Unsteady Hyporheic Flow

Our research team is composed of students Andrew Huffman (Mathematics), Sheiny Tjia (Chemistry), and Ethan Zeller (Mechanical Engineering), with advisor is Dr. Stonedahl (Environmental Engineering). The purpose of our research is to study how unsteady water flow moves through sediment, and each student is applying their own skillset towards designing and building the experiment. If you wish to see the day-to-day progress being made on this project, you can read about it on our blog.

 

Design and construction

We have been working on building and designing the flow oscillator for our project. We began by completely disassembling the first try at making the flow oscillator because it leaked. Instead of having to build it again, we were able to find an aquarium store that was willing to put it together for us!  While waiting for the tank to be completed we worked out a method of holding the pressure sensors in the exact same spot every time but also being able to remove when we need to. Our idea consists of an L shaped beam where we were able to bend it to fit perfectly over our glass and have 12” inches hanging down on both sides of the glass. Having this L shape will allow us to secure to the sensor tightly with Velcro. We have also made over flow “gutters” from sheet metal and were able to silicone it to the sides of the tank where the will flow over. With that same sheet metal we designed a three part divider to separate the low head and high head of water. One part is just one long strip of metal 14” inches long, which we glued to the middle of the tank with silicone. We then made other two parts that have bends on the sides of them to allow for more surface area on the glass.  When the glass came back from the Aquarium store we found that the divider made from glass was moved over about half an inch from the 26 inches we asked for.  Fortunately this was 65 cm, so we are switch from 2 inches to 5 cm cubes.  We are now working on designing a new “sand grid maker” (which are 3D boxes we can put sand in to have it keep its shape while we put the sand in initially) that we can 3D print to be able to perfectly set the sand up.

 

When we started working with the pressure sensors we found out that both of the sensors were not reading the same depth all the times. So we created an experiment to have both sensors at the same level and put them in a large bucket. We then taped the ruler to them and recorded the data we found in excel.

 

Arduino Programming

The waterflow through the experiment is controlled with an Arduino device, called a BottleLogger v2.2.0. This device has three sensors: a temperature probe and two pressure transducers. The programs that are run on this device use the readings from these sensors to determine water density, and the length in cm of the column of water above each pressure sensor.  Using this information, we want our programs to accurately control the rise and fall of the water level on the variable side of the tank our experiment is using. The device also collects time-stamped data from the sensors in quick periods, giving us raw data for pressure and temperature.  Programming the Arduino has been a challenge because many libraries written by other programmers, which are challenging to understand and don’t seem to behave as expected.

20170620_103005

Electrolytic Conductivity Investigation

In previous years’ experiments the EC value exiting the system never reached the value entering the system.  We decided to try to find out why.   We are devising an experiment to help understand the system better. Our early hypothesis was that the sand or the aluminum in the system might cause a change in electrolytic conductivity.  So far, however, we found that the diameter of the container had a huge effect on the reading.  What we originally measured in the big bucket, changed when we put it into different container.  So we devised an experiment in which we chose containers with a variety of diameters (some plastic and some glass) and measured the Electrolytic Conductivity of the same liquid in each container.   We found, that the reading was consistent no regardless of the material (glass or plastic) and that after hitting 7cm the diameter no longer interfered with the reading. We also looked at the fraction of the true value and the results showed that the ratio is consistent regardless of EC value of the water.

ECpicture

We also tested small pieces of sheet metal and the metal used to hold the sensors in place in the solution overnight to see if it will affect the EC meter.  Our initial finding is that it did not change the reading on the EC meter. Further testing is needed to make sure the sand will not absorb the salt in the water and change the outcome on the EC meter.

 

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