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Restoring the Hydrologic Cycle through Roof Leader Disconnection – How to Get Your Residents to Help

February 19th, 2014 by Eileen Pannetier


Guest Blogger – Rebecca Balke, P.E.

What happens to all that water when it rains?

In natural, forested settings, most of the rain is:

  • intercepted by tree canopy and put back into the atmosphere through a process called evapotranspiration; and
  • infiltrated through the soils to replenish groundwater baseflow. This groundwater baseflow is what feeds our streams and ponds during the drier summer months.

 

Very little surface runoff is produced in a natural setting. This process is known as the hydrologic cycle. As land is developed with impervious surfaces such as roof tops, roads and parking lots, the hydrologic cycle is drastically changed, resulting in a greater ratio of stormwater runoff to groundwater baseflow. This change in the hydrologic cycle costs communities money by:

  • requiring larger capacity drainage systems to carry the larger stormwater runoff flows;
  • increasing flooding, which damages infrastructure that must then be repaired and/or replaced; and
  • polluting waters, which must then be cleaned under state and federal regulatory programs for drinking water, recreational or aquatic habitat purposes.

Local and state regulations have come a long way in requiring stormwater design standards that promote infiltration at both new and redevelopment sites, however, these typically focus on larger developments. So, an existing commercial property may be subject to these regulations when it redevelops, but an existing single family home will not.

How much impact do these single family homes really even have? One home by itself, not much, but there is strength in numbers. When you are talking about hundreds or thousands of homes, the impervious area really adds up and so does the stormwater runoff coming from these surfaces, particularly in denser, more urbanized areas, where lot sizes are small and impervious surfaces are directly connected to the municipal drainage system. In these situations, disconnection of impervious surfaces can go a long way and every little bit counts.

For example, an average residential roof area of 1,600 square feet can produce 44,530 gallons of runoff per year, based on an annual precipitation of 47 inches. One thousand homes would produce 44.53 million gallons of runoff per year. Assuming all of these rooftops are directly connected to the municipal drainage system, either through a direct pipe connection, or runoff down the driveway and into a catch basin, disconnection and redirection to a drywell could result in 90% or 40 million gallons per year of runoff being directed back into the ground. Wow, that’s a lot of water!

Why would you want to promote roof leader disconnection? Bottom line – to save money. The less stormwater runoff you generate, the less you have to manage and the more money you save. If you are subject to the National Pollutant discharge Elimination System (NPDES) Phase II Small Municipal Separate Storm Sewer systems (MS4s) General Permit you can also count this towards your permit compliance. The new permit will likely require regulated MS4s to track changes to impervious and directly connected impervious areas each year, with a push to increase recharge. Roof leader disconnection is a perfect match.

How do you get homeowners to disconnect? That’s the tricky part, but it can be done, and has, but usually as part of a program to reduce stormwater flows into a sewer system to reduce treatment costs. Approaches that have been used include:

1. Incorporate information into a public education program that encourages residents to disconnect their roof leaders and provides them with the information they need to do it. These same materials could also be provided to developers to incorporate these practices into new construction;

2. Provide incentives, such as monetary, for residents to disconnect their roof leaders;

3. Work with an organization or group (e.g., local watershed group, boy scouts, etc.) to perform the disconnection at a reduced cost;

4. Community staff disconnects roof leaders or community bids out disconnection to contractor at community expense; and/or

5. Develop an ordinance requiring homeowners to disconnect their roof leaders from the municipal drainage system.

Get the word out and start saving.

For more information please contact Rebecca directly at 603.424.8443 or rbalke@ceiengineers.com.

Posted in the category Stormwater.