Adaptive Hydraulics Model The Adaptive Hydraulics (AdH) code was applied to simulate the hydrodynamic conditions in lower Knik Arm near the Port of Anchorage, Alaska. This study demonstrates AdH's ability to accurately model a macrotidal system with complex hydrodynamics, including the formation and evolution of numerous gyres. Lower Knik Arm is an ideal system for this type of demonstration due to the significant tide range (approximately 10 meters in Anchorage) and complex geometry of the system which results in high velocities and the formation of numerous eddies throughout the study area. To improve model stability associated with the extreme wetting and drying and high velocities present in the model, the AdH simulations utilized an adaptive time stepping method which reduced the time step size when certain convergence tolerances were not accomplished. For validation purposes, the AdH numerical model results were compared to field data (water surface elevations, fluxes and velocities) collected in August of 2002 and 2006. These favorable comparisons illustrate AdH's ability to reasonably reproduce the complex hydrodynamic conditions in lower Knik Arm.