APPROACHES FOR QUANTIFYING SEABED MORPHOLOGY – TECHNIQUES FOR UTILIZING ROTARY SONAR SYSTEMS. L. M. Kraatz 1 , A. D. Skarke 2 , A. C. Trembanis 2 , C. T. Friedrichs 1 1 Virginia Institute of Marine Science College of William & Mary, PO Box 1346, Gloucester Point, VA 23062, USA. lindsey@vims.edu and cfried@vims.edu 2 University of Delaware College of Earth, Ocean, and Environment, 107 Penny Hall, Newark, DE 19716, USA. askarke@udel.edu and art@udel.edu Abstract: Rotary sonar instrumentation is a versatile tool for the observation of seafloor morphology with a wide variety of potential applications. Here we present a review of rotary sonar development and implementation, followed by analysis of seafloor morphological evolution based on rotary sonar observations made in two contrasting depositional environments: the Delaware Bay mouth, a non-cohesive high-energy environment, and the York River Estuary, a low-energy cohesive environment. Additionally, we present a methodological approach for rotary sonar deployment, utilization, and data analysis. Introduction Precise observations of the dynamic processes interacting at the sediment-water interface are crucial to understanding seafloor morphology. The magnitude and frequency of hydrodynamic forcing often dictates the resulting morphologic response. Large-scale events, including extratropical storms and nor’ easters, can be a catalyst for abrupt changes that may dissipate quickly; conversely, daily processes acting on the seafloor (i.e. tides, waves, and currents) may not provide an instantaneous response, but rather yield gradual changes and environmental impacts over longer timescales. Rotary sonar technology has allowed for precise observations of seabed morphologic evolution. In this paper, we review the use of rotary sonars and present analysis of two contrasting environments in the Delaware Bay and the York River Estuary The transport and fate of seafloor sediments are critical factors affecting the physical conditions, chemical composition, and the biological health of ecosystems, especially in estuaries, along shorelines, and on continental shelf environments (Whitehouse, 2000). The erodibility potential of sediment beds is