March/April 2013: Ask Dr. HOG

Ask Dr. HOG About Water and Earthquakes: Water Tanks in Seismically Active Zones

Dr. HOG recently visited a school in Northern California that wants to install a large, round 1,500 gallon tank on a hill above the playground for decent gravity feed. They felt that steel was a sturdy, durable choice. What’s wrong with this scenario?

The Problem
There’s a reason many steel tank manufacturers do not sell in California – and its all about rock ‘n roll. Well, actually its slip ‘n slide as the Pacific Plate and the North American Plate grind together. When the ground moves abruptly under a large or medium body of water contained in a tank the top section of water sloshes, and the bottom section moves with the tank body, effectively creating some very powerful shear.  A riveted tank might just pop its rivets, pouring around 6 tons of water down onto the playground.  A welded tank attached to a stiff foundation could shear in the middle.

The Solution
The volume the school wants to store is not a viable project for Rainwater HOGs, so I recommended daisy chaining two 660-gallon round Bushman tanks with a secondary fastening system to the ground, and allowing room for an additional tank when funding became available.  Daisy-chaining smaller tanks has a number of advantages to the monolith proposed:

1. It acts as a baffle to prevent the water mass gaining too much momentum in a seismic event, giving the system more chance of surviving an earthquake without spilling.

2. It facilitates a progressive installation as funds become available.

3. It prevents large scale failure – in the event that a tank fails (this is known to happen with some thinner walled tanks, although a Bushman quality tank means that it probably won’t), there is still functional storage in place.

4. It is less expensive and a more residential-scale installation of compacted gravel vs. the large scale concrete or other substrate that a big tank requires.

Click here for real time earthquake monitoring. And click here for more answers from Dr. HOG.

March/April 2013: Marin Home and Garden Expo

Simple Sustainable DIY Rainwater Harvesting with Sally Dominguez
Sunday, June 2nd at 1 pm, Marin Center Fairgrounds,  San Rafael, CA

Rainwater HOG’s own Sally Dominguez, multi award-winning sustainable designer and educator, will present Simple, Sustainable DIY Rainwater Harvesting at the 2013 Marin Home and Garden Expo. She looks to all corners of the globe for ways to use rainwater on the garden and inside the home. From selecting BPA-free vessels and calculating rainwater storage potential to the effective filtration of roof water and even using rainwater to flush toilets and wash laundry, Sally draws on her experience designing for Australia and for the Bay Area to guide you to the best sustainable choices for rainwater re-use.