Continuous dam movement raises concerns in Kremmling CO

Continuous movement and settlement accumulation occurring in Ritchard Dam, in Wolford Mountain Reservoir, is brought to the attention of the Colorado River District board of directors, which will now be responsible for adressing the issue. The 125ft dam, located 5 miles upstream of Kremmling, Colorado, holds back nearly 66,000 acre-feet of water and downward settlement, exceeding acceptable levels, is being recorded since 2008.

Ritchard Dam measuring 125ft in height and 2,100ft in width, is located along Muddy Creek flowing into the Colorado River, east of Gore Canyon. It was constructed between 1993 and 1995 and cost $42 million. It consists of an impervious clay core, covered both upstream and downstream of a zoned earth and rockfill embankment, inclusing shale, excavated onsite during construction. It forms a reservoir of total embankment volume of 1.4million cubic yards. 

First signs of dam deformation were observed in 2008, by engineers working for the river district, who noticed downward settlement of 1 foot and a half, as opposed to the normally expected settlement of one foot. Since then, the network of  monitoring devices installed upon the dam, has indicated that the dam has moved downward more than 2 feet, whereas an 8-inch horizontal movement was also recorded at a location about 40 to 50 feet from the dam's crest. 

AECOM's engineer Mike May attributes the downward movement to the poorly compacted rock fill of the dam and stresses out that the inner elastic clay core also deforms, being at risk of cracking, if the observed deformation pattern persists. In such a case, water filled cracks will place the dam under great risk of global failure, releasing up to 600,000 cubic feet of water per second to the downstream areas. It is estimated that within eighteen hours water would inundate Glenwood Springs.

Bill McCormick, the chief of dam safety for the state of Colorado, stated that "the extensive investigations and analysis to date show that the dam remains strong and stable but that if left unabated, the movements could ultimately (in decades) create greater damage to the dam structure", but senior engineer and dam expert Dick Davidson is supportive of a more direct and immediate solution to the problem.

To identify the deformation mechanisms behind the dam movement, a series of field and laboratory testing is under way in the embankment and foundation material as well as the execution of embankment stability analyses. With complete proposals being expected at April's and July's board meetings, so far available options range from lowering the reservoir's water level - not solving the problem permanently - to reconstructing the dam, spending nearly $30 million.