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Source: https://erdc-library.erdc.dren.mil/jspui/ ; In October 1984, severe vibrations of the outlet works gate tower of Gillham Dam, southwestern Arkansas, were observed by US Army Corps of Engineers project personnel. The reservoir elevation was about 50 ft above conservation pool when this occurred. Prototype tests were conducted to determine the severity and cause of vibrations of the intake tower at Gillham Dam. The test program measured the vibrations at the intake tower, wet well, and both service gates; sluice pressures upstream and downstream of each service gate; and the air demand through both air vents. The vibration data recorded on the intake tower and the wet well showed a predominant frequency of 4 cps. This correlates with the upstream pressure fluctuations measured. The tests in which motion was most severe occurred when gate 1 was at an opening of 4.8 ft or higher. A tapping noise heard off the upstream side of the intake tower was determined to be the bulkhead slot covers of gate 1 bouncing up and down at a 4-cps frequency. Cross-spectral density plots indicate a relationship between the upstream pressure fluctuations and the intake tower and wet well vibrations at a 4-cps frequency. The pressure fluctuations are approximately five times the pressure fluctuations considered normal for turbulent flow and therefore seem to be the driving force of the intake tower and wet well vibrations. Neither the air vent system, which provides sufficient air into the conduits, nor the downstream pressure fluctuations are a cause of the structure vibrations.