Arenal: A New Arch Dam for Honduras' Energy Security

The main structure of the new Arenal hydroelectric power plant is an arch-gravity RCC dam impounding the Yaguala River in 75 million m3 reservoir. The river discharge is characterized by strong seasonal fluctuations, with an average annual discharge of 34 m3/s, but with common events of more than 1,000 m3/s in the rainy season. For the safe discharge of these water volumes, the dam is equipped with a free overflow spillway and, in addition, one of the two tunnels on the right bank, which were used for the river diversion during construction, has been converted into a bottom outlet. The total discharge capacity at the dam is over 6’000 m3/s.

The dam (H = 100 m, L = 273 m, V = 305,000 m3) was designed to make the most of the RCC versatility and minimize construction time. The construction confirmed all the advantages of RCC, which has established itself as a material for concrete dams in recent decades. In fact, thanks to the expertise of Sinohydro as civil contractor and of Lombardi as site supervision, the construction was successfully advanced and completed, despite two unexpected interruptions due to the Covid19 pandemic and the passage of two hurricanes in 2020.

The waterways for generation are on the right bank and include an intake, a pressure tunnel (A = 29 m2, L = 4’600 m + 2 adits), a surge shaft (A = 72 m2, H = 94 m) and two penstocks (D = 2.40 m, L = 2 x 270 m). The powerhouse (W = 19.0 x L = 30.7 x H = 35.8 m) is equipped with two vertical Francis units (Q = 2 x 25.5 m3/s, H = 130 m, P = 60 MW) interconnected to the national grid through a switchyard and a transmission line (L = 25 km, U = 230 kV). An ancillary powerhouse for the environmental flow at the dam (Q = 2.8 m3/s, H = 54 m, P = 1.4 MW) complements the plant.