No creatures on earth can change their environment more drastically than humans and beavers. In the natural world, beaver dams create new wetland habitat for a variety of wildlife. Fishermen, hunters, bird watchers, hikers and outdoor recreationists love to visit beaver dams. But when beavers cut down trees, obstruct and divert waterways, and flood fields, septic systems and basements, their “damming” activities place beavers in direct conflict with humans.
Such a beaver-human conflict happened recently on Scrabble Road near Shepherdstown. Over the past six months, a colony of beavers has been building a series of dams which have destroyed private property. The resulting high water has disrupted several months of data the United States Geological Survey (USGS) collects at one of its stream gaging stations. The gaging station stands along the bank near the bridge over Rocky Marsh Run. The USGS has been aware of the disruption at the bridge and has removed beaver dams from this stretch of the creek several times.
Meanwhile, a local trapper removed several beavers. Then during heavy rains Christmas eve, the beavers tried to keep their dam under the bridge from flooding. We discovered they had cut down and removed two of our neighbor’s large shrubs to make their dam repairs. Days later another beaver was trapped and the dam under the bridge was again torn down.
I had always been curious about the USGS stream gaging* stations I’ve seen at various spots along local waterways. To learn more about how they operate, I contacted Mark Gress, Field Office Chief Supervisory Hydrologic Technician of the USGS in Leetown, WV. He gave me an overview of how the federal agency monitors its nearly 8,000 stream gages nationwide.
The USGS provides continuous information to water managers, scientists, engineers and the public on the stage and discharge of the rivers and streams in the United States.
Measuring the height and rate of flow
“Stage” is the measurement of water level. River stage used to be measured with a simple float and a paper tape installed inside a roofed cylinder (called a stilling well). This system was expensive, time-consuming, and labor intensive.
Gage houses like the one near Scrabble Road are a more recent innovation. Such stations use a pressure sensor attached to a gas line in the water to measure stage data. The pressure transmitted through the gas line and into the sensor is directly proportional to the height of the water. Data is recorded and transmitted via satellite radio antenna.
Stage monitors using radar are the latest innovation. These new sensors use radar technology to measure the height of the river without ever touching the water surface. They can be mounted some place above the river, such as on the side of a bridge, where they’re less likely to be washed away or destroyed by floating debris during floods.
“Discharge,” a combination of the rate of flow and the amount of water, is calculated in several ways. For many years this simply involved a hydrographer wading into the water and carrying a rod attached to a current meter. Sometimes the current meter was suspended in the water using a weight cable system.
Nowadays the USGS uses hydroacoustic meters that measure water velocity with doppler radar. Pulses of sound from a transducer are reflected back when they bounce off solid particles in the water. The shift in the sound frequency is proportional to how fast the solid particles move in the water, thus measuring the water velocity. To measure low flow with more accuracy, acoustic doppler velocimeters can be mounted on a wading rod and carried into the water by a technician. Hydroacoustic instrumentation to calculate discharge has been adapted in a variety of ways for use by manned, remotely controlled or stationary watercraft.
Reporting the data
Water courses all fluctuate naturally over time and change because of low or highwater during floods, drought, debris from storms, or obstructive beaver dams. So, measurements are collected and tabulated at 15-minute intervals and transmitted electronically each hour. Discharge and stage data are plotted immediately and are available to the public within minutes. Additional measurements are made by the USGS at intervals of 6 to 8 weeks or during significant weather events. This information is vital to the National Weather Service, the Army Corps of Engineers, climatologists and a host of private and government agencies.
Now it’s possible to follow the depth and rate of flow of our waterways minute by minute. And we can monitor droughts and floods, detect blockages by debris and measure the results of natural events all from a distance and in real time. But sometimes beavers can still mess things up.
A note about the “gage”
In 1888, USGS Director John Wesley Powell met a very forward-thinking graduate student named Frederick Haynes Newell. Powell was so impressed that he made Newell the first full-time appointee to the new Irrigation Survey, which was created to investigate the potential for dams and canals in the western United States.
At that time, there were no practical and systematic techniques for obtaining daily streamflow (or discharge) records, so Newell set up a training camp on the Rio Grande River at Embudo, New Mexico. Newell’s Camp of Instruction developed water measurement methods that are widely used by the USGS today. During the next ten years, Newell continued to play an important role in the development of streamflow gaging techniques and methods, and he eventually became the first Chief Hydrographer of the USGS.
Newell is purported to be the person responsible for the adoption of the USGS spelling of “gage” instead of “gauge”. Around 1892, Newell reasoned that “gage” was the proper Saxon spelling before the Norman influence added a ‘u’. USGS historian Robert Follansbee speculated that Newell might have also been influenced by the adoption of “gage” in the Standard Dictionary (the first dictionary produced by Funk and Wagnalls).