Stormwater Library

resources for stormwater professionals

Archive for Research Studies

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.



Watershed Imperviousness: 3 Recent Studies

Numerous studies have been conducted over the years that correlate the degree of imperviousness of a watershed to overall quality of surface waters fed by that same watershed.  Three studies completed in the last few years are worth noting:

Neighborhood Sidewalk/Street Watering Survey

This is a little impromptu survey that I ran over the last two nights in my neighborhood. While walking the dog at 11pm, I found roughly 10% of my neighbors were overwatering their lawns or missing their lawns altogether – and watering the sidewalks and streets.


If I estimate that each house had 6 half circle nozzles (1 GPM) and 4 quarter circle nozzles (0.5 GPM), that gives me a total rate of 8 GPM.  The total average cycle appeared to be 10 minutes – resulting in 80 gallons per household.  In most cases sprinklers were completely overspraying, but I will estimate that only half of this volume was runoff.  If I make the assumption that each of these households operated sprinklers on a 3 day a week program, then that would give me 120 gallons of runoff per household per week.  This results in a total annual runoff volume of 6240 gallons.  Take the 23 homes that I surveyed (represented by the yellow blobs on the aerial photo) and you get a total anual runoff volume of 143,520 gallons for my neighborhood during the 11 o’clock hour.

And that’s just one hour in the day.

Dry-Weather Runoff: Case Studies of Pollutant Loading in Southern California Watersheds

A great deal of time is devoted to issues related to stormwater runoff these days. Back in 2004, the Southern California Coastal Water Research Project completed two studies focusing on dry-weather runoff in local watersheds. The project aims were to characterize nutrient, metal, and bacteria loadings from urban runoff. Some of the findings that standout inlcude:

  • bacteria concentrations exceeded water quality standards in 72 to 98 percent of storm drain samples.
  • while in-stream acute and chronic toxicity did not typically exceed the California Toxic Rule standard, 10 to 35 percent of storm drain samples resulted in copper or lead concentrations that exceeded the standard.
  • metals from dry-weather runoff had more potential to impact toxicity versus stormwater runoff due to their bioavailability in dissolved phase.
  • nutrient loading was typically low in storm drain sampling.

Highlights of the studies can be found on the SCCWRP website.

Using Trees to Manage Stormwater – (Green Street Series)

Trees have an integral part in the green street stormwater strategy. Essentially, they help to collect rainwater in the canopy and then direct that water to the ground – allowing the water to infiltrate and recharge the groundwater table in a controlled manner. Water stored in the canopy is transpired back to the atmosphere.

The key factor impacting the tree’s ability to peform these tasks effectively is inadequate soil volume. Trees often have their root movement restricted within tree box installations. Highly compacted soils from pavement installation also impedes the roots from growing to full potential. The compacted soil acts as a deterent to stormwater infiltration, as well. The net effect is that the trees are smaller with reduced canopies.

Research by the Urban Forestry Department at Virginia Tech focused on the use of structural soils in the pavement surrounding the trees. The structural soil was shown to provide necessary strength for support of the pavement. More importantly, the porosity of the soil allowed for more infiltration, water storage, and provided sufficient soil volume to allow the trees to grow.

A .pdf of the presentation on how trees and structural soils work together to effectively manage stormwater can be found here.

Local Stormwater Management Practices

A research study conducted by James Scholl of Malcom Pirnie and presented at the WEFTEC 2007 conference looked at the myriad of local stormwater management programs across the country – focusing on major differences in organizational structures, funding sources, and the impetus for their development. Some interesting conclusions from the report include:

  • Historically, flooding has been the impetus for creating a local or regional stormwater program.
  • Currently, compliance issues and water quality protection are the forces behind creating new programs or modifying existing ones.
  • Using an existing public works to house the program is the most common approach to organizational structure.
  • Funding for new infrastructure projects is the biggest challenge, even with an existing revenue structure from fees.
  • Recent trends point to municipalities coordinating with other local agencies and authorities to manage stormwater programs. A good example of this kind of model is discussed in a previous post.

Saving Urban Streams: A Research Project by the Pennsylvania Environmental Council

I recently reviewed a research report conducted by the PEC (Pennsylvania Environmental Council) in September 2007 outlining the efforts by the Council to examine the efficacy of its watershed protection programs. As part of this effort, the Council held a practitioners meeting consisting of attendees from professionals in engineering, planning, academia, watershed organizations, and community groups. The focus of the meeting touched on identifying the challenges to fixing stormwater issues, as well as ways to work together to successfully solve these problems.

While the issues were localized to Pennsylvania, the points addressed are broad and applicable across the country. Furthermore, the cooperation seen through this process is the kind of proactive approach that needs to be taken up to address the multitude of stormwater issues impacting surface water in all regions.

To summarize:

The Challenges

  • The need to identify an end result
  • Inability to monitor overall BMP effectiveness
  • Unclear guidelines for operation and maintenance of BMPs
  • Limited sources of funding
  • Letting opportunity rather than need control implementation of BMPs

The Opportunities

  • Developing better planning and design
  • Identifying sources of funding
  • Connecting stormwater activities to other community priorities
  • Educating public on the importance of stormwater management

The full text of the report can be read at the PEC website.