TEACHING GROUNDWATER HYDROLOGY PRINCIPLES INEXPENSIVELY: PERMEAMETERS AND DARCY’S LAW

Teaching groundwater hydrology at a small institution can be difficult due to the costs of the equipment, however exposure to permematers and Darcy’s Law are fundamental for understating groundwater hydrology. Fortunately permeameters and Darcy’s chamber can be built: 1) with few tools commonly found in a college’s machine shop; 2) inexpensively, and; 3) perform well in the teaching environment.

Permeameters can be built from acrylic pipe, which serves as the sample cell, and PVC stock, which is used as the end pieces with brass fittings tapped for inflow and outflow. Threaded rod can be used to hold the ends together and provide a stand for the apparatus to rest on. These permeameters can be configured for both falling head and constant head experiments. Five-gallon buckets can be fitted with bulkhead fittings and used to maintain constant head. Each permeameter can be produced for $100.

Teaching Darcy’s Law can also be difficult and cost prohibitive. However, the experiment can be reproduced using clear PVC pipe held in a cradle at an angle. The PVC can be tapped at the angle of the cradle and fitted with brass nipples which allows for polyvinyl tubing to be attached to measure head. Flow in and out the end is controlled by end caps that have been tapped for brass fittings and attached to polyvinyl tubing. Constant head can be maintained by using the same five-gallon buckets with bulkhead fittings as were used with the permeameters. Each Darcy’s chamber can be produced for $120.

For the lab component, students can use different sediment samples to conduct grain size analysis, and calculate the hydraulic conductivity for each sample using falling and constant head permeameters, and Darcy’s chamber. Each method should be run at least 10 times for each sediment sample. The students are then able to compare the hydraulic conductivities between the methods and comment. Student analysis demonstrated that the methods produced similar (if not always statistically significant) results for the individual sediment packages. The lab takes four lab periods to complete but at the end of it the students learn about grain size analysis, hydraulic conductivity, statistical analysis, and experimental design - all fundamental for a deeper discussion into groundwater hydrology.