Thursday, October 16, 2008

Extraordinary floods

A new USGS assessment of 30 extraordinary floods between 1927 and 1978 found that the peak discharges for two of them were revised upward. One of those two extraordinary floods was in Bronco Creek, Arizona.

The USGS report has to be ordered, so I didn’t find the details online of just how large the revised flood peak flow was.

A big part of the USGS study deals with the reliability of peak flow measurements and errors in data collection and processing.

The study concludes that “Within the U.S. Geological Survey, new approaches are needed to collect more accurate data for floods, particularly extraordinary floods. In recent years, significant progress has been made in instrumentation for making direct discharge measurements. During this same period, very little has been accomplished in advancing methods to improve indirect discharge measurements.”

1 comment:

  1. Of note is that past AZGS geologist, Kyle House, and present AZGS geologist Phil Pearthree, studied the Bronco Creek flood in detail in the mid 1990s and left a trail of publications that bring the original Bronco Creek discharge estimate into serious question as being too large to begin with.

    The principal argument is outlined in:

    House, P.K., and Pearthree, P.A., 1995, A geomorphologic and hydrologic evaluation of an extraordinary flood discharge estimate: Bronco Creek, Arizona: Water Resources Research, v. 31, no. 12, p. 3059–3073.

    The fact that this number has now been increased without any substantial re-analysis or, at least, explicit characterization as a local hydraulic anomaly is very unfortunate. It now stands as a federally codified (sanctified?) misleading estimate of peak runoff in western Arizona and surrounding regions.

    In fact, this development is clear and elegantly ironic proof of the quote that you placed at the end of your post.