Harvesting Rain – a precious commodity

Stormwater is a primary source of water in many parts of the world and a sustainable approach to the control and use of rain water is something that should be taken to heart. As part of our pursuit of LEED certification for the Visitor Center, a significant number credit points is being gained from the incorporation of a Rain Harvesting system. Up to 6 points are in the balance based on being able to achieve 3 specific credits well. The credits are as follows:

Sustainable Site credit 6.1 Stormwater Quantity Control (1 point) is focused on managing on site filtration and stormwater runoff where post-development discharge does not exceed pre-development discharge off the site. This means capturing the runoff and providing a controlled discharge after collection.

Sustainable Site credit 6.2 Stormwater Quality Control (1 point) is focused on reducing water pollution through reuse of run off for irrigation on site (rainwater recycling). This means after we collect it we need to use it for landscape irrigation.

Water Efficiency credit 1.0 Water Efficient Landscaping (2-4 points) is focused on the use climate tolerant plants and efficient watering practices that include the use of a rainwater collection system.

The core of our harvesting system is located under the pavement of the south parking lot and consists of 4 – 48 inch diameter pipes that are 65 feet long that collectively create a storage tank. The tank will hold about 30,000 gallons of water. Rainwater is collected off of all roof surfaces into gutters that are then taken through downspouts into underground piping into a rainwater sump similar to a deep manhole. Rainwater runoff is also collected from paved driving and walking surfaces and landscape/lawn areas into catchment basins that have a solids separator and then travels through underground piping into the same rainwater sump.

As the rainwater sump fills, it fills the storage tank. When the tank is full there is an overflow pipe that discharges the excess water into the stormwater sewer. There is a submersible pump in the bottom of the rainwater sump that then sends the water to the landscape irrigation system. When the water in the storage tank is eventually used up, the landscape irrigation switches over to being fed by city water.

The average rainfall in Sulphur, Oklahoma is 41.5 inches per year. While that’s not what it’s been for the past few drought years here in Oklahoma, it does provide a reference joint for the amount of rain we could potentially harvest. The area of rainfall catchment of our site is approximately 28,056 square feet. That means we could collect about 97,027 cubic feet of rain water per year. That’s equivalent to 725,859 gallons. Of course this assumes that the rain is perfectly timed with when the storage tanks are empty. Well, anyway that’s a lot of rain barrels full of water.

Our Rainwater Harvesting system also punches a regulatory requirement. Remember that highway 177 is on the west side of our site and since the stormwater sewer is the property of the Oklahoma Department of Transportation (ODOT) we must meet ODOT stormwater retention requirements. We have actually sized the storage tanks per ODOTs requirement which exceeds the requirement for the LEED SS credit 6.1. Bam!

I’m thinking of letting the civil folks use my dandy schematic diagram for their construction drawings. We’ll see if I get any traction with that…