Stormwater Library

resources for stormwater professionals

Archive for LID

Low Impact Development Project Database

One of the trends that I have been spotting in research studies of LID acceptance into practice has been this concept of “proof of benefit”.  Essentially, the idea is that by having high-profile, high-traffic demonstration projects, stakeholders will see the benefit and will encourage LID’s spread through new development, as well as through retrofits in urban settings.  It’s a great concept, but one that takes a decade to truly take hold in a municipality.

The idea behind this website has been pretty simple.  Take a look at the tools that are available in stormwater BMP design and point out the more novel approaches and interesting research being done in sustainable stormwater engineering.  To help further the development of “proof of benefit” as a way of spreading Low Impact Development in communities, I am proposing the development of an LID project database.  It is possible this has been done to a certain extent.  I claim no mantle of originality to any ideas presented on this site and this is certainly no different.  Simply, what I would like to see is a much more comprehensive look at projects that have been completed, are currently in progress, or are in their infancy.  This will be a laborious process – one that will certainly require input and collaboration.  To this end, I make my formal request to others right now.

The idea is this.  Send me information on any project that is available in the public domain.  In particular, I need to be able to start with the basics such as: project location (street address), general description of the project, type of LID approach being used, status of the project, and if possible, a project contact.  I will most likely expand the database to include other fields as development progresses, but starting off simple will get me to a finished product more quickly.  Ideally, I would like to see this be a living databse that is fed by users as new projects spread through North America.

In addition to serving as a way of finding demonstration projects, I envision a database that is tracking the popularity of different LID approaches and spotting trends in technology – perhaps even helping to shine a light as to where LID is falling behind in acceptance.

Email your project lists and ideas to Matt Baumgardner at


Identifying the roadblocks to LID – 2008 Puget Sound Study

In 2008, a research study was sponsored by the State of Washington to survey the progress being made by 19 local governments in adopting LID controls into their building codes. A representative from each of the 19 municipalities was asked the same set of questions regarding the barriers seen to LID implementation. Some of the trends they found in the responses include the following:

  • Perception that LID is not a proven technology
  • General public and government officials lack understanding of LID
  • Perception that LID is more expensive when compared to traditional BMPs
  • Planning departments lack training to review and inspect LID controls
  • Developers lack knowledge of LID
  • LID difficult to use in urban settings, difficult to retrofit

One of the more interesting solutions to the obstacles focused on funding of “high traffic” demonstration projects to help provide a local proof of benefit.

The report can be read in its entirety here.


Stormwater Retrofits in Urban Settings

The most recent edition of the journal Stormwater included an article on urban retrofitting. The article focused its attention on 3 retrofit projects in Portland, Minnesota, and Seattle. In particular, the article zeroes in on how each project managed the challenge of incorporating the retrofits with limited space.


In the case of the Portland project, a parking garage was redesigned to reroute stormwater to infiltration planters along two sides of the structure. The major challenge was redesigning the plumbing to properly redirect the stormwater to planters. Narrow infiltration planters were constructed with permebale soil mix and native plants to help treat and infiltrate the runoff. The planters are able to infiltrate a minimum of 2 inches of rainwater per hour and can handle practically all of the stormwater from a 2-year storm event.


By taking a street in the town of Burnesville, narrow strips in front of residential properties were carved out, sometimes using retaining walls, to cluster together a series of rain gardens. Getting buy-in from the the residents was the biggest challenge, but an educational outreach program was developed and helped to achieve 80% participation rates. Sidewalk cut-outs were incorporated to help direct street runoff to the raingardens, which were able to accomodate 0.9 inches of runoff from the tributary hardscape. There hasn’t been any concern with vector control issues, as gardens have typically dried in a 3-4 hour period. When compared with a similar nearby street also feeding Crystal Lake, runoff volumes have been reduced by 90 percent.


On a much grander scale, the city of Seattle took on a retrofit project incorporating 32 acres and 15 residential blocks. Working with the existing topography and regrading portions of streets to create a more meandering path through the neighborhoods, the engineers were able to divert stormwater to culverts, catch basins, vegetated swales, raingardens, and cascades. Swales were used in steeper areas to help control runoff velocity and volumes, while raingardens were a common feature in flatter terrain. As with the Minnesota raingarden clutstering, this large project involved networks of stormwater BMP features that worked to slow runoff, treat it, and infiltrate it to help recharge the groundwater tables.


The article touches on several of the challenges to projects like these. Limited space can be one of the largest obstacles and requires a great deal of coordination with project scheduling to prevent disruption to business and residences. It obviously impacts the design and overall effectiveness of the project and requires creative solutions to address proper stormwater management.

One of the other important considerations is educational outreach efforts. Business and homeowners often need to be educated on the need to promote infiltration. Allowing for buy-in keeps the project strong and growing. Homeowners are a critical part of the maintenance to residential BMPs, while business owners can get LEED credits and can promote their reputation as green businesses.

The biggest challenge is funding. The three examples cited in the Stormwater article all had significant funding from city grant programs. These projects require large inflows of funds to carry through all the design objectives. However, more successful projects cropping up like these examples can make it easier in the future for public works agencies to seek the necessary funds to promote urban retrofits on a larger scale.

Low Impact Development Video on Green Runoff Solutions

The US EPA and the US Botanic Garden produced a 9-minute video highlighting LID techniques demonstrated at a Botanic Garden-sponsored exhibit in 2008. The video focuses on easy-to-implement solutions like rain gardens and rain barrels, as well as green roofs and cisterns. It also provides useful tips on building a rain garden at your site – from testing the drainage (min. 1 inch per hour) to providing the right mulch and plants for your particular environment.

Developing Narrower Streets (Green Street Series)

The first approach in green street design comes before consideration of any BMPs. In the planning stages, a look at how to reduce the overall impervious area is going to make the biggest impact on effective stormwater management. According to a 1995 Center for Watershed Protection study, nearly half of all impervious cover in residential developments comes from streets. Narrowing of streets can offer as much as a 20% reduction of this impervious cover.

Addressing the misconceptions

Considerations such as emergency and large vehicle access, parking, and safety are often assumed to be at loggerheads with narrow street design. When designed properly, fire and emergency services vehicles have the ability to manuever successfully. This has also been the case with larger service vehicles like garbage and delivery trucks. Parking demands in most residential areas typically can be satisfied through use of one parking lane (rather than two) coupled with driveways. Safety studies have indicated that narrower streets have lower auto and pedestrian accident rates primarily due to speed reduction.

Obvious benefits

The significant reduction in impervious cover is going to help control maintenance costs. An even bigger savings is going to be realized when installing narrower streets. By reducing the overall width of a street by even one foot, $10,000 is saved per residential mile. Stormwater management savings associated with this street reduction should be significant, as well.

Zoning roadblocks

The challenge to implementing narrow street design comes when facing zoning laws which force the hand of many designers to follow street width minimums. While some municipalities have adopted narrower street width requirements, greater steps will need to be taken to involve more decision-makers in the process. Going forward, studies of successful narrow street programs in cities such as Portland, Oregon, need to be published to help build the case for these decision-makers.

Green Streets

A strong resource to include in your library is the Green Streets website created and maintained by the Low Impact Development Center. With respect to green infrastructure, the LID center has been leading the way in research, design, guidance documents, training, and sustainable stormwater planning. The focus of the Green Streets website is to outline the five major approaches in design. Over the next several weeks, I would like to touch on each of these approaches in more detail.

Examples and photos of the five green street design approaches are found at the website and highlighted below:

  • Alternative street design – One of the best ways to address the stormwater problems begins before the process of considering BMPs. Through careful planning and consideration of existing hydrologic features, overall impervious area can be reduced.
  • Vegetated swales – These are successful at reducing flow through overall channel roughness, reducing volume through infiltration, and improving water quality through vegetative and soil filtration.
  • Bioretention features – A good feature to include in street design is a tree box, which forms a bioretention cell that reduces volume, attenuates flow, and treats the stormwater through biological/chemical reactions in the mulch, soil, and root zone.
  • Permeable pavement – Success of permeable pavement systems is well-documented. While providing structural support, these systems allow runoff storage, as well as pollutant removal through filtration.
  • Sidewalk trees – Considering their ability to reduce stormwater runoff, attention needs to be paid to the overall soil volume provided to trees. Inadequate tree box size and overcompaction of the soil during pavement installation are cited as two examples threatening the ability of trees to properly assist in reducing runoff.