An Integrated Approach to Quantify Thermal Effects on Migrating American Shad

We used an integrated approach to overcome the complexity of hydraulics due to hydroelectric station operations and natural hydrological fluctuations to isolate thermal effects of Peach Bottom Atomic Power Station (PBAPS) on migrating adult American shad, Alosa sapidissima, in Conowingo Pond. We quantified whether the thermal discharge individually and synergistically, with operations of Muddy Run Pumped Storage Station (MRPSS), contributes to the failure of a large proportion of American shad to reach upstream spawning areas. The two power stations are approximately five miles apart with PBAPS located on the western shore of the Pond and MRPSS on the eastern shore.

Pre-spawned American shad migrate upstream through Conowingo Pond from April to early June and post-spawned shad emigrate downstream from late May through July. Our approach integrated biological data, hydrological information and a 3-D time-varying hydrothermal model which included the operations of the two power stations relative to the American shad migration.

The PBAPS thermal plume shifts downstream and narrows in width with no rise in temperature upstream of the discharge structure during MRPSS generation.  However, when MRPSS has been pumping for at least 12 hours at night (7 hours is typical), the thermal plume disperses upstream (approximately 1,000 ft beyond the PBAPS intake) at river flows ≤12,500 cfs. Modeled maximum surface velocity of the upstream shifting plume is <0.3ft/s and its ΔT is ≤4.0°F; changes are negligible at depths >5ft. Most of the Pond remains within the temperature and velocity tolerance range of migrating American shad allowing a wide migration corridor. The probability of occurrence of upstream plume dispersal is 0% in April, <0.1% in May, 9.0% in June, and 35.6% in July.

Almost the entire population (80-91%) of radio-tagged pre-spawned American shad successfully migrated past the two stations with minimal delay. Estimated travel speed (4.0 to 6.7 mi/d) was similar to that reported by others.

We concluded that high natural river flows (≥55,000 cfs) pose significantly greater impedance to American shad upstream migration than the operation of either power station individually or synergistically.