Science Buddies: "Ask an Expert"

So my son and I picked this project because it looked interesting, but it is turning out to be quite difficult. It is too late to turn back, so we need some help figuring out how to complete this project on time, and accurately.

We are planning to use the recommended experimental procedure that we found here at Science Buddies, using the 2 litre bottles filled with different rocks/dirt but need some more help figuring out how to measure the inlet/outlet, etc...

Also we need to list the Professional in this field we got advise from. Um? Where would I find one and what would their position be called?

Please help.

Hi inferno,
If you need an online professional in this field, I'm glad to help. My official job title is "Research Hydrologist".
If you'd like to meet a professional face to face, there are a few possibilities. Most government agencies that deal with environmental issues (EPA, USGS, USDA, etc) have staff that work on this sort of topic. Most universities have professors who would qualify in the departments of geology, environmental science, or civil engineering. Many environmental consulting firms also have staff who would qualify. If you need more specific help finding a local mentor/professional, please let us know.

What sort of problem are you having with the experiment?

Looking forward to hearing more about your project,
Chris

Thank you for your reply and the information you listed.

We are trying to do the experiment listed here on Science Buddies, but need help with the math involved. Mainly, how do I measure the inlet and outlet head and all the other measurements i need to do this project in a bottle instead of something square and straight? Is there a way to get the value for K (the porosity of the underground formation) without solving the equation? I know my algebra, but need to be able to plug in the numbers. I'm so confused.

inferno wrote:Mainly, how do I measure the inlet and outlet head and all the other measurements i need to do this project in a bottle instead of something square and straight? Is there a way to get the value for K (the porosity of the underground formation) without solving the equation? I know my algebra, but need to be able to plug in the numbers. I'm so confused.

Inferno, hang in there. I know this can seem confusing at first, but we can help you to understand.

Just to confirm, are you doing this experiment?
https://www.sciencebuddies.org/science- ... p014.shtml

If you are doing this experiment as it is shown, you can measure the head by measuring the height of the holes above the bottom of the bottle. You will also need to calculate the cross-sectional area perpendicular to the direction of flow. For a cylindrical bottle, this can be approximated as the area of a horizontal slice through the standing bottle, which is a circle with area of pi * radius * radius. For this experiment, you cannot solve for K without solving the equation. In fact, K is not porosity. K is hydraulic conductivity, which depends on porosity, but also depends on other properties of the sediments such as grain sizes.

If you need any further explanation, please let us know.

Chris

The project we are doing is slightly different. Instead of a 2-liter bottle, we are using 1-liter bottles, four of them. Each bottle we are filling with a different substrate, large round rock, small coarse gravel, sand and potting soil. Each bottle we drilled a hole the same distance on each, 3" from the bottom, and attached the plastic tubing and sealed it with putty. We poured water consistantly into the top of the bottle and timed 30 seconds, reading our measurements and writing them down. Those measurements are in mililiters. So, for each bottle the height of the inlet head and outlet are the same, but have to measure "L" and "A". I will look at your reply again to figure them out.

Bigger problem - do I need to convert inches to mililiters? or mililitres to cubic inches?

I'm now wondering what the point is of even trying to solve the equation for "K". Perhaps it is not necessary? This is why: The first experiment we timed thirty seconds from the time the water began to pour into the bottle and stopped the water flow and took our measurements. Then we realized that some of the substrate (sand) didn't even output any water because it was dry and absorbed all of the water we could feed into it. So experiment 2 we did with the sand and soil dampened from top to bottom to see if the water would flow faster. For experiment 3 we didn't start timing the thirty seconds until the water was beginning to flow through the outlet, and experiment 4 was timed the same way but we used warm water instead of cold to see if the results were any different.

Could we base his experiement just on the differences we made to each experiment we performed? Sorry, I know this is a lot...

Hi inferno,
I'm not an expert in this particular field, so maybe other Experts will be able to help you out as well. I think that the K value will be important in distinguishing between the experiments and giving important information about the porosity and other properties. As Chris mentioned, the cross sectional area of a cylindrical bottle will be calculated by pi * radius * radius. Here is a website that lists some of the units you may need for calculating this equation-
http://biosystems.okstate.edu/Darcy/LaLoi/basics.htm
Hope this helps, best of luck!

Thankyou! I will do more digging tomorrow, my brain is fried for the night! Thanks for all of your help!

inferno wrote:The project we are doing is slightly different. Instead of a 2-liter bottle, we are using 1-liter bottles, four of them. Each bottle we are filling with a different substrate, large round rock, small coarse gravel, sand and potting soil. Each bottle we drilled a hole the same distance on each, 3" from the bottom, and attached the plastic tubing and sealed it with putty. We poured water consistantly into the top of the bottle and timed 30 seconds, reading our measurements and writing them down. Those measurements are in mililiters. So, for each bottle the height of the inlet head and outlet are the same, but have to measure "L" and "A". I will look at your reply again to figure them out.

Bigger problem - do I need to convert inches to mililiters? or mililitres to cubic inches?

I'm now wondering what the point is of even trying to solve the equation for "K". Perhaps it is not necessary? This is why: The first experiment we timed thirty seconds from the time the water began to pour into the bottle and stopped the water flow and took our measurements. Then we realized that some of the substrate (sand) didn't even output any water because it was dry and absorbed all of the water we could feed into it. So experiment 2 we did with the sand and soil dampened from top to bottom to see if the water would flow faster. For experiment 3 we didn't start timing the thirty seconds until the water was beginning to flow through the outlet, and experiment 4 was timed the same way but we used warm water instead of cold to see if the results were any different.

Could we base his experiement just on the differences we made to each experiment we performed? Sorry, I know this is a lot...

Hi,
Sounds like you did a good job with the experiment.

To use Darcy's equation, you will need to be consistent with your units. If you measure head and L in inches, then you need to calculate A in squared inches, and flow rate in cubic inches per second (or whatever time unit you use). Scientists do generally prefer to use metric units, such as centimeters, square centimeters, and milliliters, because conversions between distance, area, and volume are more simple.

Solving for K allows you to make a comparison of the properties of the different sediments. If you try to compare the sediments based on flow rate, for example, you may have difference in flow rate that result from differences in head or dimensions of the containers, or fluid properties, and not from the sediments themselves. Also, hydraulic conductivity (K) is used very often in hydrology, and it is mathematically analogous to electrical conductivity which is used very commonly in the study of electricity, so it is a useful concept to understand even if you don't plan to become a hydrologist.

It sounds like you might have set this up as a "unit gradient" experiment". The "gradient" is the part of the equation written as (h1-h2)/L. For a "unit gradient", this part of the equation is equal to 1, because the distance between the points of measurement of h1 and h2 is equal to L. This will simplify your calculations, *BUT* you will need to make sure that the experiment is "steady state" which means that the flow rate does not change over the the period of measurement. The easiest way to do this is to fill the bottle all the way to the top and keep it filled to that level for the entire experiment, but you can fill the bottle to any level above the outlet (for example, the top of the sediments) as long as the water stays at that exact level for the entire experiment. I can explain more about this if you want.

I like the idea of using warm and cold water. Do you have a hypothesis about what sort of differences you might see?

Chris

So to measure L, i take a diagonal measurement of the bottle from top to bottom, correct? We filled each bottle up to the top with the different media. I hope I understood that correctly. And for A, I multiplied the radiusXradiusXpi, so since this is a small one-liter bottle, the radius measured 1.5 inches, so our answer for A is 7.065 inches squared. Now I need to find out how to convert Milliliters into inches per second...I'm sure there will be a calculator on the net somewhere for that! Does this all sound correct?

We plan on trying to solve for K if we can figure this out in time, my son's project is due this thursday, so wish us luck. We did have fun doing it for the most part and I can't thank you enough for the help you have given us!

And yes, we did have a hypothesis about the warm vs. cold water. And for each bottle our hypothesis was correct, more water was collected than the cold water EXCEPT for the bottle containing the Desert Sand. That bottle gave us very strange readings every time! In fact we collected LESS water when it was warm than when it was cold!

Thankyou again!

Yay!!! I found this site with a Darcy's Law calcultator that you can adjust for what you want to solve for, and it will even convert for you!

http://www.ajdesigner.com/phpdarcyslaw/ ... w_rate.php

Hope it is accurate, but I wouldn't know if it was or not!

Congratulations! It sounds like you have done a careful experiment and gotten some very interesting results.

Just out of curiosity, what were the different temperatures that you used, and how much of a difference did you see in the K values or flow rates?

If you want to double check the results of that ajdesigner.com web page, this page can help:
http://www.onlineconversion.com/

Chris