A Century of Watching the Colorado River

Right where the Colorado River flows into the mouth of the Grand Canyon, an inconspicuous 20-foot-high concrete tower rises from the riverbank.  

Inside the tower is a U.S. Geological Survey streamgage that will mark its centennial year of monitoring the river on October 1, 2021. At a time when the Roaring Twenties were in full swing, the streamgage began collecting information about the water’s level and flow. USGS scientists chose the site in 1921 because it was readily accessible and strategically located to study the hydrology of the Colorado River drainage basin. 

Now, seven states within the basin depend on the river for water supply and hydropower production. Natural resource managers look to the 100-year-old streamgage to make informed decisions while recreationists and trout seekers check the streamgage’s information before they set off in their boats and scientists use it to study region’s geology and ecology.  

The gauge sits right across the river from Lees Ferry, named after John Doyle Lee. In a twist of fate, Lee started the ferry in the late 1800s after John Wesley Powell, the second USGS director, gifted him a boat while he was exploring the Grand Canyon.  

Although its equipment has been updated over the last century, the streamgage is not that different from its initial installation a century ago. 

“The gauge at Lees Ferry is among the most watched and accurate big-river monitoring locations in the country and is an excellent example of how consistent, long-term scientific information beneficially informs water-management decisions in a changing world,” Jim Leenhouts, the Director of the USGS Arizona Water Science Center, said.  

September 21, 1923, 9:00 a.m. — Colorado River at Lees Ferry. 

(Credit: G.C. Stevens, USGS. Public domain.)

A basin splits into two 

One year after the gauge was established, the seven states in the Colorado River Basin negotiated the 1922 Colorado River Compact that divided it into the Upper and Lower Basins. The Lees Ferry gauge as well as a streamgage on the Paria River are used as critical, continuous measurement points to determine how much water passes to the Lower Basin each year.

USGS scientists have collected various data at the site, from streamflow to water quality. The gauge’s longevity means scientists have been able to tease out long-term trends and note how dramatic changes impact the river.  

Glen Canyon Dam as seen from an overlook on the south side, downstream of the dam in Page, Arizona.

(Public domain.)

In 1963, the basin experienced a particularly dramatic change – the construction of the Glen Canyon Dam 15 miles (24 km) upstream of the streamgage. The gauge recorded the difference between unregulated water flow, prior to the construction of the dam, and regulated flow following the dam’s completion.   

The U.S. Bureau of Reclamation constructed the dam to harness the power of the Colorado River and provide water to millions of people in the West. Glen Canyon Dam impounded 186 miles (300 km) of the Colorado River, creating Lake Powell. 

The dam stores water for the Upper Colorado River Basin states of Utah, Colorado, Wyoming and New Mexico to ensure those states are able to access the river especially during droughts. Releases from the dam ensure that the Lower Basin states of California, Nevada and Arizona are able to access these essential water supplies from the Colorado Rivers.

“We built this streamgage in the Middle Ages of gauging,” Daniel Evans, a USGS scientist said. “And yet, it has consistently collected accurate information that accounts for how much water is released by the Glen Canyon Dam and enters the Grand Canyon on its way to Lake Mead,” Evans said. 

“Per the 1922 Colorado River Compact, the states of the Upper Division must ensure the flow of the river at Lee Ferry doesn’t deplete below an aggregate of 75 million acre-feet for any period of 10 consecutive years,” said Reclamation’s Upper Colorado Basin hydraulic engineer Heather Patno. “Reclamation works closely with the USGS and utilizes the gauge at Lees Ferry to calculate the flow of the Colorado River at this important measuring point,” Patno said.

When in drought, check the streamgage 

Since 2000, the Colorado River Basin has been in a historic drought. The combined water storage in Lake Powell and Lake Mead are at their lowest levels since Lake Powell initially began to fill in the 1960s.  

On August 16, 2021, the Bureau of Reclamation announced the first-ever water shortage declaration for the Lower Basin.  Downstream releases from both Glen Canyon Dam and Hoover Dam will be reduced in 2022. The streamgage at Lees Ferry, as well as other streamgages in the area, will be there to capture how changing dam operations affect streamflow.

“Like much of the West, and across our connected basins, the Colorado River is facing unprecedented and accelerating challenges,” said Assistant Secretary for Water and Science Tanya Trujillo in an August 2021 statement. “The only way to address these challenges and climate change is to utilize the best available science and to work cooperatively across the landscapes and communities that rely on the Colorado River.” 

Lees Ferry streamgage and cableway downstream on the Colorado River, Arizona

(Public domain.)

Once upon a streamgage 

The Grand Canyon survey party at Lees Ferry in 1923. 

(Public domain.)

The streamgage at Lees Ferry is one of over 8,000 that measure streamflow year-round in every state as well as the District of Columbia and the territories of Puerto Rico and Guam.  

The gauges are often stored in waterproof boxes perched near flowing water. They contain instruments that measure and record the amount of water in a river or stream approximately every 15 minutes. If there’s a flood, the gauge will collect measurements more frequently.  

Sometimes, as in the case of the streamgage at Lees Ferry, the only way to access the gauge is by boat or cableway. “With a cableway, we basically zipline across the river to the streamgage,” Kurt Schonauer, a USGS scientist, said. 

Schonauer visits the gauge about 10 times a year to ensure it’s working properly, do any necessary repairs and soak in its majestic locale. “It may not have a whole lot of fancy instrumentation, but it produces high-quality data,” Schonauer said. 

The streamgage at Lees Ferry measures water height using a stilling well. Water from the river enters and leaves the well through underwater pipes, allowing the water surface in the well to be at the same level as the water in the river. The water level is measured inside the well using a float and noted in an electronic data recorder.  

To determine how fast the water is flowing, USGS hydrologists and hydrologic technicians take streamflow measurements on the river or stream. Then, they develop a mathematical relation between the streamflow measurement and the water height values that the streamgage regularly collects. They use that mathematical relation to compute streamflow information every 15 minutes.  

Anglers on rafts departing the boat dock at Lees Ferry, AZ.

(Credit: Lucas Bair, USGS. )

“This streamgage is at a really beautiful site,” Schonauer said. It’s a popular spot for recreation and a renowned trout fishing area. “A lot of people who go on rafting trips down the Grand Canyon check the gauge to make sure conditions are safe on the river,” Schonauer said.  

When he’s not gazing at the beautiful layers of geology, working on the streamgage, or taking a streamflow measurement, Schonauer likes to check in on the local wildlife. “We have a resident beaver that we see from time to time,” Schonauer said.  

As scientists, decision makers, recreationalists, fishermen, and, possibly, a beaver or two, celebrate the stream gage’s 100th birthday, they also look forward to 100 more years of robust and reliable information. 

---