One of the biggest challenges for dam owners is addressing their repair needs for aging components installed decades earlier. Dam owners generally understand basic operation and maintenance needs of their dams, but some of those needs go beyond basic operation and maintenance. For instance, in the early stages of the small watershed program NRCS designed and installed approximately 2300 corrugated metal pipe (CMP) conduits across the nation. Some of these serve as the complete principal spillway for their flood control dams. While the cost savings at the time allowed for the construction of many more flood control dams, that cost is now a burden to dam owners needing to repair or replace those corroded and aging metal components.
To assess this concern, Oklahoma NRCS, in partnership with the Oklahoma Conservation Commission (OCC) devised a pilot program to begin evaluating several dams in 2019. With special funding provided by the NRCS national office and OCC, the CMP Pilot became a reality. Fifty of Oklahoma’s more than 400 dams originally constructed with metal pipes were analyzed. Dams were chosen from across the state to address a variety of site conditions and design configurations. On-site evaluations revealed that 25 of the 50 were still in good shape. The remaining 25 went into design. As a Pilot study, various methods of repair and replacement were employed. These included techniques from slip lining and tower replacement with HDPE materials to full principal spillway replacement.
To date, 8 repairs have been completed, 13 are ready for construction, 2 are in the final stage of design. One sponsor opted not to pursue repairs. Some of the issues encountered during the Pilot were: accurately determining needs, staffing and workload, sponsor commitment, and funding.
Additional study is needed to determine why some metal pipes corroded faster than others. Most had various types of coating applied to the pipe at the time of construction, many of these coatings no longer exist or are allowed to be used. However, providing some insight into what can cause or prevent pipes from corroding can help dam owners understand where and when their dam may need some major repairs. The study is helping develop a design guide and will lead to a better understanding of coatings and other insights to benefit dam owners. Additionally, we will look at other potential needs that are beyond O&M.
