DESCRIPTION
This system consists of elements included in and processed through the local water cycle.

HYDROLOGIC FUNCTIONS

Attenuation: one of the basic functions of the hydrologic system is to hold, or attenuate, water in the landscape, so that those function more like sponges than umbrellas. Sponges absorb moisture, holding onto it and letting it slowly leak out over time. This function allows derived functions like Floodplain management or Flow control.
Groundwater recharge: there are many problems that arise when we do not attenuate our stormwater and one of the biggest is a lack of groundwater recharge. Groundwater recharge isn’t just about replenishing “fossil water” repositories, but it is also about ensuring creeks and streams are able to maintain their flows throughout the warm dry months of summer.
Water quality: when water hits our impervious surfaces, it also collects contaminating metals, minerals, fertilizers and other pollutants. This has had a devastating impact on coastal fisheries and other ecosystems. One of the functions of the typical hydrologic system is to clean and purify water, removing toxins from the flow of materials before it gets to a “receiving” body, and thereby improving water quality.
Water reuse: in nature, there is no such thing as “wastewater", everything is used, cleaned and reused again and again. New technologies are allowing us to make it possible to do the same in our human environments, eliminating wasted water in favor of using and reusing all water including air conditioner condensate, stormwater, gray water, and black water.


PERFORMANCE METRICS
Evaluation of the quantity and quality of clean water sources, stormwater, gray water, black water, and aquatic environments.
Amount of water retained/detained: the amount and time of attenuation are critical measures of the health of the hydrologic system. A hydrograph of stormwater discharges from various land covers shows the umbrella effect in urban areas (spikes soon after a rain event: impacts of impervious surfaces sluice water straight off of the land) and the sponge effect in forests (where the leaves, branches, shrubs, and soil all conspire to hold onto any water and to use it).
Amount of pervious surface: within a development, a number of things need to be impervious, but not nearly as much as we currently create. Technologies like porous pavements, green roofs, green walls, bioswales, etc which reduce our “effective impervious surfaces” by holding water in a series of distributed infrastructures.
Pollution abatement/removal: by analizing water quality. For example, a study from Ontario comparing runoff from a normal parking space, a parking space with a bioswale adjacent to it and a parking space using permeable pavements showed a significant reduction in a variety of pollutants including lead.
Hydrologic connectivity: one fundamental measures of hydrologic system health is connectivity, which refers to the “transfer of matter, energy and/or organisms within or between elements of the hydrologic cycle.” (Pringle, 2001).
Cost savings over traditional infrastructure.


WHAT IS LOW IMPACT DESIGN AND HOW CAN IT IMPACT YOUR PROJECT?
Simply stated, Low Impact Design is a way to approach stormwater management. It is intended to minimize the quantity and maximize infiltration & reuse of runoff. It is intended to, as closely as possible, replace the hydrologic cycle that existed before development.

CASE STUDIES: PLANNING AND POLICY
Water sensitive urban design program
Portland Stormwater Discount Program
Puget Sound Partnership's LID resources
LIUDD Policy Report from New Zealand
Rainwise, Seattle, WA

CASE STUDIES: HIGH PERFORMANCE LANDSCAPES
Mt. Tabor Middle School, Portland, OR
8th Avenue "Industrial Strength" Natural Drainage


HYDROLOGIC SYSTEM RESOURCES

1. Model stormwater BMP operations and maintencance ordinances:http://www.epa.gov/owow/nps/ordinance/stormwater.htm
2. High-performance infrastructure article from Urban Land
3. Washington State University Extension, Pierce County LID Links
4. NRDC'S Rooftops to Rivers report
5. City of Portland'sStormwater Solutions Handbook
6. Case study of Seneca College porous paving and bioswale performance
7. Powerpoints from a 2007 LID conferences
8. NSCU stormwater engineering group
9. Low Impact Development Center
10. Center for Watershed Protection
11. Oregon's Stormwater Solutions: Turning Oregon's Rain back into a Resource
12. Facility for Advancing Water Biofiltration
13. TheEPA's Low-Impact Development website, with some great links and reports
14. EPA's report with LID case studies and favorable cost comparisons with typical infrastructure
15. Stormwater Magazine:How Green Infrastructure Measures up to Structural Stormwater Services
16. EPA Green Infrastructure Strategy Statement
17. Soil for Salmon
18. Building Soil
19. Water Environment Research Foundation's Online Tool Using Rainwater to Grow Livable Communities
20. EPA - Urban BMP Performance Tool
21. LID Urban Design Tools
22. Water Management Strategies: Seattle Case Studies, by Matt Martenson, Berger Partnership intern
23. Casey Trees' Green Build Out Model for Green Roofs and Trees in Washington DC
24. EPA Grey Funnels to Green SpongesPodcastandTranscript
25. Water Sensitive Urban Design program
26. EPA Watershed Academy Webcasts
27. LID Center's Green Highways, Green Streets websiteplaNYC Sustainable Stormwater Management Plan 2008
28. Matt Baumgardner'sStormwater Library Blog
29. Brad Lancaster'sRainwater Harvesting for Drylands and Beyond
30. Kentucky Wet Growth Tools for Sustainable Development
31. Green Infrastructure Retrofit for a Vacant Shopping Center