Tiny steps toward flood control

More than once on this blog, including last week, I’ve described streams as sleeping creatures that wake up in floods. Kittens that turn into tigers, nebbishes that become the Incredible Hulk, pick your own metaphor — streams do most of their geological work in spasms. The downpour that happens once in a century, filling a creek and scouring its streambed a bit deeper and wider, is one hour in a million hours.

Last week one such rainfall made a shambles of Ellicott City, Maryland. Hydrologist Anne Jefferson looked at this flood with a geologist’s perspective. Her insights apply here as well as there.

Oakland’s Lake Merritt is prone to floods as well as high tides. The tides are slowly growing as sea level rises, of course, but the greater threat of flood comes from the land side. Oakland’s soil absorbs much less rainwater than it used to. As Oakland grew, its dusty streets were sealed under asphalt, its grassy lots occupied by homes with guttered roofs, its footpaths paved over in concrete. Today these impervious surfaces shed the rain, and the runoff drains swiftly away to the nearest body of water.

In October 1962 the Columbus Day Storm dumped over 4 inches of rain in a single day. Lake Merritt rose more than 7 feet and left the surrounding roads waist-deep in stormwater. A few years later a large flood-control station was installed at 7th Street that regulates the tidal lake.


We can do better on the land side. Greener building practices, sustained from now on, will gradually offset our disruption of the local hydrology. This is one of those — panels of pervious pavement flanking the street trees near the lake on East 18th Street. They’re made of a porous concrete that lets water through, like a super mulch. They let the tree roots breathe, too.


Another green practice you’ll see near the lake and elsewhere around town is rain gardens, shallow basins filled with vegetation that catch and absorb rain runoff before it can reach the lake.

6 Responses to “Tiny steps toward flood control”

  1. P. Michael Hutchins Says:

    Google(“rain garden” near oakland) is a good start.

  2. Arleen Feng Says:

    At http://www.bringingbackthenatives.net/gardens-at-a-glance you can use the filter to find past BBTN garden tour sites that include rain gardens, but no guarantee there are photos specifically of the rain garden portion. There may be more at websites for similar native or “bay-friendly” garden tours in the Bay Area.

    Most rain gardens around here do need some summer water to survive during the first year, and after that to look nice by conventional landscape standards.

    A photo of a more commercial/institutional rain garden in Fremont is at top of http://cleanwaterprogram.org/uploads/09_ACCWP_section_6.01_bioretention-OCT19.pdf (this doc is aimed at getting larger developments to include vegetated stormwater treatment facilities, as we stormwater management bureaucrats call them). For Bay Area plant suggestions see “bioretention” column at http://www.cleanwaterprogram.org/uploads/C3TG_v5.0_April_2016_Appendix_B_Plant_List.pdf These are plants that tolerate short-term flooding as well as long mediterranean-climate dry seasons.

  3. Nancy Caton Says:

    Are there pictures of local rain gardens some place? I looked at the Rain Garden website link and all of their items seemed to be related to rain gardens and practice of r-g on the East Coast and in the midwest. Our torrents of rain in Oct-Feb followed by dry spell likely would want different plants, no?

  4. whollyword Says:

    I’m delighted to know that more porous concrete is now a thing. If water can filter into the water table instead of flooding streets, that seems like a win on multiple counts.

  5. Andrew Says:

    The Bay area’s tide station has recorded a steady rise in sea level for the last century. The basic physics is unassailable — the warming atmosphere is warming the upper ocean, and the water is expanding. Anyone can cherry-pick a few graphs, layer on a bit of snark, and get paid by a website. Nobody can outweigh the Intergovernmental Panel on Climate Change, the IPCC, which has been documenting the facts of climate change for 20 years and counting.

  6. P. Michael Hutchins Says:

    re lake-level rise:

    I highly recommend the article at http://thefederalist.com/2016/07/29/james-camerons-climate-change-lies-at-the-dnc/

    If you can get past the polemics, I think that the facts that he gives are startling and important.

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