Flows and Transport in Rivers - Hydro-Environmental Analysis: Freshwater Environments - page 93

4.3.4 M eaSureMent of S taGe
The measurement of stages is a useful hydraulic characteristic for a number of purposes. Stage mea-
surement methods include a variety of manually read or automatic stage recorders, and may be as
simple as a graduated plate or rod that is set vertically in a streambed or attached to a solid structure.
These manual gages do not produce a continuous record, but a single point in time measurement;
they are of particular use in times of looding. Another point-measurement gage is the crest gage,
which records the maximum stage in rivers.
One of the most common uses of stage measurements is in the indirect estimation of lows using
a rating curve (see Figure 4.4). Stage measurements for low estimation typically include some type
of water level measurement actuator, a recorder, and a stilling basin (Figure 4.13). A water level
recorder is an instrument that records water levels in analog or digital form and it may be actuated
by a loat or by any one of several other sensor types. Historically, the recording device was a pen
and graph, while more commonly today the stage is recorded electronically. For many USGS gaug-
ing stations, the electronic measurements, typically recorded at 15-60 minute intervals, are trans-
mitted to USGS ofices via satellite, telephone, and/or radio and these real-time data are available at
their National Water Information System (NWIS) via web interface (Figure 4.13).
The general practice of the USGS for stage data collection is described in USGS Water-Supply
Paper (WSP) 2175 (Rantz et al. 1982) and USGS Techniques of Water-Resources Investigations ,
Book 3, Chapter A-7 (Buchanan and Somers 1968).

4.3.5 M eaSureMent of f Low u SInG t racer t ecHnIqueS
Tracer studies are used to provide low estimates such as by using the dilution method as described
by Kilpatrick and Cobb (1985). Dye studies are also commonly used to estimate the time of travel.
Tracer studies typically involve injecting a dye tracer such as Rhodamine WT at one location in
a stream and later measuring the dye concentration at a downstream location. The principal prop-
erty of commercial dyes such as Rhodamine WT is that they are highly luorescent. For example,
Rhodamine dyes (such as Rhodamine B and WT) have greatest excitation at a wavelength in the

Satellite
radio antenna
Recorder

Shelf

Floor

Water surface
Float

Water surface

Intakes

FIGURE 4.13 Stage recorder and stilling well. (From USGS, Stream-gaging program of the U.S. Geological
Survey, U.S. Geological Survey Circular 1123, Reston, VA, p. 4, 1995.)