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Keeping cool: Water reservoir expansion completed 60 years ago

This photo from 1961 shows how the secondary reservoir on Arnold Air Force Base appeared following the completion of a 45-million gallon capacity addition to the original 13-million gallon reservoir. (U.S. Air Force photo)

This photo from 1961 shows how the secondary reservoir on Arnold Air Force Base appeared following the completion of a 45-million gallon capacity addition to the original 13-million gallon reservoir. (U.S. Air Force photo)

ARNOLD AIR FORCE BASE, Tenn. --

Thirteen million wasn’t enough.

Sixty years ago, a massive undertaking was completed that more than quadrupled the original capacity of the secondary reservoir at Arnold Air Force Base.

The project that increased the amount of water the secondary reservoir could hold from 13 million gallons to 58 million gallons was necessary to meet new testing demands that had begun to present themselves by the early 1960s. The site and facilities at Arnold AFB, then known as Arnold Engineering Development Center, were originally designed for testing air-breathing engines and winged aircraft. However, technology was evolving, and much of the work at the center began to focus on advanced rocket and aerospace environmental tests to support a variety of missile, satellite and space programs.

This shift necessitated changes to test units and their support systems which, in turn, placed a greater demand on the center’s cooling water system. The amount of water needed to accommodate the new types of testing far exceeded the 13-million gallon capacity of the secondary reservoir.

In a 1961 article published in High Mach after the 45-million gallon reservoir addition was completed, Lt. Col. William C. Langley, Tullahoma Area Engineer with the U.S. Army Engineer District, Mobile, Alabama, highlighted the need for the capacity upgrade by describing what occurred over a three-day period shortly after the project was finished.

“In an eight-hour period of one day, 78 million gallons of water were pumped through the Secondary Pumping Station; in the same time another day, 75 million gallons were pumped; on the third day 63 million gallons were pumped,” Langley wrote. “The primary pumping station was filling the reservoir as the secondary system emptied it.”

According to Langley, if these requirements had arisen prior to completion of the reservoir addition, some vital tests would have been interrupted, as the previous amount of water available for an 8-hour period was 59 million gallons starting with a full 13-million gallon reservoir.

The addition was the result of a collaboration between staff members from the U.S. Air Force, U.S. Army Corps of Engineers and Arnold Research Organization, or ARO, which managed AEDC at the time, as well as expeditious work from the outside contractors tasked with its construction.

In its request to the Corps of Engineers to design the addition, the Air Force specified it would need to connect to the existing reservoir. Specifications also called for a downtime not to exceed seven days.

A variety of plans to accomplish the connection were examined, and it was decided that an “open cut” would be used to adjoin the existing reservoir and the large addition. This method, which called for the removal of a portion of the original reservoir wall, was determined to be both the least expensive option and the one that would result in the least interference with testing operations.

“The method called for progressively lowering the water in the existing reservoir on a timetable geared to programs in the wind tunnels and test cells so that tests would not be interrupted,” Langley wrote in 1961. “At the same time, annual maintenance down-time for the facilities was scheduled to coincide with the reduced available water supply.”

The cut-through was accomplished in three steps. First, the water level in the original reservoir was dropped 13 feet and kept there for 13 days while the first part of the cut-away was made. Finish surfaces were applied. On day 14, the water level was decreased another 12 feet, and the next 12 feet of the cut-through were completed. Over the subsequent 10 days, this portion of the cut-through, just as the first had been, was treated and covered with gunite, concrete sprayed on using compressed air and a special spray gun.

While the second part of the cut-through was being performed, the Propulsion Wind Tunnel (PWT) and the Rocket Test Facility (RTF) were shut down for routine annual maintenance. No operating limits were imposed upon the von Kármán Gas Dynamics Facility (VKF).

On day 25, the existing reservoir was emptied completely. It would remain in this drained state for the following five days, during which time the remainder of the cut-through was completed and remaining surfaces, including the bottom of the channel, were paved. By this point, VKF, like PWT and RTF, had been shut down for annual maintenance.

“During the five days the secondary reservoir was completely empty, ARO provided an interim water supply primarily by filling the retention pond and return cooling water ditch that leads from the center to the lake,” Langley wrote. “Portable pumps were used to supply the potable water necessary to meet the center’s air conditioning and housekeeping requirements, as well as for the water required for gunite and concrete curing in the addition.”

The dikes making up the walls of the addition measure between 130 to 150 feet in base width and 31 to 34 feet in height. They are 8 feet wide at the top, sloping outward at an angle of around 27 degrees, with an interior slope of about 22 degrees.

According to Langley, the original reservoir was about 325 square feet. The addition extends about 640 feet from it, resulting in a dike enclosure of almost 1,000 feet in length. The addition is 470 feet wide. An 18-inch wall was placed along the top of reservoir 3-and-a-half feet above the maximum storage elevation to prevent waves from sloshing over the sides and eroding the outside slopes.

The cost of the addition in 1961 was $499,300, the equivalent of approximately $4.5 million today.