Peak Values

The peak values, in pre-electronic days, were taken by the gage reader, who examined the highwater mark, correlated it to discharge, and recorded it. With automatic stage recorders and telemetered gages, the peak is automatically written to the unit values file, then later separated and written to the peak values file. Peaks are divided into the annual peak, which is the highest discharge recorded during a water year (annual peaks of 0 cfs are common in the southwest); and the partial duration series, flows above a defined base level which are recorded only once per event. The base level for a station is chosen to make sure there are fewer than 30 partial duration series peaks per year. Thus it is possible to have annual peaks that are not in the partial duration series because they didn't exceed the base level.

Major, gage-wrecking peaks are measured post facto by variants on the technique used by the early gage readers. Because the real peaks carry the remains of the gage away to California, the highwater marks are surveyed, resulting in a slope and bed perimeter measurement. From this and known roughness constants, the discharge can be calculated. Other techniques are also used, depending on the site.

Browsing the peak values, the failure of Teton Dam apparently "wins" for the continental United States: 2.3 million cfs. We are waiting for the data from the failure of Auburn Coffer Dam in 1986, and we have heard rumors of a reversing flood in Florida where a spring tide and a hurricane shoved a hump of about 4 million cfs upriver, setting a reverse record and then a drainage record the next day. Missing from the database is our favorite, the Spokane Flood, which apparently crested at about 9.5 cubic miles/hr (400 million cfs) according to J Harlan Bretz; by the time (some 20,000 years after that Pleistocene event) reliable estimating techniques were invented, the highwater marks were obscured, so precision is not possible. We know of no estimates for the Noachic deluge or the flood of Deucalion.


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Last Updated March 10, 1998
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