Introduction 1 Field methods and data collection 2 Survey and literature search 2 Acknowledgments 3 Catalog of tidal bores 3 Tidal bore characteristics 12 Observations and experiments in Turnagain Arm, Alaska 13 Conclusions 1S References cited 1S FIGURES 1. Photograph of tidal bore, Turnagain Arm, Alaska 2 2-4. Maps showing: 2. Distribution of tidal types 5 3. Distribution of tidal range 10 4. Distribution of tidal bores 11 5-6. Photographs showing: 5. Undular bore and whelps near the mouth of Araguari River, Brazil 13 6. Complex wavefront of the Turnagain Arm, Alaska, bore 14 TABLES 1. Responses to questionnaires inquiring about existence of tidal bores 4 2. Known tidal bore locations in the world and their characteristics 6 3. Bore-producing regions classified according to tidal type 12 Contents Ill

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Aggradation of intertidal sediment in upper Turnagain Arm, a macrotidal estuary located in southern Alaska near Anchorage, began because of subsidence caused by sediment consolidation and tectonic lowering of the land during the earthquake of March 27, 1964. At the head of the Arm, decrease in percent sand of surface sediments with time and return of rodents, pulmonate gastropods, trees, bushes, and grasses to the intertidal region, indicate that the rate of sediment deposition has slowed and the Upper Turnagain Arm area has returned to a state of preearthquake equilibrium only 17 years after the event. Comparison of channel locations before and after the earthquake indicates the possibility of regional postseismic tilting of the estuary.

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