Lake Cachí

Lake Cachi Represa de Cach
View of Lake Cachi
Location	Costa Rica
Coordinates	9°49′38″N 83°49′0″W / 9.82722°N 83.81667°W / 9.82722; -83.81667Coordinates: 9°49′38″N 83°49′0″W / 9.82722°N 83.81667°W / 9.82722; -83.81667
Type	Artificial reservoir
Primary inflows	Reventazon River
Primary outflows	Reventazon River into Atlantic Ocean
Catchment area	919 square kilometres (355 sq mi)
Basin countries	Costa Rica
Max. length	70 metres (230 ft)
Surface area	324 hectares (800 acres)
Average depth	69 metres (226 ft)
Max. depth	80 metres (260 ft) to deepest foundation
Water volume	51 million cubic metres (41,000 acre·ft)
Surface elevation	970 metres (3,180 ft)

Lake Cachi (Spanish: Lago de Cachí ) is an artificial lake in central Costa Rica created by the Cachí Dam (Represa de Cachí), an arch dam which is located north of Tapantí National Park, to the east-southeast of Cartago in Cartago Province. The main town is Cachí, located away from the east bank of the lake. Built in the 1970s, it was one of the first hydroelectric projects in Costa Rica. It has an installed capacity of 102 MW with three units of 34 MW capacity each (Vertical Francis turbines).

The project became operational with the first unit commissioned in 1966, second unit in 1967 and the third unit in 1978. The Reventazon River provides multiple benefits through the three dams built on it. Out of the three dams, Cachi Dam not only provides power generation benefits but also controls floods, and recreational facilities in the Lake Cachi. The Rio Macho project on the upstream provides hydroelectric power and the downstream Birris power project also provides drinking water (40% of the metropolitan city’s water supply needs).

The reservoir, located in the Rio Reventazón, is an important supplier of electrical power to Costa Rica. It is operated by Instituto Costarricense de Electricidad (ICE).

Lake Cachi contains the Cachí Dam (Represa de Cach) in the northeastern part of the lake, near the village of Ujarras along the 225 road in the middle reaches of the Reventazon River in the Ujarras valley. The lake is created by the dam on the Reventazon River as it flows in from the northeast winding through the steep-sided valley. The river has a total drainage area of 3,000 square kilometres (1,200 sq mi) lying in an elevation range varying from 3,432 metres (11,260 ft) above mean sea level at its highest point to the lowest outflow point into the Atlantic Ocean; out of this, the reservoir created by the Cachi dam intercepts the upper catchment area of 919 square kilometres (355 sq mi). The annual precipitation in the entire river basin varies from 1,200–8,000 millimetres (47–315 in). In 80% of the total catchment area, the relief varies distinctly, with mountains which have slopes between 20 and 85 degrees. The average annual water inflow into the reservoir is at the rate of 104 cubic metres (3,700 cu ft)/second. The gross storage capacity of the reservoir is 51 million cubic metres. The design flood discharge is 3,500 cubic metres (120,000 cu ft)/sec. The reservoir has a water spread of 324 hectares (800 acres) which stretches over a length of 6 kilometres (3.7 mi) with maximum water depth of 69 metres (226 ft). Sixty percent of the reservoir's catchment is forested, the remainder is agricultural land. Density currents are formed in the reservoir on account of a combination of temperature gradients and high sediment concentration.