Western Flood Risk

Time magazine reports:

First came the Mississippi. Then the Missouri. Now the nation’s West waits as the mountain snowpack perches at 300% more than average and flood watches blanket the region.

With minor flooding already hampering life in Montana, Wyoming and Utah, a sudden spike of warm temperature will send even more melting snow rushing into already filling rivers throughout the Rockies, Cascades and Sierras.

The big question is whether we get a temperature spike at high altitudes that would cause a large, sudden melt.

In the meantime, government agencies are hard at work with flood preparations — hopefully, they’ll get that done before the U.S. defaults on its debts and the government shuts down.  In terms of flood control, there’s a certain irony to Grover Norquist’s famous goal of shrinking the government to the point where it can be drowned in the bathtub.  Hopefully, he doesn’t live near any large bodies of water.

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Reader Comments

One Reply to “Western Flood Risk”

  1. In its blog, PG&E agrees that the Sierra snow pack in June is 300% of normal, but they call this year’s snow pack a “healthy boost” for customers and the environment:
    http://www.next100.com/2011/06/ample-hydro-greens-pges-energy.php?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+next100blog+%28NEXT100%29&utm_content=Google+Feedfetcher

    PG&E’s management of this summer’s oh-so-bountiful hydro flows may determine whether PG&E shareholders receive a healthy boost, too.

    Temperatures throughout much of the Sierras are forecast to reach well into the 80s (daytime highs) beginning Friday and lasting for about a week.

    DWR has done a lot of work, but I could not find an estimate of how large peak delta flows might become. We’ll know soon enough.

    If I lived in a low lying area (Sacramento comes to mind), I’d stock up on sandbags and oil the sump pump.

    http://www.wrh.noaa.gov/sto/ (watch those levees!)

    The extent of flooding will depend in part on whether the maximum flows into the Delta coincide with high water levels (tide plus surge). There is a 2009 report paid for by the California IOUs, administered by the CEC and written by Scripps:
    Projections of potential flood regime changes in California. California Climate Change Center publication CEC-500-2009-050-F, 68 pages.
    Dettinger, M.D., H. Hidalgo, T. Das, Cayan, D.R., and Knowles, N., 2009.
    http://www.energy.ca.gov/2009publications/CEC-500-2009-050/CEC-500-2009-050-F.PDF

    I think I recall seeing this report referenced in the statewide adaptation strategy.

    The report states:

    “Very often the high sea-level stands occur when river flows are small to moderate; however, on a disconcerting number of occasions, high sea-level stands coincide with high river flows. The number of occasions when high sea levels and high river flows coincide increase markedly in the twenty-first century under the GFDL A2 climate. For example, during the 1950–2000 period, flows on only two occasions of high sea level stands reach 15000 m3/s, whereas during the twenty-first century flows during high sea level stands surpass that discharge more than 40 times. The flows during high sea level stands exceed 15000 m3/s to a considerable extent on most of those high sea level/high flows occasions, rising to 30000 m3/s on one occasion.

    Thus the general drift toward moderately larger and more frequent floods simulated as following from the GFDL climate changes under A2 emissions combines with the relatively rapid sea-level rise projected under that scenario to yield many more occasions when high sea level stands might combine with high flows and freshwater stages in the rivers to severely stress the levees of the Bay and Delta. The present study does not attempt to route the reservoir inflows through the flood-management operations at the state’s reservoirs, and thus many of the flows shown in Figure 28 might be considerably ameliorated by reservoir operations in the real world. Historically, though, reservoir management has not done as much to ameliorate the number of levee breaks in California as might be expected (Florsheim and Dettinger 2007). Thus, even the moderate sea-level rises and relatively modest flood frequencies increases currently being projected may be sufficient to threaten the estuary’s levee systems as a result of more frequently coinciding flood stages.”

    [end quote]

    The report indicates that during the twenty-first century, high end outflows coinciding with high sea level stands might occur 15 to 20 times more frequently than they have occurred historically since 1950. Stunning finding!

    Watch those levees,

    Greg San Martin

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Dan Farber

Dan Farber has written and taught on environmental and constitutional law as well as about contracts, jurisprudence and legislation. Currently at Berkeley Law, he has al…

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