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IIHR Research Team Explores TDG Modeling

IIHR Associate Research Engineer Marcela Politano (left) with graduate students Antonio Arenas Amado and Michael Carbone.

IIHR Associate Research Engineer Marcela Politano (left) with graduate students Antonio Arenas Amado and Michael Carbone.

TDG refers to the total amount of gases present in water. The ability of the gases to dissolve in water is the solubility, which depends on pressure and temperature. The solubility increases with the partial pressure of the gas. On the other hand, gases usually become less soluble in water as the temperature rises.

Fish migrating through a hydropower tailrace and the river downstream may be exposed to harmful stresses due to elevated TDG. The main source of elevated TDG on the Columbia River Basin is the dissolution of air from bubbles entrained during spill events. When bubbles are carried down to deep, high pressure regions in the stilling basin, the solubility increases and air is transferred from the bubbles to the water. Fish exposed to the resulting supersaturation of TDG may suffer from gas bubble disease, which is comparable to the bends in human divers.

Gas transfer processes downstream of a spillway.

Gas transfer processes downstream of a spillway.

One way to minimize the supersaturation of TDG at hydropower dams is to install spillway flow deflectors that redirect spilled water horizontally. This forms a surface jet that prevents bubbles from plunging to depth in the stilling basin.

Spillway flow deflectors in this illustration redirect spilled water horizontally. This forms a surface jet that prevents bubbles from plunging to depth in the stilling basin.

Spillway flow deflectors in this illustration redirect spilled water horizontally. This forms a surface jet that prevents bubbles from plunging to depth in the stilling basin.

Last modified on July 5th, 2016
Posted on March 14th, 2012