One of our main concerns in regard to the construction of the hydroelectric plants is how they will affect the flow of the river during the year, especially in the summer months when there is more tourist activity. Will the Achibueno pools be dried up due to the plant activity? The answer to this question depends on at least two factors:

  1. Plants operating in the summer: the water rights acquired by the hydroelectric company oblige it to leave an ecological flow of 3 m3/s downstream of each intake (one in Potrero Grande and the other in Las Ánimas). What is the river’s flow during the summer months at each one of these intake points? If the flow were, for example, 6 m3/s or more at these points, the plants would be obliged to leave less than half of the river’s flow downstream from the intakes ; that is, they would practically dry it up on a stretch of nearly 30 km of length.
  2. Alteration of the subterranean flow: to extract from the river nearly 80% of the total surface volume of water during the year has to have an important effect on the underground flow.  The underground flow moves slowly and if part of the superficial volume that normally flows in the month of November is extracted, it is possible that the water will not be able to totally infiltrate the underground riverbed. This would affect the river’s flow in the summer months: if the riverbed is not saturated ahead of time, the surface flow will infiltrate, which would significantly decrease the river’s water levels in the months of   December, January, February, and March. The authorities must require the hydroelectric company to deliver all the technical studies necessary in order to rule out this type of scenarios.

Another reason for concern is the impact that the decreased flow on the aquatic ecosystem of the Achibueno River. According to a SAG study (Concepts and criteria for the environmental assessment of wetlands , 2006), “(the flow) is the principal factor that regulates the behavior of  aquatic ecosystems in the rivers. Any change in the flow of the rivers can affect the structure and function of the aquatic ecosystems, even when there is a range of variation that can be absorbed by the capacity of resilience and resistance of the biological systems. The reduction of the flow to under the minimum historic values registered and the alteration of the seasonal pattern during the hydrological cycle, will strongly modify the structure and function of the wetlands”.

In accordance with the aforementioned study: “A modification in the flow implies a reduction and/or alteration of its regime or average behavior, so that it is necessary to maintain a minimum environmental flow. The General Water Office (DGA) establishes 10% of the average annual flow as a minimum threshold, determined by hydrological methods; however, it is necessary to incorporate ecosystem criteria for its determination. For example, the seasonal regime defined by the hydrography of each river, must be maintained even when the flows diminish”.

Achibueno River

Achibueno River