FINAL TAKE HOME SECTION FOR 106 GEOGRAPHY
PHYSICAL GEOGRAPHY TAKE HOME
PORTION of the FINAL
CALCULATE AND ANSWER ALL OF QUESTIONS BELOW
KNOW THE ANSWERS TO ALL THE FOLLOWING QUESTIONS AND BRING THE
ANSWERS WITH YOU (IN YOUR MIND OR ON A SHEET OF PAPER) TO THE
FINAL EVALUATION THESE QUESTIONS WILL BE PART OF THE MULTIPLE
CHOICE EVALUATION.
Dr. M. Mustoe
This is the final take home. Bring the answers with you to put onto the final evaluation in class.
Final Take Home
This part of the evaluation is concerned
with the relationship between velocity and competence in stream
flow.
The sixth-power law:
This "law" states that:
The size (weight or volume) of material
that can be moved may increase (or decrease) up to a maximum of
the 6th power of the increase (or decrease)of the velocity of
the stream.
In Other Words:
If a flood doubles the velocity of
a stream, the current is then theoretically strong enough to move
a block of rock 64 times as large as it could move at normal velocity.
This relationship between velocity and competence is sometimes
referred to as the sixth-power law, as 64 is the
sixth power of two. If the velocity increases to three times the
original, then the theoretical increase in competence is three
to the sixth power law, or 729 times the original
competence. This maximum theoretical value in increased transporting
power may not be possible to reach due to natural conditions,
but this phenomenal increase helps to explain how floodwaters
can cause such extensive destruction.
For Example:
What is its predicted maximum load
carrying capacity of a stream that is:
A) flowing 2 mph and increases to 4 mph?
B) Given that its is it observed picking up material of the size
of .2 grams initially?
HOW TO FIGURE IT:
4mph -2mph = an increase in velocity
of 2 or = 2
2 to the 6th Power = 64Xs
.2 grams X 64 12.8 grams
In other words....the maximum that this stream could carry given this increase is 12.8 grams.
1. Consider a stream which increases its velocity from 3 m/sec to 6 meters per second. If the stream originally carried a load of particles averaging .2 grams, theoretically the maximum size of particles the stream could carry at its increased flow would be?
The following does not use the 6th power law....but deals with water force.
2. Water moving at 4 mph exerts a force of 66 pounds per sq foot. Given a car moving through water (water moving at 4 mph) and exposing a surface area of the car of about 15 square feet (that is, the car is going through moving water that is running up a little higher than the bumper). What is the total force (derived from the water) that will be exhibited on the car?
3. Water weights about 64.2 lbs. per cubic foot. An average down flow velocity of water is anywhere from 6 to 12 mph. If you drive a 1500 pound automobile into this moving water and it stalls there is an estimate of 500 pounds of force from the water that will be applied to the vehicle for every foot of rise in the water level of the stream. In addition, for every foot the water rises up the vehicle the vehicle will displace 1500 pounds, (the weight of the automobile) This is the buoyancy force of the car. In essence for every foot of rise in the water, the car weighs 1500 pounds LESS. When buoyancy lifts the vehicle and exceeds the frictional force that "sticks" the car to the road, lateral force will push the floating car down the stream. So about how many feet of water would it take to float/move a 1500 pound vehicle? I'll give you the answer.....it doesn't take much more than two feet to float your car. Don't drive in flood waters. It is not worth the risk.
4. Soil Porosity
Soil porosity is the physical amount of space there is between soil particles. It is an important measurement especially when dealing with the moisture factors of the soil for issues such as mass wasting as well as agriculture. The way you determine soil porosity is by taking a completely dry clump of the soil at issue, and infuse it with water until it cannot hold any more of the water. Here is the procedure:
1. Weigh out the dry core sample in grams
2. Wet the sample until saturated and weight the saturate sample
3. Find the difference between the two weights above. This gives
the CCs of the water in the sample
4. Divide the CC of water by the CC of core sample and multiply
this by 100
5. This procedure provides the percentage of pore space which
is the porosity of the soil
4a. Determine the porosity of a soil that has a sample of 400 cc dry and a soil weight of 600 grams dry. When this sample is saturated this soil has a weight of 760 grams. What is the porosity of this soil?
4b. A 400 cc sample of dried soil weighs 520 grams. When saturated with water this sample weighs 720 grams. What is the porosity of this soil.
And that's all folks. Remember to bring your data to the meeting of the FINAL.