# Water Flow Through Soils

By Liz Snyder

Background:

Precipitation in the water cycle can follow one of two paths once it falls on the land surface. The water can infiltrate into the groundwater system or run-off the surface into various bodies of water. The amount of precipitation that percolates into the groundwater system will be governed by the porosity and permeability of the material through which the water has to flow. The size and spacing of particles in the material will directly effect the ability of that material to transmit water.

Objective:

Determine the relationship between particle size and rate of water flow through soil. Suggest other variables that affect water flow through a soil.

Materials:

• 3-4 clear tubes ~ 2 long per group
• 3-4 large rubber bands per group
• 3-4 squares of fiberglass window screen
• samples of gravel, silty soil, and local soils
• 400 ml beaker
• food coloring
• water
• transparency with grid for graphing, and overhead pen

Procedure:

1. Before Activity
• Students need to collect local soil samples.
• Students need to describe the area in which they collect the samples.
2. Data Collection
• Record the relative size of the samples in the data table.
• Make a prediction about the relative rate of water movement through each material. Record your prediction in the data table.
• Measure the length of each tube to be used and record in the data table.
• On each tube cover one end with screen and secure with the rubber band.
• Fill each tube with a separate sample.
• Fill a beaker with water. Add 3-4 drops of food coloring to the water.
• Measure the rate of water flow through the tube for each sample. Use the following procedure for each sample. Record your results.
• Hold the tube vertically.
• Begin timing when you pour the colored water into the top of the tube.
• When the water reaches the end of the tube record the ending time.
• Determine the rate of water movement. (Divide the tube length by the time). Record in data table.
• Repeat steps a-e for each soil sample.
3. Analyzing Data
• Complete the conclusion questions.
• Explore expanding the concept.

Data Table:

 Particle Size Prediction Length of Time actual Calculation Description at flow tubing water flow

Conclusion:

1. On the overhead transparency grid, make a bar graph of the particle size versus water flow rate.
2. After analyzing the graph, write a one sentence description of the relationship between particle size and water flow rate.
3. Present graph and description to class. Each group overlaying graphs as presented.
4. As a class agree on a one sentence description of the relationship between particle size and water flow rate.

Expanding the Concept:

1. Explore other variables that affect the rate of water movement through the materials.
2. How could a city's water system use the knowledge gained in this lab? How could farmers use this knowledge? (Think about the groundwater flow model and information from the water cycle.)