The original Stony Gorge Dam was completed in 1928 and is a reinforced concrete Ambursen type dam with a concrete slab and buttress. The existing dam had a 868-foot-long crest with a structural height of 139 feet.
To improve the dam’s performance, Shimmick increased lateral support of the dam by adding diaphragm walls, additional struts, and capital struts. Shimmick placed a 90-foot-high diaphragm wall in each bay, the area between the two buttresses. The additional strut was a two-by-two-foot strut located at the midpoint of the buttresses. At the top of the buttresses, capitals with struts spanned across each bay. In total, Shimmick modified 45 bays, requiring more than 7,000 cubic yards of concrete.