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River stages are our most important type of data. River stage data is collected
in one of three ways:
1. Gage Houses
Gage houses are the most common sources of river stage data. Here is a diagram
of a typical gage house:
A gage house consists of a well dug along the riverbank with an instrument
house above it. Water enters the well through one or more inlet pipes.
The water in the well will be at the same level as the river, so the recording
equipment above it actually records the water level in the well. This
data can be either saved at the gage site and queried by telephone, or
can be transmitted via satellite or radio.
2. Wire Weight Gage
This type of gage is usually mounted to the side of a bridge. It consists
of a spool of wire, with a weight attached to the end of the wire. The river
level is measured by lowering the weight until it touches the river surface.
The distance between the bridge and the water is measured, which is then
subtracted from the distace from the bridge to the riverbed. The resulting
number is the river stage.
3. Staff Gage
The third type of gage is by far the simplest. A staff gage is basically
a ruler attached to the river bank, a bridge piling or anything next to
the river. The river level is measured by reading the markings on the gage.
Rainfall amounts are also necessary for river forecasting, since, without
rainfall data, one cannot predict runoff, and therefore, future stages.
There are three general types of rain gages, plus another unusual tool for
1. Weighing Gage
This type of gage consists of an antifreeze-filled collection bucket mounted
on top of a scale. As rain, snow, hail, or any type of precipitation falls
into the collecting bucket, the bucket becomes heavier. The antifreeze is
there to allow the liquid content for frozen precipitation to be measured.
Every few minutes, a recorder attached to the scale records the weight of
the bucket contents. Since the size of the bucket, the weight of antifreeze,
and the density of water are known, a precipitation amount can be measured
from the weight of the bucket.
2. Tipping Bucket
A tipping bucket rain gage consists of a funnel and a rocker mechanism with
two little "buckets" on it, located underneath the funnel. When
rain falls into the funnel, with fills one of the little buckets on the
rocker mechanism. Once a given amount of rain falls into the funnel, usually
0.01 inches, the rocker "tips" over, emptying one of the buckets
and moving the other one underneath the funnel. A recorder in the gage records
each tip and the time it occurred. The tipping bucket gage has its disadvantages,
however. It cannot be used in freezing weather because the mechanism or
the funnel hole can freeze solid. Sometimes the tipper mechanism doesn't
work or double tips.
3. Standard Rain Gage
A standard rain gage consists of only three parts, a funnel, a can, and
a measuring tube. Rain fall into the funnel and into the measuring tube.
Since the funnel is wider than the measuring tube, the depth of water in
the measuring tube would be greater than if the tube was as wide as the
funnel. This allows rainfall to be measured to the nearest 0.01 inch. When
frozen precipitation is expected, the funnel and measuring tube are removed,
and the precipitation is collected in the can. To measure the liquid equivalent
of the frozen precipitation, the contents of the can are melted and poured
into the measuring tube to be measured.
4. Doppler Radar
That's right, it says Doppler radar. One of the functions of the new Doppler
radar is estimating one, three, and storm total rainfall amounts based on
the intensity of the radar echoes. A program is being tested to take the
radar-derived rainfall amounts and combine this data with rain gage data
and show the resulting rainfall estimations on a map.
Temperature and Sunshine Data
Temperature and sunshine data are useful with both snowmelt and evaporation
estimations used in our river model. Hourly temperature data comes from
official NWS observing sites, usually at airports. Some of these airports
also report total minutes of sunshine observed in the previous day. Volunteer
NWS cooperative observers also report the previous day's maximum and minimum
Next: how we get the data we receive.
Monday, November 17, 2003