Stormwater Library

resources for stormwater professionals

Archive for Residential BMPs

Properly Designing the Rainbarrel

Here are some things to weigh when considering rainbarrels as part of a stormwater BMP. While rain-harvesting and storage are nice potential side benefits of the barrel, its future success relies on keeping the focus squarely on stormwater capture. If you look around the internet and review municipal rainbarrel programs that are being promoted, they are often discussing the 50- to 60-gallon barrel like it is a viable option.

It simply isn’t. Consisder these conservative assumptions:

Let’s say a typical residential roof is 1200 square feet (it is closer to 1600). And, let’s say that a minor storm passes through – on the order of 1/4″. That would create a runoff volume of approximately 187 gallons. Let’s assume that only 60 percent of that runoff made it to the downspout due to ponding and poor pitching of the roof. That would result in a runoff to the downspouts of approximately 112 gallons. If the homeowner had 2 downspouts and 2 50-gallon barrels, the system is are already overflowing. With 4 downspouts and 4 barrels, the system is more than half full after a very small storm – just one storm. Furthermore, the overflow checks that are typically designed into a rainbarrel are not able to discharge at a rate that can keep up with the runoff rate into the barrel. So, the notion that the barrel is safe from overflowing during a storm is on shaky ground.

Here comes the next issue. The homeowner wants to be able to store this rainwater for future use, but the weather is a little rainy and the need to irrigate is not currently there. A couple of days later, the next small storm comes through and your barrels that should be empty are starting off at 56 percent of capacity. The new 1/4″ storm overflows the barrels. And, this is if 4 barrels are installed – not typically the case.

Where does that leave us? If rainbarrels are to be considered as a viable BMP, then larger ones need to be used. Successful programs like those used in the cities of Pittsburgh and Washington, D.C., use barrels with 3 times the typical volume capacity at 150-gallons. This could provide some storage capacity for future use in more arid regions of the country. In the areas prone to heavier rainfall, use of a couple of larger barrels offers the ability to capture runoff from more substantial events, but still not likely act as a harvesting tool.

The long and short of it is this. Focus should primarily be on stormwater capture, especially of that first flush. Once that water is captured, it will likely need to be emptied onsite through controlled overflow to a drywell or dedicated infiltration area on the property. Homeowners need to be educated on these issues and keep tabs on capacity and maintenance.

A final point should be considered when designing rainbarrels for storwater capture. Is it properly constructed? I run across a lot of make-your-own barrel websites that are not always considering issues such as proper overflowing or covering of the barrel. The last thing a homeowner wants to deal with is a massive buildup of water right next to the foundation, or a mosquito population explosion in the sideyard.

While the DIY approach has some appeal, by and large the focus should be on proper design and engineering. If we can get away from poor planning and design, rainbarrels can be a great addition to the lot-level approach of managing stormwater.

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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.

Portland

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.

Minnesota

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.

Seattle

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.

Challenges

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.

Onsite Stormwater Management – Homeowner Responsibility in Portland, Oregon

In the city of Portland, homes that were built after 1999 were typically equipped with onsite stormwater systems that help promote infiltration rather than runoff. That is interesting in itself, but what makes the Portland example so unique is that it puts the responsibility of management and mainteneance of the systems on the homeowner. Routine inspections must be done and logs kept recording the types of systems used on the property, condition, and any actions taken.

Portland’s Bureau of Environmental Services puts out a very informative, easy-to-follow manual (including inspection logs) that directs the homeowner on what to look for and steps to take to keep the onsite systems viable. The manual can easily be used as a model for other communities considering such a program or for the invidual homeowner interested in promoting stormwater infiltration.