Field saturated hydraulic conductivity
This is a field-based lab that allows students to measure field saturated hydraulic conductivity of the unsaturated soils. This is done by keeping a constant head in an augured hole and measuring the time required to transmit a predetermined amount of water through it. The activity can be done in one lab period from start to finish.
This lab is designed for upper division undergraduate hydrology and hydrogeology courses.
Skills and concepts that students must have mastered
Students should have mastered basic scientific measurements on the metric scale (e.g., height, diameter), conversions (e.g., ml to cm3), and calculations (e.g., radius, flow rate), as well as concepts for the zone of saturation, zone of aeration, grain size, porosity, permeability, and Darcy's law. It would be helpful, but not critical, if the students also understood intrinsic permeability, storativity, and transmissivity.
How the activity is situated in the course
This lab can be done as a standalone project, or it can be combined with grain size, soil analyses, and other experiments to measure hydraulic conductivity and characterize soils.
Content/concepts goals for this activity
Students will better understand the basic concept of hydraulic conductivity, its relationship to sediment type, and how this information is obtained by basic field experiments. Students can also make connections to grain size, infiltration, surface runoff, and Darcy flow and their respective relationships to hydraulic conductivity. Finally, students will gain basic field experience, and see how the concepts learned in the classroom are actualized in the field.
Higher order thinking skills goals for this activity
This lab engages higher order thinking skills such as the measurement and calculation of hydraulic conductivity using a field experiment. Students may also compare results to improve understanding of measurement error and uncertainty, as well as building consensus. The knowledge gained in this activity helps students to hypothesize about a medium's ability to transmit fluid, which helps them to evaluate hydrologic characteristics on local and regional scales.
Other skills goals for this activity
Students will work with soil hand augers and learn basic field equipment management. Students will work collaboratively in small groups collecting field data and making observations.
Description and Teaching Materials
Saturated hydraulic conductivity reflects the ease with which a medium can transmit fluid through its pore spaces or fractures. Hydrogeological investigations require field saturated hydraulic conductivity (Kfs) data of the unsaturated zone that are collected during field experiments for many applications including soil suitability for septic systems, landfill performance, soil erosion, and hydrological modeling. An approximate value of Kfs can be obtained by a simple and rapid methodology which requires minimal equipment and measurements to be carried out in the field. The following exercise demonstrates a practical method for sampling at one location which can be repeated for the repetitive sampling of a region of interest.
Activity Description Field Saturated Hydraulic Conductivity (Microsoft Word 2007 (.docx) 118kB Dec16 20)
Instructor's Notes for Measuring Field Saturated Hydraulic Conductivity (Microsoft Word 2007 (.docx) 15kB Dec16 20)
Solution Set Field Saturated Hydrualic Conductvity (Excel 2007 (.xlsx) 28kB Dec16 20)
Teaching Notes and Tips
6-8 2000 ml graduated cylinders (preferably plastic)
1 rolling cart
2 5-gallon water containers or carboys
3-4 colored (not clear) rulers with metric scaling (~30 cm length)
2-3 soil hand augers
3-4 devices to use as stopwatches or similar
Activity handouts and clipboards
This activity works best when the students work in small groups of 3 or 4. Multiple runs (e.g., 3 per group) are conducted so that students can share the responsibilities of the lab. The activity includes set-up, walking out to a preselected field site on campus, taking measurements, and then walking back to the classroom to complete the calculations. We conduct this lab during one 2.25-hour, lecture-lab combined class meeting. However, with proper preparation, this lab could be completed in less than 2.25 hours.
Each group is given two plastic 2000 ml graduated cylinders filled with tap water before traveling to the field site. Water for the second and third runs is carried out by cart using either two 5-gallon water containers or two large carboys. Bring 2-3 augers, timers, rulers, classroom handouts, and clipboards (if available).
Field Site & Taking Measurements
Choose a site on campus where the soil is not saturated with water and where the groups can work together close by. Auger depths between 10 and 20 centimeters seem to work well for sand, but it is recommended to experiment to see what depth works best for your soil type. The need for two 2000 ml graduated cylinders filled with water per group is for the initial experiment. The first one is used to saturate the augured hole to a chosen height on the ruler. It is key to remember that water level readings need to be made with the ruler in the hole and pressed to one side so that it is stable and stationary with the highest value of the centimeter scale at the top of the hole. Students might put the ruler into the hole upside down, so the measured height of the constant head will be incorrect and create errors. The second 2000 ml graduate cylinder is used to keep the water height constant in the hole while measuring the time it takes to pour all of the 2000 ml into the hole. Errors can occur when the students pour the water into the hole at too high of a rate. Minor collapse of the hole during water addition does not seem to affect the experiment's outcome.
Classroom Calculations & Wrap Up
After all runs have been conducted for each group, students return to the classroom to calculate their answers using calculators. The final answer should indicate the sediment type used to conduct the experiment based on the hydraulic conductivity calculation. Students are commonly unfamiliar with the inverse hyperbolic sine function, so you may need to demonstrate this function on a scientific calculator.
We have evaluated this labs ability to reinforce the concepts of hydraulic conductivity by post-activity assessment. The scores on this assessment have displayed that students are making good connections between this lab, hydraulic conductivity, and related course content.
Due to the fundamental nature of hydraulic conductivity, there are many ways to evaluate the effectiveness of this lab. Creating assessments that link hydraulic conductivity to basic concepts, like porosity, grain size, and infiltration, as well as more advanced concepts, can help measure the effectiveness of this lab. This can be done with pre- and post-test assessments. Also, linking hydraulic conductivity assessment questions to other hydrology or hydrogeology concepts, like Darcy's law, intrinsic permeability, transmissivity, etc., can help evaluate the effectiveness of this lab.
References and Resources
Amoozegar, A., 1989, A Compact Constant‐Head Permeameter for Measuring Saturated Hydraulic Conductivity of the Vadose Zone: Soil Science society of America Journal, v. 53, p. 1356-1361.
Sanders, L.L., 1998, A Manual of Field Hydrology, Prentice Hall, Upper Saddle River, New Jersey, 379 p.
Thomas, S.K., Conta, J.F., Severson, E.D., and, Galbraith, J.M., 2016, Measuring saturated hydraulic conductivity in soil: Virgina Cooperative Extension, Publication CSES-141P, 13 p.