A 2000 year natural record of magnitudes and frequencies for the largest Upper Colorado River floods near Moab, Utah. Issue 6 (30th June 2014)

• Record Type: Journal Article
• Authors: Greenbaum, Noam; Harden, Tessa M.; Baker, Victor R.; Weisheit, John; Cline, Michael L.; Porat, Naomi; Halevi, Rafi; Dohrenwend, John
• Is Part Of: Water resources research. Volume 50:Issue 6(2014:Jun.)
• Page Start: 5249
• Page End: 5269
• Publication Date: 2014-06-30
• Subjects: Hydrology -- Periodicals; 333.91
• DOI: 10.1002/2013WR014835
• Languages: English
• ISSNs: 0043-1397

Abstract

<abstract abstract-type="main"> <title>Abstract</title> <p>Using well‐established procedures for paleoflood hydrology and employing optically stimulated luminescence (OSL) geochronology, we analyzed a very well‐preserved natural record of 44 Upper Colorado River extreme floods with discharges ranging from 1800 to 9200 m<sup>3</sup>s<sup>−1</sup>. These are the largest floods occurring during the last 2140 ± 220 years, and this natural record indicates that large floods are much more frequent than can be estimated by extrapolation from the stream gaging record that extends back to 1914. Most of these large floods occurred during the last 500 years, and the two largest floods in the record both exceeded the probable maximum flood (PMF) estimated at 8500 m<sup>3</sup>s<sup>−1</sup> (300, 000 cfs) for nearby Moab, Utah. Another four floods, with discharges greater than 7000 m<sup>3</sup>s<sup>−1</sup>, occurred during the last two millennia. Flood frequency analyses using the FLDFRQ3 model yields the following values, depending on the Manning <bold><italic>n</italic></bold> roughness coefficients: 100 yr flood—4670–4990 m<sup>3</sup>s<sup>−1</sup>; 500 yr flood—6675–7270 m<sup>3</sup>s<sup>−1</sup>; 1000 yr flood—7680–8440 m<sup>3</sup>s<sup>−1</sup>. The presumed PMF discharge (8500 m<sup>3</sup>s<sup>−1</sup>) gets assigned a recurrence interval of about 1000 years, and the largest historical 1884 flood (3540 m<sup>3</sup>s<sup>−1</sup>)—a recurrence interval of <100 years. Flood frequency analysis for the Moab Valley based on the gaged record (1914–2012) yield 2730 m<sup>3</sup>s<sup>−1</sup> for the 100 yr flood and 3185 m<sup>3</sup>s<sup>−1</sup> for the 500 yr flood. This underestimation of the frequency of large floods from the gage data results from effects on that record by modern regulation of upstream river flow and associated water extraction for agriculture.</p> </abstract>