Sediment in the Western Duck Pond
Introduction:
We are interested in discovering the amount of time it will take for sediment flowing
through the creek that feeds the Western Duck Pond to fill the pond with sediment.
Hypothesis:
The Western Duck Pond will fill its existing boundaries with sediment in 500 years assuming it will not be dredged and there will be no major changes in the area. One tenth of a cubic meter per second of water flows into the pond carrying with it one cubic centimeter sediment per second. There will be more sediment carried into the pond than out of the pond.
Discussion of variables:
We have many variables that we need to consider. First is the problem of how to measure sediment. Our initial idea of measuring the sediment was based on time passed, but it is more efficient to measure the amount of sediment per unit of water. This enables us to estimate the amount of water per day, and also allows us to use factors such as rainfall because the amount of sediment will change depending on how much water will flow in. Another variable for us to consider is the amount of sediment flowing out of the pond. All of the sediment that is retained into the pond is less than the amount that flows into the pond because of the sediment being carried out of the pond by the stream. The final main variable that we need to consider is the density of the sediment on the bottom of the pond. The sediment that settles on the bottom is compacted by the weight of the water, and therefore has less volume and a higher density. Yet another variable is leaf fall, which will contribute to the amount of sediment in the pond. We will use the results from the experiment presently being conducted on the leaf fall in this area. We would also like to consider the amount of furniture thrown in the pond each year by students.
Materials:
measuring tape
film cartridges
scale
graduated cylinder
stopwatch
string
Styrofoam
liter bottles
coffee filters
Statview
data sheets
online journal
Procedure:
We will first need to find the volume of the pond from the website
http://jrscience.wcp.muohio.edu/html/TeachPhilos.html. This will give us the approximate volume of the pond so we will know how much sediment we will need to fill the pond. Second, we need to determine other constants such as density of the bottom of the pond and width of the stream flowing into the pond and flowing out of the pond. To find the density of the bottom, we will take four different samples of the compacted sediment along the banks. Then, we will run a t-test to ensure the data shows the samples show no significant difference, and therefore proves that the samples are reliable and from the same area. Then we will make a ratio of density of the bottom to the depth of water at the place where we took the sample. Then we will mwasure the depth of water at ten different locations in the pond, and will use our ratio of density to water depth to find the density of the bottom at ten different locations. We will use the mean of these densities for the density of the bottom of the pond.
The next step will be to find the velocity of the water flowing into the pond and out of the pond. We will stretch a string across the stream using two posts two meters from the mouth of the stream. Next, we will use the same process to stretch a string across at the mouth. Using a piece of Styrofoam, we will measure the time it takes to pass in-between the two strings. We will do this three times for the flow in and repeat for the flow out of the pond.
Determining the cross sectional area of the stream will be the next focus. Using a measuring tape we will find the width of the stream at the mouth flowing into the pond, and the mouth flowing out of the pond. Then, we will measure the depth along this line at seven different points. Using the seven different points we will develop an equation for the bottom of the pond. With this equation, we will find the area bounded by the curve and the line, which will give us a cross sectional area of the stream at that point. Using the data we have found we can multiply the cross sectional area by the velocity to find the volume of water and sediment flowing through the stream per unit of time.
Now we need to sample the sediment in per unit water flowing in and out of the pond. To do this we will use liter bottles and take random samples of the water in locations ranging from the mouth of the stream entering the pond to the mouth of the stream exiting the pond. Each sample will be filtered using a coffee filter, dried, and measured for mass and volume. We will do this for ten days straight assuming the weather will change during the period. Using the National Weather service we will be able to make sure we have a true model.
After finding and documenting the samples of sediments we will run three t-tests on the amount of sediment found in the water at the entrance, in the pond, and at the exit of the pond ensuring the reliability of our samples. This gives us the amount of sediment per liter coming in, going out, and staying in the pond. Using our knowledge of the amount of water flowing through the pond in a given amount of time, we can find the amount of sediment that flows into the pond per unit of time. We will predict the change in sediment amount due to seasonal changes and changes in amount of rainfall. From this we can find the time it will take to fill up the pond with sediment. Using the density information of the bottom of the pond and sediment we will adjust the results to allow the same density of the bottom of the pond.
Our Teaching Day
On our teaching day we will have the students take samples of the water flowing into and out of the pond. We will present a summary of the project, and show them how this taking of samples will be used in estimating the sediment buildup in the pond.
An Overall View
This project can help us to understand the effect that erosion and water flow plays in shaping the landscape. Many different things could happen due to filling of the Duck Pond. Loss of land and wildlife could follow the filling of the Duck Pond, and also a larger creek and more flooding in the general area could happen.
Resources:
http://jrscience.wcp.muohio.edu/html/TeachPhilos.html
National Weather Service
Long, Leon E. Geology Austin: McGraw Hill: 107-118
Zumberge, James H. and Clemens A. Nelson Elements of Physical Geology New York:Wiley and Sons, 1976 253-255
Eardley, A.J. General College Geology New York: Harper and Row, 1965. p123
Eardley, A.J. Science of the Earth New York: Harper and Row, 1972 p166-180
Lambert, David The Field Guide to Geology New York: Diagram, 1988 p114-132
Barnes, Charles W. Earth, Time, and Life: An Introduction to Physical and Historical Geology New York: John Wiley and Sons, 1980 570-580
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