Rehabilitating an Aging Embankment Dam with RCC for Overtopping Protection

Middle Branch Dam is located on Middle Branch Reservoir in Carmel, New York, situated within the Croton Watershed system. Originally constructed in the late 1870s, the 94-ft high dam consists of an earthfill embankment with a granite block corewall. The principal spillway for the structure consists of a bypass weir located to the west of the embankment structure. In order to increase the emergency spillway capacity for overtopping protection, a section of the embankment was armored with roller compacted concrete (RCC) overlay, making this the first dam remediation project for the New York City Department of Environmental Protection to use RCC for dam rehabilitation.
Upon completion, approximately 13,000 cubic yards of RCC overlay was placed on the downstream slope, crest and upper portion of the upstream slope to form the 70-foot high RCC emergency spillway. A detailed quality assurance and quality control (QA/QC) program was implemented consisting of placement control in the field and mixture proportioning control at the RCC batch plant. Careful observation and testing was made of the materials, delivery, handling, placement, and compaction of the mix to ensure optimum performance. During the course of RCC placement and emergency spillway construction, mix segregation, mix placement temperature, and curing and protection issues were identified through the quality assurance program and successfully resolved by the resident engineer, quality assurance personnel, and the design team through modifications to the placement and batching procedures.