Rainwater Catchment – Why and How?
Why Collect Rainwater?
When it comes to saving the plant, most people think rainwater catchment is insignificant and not worth the effort. Fortunately, they are wrong. Let me explain:
Imagine a typical house with no rain catchment: Rainfall lands on the roof, flows to a downspout, and out to the nearest storm drain. Along the way, the water picks up surface pollutants such as oil, grease, chemicals, and fertilizers and carries them to our rivers and the ocean. These pollutants are called Non-Point Source Pollution, or NPS. Since the water flows over concrete and asphalt, very little is absorbed into the soil, meaning no groundwater recharge. Later, the homeowner has to use city water for landscaping.
Now imagine a house with rain catchment: Rainfall lands of the roof, flows to the downspout, and into a rain barrel or cistern. Once the rain tank is full, the overflow is directed into surrounding planter boxes in order to allow water to infiltrate the surface and recharge groundwater tables. Since little water left the property, significantly less Non-Point Source Pollution was transported to the nearest river. A week later, the homeowner uses collected rainwater for landscape irrigation, thus increasing groundwater recharge and reducing demand for city water.
Now imagine if an entire community participated!!
How To – Article 1.09:
Rainwater Catchment
Step 1 – Volume Estimate: Estimate the amount of water that falls on your watershed during a storm. Use the following equation:
Eq. 1.09: 1,000 square feet = 600 gallons = 1-inch of rain
Instruction: Estimate the size of your watershed (or roof) and use Equation 1.09 to calculate the amount of rain that will fall in that area during a solid overnight rain (1-inch) and over an average rain season (about 20-inches in Santa Cruz). For roofs, estimate the percentage of roof space that flows to each gutter and calculate the resulting volume of water per storm (in gallons).
Example 1.09: How much water falls on a 1,000 sq. ft. roof?
(1,000 sq. ft roof) x (600 gallons/1 in. rain) x (20 in. rain/season) = 12,000 gallons
Step 2 – Decide where you want the rainwater to go:
- Locate the downspouts at your house that drain the largest rain area – these will be the best places for collecting rainwater.
- Use whatever you can to collect and store rainwater: buckets or barrels work, but are not ideal. If you can afford it, hire Allterra to install a RainwaterHog, which is ideal for residential settings.
- For areas where you can’t collect and store water, simply divert your downspout into a flower bed or lawn. Make sure to properly mulch these areas to maximize water absorption and infiltration.
Summary
For simple, low-tech rainwater catchment, that’s about all there is. For people that want to go bigger and badder, Allterra can help. How about a 3,000-gallon rainwater cistern underneath your driveway?
Tags: aquifer recharge, groundwater recharge, nonpoint source, nps, rain barrel, rainwater, rainwater calculator, rainwater catchment, rainwater equation, santa cruz solar, solar, solar santa cruz, stormwater pollution
This entry was posted on Wednesday, May 20th, 2009 at 5:34 pm and is filed under How-To Articles. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
2 Responses to “Rainwater Catchment – Why and How?”
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You guys are on it! Perusing through your website inspires. Many the ideas I learned about in the environmental studies program at SFSU and the Intregal Urban House in Berkley in the late seventies are here: A well-placed Howard Zinn quote, solar energy systems, rainwater catchment, greywater systems, etc. Go Team Allen!!!
gmarris…
Excellent advice. I’m going to post a link of this Allterra Environmental Science and Engineering, Santa Cruz … articles about environmental science articles on my blackboard website on Tuesday for my students. Everything you said works for discussi…