Fix it with PHOSCRETE.

Weather Conditions: Clear, sunny, no precipitation.
Ambient temperature: Begin at 9:30 AM: 62°F End at 12:30 PM: 67°F

Product Used: Phoscrete^® 601 
10.5 units used to complete repairs
Form Placement: 45 minutes
Working time: 30 minutes
Set time: 30 minutes
Clean up and Form Removal: 30 minutes

Installation Notes:
The Spalled Concrete was removed using small pneumatic chipping hammers, plywood forms were placed over the wall to create a cavity, and Phoscrete 601 was mixed in buckets and poured directly into the cavity at the opening on top.

Forms and Form Placement: 
Tapcon 1/4" dia x 2.5" large concrete screws and kick boards used to secure the forms. Note: the Tapcon screws were inadequate, many broke from the "twisting torque" and caused some delays.  

Two methods were used to create a bond release from the ¾” Plywood and the Phoscrete Concrete:

1. The lower section form was lined with plastic sheet material. Note: The process was time
consuming and the surface had several small wrinkles from the plastic.

2. The upper section form was lightly coated with the Phoscrete Liquid Activator. Note: It took less
than one minute to brush on the liquid activator and the surface was free of wrinkles. The form
coated with the liquid activator provided a superior releasing mechanism. It should be further noted that the
plywood form material should be “clear on one-side.”

Conclusion:

The Phoscrete repair was exceptional. The bond to the host concrete is strong and substantial. The repair will easily last the life of the existing concrete in the Spillway Wall.

Follow Up:
In July, 2011 Stellar Materials' contact at the USBR reported that the repair "looks good and is unchanged from the installation date."