In sedimentology courses, I emphasized the flow regime; how bedforms and their internal structure develop and transform at the sediment-water interface. It is essential for geology students to understand the flow regime concept and apply it to interpretating paleo-hydraulic conditions and parent bedforms responsible for stratification in sedimentary rocks. Water flowing at threshold velocities across a bed of fine sand (0.1-0.2 mm) initiates grain motion. As flow velocity increases, bedforms evolve from straight-crested to lunate, linguoid, and rhomboid ripples in the lower flow regime to plane beds and antidunes in the upper flow regime.
I created a field exercise at Scripps Coastal Reserve (SCR), La Jolla, California for geology students to witness how flowing water interacts with sand to generate a spectrum of bedforms, from straight-crested ripples to antidunes, the deposits of which are preserved as distinguishable laminations and beds in sedimentary rocks. At SCR, seawater, recycled from research aquaria at Scripps Institution of Oceanography, cascades onto upper foreshore sand and flows seaward while scouring a channel ~12 cm deep near the channel head then splaying into braided rills < 1.0 cm deep near the swash zone. Teams of four students, spaced at varying intervals along the channel, insert garden stakes flagged with colored vinyl tape on opposite banks. A meter tape, extended across the channel between stakes, defines a transect, along which students measure water depth, identify bedforms, and describe sand grains at 10 cm intervals. Average velocity of stream flow is calculated from the time taken for a colored cork to travel a given channel distance. Cross-channel profiles drafted to scale by each team summarize the sedimentologic character for the section of channel studied. With this field exercise, students are engaged and derive satisfaction in constructing an original, meaningful visual product from data they collected.