JGE 1997 - Volume 45

Students generally leave their introductory geoscience classes with the notion that strams behave like conveyor belts wherein all flow regimes contribute more or less equally to the work done in the transportation of sediment. This view ignores both the frequency distribution of flow regimes and the exponential increase in stream capacity with increasing discharge. The reality is that some flows transport much more sediment than others. Low flows occur frequently but lack the power to move much material. Extreme flows can move large quantities of sediment in short periods of time but occur so infrequently that they do not transport a great deal of sediment in the long term. It follows that there is an intermediate flow, referred to as the effective discharge, that is frequently enough and powerful enough to move the most sediment in the long term. This exercise introduces upper-level geoscience students to this concept by asking them to calculate by asking them to calculate the effective discharge of a stream using statistically and empirically based solution technologies. The expectation is that the exercise will foster a more realistic view of the relative importance of various flow regimes in the transportation of sediment.

As ricks weather, their surfaces may become more pitted or smoother depending on the mineralogy of the rock being investigated. A laboratory device which measures surface roughness (the Shore scleroscope) enables quantitative measurements of the change in surface roughness with time in laboratory simulations of weathering. The data can be interpreted in terms of the kinetics of diffusion and surface reaction-controlled processes, and students can then suggest the likely processes involved in the early weathering of reocks. In a specific example, smooth granite surfaces weather (that is, become rougher) ten times as fast as smooth marble surfaces, while rough granite surfaces become smoother at about the same rate as marble. This approach could be used as a complement to the more usual laboratory simulations of weathering that monitor the changing compositions of solutions in contact with rocks over time.

I have devised a spreadsheet approach that is designed to help students better understand the terrestrial of "basin" hydrological cycle. Students are assigned problems to create spreadsheets accounting for the flux in and out of the major surface and subsurface "reservoirs." The effects of hydroclimatic variation upon runoff are tested in the spreadsheet model. The assignment is given to upper-level undergraduates and graduate students in order to promote proficiency in the use of the spreadsheet, a potentially important too in the geoscience curriculum.

About 1500, Leonardo da Vinci sketched a tree with arcs through each yearly growth of branches. In his mirror-image handwriting, and including an equation, he noted that the sum of the thicknesses of all the new branches produced each year will equal the sum the thicknesses of branches from each previous year, down to and including the trunk. He wrote further that the same relation exists between a main watercourse and its branches. Leonardo's tree and notes clearly ilustrate the principle of stream ordering in drainage-network composition. Indeed, Leonardo combined network morphometry and hydraulic geometry, which together have thus far been inadequately investigated. Leonardo's tree drawing marks the discovery of quantitative drainage-network analysis, which was rediscovered by R.E. Horton more than four hundred years later. We use it to combine science and art in K-12 education.