INCREASING FLOW STRENGTH 







LINEAR 



TWO 

 DIMENSIONAL 



UNDULATORY CUSPATE 



PLANED OFF 

 RHOMBOID 



FLAT BED 



h 



THREE DIMENSIONAL 



Figure 11. Gradation from two-dimensional to tinree-dimensional bed forms and flat beds 

 with increasing flow strength (after Reineck and Singh (1986)) 



Table 4 



Hierarchy of Bed Form Formation by Increasing Energy (after 



Harms etal. (1975)) 



Parameter 



Ripples 



Megaripples 



Low-energy 

 Sandwaves 



High-energy 

 Sandwaves 



Spacing 



<60cm 



60 cm - 1 m 



>6m 



> 10 m 



Height/Spacing 

 Ratio 



Variable 



Relatively large 



Relatively small 



Very small 



Geometry 



Highly variable 



Sinuous to highly 

 three-dimensional 



Straight to sinuous 



Straight to sinuous 



Characteristic 

 Flow Velocity 



Low (> 25-30 

 cm/s, < 40-50 

 cm/s) 



High (> 70-80 

 cm/s, < 100-150 

 cm/s) 



Moderate (> 

 30-40 cm/s, < 

 70-80 cm/s) 



High (> 70-80 

 cm/s, may be 1 50 

 cm/s) 



Velocity 

 Asymmetry 



Negligible to 

 substantial 



Negligible to 

 substantial 



Usually substantial 



Small to 

 substantial 



Formation and movement of inner shelf sedimentary features, primarily 

 the smaller scale ripples, are primary methods of inner shelf cross-shore 

 sediment transport. These bed forms are formed only during turbulent 

 flow conditions (water flow in which the flow lines are confused and het- 

 erogeneously mixed (Bates and Jackson 1984). These turbulent condi- 

 tions are created by wave and related oscillatory motion, or tide-generated 

 currents near the bottom which roll and creep sediment particles along the 

 sediment-water interface (Reineck and Singh 1986). As sediment parti- 

 cles continue to move from the trough to the crest on both sides, ripples 

 eventually form. As velocity increases and greater amounts of sediment 



46 



Chapter 4 Sedimentary Features/Stratigraphy of the Inner Shelf 



