Until 2013, gage height is sensed by pressure transducers (Druck Model PDCR 10/D) and recorded on the CR-21X datalogger (Campbell Scientific Company), or by a SUTRON Accubar Constant Flow Bubbler with integrated data logger. In 2013, pressure transducers were replaced with air bubblers with an integrated pressure sensor (YSI WaterLOG Bubbler/Pressure Sensor H-3553) and data are recorded on a CR800 datalogger (Campbell Scientific Co.). Conversion to stream discharge requires two steps:

1) Correction of measured gage height to actual gage height using direct measurements of stage made approximately three times per week with a ruler at a reference point at each flume. Until 2018, corrections were applied annually by conducting a linear regression between time-matched manual (x) and bubbler (y) measurements of gage height using all data collected in a year. All bubbler measurements of gage height from that year were then corrected with the resulting regression equation. Starting in 2018, a two-point regression method has been employed by examining the linear relationship between two consecutive points with manual and bubbler measurements of gage height. Manual measurements were collected approximately three times per week, therefore corrections were applied with the same frequency. All these corrections have been applied separately to each sampling station. Each sampling station is tested for high flows one time per year by plugging the stilling well and filling the well with water to artificially increase gage height. Water level in the stilling well is measured with the aid of a clear plastic tube running through the plug that fills to the same height as the well.

 

2) Translating gage height to stream discharge using a rating curve.

Two rating curves employ geometric relationships which are assumed to be valid at certain stage heights. The relationship used for calculating discharge at gage heights > 18.25 cm is:

Qm3/s = 4.64 x 10-5 * s^2.587

The relationship used for calculating discharge at gage heights between 0-18.25 cm is: Qm3/s = 6.49 x 10-5 * s^2.4714

Where Q is discharge in cubic meters per second and s is gage height in cm. These equations were derived using procedures in Replogle, J. A., H. Reikerk, and B. F. Swindel. 1978. Water monitoring in coastal forest watershed studies. IMPAC Report 2, Vol. 3, No. 2.  Southwestern Forest Expt. Station, USDA, Gainesville, Florida.