Reservoir releases for generating power need to be reconciled to maintain healthy ecosystems in regulated rivers. Fluctuating, complex flow patterns near river obstructions such as boulders provide unique habitat for many aquatic organisms. In this book, the ability of two- and three- dimensional hydraulic models to reproduce the localized complex flow features at both steady and unsteady flows is examined. The performance of the hydraulic models is evaluated by comparing the numerical results with measurements of flow around boulders located at a reach of the Smith River in Virginia, U.S.A. Further, time-dependent flow features affecting channel morphology and aquatic physical habitat are investigated. Issues related to the adoption of either a truly dynamic modeling approach or a quasi-steady methodology for simulating unsteady flows are examined through a proposed unsteadiness flow parameter. The insights obtained from this study can assist in properly accounting for the impact of hydropeaking operations on fish habitat and instream flow management.