Reconstructing river reservoir NO. 3 - From emergency action to breach to safe operations in 21 months

River Reservoir #3 is located in east central Arizona near the town of Greer. The zoned embankment dam was originally constructed in 1896 and has been modified at least 4 times. Currently the dam is approximately 1,100-feet-long and has a maximum height of about 70 ft. During the last two weeks of March 2004 the water surface at River Reservoir #3 was at higher than normal levels and began spilling through the spillway on March 22nd. On March 28th, the Round Valley Water Users Association (RVWUA), who own and operate the facility, reported that the left abutment drain was discharging more than 120 gallons per minute (gpm), a rate 10 times the normal amount. On April 1st, sediment was observed in the weir box located at the end of the left abutment drain. This material was mainly sand with some clay, and was assumed to be originating from the sandy clay core of the embankment. In the first week of April, the Arizona Department of Water Resources (ADWR) requested instigation of the emergency action plan, the Governor of Arizona declared an emergency situation, and Apache County emergency responders began 24-hour-hour surveillance of the dam. Simultaneously, TCB was contracted by the ADWR to begin emergency engineering services in close cooperation with their office. The scope of work of these services included: Continued observation and monitoring of the behavior of the River Reservoir #3 dam until a safe situation existed; Performed investigations of the dam to establish an understanding of the conditions within the embankment and the causes of the internal erosion. Besides conventional drilling and sampling, the investigation included dye tracing and a magnetic-based groundwater mapping survey; Development of preliminary and final designs for a repair that eliminated the present problem and allowed the reservoir to operate in a safe manner. This paper describes the results of the monitoring, evaluation and repair of the River Reservoir #3 dam. The reconstructed dam is currently operating as designed and began providing water to the Round Valley Water Users Association less than two years after nearly failing. 11 pp., 6 figures.