North Diversion Structure Albuquerque, New Mexico. Hydraulic Model Investigation.

The North Diversion Structure diverts storm runoff around Albuquerque, New Mexico, to the Rio Grande. Observed flow conditions at the Alameda Outlet Structure AOS, where the flow is transitioned from supercritical to subcritical, have caused concern about the capacity of the as-built channel. A 140-scale model was used to determine the flow conditions approaching and through the AOS. Included in the model were approximately 1,500 ft of trapezoidal channel, the vehicle access ramp cut in the side of the trapezoida channel, the trapezoidal to rectangular transition, the super-elevated curve, Camino Arroyo Inlet, the flaring AOS with the railroad bridge and high-velocity pier, and the outlet channel with the graded riprap protection. The design capacity of the North Diversion Structure is 44,000 cfs. Flows in the hydraulic model overtopped the channel walls for discharges above 30,000 cfs due to standing waves that formed at the vehicle access ramp. Removing the vehicle access ramp kept the flow within the channel except on the downstream side of Camino Arroyo Inlet where the flow ran up the wall. A deflector was designed to contain the runup flow within the channel. Scour conditions in the outlet channel were identified. The riprap protection for the channel invert was stable with discharges up to 28,000 cfs. Flow in Camino Arroyo Inlet overtopped the converging walls in the drop inlet for flows above 2,700 cfs.