Stormwater Library

resources for stormwater professionals

Archive for BMPs

LID Implementation in Low Infiltration Areas

One of the questions that comes up quite often in the research about Low Impact Development is how to implement the design when you have naturally low infiltrating conditions (i.e. low permeable soils or shallow groundwater/bedrock).  In design scenarios like these you are inevitably going to be faced with major drainage issues, ponding, and vector control problems.  Using the State of California as an example, ponding present after 4 days is going to be the limiting factor on your BMP design.

Daniel Apt of RBF consultants presented a nice discussion on this very subject in 2008.  Mr. Apt summarized the measures to help reduce runoff from these sites as follows:

  • Reduce/Minimize Total Impervious Areas
  • Minimize Directly Connected Impervious Areas
  • Limit use of sidewalks
  • Reduce road/driveway length and width
  • Modify/Increase Drainage Flow Paths
  • Maximize overland sheet flow
  • Conserve natural areas
  • Minimize disturbance
  • Preserve infiltratable soils
  • Preserve natural depression areas
  • Preserve vegetation

The presentation goes into the benefits of using measures such as green roofs, rain barrels, cisterns, bioretention strips, and grassed swales as possible ways to working around infiltration issues on a site, while still drastically reducing offsite runoff.

Review the power point presentation in its entirety here.


Stormwater Factoid: City of Philadelphia

The City of Philadelphia owns and maintains over 90,000 trapped inlet catch basins.  Over 13,000 tons of debris are cleaned from the inlets on an annual basis.  The City spends over $46 million each year on operation & maintenance of stormwater BMPs.

Source: Leading Stormwater Management Programs in Pennsylvania


Impact of Street Sweeping Programs on Pollutant Reduction

A research study conducted by the Center for Watershed Protection was released in September 2008 detailing findings and recommendations of a 3-year study on street sweeping and storm drain cleanout programs. The study, which was conducted in phases (literature review, program surveys, and field monitoring), cites the difficulty of the research endeavor due to factors such as street sweeping technology, frequency, and operating conditions. Results of the study focus on recommendations such as:

  • targeting critical areas and times of years for sweeping/cleanout.
  • implementing programs that redirect/treat stormwater before it reaches discharge system.
  • expanding programs to maximize the reduction of leaf litter and prevent it from entering the storm drain.
  • conducting additional research that focuses on evaluting current sampling techniques and developing alternative techniques.

The report can be read in its entirety for free here.

Getting Started

Off the top of my head, I can think of 2 essential resources for getting started with your stormwater treatment design.  First, check out the selection matrices provided at the Stormwater Manager’s Resource Center.  Their selection guide focuses on 7 areas of concern:

  1. Land Use
  2. Physical Feasibility
  3. Climate/Regional Factors
  4. Watershed Factors
  5. Stormwater Management Capability
  6. Pollutant Removal
  7. Community and Environmental Factors

In addition to their selection matrices, there are plenty of valuable resources for getting started including construction specs for stormwater BMPs.

Second, check out the International Stormwater BMP Databsefor their valuable assessment of the efficacy of the most common stormwater BMPs (Detention Ponds, Wet Ponds, Wetland Basin, Biofilter, Media Filter, Hydrodynamic Devices, Porous Pavement).