The Equipment Page

Primary control structure for measuing streamflow at Station WK on Waiakeakua Stream. This structure consists of a Parshall flume for measuring flows during relatively low-flow conditions and a weir for higher flows. The relationship between stage (water level) and discharge (streamflow) is well known, therefore, stage, measured by our Isco flowmeter is easily converted into discharge using the established stage-discharge relationship.
USGS instrument housing containing the USGS stream gauge and the housings containing the UHM Isco bubbler-type flowmeter and Isco automated, sequential sampler. The YSI Model 6920 water quality sonde is protected by an armored housing that attached to the concrete wall and secured by a stainless steel safety line attached to the bridge overhead. These safety precautions are particularly important during high storm flow events when water levels can increase by 1 to 2 m.
Closeup view of the housing for the YSI water quality sonde and the Isco sampler intake and flowmeter bubbler line.
Removing stormwater samples from the WK Isco sampler. Note that the base of the sampler contains 24 wedge-shaped bottles. The sampler is programmed to initiate sampling when the stage reaches a pre-determined level. The sampler will then continue to collect a sample every 1/2 hour until the stage drops below the trigger level. Stage information is provided by the Isco flowmeter (see below).
Stage data are downloaded from the Isco flowmeter to a noteboook PC. Most communications between the operator and the flowmeter are made through the PC, however, various programming information can also be entered via a key panel on the flowmeter. This type of flowmeter (Isco Model 4230) senses the amount of pressure required to inject a bubble into the water in the Parshall flume thereby measuring the stage, i.e., water level. In the laboratory, these stage data are used to calculate discharge (streamflow) using a pre-established stage-discharge relationship.
A portion of a storm hydrograph recorded by the Isco flowmeter. In addition to stage, which is recorded every 5 minutes, the flowmeter record also indicates the time each sample was collected.
There are two options for programming the YSI water quality sonde and downloading data from the sonde: a PC or the YSI 610-DM data logger. The PC, while not as rugged as the data logger, does allow the operator to examine the raw water quality data to see if all of the probes are functioning properly (see below).
Closeup view of the various probes on the YSI Model 6920 water quality sonde.
Example of a YSI water quality record that includes the 02APR99 storm that is shown in the partial Isco record above
Instantaneous streamflow measurements, in this case, on Kane'ohe Stream, made with a pygmy, vertical axis, current meter (see below).  By measuring the velocity across the stream and the cross-sectional area, the streamflow (or discharge) can be measured.  Pollutant concentrataions are often expressed as pollutant loads (usually kilograms or pounds per day) = pollutant concentration X streamflow.
A close-up view of the pygmy, vertical axis, current meter.  Notice how the current meter resembles an anemometer that meteorologist use to measure the speed of the air (wind), another fluid.  Each rotation of the cups results in an audible click which is counted by the observer over some predetermined time.  A series of velocity measurements is made across a stream.  The location of the these measurements across the stream is determined with a tagline, i.e., non-stretching measuring tape, usually made of fiberglass.

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