II.9 - Fish Guidance Efficiency
II.9.1 - FGE Theory

Constant FGE

Fish guidance efficiency is fixed in time and set for day and night from the fge window selected from the DAM menu. This is activated by switching "off" the age dependent fge toggle in Runtime Settings from the RUN menu (this is the default setting). Note that only the mean remains constant; FGE can still vary in a stochastic fashion if variance suppression is disabled.

Age Dependent FGE

Studies on fish guidance at several dams in the Columbia system indicate that fge varies with seasons from a number of factors including the water quality and the degree of smolt development in the fish, which changes with age. If the age dependent option is selected, fish depth in the forebay varies with age, which in turn alters the fge. The algorithm assumes that fish above some critical depth z enter the bypass system and fish below z enter the turbine (Fig. 57). Thus, to define age dependent fge, fish depth in the forebay is defined as a function of age. If the surface drops below the level of the bypass orifice fish bypass goes to zero.

Fig. 57 Critical parameters in fish guidance are fish forebay depth z, screen depth D and elevation drop E. Only fish above z are bypassed. Bypass stops when the surface is below the bypass orifice depth.

The fge is based on the fge model of Anderson (1992). Behavioral and hydraulic factors affecting fge are combined into a calibration factor D_c. In addition, the affect of drawdown on fge can be expressed in terms of screen depth relative to the surface. The modified equation is

(147)

where

• fge = fish guidance efficiency
• z = median depth of fish in the forebay at a distance from the dam where fish are susceptible to being drawn into the intake.
• D = screen depth relative to full pool forebay elevation
• D_c = fge calibration parameter
• E = amount the pool is lowered below full pool elevation

Changes in fge with fish age are represented by changes in fish forebay depth which is described by a linear equation

(148)

To implement the fge equation define the calibration coefficient

(149)

Combining eq (147), eq (148) and eq (149) the final fge equation is

(150)

where

• t = fish age since the onset of smoltification, see eq (55)
• t₀ = onset of change in fge relative to the onset of smoltification set in the release window
• t = increment of time over which fge changes
• z₀ = initial mean fish depth (at age t equals 0) in the forebay
• z₁= final mean fish depth (at age t equals t₀ + t) in the forebay
• fge₀ = fge at onset of smoltification
• E(t) = elevation drop.

Fig. 58 Fge and fish depth over fish age