Homework #8 GEOL 4880 Humphrey Fall 2022

(Please make your homework somewhat neat and readable! it does affect how generous I am when marking)

1 A) 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. (make sure you report the sinuosity you use, so answer with a sinuosity and a slope for each river).

B) and C) Do the same and get the slope of the Mississippi near Memphis, and of the North Platte where it crosses the Wyo-Colorado state line (south and a bit west of the Medicine Bow mountains)

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)

a Basal Shear stress

b Basal Normal stress

c The shear velocity (V*)

d Thickness of the laminar sub-layer

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

· the Laramie River,

· the weather (atmosphere) above Laramie (hint, the air tends to be layered, with most of the shear and mixing below the clouds layers),

· a cup of coffee as you add cream and stir,

· 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 (hint, you probably don’t want to use the river surface velocity),

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 [hard, this requires clear thinking and your good notes] Our discussion of stresses on particles due to wind, apply quite well to any fluid. Give a “Scale” ratio of the lift force on a 1cm diameter particle (in the Laramie river from question 4) ratioed to the gravity force on the particle. You can express this as a non-dimensional ratio of forces in a simple equation, and then give its numerical value. [note since this is a “scale”, the numerical value only has ‘order of magnitude’ meaning]

5             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 or process within 50miles of Laramie. You will then discuss it, in terms of it’s process geomorphology. (if possible, take a picture of it, either on the ground or using Google earth). To answer this question, I want 2 sentences. The first describes the feature/landscape and location. The second will be why it is geomorphically interesting. Beware, next homework, I will expect a paragraph on sentence 2, including some thoughts on your thinking.