The Arenal Reservoir

Investigations of Floating Islands in a Tropical Environment

The reservoir is the main supplier of electrical power to Costa Rica. It is operated by ICE (Instituto Costarricense de Electricidad). It can generate, in three power stations, over 400 MW.

The problems experienced are related to clogging of the intake by floating islands of peat from the former Lake Arenal, which was inundated. It was more a seasonally flooded swamp, covered with a grass vegetation (called gamalote) than an open-water lake. The extension of this vegetation is almost identical to the extension of the old lake on the map below.

A full-scale investigation project, with AB Hydroconsult as the contractor, has just been concluded. A side-scan sonar mosaic has been made of the bottom in order to evaluate the future trend of the problem. The map and photos below are from that field study. A summary of the results is available.


1. The survey vessel is one of the tug boats ICE uses to move those floating islands that may reach the intake.


2. The dam was built close to the active Arenal Volcano, creating a spectacular scenery.


3. Bordering the reservoir is a large forest reserve. The road standard in this part is pretty basic.


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