About two miles from Tehachapi down Highway 58 toward Bakersfield, there is a small structure that nearly everyone has seen but not really noticed, and few can identify it.
Consisting of a three-foot diameter corrugated culvert pipe painted green and standing upright, the seven-foot tall structure has a conical roof cap and a hinged door. Located alongside the eastbound lanes of Highway 58, this device is a sentinel of sorts with one purpose: to measure the amount of water flowing through Tehachapi Creek.
This streamflow measuring station was a project of the United States Geological Survey and was installed in the 1930s following the disastrous September 1932 Keene flood downstream that killed more than 40 people.
The measuring station consists of a stilling well and a control structure. The control structure is essentially a short segment of concrete canal, about 30 feet wide at the bottom and 100 yards long with sloping sides that are about 25 feet tall.
The stilling well is the green culvert with the pointed roof. A perforated pipe down in the channel allows water to enter the stilling well and maintain the same water level as Tehachapi Creek but without the movement or turbulence of the stream — creating a circular pool of still water (hence the name).
A float in the stilling well indicates the height of the water, and this information is continuously recorded on a graph paper mounted on a drum apparatus that is akin to the seismographs used to record earthquakes.
Data generated by this battery-powered chart recorder is collected by the Kern County Water Agency and used to calculate the amount of water that flows through Tehachapi Creek.
"The velocity of the water is fairly constant, so if you know the exact configuration of the channel and the height of the water, you can accurately determine the streamflow," Tom Haslebacher once explained to me. He was a geohydrologist with the water agency who was involved with the monitoring of Tehachapi Creek for about 20 years.
The USGS was originally responsible for the streamflow station but budget constraints in the early 1980s led the federal agency to seek local partners to assume maintenance and monitoring of many of its gauges. The KCWA accepted responsibility for the Tehachapi Creek measuring station and another on Poso Creek in northern Kern County.
The KCWA is a non-regulatory agency headquartered in Bakersfield whose functions include serving as a data repository for flood control and groundwater supplies.
Haslebacher was among the bright and capable scientists employed at KCWA, and he shared some of his encyclopedic knowledge of local water issues with me.
He noted that Tehachapi Creek was a temperamental water course that could experience wide fluctuations in flows.
"As you know, Tehachapi Creek is a very, very dynamic stream," Haslebacher explained. "There is a huge watershed behind it, but the majority of the precipitation stays in the basin — it either permeates or evaporates, but most of the water doesn't disperse down Tehachapi Creek."
Unless there is a big storm. Then the scenario changes.
"The Tehachapi watershed is excellent in that it retains most of the moisture that falls, and it takes a heavy storm or an El Nino year to overwhelm the holding capacity of the watershed and send a lot of water down the creek," Haslebacher said.
When this happens, normally placid Tehachapi Creek can go from a trickle to a torrent.
Data from the measuring station reveals that on January 20, 1999, following a substantial storm, flows on Tehachapi Creek peaked at 143.1 cubic feet per second (cfs). That's easily enough to sweep a car downstream.
After heavy rains, the creek will start dropping within hours, though in wet years (certainly not this one) Tehachapi Creek may show elevated water levels for days or even a week or two after the storm.
Through wet years and dry ones, the Tehachapi Creek measuring station will likely continue to generate hydrology data as it has for about 80 years.
Have a good week.
Jon Hammond has written for Tehachapi News for more than 30 years. Send email to firstname.lastname@example.org.