Changuinola II
Bocas del Toro Energy S.A. is undertaking the development of the new Changuinola II hydropower project that is scheduled for completion in 2029. This forms part of the 2020 – 2034 expansion plan of the country’s national interconnected electricity system. At present there is no set date for the public bidding process.
Located in Valle del Risco in Panama’s Bocas del Toro Province, the 223.8MW Changuinola II plant will have an average annual energy production of 1120GWh. Its main components include:
· 174m high RCC arch-gravity dam
· 994 Mm3 reservoir with a surface area of 18 km2
· Construction diversion arrangements – cofferdams and diversion tunnel
· Headrace intake works
· Headrace tunnel and penstock
· Power station with three units and outlet channel
Cochea Dam
Located in the province of Chiriquí on the Cochea River, Cochea Dam was built in 2013 on a foundation of volcanic lahar (a cold mix of water, rocks, and sediments) from the Baru volcano at 3475masl.
Cochea is a run-of-river dam with a small reservoir of 115,000m3 which remains within the normal course of the river. A conventional concrete gravity dam, it is 13.2m high and 40m long and is one of the 20 dams less than 15m high that exist in Panama for electricity generation. The hydroelectric plant is located 4.3km downstream of Cochea with a total capacity of 15MW and an average annual energy of 50GWh.
The average annual rainfall in the Cochea River basin is 3500 mm and the discharge capacity of the spillway is 520 m3/sec. Several periodic controls are carried out to evaluate the biodiversity and quality of the water in the reservoir and in the discharge of the plant.
This type of small hydroelectric plant produces more energy annually per affected area (1386MWh/Ha) during its construction and operation than that produced by photovoltaic plants in Panama. Cochea Reservoir did not impact any houses or public structures during construction and operation.
Concepción Dam
Operated by Fontus Hydro, the Concepción dam was built in 2008 and is located in the province of Chiriquí on the Piedras River. Sited on a bed of river gravel more than 15m deep, the dam diverts 20m3/sec to three hydroelectric plants in cascade with a total capacity of 30MW and an average annual energy production of 158GWh. The central spillway is 12m high and the 70m long conventional concrete gravity dam has two lateral gravel abutments with an impermeable clay core. The waterproofing of the permeable foundation was achieved with a 10m deep cement grouting screen.
The Piedras River is a mighty mountain river that floods rapidly with large amounts of sediment (sand and stones of more than 1m deep). The dam is located on a 200m bed in the flattest part of the river. The speed of the water during floods can exceed 7m/sec, posing a challenge for the design and maintenance of the hydraulic structures. Two 60m long sand traps in parallel properly contain the sediment before the water flows into the penstock.
The generation design of the Concepción, and neighbouring Las Perlas Norte and Las Perlas Sur hydropower plants results in one of the most efficient run-of-river hydroelectric complexes in Panama, producing 3072MWh per year per affected area (Ha) during construction. For comparison, solar plants in Panama produce an average of 700MWh/Ha of affected area. This scheme means less project footprint and less impact on biodiversity and wildlife and more environmentally friendly energy.
Las Cruces Dam
Built in 2015, Las Cruces dam in the province of Veraguas is situated on the San Pablo River on sound bedrock, producing a 40Mm3 reservoir in an area of 280 Ha in a mid-elevation rocky mountain region. Las Cruces is a 56.5m high and 276m long RCC concrete gravity dam. It is part of a hydroelectric plant dam-toe scheme with a total capacity of 21MW and an average annual energy production of 109GWh. The ungated spillway is 50m wide.
Las Cruces Reservoir is located in an unpopulated area with very little agricultural activity. No housing or public structures were impacted during construction. Wildlife surveys in Las Cruces since 2016 have recorded a total of 18 amphibian species, 27 reptile species, 161 bird species, and 19 mammal species, as well as protected species.
Las Cruces Dam is one of the six medium-height dams (50-60m) in the Republic of Panama with the least social impacts and land use change in the region. The average annual rainfall in the San Pablo River basin is 3000mm and the discharge capacity of the spillway is 1550m3/sec.
This article first appeared in International Water Power magazine.
