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WILLOWSTICK CASE STUDY: DAM LEAK
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In April 2004, the River Reservoir #3 earthen dam near Eagar, Arizona was in danger of imminent failure due to high volumes of water and silt leaking through the dam's toe drain. Willowstick and ECI (Engineering Reservoir Consultants) were asked to investigate and address this rapidly deteriorating situation. Willowstick was able to map the leak through the dam using its patented AquaTrack™ technology. Willowstick determined the flow path of the leak with two days of field survey work. The location of the leak, as determined by Willowstick, was confirmed through targeted dye tests and subsequent drilling and test pitting. ECI provided the geotechnical services to remediate the problem. The reservoir was drawn down to a level below the primary area of concern and remediation activities have been initiated, eliminating the risk of dam failure.
Imminent dam failure possibleRiver Reservoir #3 is an arched earthen dam on the headwaters of the Little Colorado River, located approximately 15 miles southwest of Eagar, Arizona. It was completed by early settlers in 1896, and was essentially constructed with available materials and limited engineering; hence no clay core was installed. In 1996, the dam underwent some reconstruction, and additional rip rap was installed to reduce the original slope of the lateral (upstream and downstream) sides. Within the western confines of the dam (left abutment) there is rumored to be a perennial spring, which is possibly controlled by a clay pipe and stone drainage system dating back to the original dam construction. In late March 2004, unusual effluent from the dam (significantly higher than normal volumes of water and silt) was observed in the left abutment weir box. This indicated a potential for a structural leak within the confines of the arched earthen dam. It was suspected the leak path was related to the rumored perennial spring and associated clay pipe and stone drainage system. Imminent dam failure was possible and emergency personnel were mobilized to the site, to monitor and control the situation. Using Willowstick to Find the LeakAquaTrack is a patented non-intrusive geophysical technique capable of mapping groundwater at depths exceeding 3500 feet (1 kilometer) over large areas. The water body to be mapped is energized and the electrical current flows preferentially through saturated subsurface materials, creating an induced magnetic field that is measured at multiple points on the ground surface, typically in a grid pattern.
The measured magnetic field data are processed, contoured, and correlated to other hydrogeologic data, resulting in enhanced definition of the extent of saturation associated with the groundwater body. On this project, an electrode was installed in the lake (upstream side) approximately 800 feet south of the western abutment; a second electrode was placed in the left abutment weir box where the high silt content was observed (downstream approximately 140 feet north of the crest of the dam). The two electrodes were connected to an AC power supply. More than 125 magnetic measurements were taken on both upstream and downstream sides of the riprap on the dam and 24 measurements were taken from a boat in the reservoir. The resultant survey pinpointed the spatial area of greatest leakage in both horizontal as well as vertical profiles.
Reservoir Remediation ActivitiesThe quick turnaround of information enabled an immediate understanding and therefore an efficient mitigation of the leakage problem. Targeted dye tests were performed in concert with the Willowstick survey, verifying the location of the leak.
Subsequent excavation, drilling and lowering of the reservoir water of the area, targeted by Willowstick, again confirmed the findings. Temporary remediation of the dam has been completed pending funding for a permanent fix.
To learn more about Willowstick and our leak mapping capabilities, please contact us.
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