Stormwater regulations for new development are important ways the county can ensure compliance with watershed protection requirements. The county has a Best Management Practice manual, which includes resources for how to engineer detention or biofiltration basins. Meeting the stormwater mitigation requirements for new construction or major remodels is complex and requires calculations and design by a civil engineer. However, the go to solutions cost a lot of money, yet don’t typically provide any direct benefit to the homeowner.
Before you get too far down the path on your stormwater mitigation project with your architect and an engineer, check in with us at CatchingH2O. We have worked on many projects over the years throughout the county to change the perspective of stormwater as a “problem” to that of an important resource to be put to use. What we have been able to achieve for our clients is to put those thousands, or even hundreds of thousands of gallons of water to work as active and passive irrigation while achieve the same ultimate engineering goal of reducing volume and pollutants coming off the property. Here are TWO things we can help you design into your project:
- “Impervious area dispersion”, or earthworks – by sinking water into the landscape, starting at the top of your topography and spreading it throughout the landscape, using shallow contours, the water has a chance to soak into the landscape and more of your plants roots will have access to it for a longer period following a rainfall event (meaning you don’t have to start irrigating soon after the rain stopes)
- Large rainwater storage (Cistern) – by calculating roof runoff and matching it to appropriately sized storage, we can ensure you have a large supply of clean water to irrigate your landscape in the dry periods, or even use indoors with some additional filtration.
Once rainwater flows from rooftops to roadways, it collects sediment and pollutants and becomes “stormwater” which requires “mitigation”. The current primary solution to this problem for new construction is to require “detention basins” that can accommodate and treat stormwater from new impervious areas (rooftops and driveways). The goal here is to improve stormwater quality entering drainage channels.
One approach to eliminate the detention basin requirement is “impervious area dispersion” which is a wordy expression for earthworks. Earthworks are a strategy we frequently implement to infiltrate/capture roof and hardscape runoff by directing the flow from impervious areas onto adjacent pervious ones. This approach typically requires some gentle re-grading. A trick to optimizing this strategy is starting to implement the regrading at the highest points of the property. At these points, volume and flow are minimized so the size and structure of the earthworks is minimized, which saves cost, while also allowing more vegetation to have access to the water that is moving through the property.
Cisterns are defined by the county as rainwater storage over 200 gallons. Cisterns are considered permanent structural BMPs like impervious area dispersion and therefore an alternative to detention/biofiltation basins.
In reading the fine print on the cistern detail, you can see that in this example the cistern is being used for flow control only. The expectation is that the overflow from the tank, and and discharge from the outlet, will be flowing off site into nearby waterways and therefore require treatment for pollutant control. Rainwater collected directly from rooftops is a precious resource — essentially salt-free and very low in sediments that cause turbidity. Rainwater here in San Diego county is typically at physiological pH, about 7.4, unlike our municipal water which has been alkalinized to minimize corrosion on copper pipes. The systems that Catching H2O installs typically retain all of the stored rainwater onsite either by gravity distribution to planted areas or pump stations that connect to irrigation. We design the overflow from our rainwater storage tanks to flow into landscaped areas that can accommodate the volume of a 1″ storm and are planted appropriately,.
Catching H2O can help integrate rainwater catchment systems and earthworks into your projects that meet meet these requirements, allowing you to reduce or eliminating costly, unsightly and dangerous detention basins. We’d love your stories of any detention basins you had to implement or were able to avoid. And if you’re facing an enormous cost and inconvenience of having to install such a basin and would like a more useful and environmental alternative, we can consult with you and your team to turn that problem into a solution!