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How to Catch a Rain Bomb


Tuesday, May 31, 2016

One of the best things about "Mulch Basins Catch a Stormwater Rain Bomb" is the luscious sound of the January 31 cloudburst that Art Ludwig captures on video. He's created about 1,000 square feet of mulch basins, terraces, and swales around his Santa Barbara–foothills home, and this video demonstrates their combined ability to infiltrate 60,000 gallons of rainwater, with little runoff, from the surrounding road, roofs, and steep hillsides. With Ludwig narrating, we watch the "rain bomb" flood the basin — about six inches of mulch plus three feet of native topsoil — while the camera shows the water slowing, spreading, and sinking into the soil sponge. His Oasis Design team calculates about 50,000 gallons went down toward groundwater from the 2.5-inch storm, while 10,000 gallons remained in the root zone.

Ludwig has designed and built complex ecological systems around the world, and the effects of climate change present a challenge in this respect. Warm air holds more water, he explained, and more intense rainfall results as that water is released. The relatively small mulch basins seen in the video of January's rain burst added significantly to groundwater recharge and helped prevent flooding down Goleta-way.

In most years, the amount of stormwater that falls on and flows through our area, Ludwig stated, is larger than the supply from the Mission Tunnel, Gibraltar Reservoir, Lake Cachuma, State Water, water market purchases, and reclaimed water combined. Stormwater infiltration also offers flood control benefits, he pointed out, an attractive alternative to building larger storm drains to accommodate more extreme peak rain events from climate change. Ludwig said the most extreme peak rain intensity on record occurred in December, 2014, in the midst of the worst drought in recorded history. —Jean Yamamura

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