Articulated concrete blocks (ACBs) were installed on this dam by others in the early 2000’s to increase spillway capacity and meet dam safety standards. However, there remained historical seepage problems. In 2018, flow overtopped the dam resulting in erosion of the underlying embankment soil.


Seepage through the upstream concrete bulkhead wall and under the existing ACBs was causing significant erosion of the embankment and subsidence of the ACBs. The 2018 overtopping exacerbated the erosion problem and highlighted the design deficiencies of the existing ACBs.


GZA evaluated the existing overtopping protection and concluded that, although the ACB material was within its expected design service lifetime, it did not meet current standards for ACBs (including hydraulic testing to verify performance) and therefore the dam would not safely pass the required design storm. The shortcomings of the older style ACB system, including straight rather than staggered joints, are now widely recognized.

GZA designed a new system utilizing mats of cable-tied, tapered, open-cell ACB units installed on a stone drainage layer. GZA also designed necessary seepage control measures, which included replacing the existing upstream bulkhead wall and constructing an effective embankment drainage system to address the dam’s historical seepage problems. The project moved quickly; construction of the ACB overtopping protection and other repairs began in December 2020 and were completed by June 2021.


GZA addressed a deteriorating situation at the dam and designed a state-of-the-industry, yet cost-effective, solution to correct seepage problems and spillway deficiency.