Homework #8 GEOL 4880 Humphrey Fall 2019

Please make your homework somewhat neat and readable!! Question 4 won’t be covered until Tuesday.

1             From a topo map, Google Earth or some other source get the slope of the Laramie River.  You will have to take into account the ‘sinuosity’ (sinuosity is the ratio of actual river length to straight-line length) of the river, in other words you will have to take into account the actual river length not the straight-line length to calculate distance for rise-over-run.

2              Calculate for the Laramie River (you may have to go down to the river to take a look to see how deep it is? Use your slope from #1)

·         Basal Shear stress

·         Basal Normal stress

3             Estimate Reynolds numbers (to describe the state of turbulence) appropriate to:

·         the Laramie River,

·         the weather (atmosphere) above Laramie,

·         a cup of coffee as you add cream,

·         a water squirt gun nozzle,

·         a swimming amoeba.

·         And a hard question, a grain of 0.5mm sand on the bed of the Laramie RIver,

4             Calculate and plot(!) the logarithmic profile for the Laramie river.  So you get similar results don’t use your data from question 1 and 2, but assume a slope of 5x10^-4, a depth of 1 meter, and you can assume the size of the coarse particles on the bed of the river is about 1cm.  You can use the following eqn: v(z) = ( U* / k ) ln (z/D₈₄).  Note that in this eqn I have used the natural log.  The constant ‘k’ is 0.4.

5 You have your algorithm of rainsplash and sheetwash working from the last homework. Try 2 numerical experiments using the fault scarp from the last homework, (make the top of the scarp 2m from x=0):

• Using just creep and no sheetwash, and a zero flux condition at x=0, find out how long it takes to erode the point at x=0 to half it’s height. Compare this with the number given by our time scaling (T ~ L²/C ) [use C = 3x10^-4 in m²/years]. Note that it is NOT obvious what to use as a length L, which also points out that our time scale is just that… a scale for the approximate time.

• Using only sheetwash, and a zero flux condition at x=0, observe that the origin does not erode but becomes a spike! Why? [hint: if you don’t get a spike, you are probably not multiplying x*D by the correct location of x.]

6             Term Project. Time to start thinking seriously about what you are going to talk/write about at the end of the term. You will need to find a geomorphically interesting landscape or feature within 50miles of Laramie. You will then discuss it, in terms of it’s process geomorphology. (it would be good to take a picture of it, either on the ground or using Google earth). So to answer this question, I want 2 sentences. The first describes the feature/landscape. The second will be why it is geomorphically interesting. Next homework, I will expect a paragraph on sentence 2.