Lower Snoqualmie River Stream Gauge Traditional Geocache

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Shaddow: I like this one but it's just too hard to make it work well

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Hidden : 4/4/2010
Difficulty:
3 out of 5
Terrain:
2 out of 5

Size: Size: micro (micro)

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Geocache Description:


Lower Snoqualmie River Stream Gauge

Volume Flow Chart
Actual Flow Rate for the Last Seven Days

stream flow chart


This cache is located at the lower Snoqualmie River Stream Gauge also known to the United States Geological Survey (USGS) as USGS 12149000 Snoqualmie River near Carnation, WA.

“Latitude 47°39'58", Longitude 121°55'27", in NW 1/4 SW 1/4 Section 9, Township 25 North, Range 7 East, in King County, Hydrologic Unit 17110010, on left bank 40 feet downstream from highway bridge, 1.3 miles northwest of Carnation, 1.9 miles downstream from Tolt River, and at river mile 23.0. Drainage area is 603 mi2. Datum of gage is NGVD of 1929.”

A River Gauge

A river gauge is used to determine the volume of water flowing past a particular fixed location. This information is important for many reasons, most notably it’s used during storms to help understand if a river is going to flood downstream as well as how high the water level will reach. Often this information is presented by TV weatherman using the terms such as ‘so-an-so feet above flood stage’ and ‘flood crest.’ The water flow information is vital for many other reasons including understanding the health of the river and managing salmon runs.

A river gauge requires accurate information about the river bottom and water speeds at the gauging station so they are located at relatively flat and even sections of the river. Note how this occurs at this location.

An interesting side note about this particular stream gauge is that a picture of it is used in the Wikipedia article on stream gauges. I was very surprised when I came across it while doing research for this cache.

The Cache

A micro hidden on the stream gauge equipment building.

How Streamflow is Measured - Part 1: Measuring Stream Stage by USGS
Typical River Gauge
diagram courtesy of USGS



Most U.S. Geological Survey (USGS) streamgages measure stage and consist of a structure in which instruments used to measure, store, and transmit the stream-stage information are housed. Stage, sometimes called gage height, can be measured using a variety of methods. One common approach is with a stilling well in the river bank (image to the left) or attached to a bridge pier. Water from the river enters and leaves the stilling well through underwater pipes allowing the water surface in the stilling well to be at the same elevation as the water surface in the river. The stage is then measured inside the stilling well using a float or a pressure, optic, or acoustic sensor. The measured stage value is stored in an electronic data recorder on a regular interval, usually every 15 minutes.

At some streamgage sites, a stilling well is not feasible or is not cost effective to install. As an alternative, stage can be determined by measuring the pressure required to maintain a small flow of gas through a tube and bubbled out at a fixed location under water in the stream. The measured pressure is directly related to the height of water over the tube outlet in the stream. As the depth of water above the tube outlet increases, more pressure is required to push the gas bubbles through the tube.

Streamgages operated by the USGS provide stage measurements that are accurate to the nearest 0.01 foot or 0.2 percent of stage, whichever is greater. Stage at a streamgage must be measured with respect to a constant reference elevation, known as a datum.

Sometimes streamgage structures are damaged by floods or can settle over time. To maintain accuracy, and to ensure that stage is being measured above a constant reference elevation, the elevations of streamgage structures, and the associated stage measurement, are routinely surveyed relative to permanent elevation benchmarks near the streamgage. Although stage is valuable information for some purposes, most users of streamgage data are interested in streamflow or discharge—the amount of water flowing in the stream or river, commonly expressed in cubic feet per second or gallons per day. However, it is not practical for a streamgage to continuously measure discharge. Fortunately, there is a strong relation between river stage and discharge and, as a result, a continuous record of river discharge can be determined from the continuous record of stage. Determining discharge from stage requires defining the stage-discharge relationship by measuring discharge at a wide range of river stages.

Additional Hints (Decrypt)

va raq bs fgehg orgjrra terra obk naq ohvyqvat

Decryption Key

A|B|C|D|E|F|G|H|I|J|K|L|M
-------------------------
N|O|P|Q|R|S|T|U|V|W|X|Y|Z

(letter above equals below, and vice versa)


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