6-27-05

Effect of trashrack spacing and sturgeon size on impingement risk at 15,500 cfs at Bliss Dam.

cm/s

sturgeon total length (cm)

C

Endurance (min)

Find minimum sturgeon length with sustainable speed (>200 min endurance)

Diameter of cylindrical white sturgeon (convert to FL)

Do sturgeon smaller than the size that can escape fit between trashracks?
If so, there is no risk of impingement (but there might be a risk of turbine strike). It appears
that impingement is not a risk for trashrack spacing > 8 cm.

Trashrack spacing at Bliss Dam (cm)

Coefficient of strike risk at Bliss

Total length of sturgeon with same diameter as trash racks.

Risk of turbine strike for the largest sturgeon that pass through trash racks of 23
and 9 cm.

Risk of largest size fish that can't escape trashracks (but may pass through)

Summary: 9-cm trashracks protect fish between 9 and 23 cm in diameter, and also reduce the risk of turbine strike for the largest fish that pass through by half. This model predicts that there is no risk of impingement at Bliss because fish small enough to be impinged are also able to pass through. Larger size sturgeon with the highest risk of entrainment and turbine strike (risk > 0.34 at 15C) are predicted by this model to have the swimming ability to escape entrainment, but we don't know if they actually can or do. Compared with Swan Falls, smaller sturgeon at Bliss are capable of avoiding entrainment because approach velocities are lower; consequently the risk of those to small to avoid entrainment is lower.