Water quality modelling

Water quality modelling for Quimbo hydropower plant, for Emgesa.

The El Quimbo plant is a hydroelectric power facility with an installed capacity of 400MW in the Huila Department of southwestern-central Colombia, operated by Emgesa, the Colombian subsidiary of Endesa. The reservoir created by the dam has an area of 8,250 ha, is 55km long and has an average width of 1.4km.

Since its first days of operation, there have been water oxygenation problems downstream of the reservoir. The decomposing organic matter in the sediments reduced the amount of oxygen in the waters released by the plant, and after only a few days of operation the local authority ordered the power plant to be closed.

A very expensive water oxygenation device was installed to increase the water oxygen content at least to the legal limit (4 mg/l) and allow the plant to reopen. Meanwhile, the local environmental authority asked Emgesa to provide a numerical tool that could simulate the current and prospective state of the reservoir waters.

Emgesa asked CESI to set up this simulation tool to enable it to comply with the authority’s request and to analyse the levels of dissolved oxygen in the El Quimbo reservoir, in order to assess the potential for natural re-oxygenation near the suction outlets of the machines and how long it would take.

CESI carried out a numerical modelling of the reservoir waters using a three-dimensional code. The modelling simulated both the main macro-circulation elements in the reservoir (mainly the incoming water from six tributaries, the water released by the turbine, and the surface and reservoir bed discharges from the dam), as well as the physical and chemical characteristics of its waters (temperature and concentration of dissolved oxygen, in particular).

Emgesa also asked CESI to implement a second model to simulate the concentration of dissolved oxygen in the Magdalena river, which receives the waters released by El Quimbo, from El Quimbo to the downstream reservoir of the Betania plant, where the dissolved oxygen content of the water is of paramount importance to the aquaculture facilities there.