafers, so more and more water is running across the surface. The increase of surface water Runoff can be a powerful thing, causing erosion and flooding damage.
Every site that is not perfectly flat and perfectly level is a watershed
(the land area down which all water flows).
All land on earth is a watershed
The amount of area covered by plants affects the amount of water that will infiltrate the soil.
Greater impervious areas (like roads, roofs, and parking lots) result in greater amounts of water runoff.
Plants slow the flow of water and increase the permeability of the soil.
LID simply works
Low Impact Development manages water on your own site, focusing on slowing rainwater down, controlling the quantity and flow of stormwater, soaking it up, and using soil and plants to clean it. Slowing the water down limits erosion and runoff of polluted water, filters it, and keeps water usable onsite
When it rains in the forest, most of the water evaporates or is absorbed into the ground where it recharges groundwater or is taken up by the roots of the plants and trees. Allowing water to filter through the ground naturally, removes many of the pollutants in the water before it reaches our rivers, lakes, and marine waters.
Traditional Stormwater management (also called "gray infrastructure")
channels runoff from the site as quickly as possible. When our stormwater management process was originally created, the main concern was the potential damage to structures, so the focus was to direct runoff away from roads, buildings, and structures quickly.
Unfortunately, this type of management results in too much water, flowing along, picking up contaminants, flooding rivers, and polluting all our waterways. The gray infrastructure in many areas is aging, and it doesn't have the capacity to manage large volumes of stormwater.
Low-Impact Development (LID) (also called "green infrastructure")
is designed to mimic the natural hydrologic functions of a site.
Slowing the runoff, allows the water to filter into the soil which reduces the amount of runoff eroding land and picking up pollutants, which reduces the amount of pollutants that end up in our waterways.
Slow the flow of water, so it can be soaked into and filtered through the soil.
Water is an important resource; we shouldn't let it run amuck.
The Basics of LID
Minimize site disturbance and protect native soils and vegetation (Don't remove native trees and shrubs unnecessarily. Do not disturb or compact soil unnecessarily.)
Use on-site natural features (Let the site work for you.)
Manage stormwater close to the source (don’t let the water leave the site).
Distributed stormwater Best Management Practices (BMPs) (Use BMPs effectively throughout the site.)
The Good News!
Not only do these techniques improve water quality, restore ground water reserves, and create a healthier yard, but many of these techniques are easily accomplished, beautiful, and low maintenance additions to our homes that don't require any extra cost, just a different plan.
WSU Catching Rain fact sheets
Low impact development promotes the view of rainwater as a resource to be preserved and protected, not a nuisance to be eliminated.
When implemented broadly, LID can mitigate the urban heat island effect, save energy, reduce air and water pollution, improve neighborhood aesthetics, increase groundwater recharge, and increase habitat for wildlife, such as birds and pollinators.
LID Parking Lot
LID is economical
LID is as cost-effective as—if not more cost-effective than—conventional approaches in part because of the long term savings in maintenance and repair. Not to mention the aesthetic benefits.
Raingardens attract dragonflies, frogs, and birds
Water in a properly designed rain garden will not last more than 2 days after most storms which is not long enough for mosquitoes to use, but it will be enjoyed by many of our wild friends.
Rain gardens are designed to be self-sufficient
Some weeding and watering will be needed in the first two years, and perhaps some thinning in later years as the plants mature, but a well-planned raingarden can be maintained with little effort after the plants are established.
Why aren't more people using LID techniques?
I don't know! Maybe they haven't heard about them yet. We need to spread the word!
LID Techniques Can Be Applied at Any Development Stage
• In undeveloped areas, an LID design can be incorporated in the early planning stages. Typical new construction LID techniques include protecting open spaces and natural areas such as wetlands, installing bioretention areas (vegetated depressions) and reducing the amount of pavement.
• In developed areas, communities can add LID practices to solve problems and provide benefits such as being used to buffer structures from roads, enhance privacy among residences, and for an aesthetic site feature. Typical post-development LID practices range from directing roof drainage to an attractive rain garden to retrofitting streets with features that capture and infiltrate rainwater
Is LID required?
LID is the preferred approach to stormwater management countywide.
Inside the NPDES Permit Area and the Special Flood Hazard Area, LID techniques are required unless not feasible. When required, applicants must use the techniques in the Low Impact Development Technical Guidance Manual for Puget Sound (Puget Sound Partnership and WSU Extension, 2012) unless the Administrative Official determines the techniques as not feasible.
• Engineered systems that filter storm water from parking lots and impervious surfaces, such as bioretention cells, filter strips, and tree box filters
• Engineered systems that retain (or store) storm water and slowly infiltrate water, such as sub-surface collection facilities under parking lots, bioretention cells, and infiltration trenches
• Pervious, permeable, and porous surfaces that allow drainage between impervious surfaces such as porous concrete, permeable pavers, or site furnishings made of recycled waste
• Remove curbs and gutters from streets and parking areas to allow storm water to "sheet flow" into vegetated areas.
• Native or site-appropriate vegetation.
• Low-tech vegetated areas that filter, direct, and retain storm water such as hedgerows, rain gardens, and bio-swales
• Pervious, permeable, and porous surfaces that help break up (disconnect) impervious surfaces such as porous concrete, permeable pavers, or site furnishings made of recycled waste
• Water collection systems