Tests of crest-stage gage intakes

Various types of c rest-stage gages have been used by the Geological Survey. Most installations consist of a vertically mounted metal pipe, a wooden rod, an intake device, and a small amount of granulated cork. These gages are placed where elevations of flood crests are desired. Water rising and then falling in the gage leaves a high-water mark of granulated cork on the wooden rod. The elevation of this mark can be determined at a date subsequent to the date of the crest.

It has been found that the high-water mark left on the rod may not represent the true elevation of the flood crest in the stream at the gage site. The difference between the true elevation of the crest at the gage and the recorded elevation will be designated drawdown if the recorded elevation is less than the true elevation, or pileup if the recorded elevation is greater than the true elevation. Tests of drawdown and pileup effects have been made in the past by Survey personnel and others. (See p. 8.) These investigations have sometimes brought forth conflicting results, probably due to the varied conditions under which the gages were tested.

The purpose of this investigation was (1) to determine the pileup and drawdown characteristics of the intakes now being used by the Survey and (2) to design a better intake if existing models were found unsuitable. It was further prescribed that any new design that might result should be easily fabricated from standard pipe fittings, and should be unaffected by pileup or drawdown in excess of 0.1 foot for velocities up to about 8 feet per second.