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Activity (Hands-On)Grades 6 - 8

Does Media Matter? Infiltration Rates and Storage Capacities

Students gain a basic understanding of the properties of media—soil, sand, compost, gravel—and how these materials affect the movement of water (infiltration/percolation) into and below the surface of the ground. They learn about permeability, porosity, particle size, surface area, capillary action, storage capacity and field capacity, and how the characteristics of the materials that compose the media layer ultimately affect the recharging of groundwater tables. They test each type of material, determining storage capacity, field capacity and infiltration rates, seeing the effect of media size on infiltration rate and storage. Then teams apply the testing results to the design their own material mixes that best meet the design requirements. To conclude, they talk about how engineers apply what students learned in the activity about the infiltration rates of different soil materials to the design of stormwater management systems.

A photograph shows the yard outside a school with buckets, shovels and four piles of media: mulch (reddish fibers), topsoil (dark brown), limestone (pale beige), and sand (white). These materials were used to create a municipality-scale rain garden at Young Middle Magnet School in East Tampa, FL.Does the particle size of different types of media affect the infiltration rate of stormwater?

The goal of low-impact development and green infrastructure design is to manage stormwater at its sources using natural means, and to establish conditions so that the hydrology and, more specifically, water quality, of developed sites approaches that of pre-development conditions. (Davis, 2006) An understanding of porosity, volume storage, void space and infiltration rates is necessary for the correct design of these systems. Civil and geotechnical engineers must have a comprehensive understanding of in-situ soil mechanics and groundwater flow in order to design effective systems to manage stormwater and design safe foundations for buildings, roads and bridges. Environmental engineers must understand the movement of water as it percolates through different soil layers in order to design technologies that address water quality and treatment of stormwater, groundwater and remediation projects.

After this activity, students should be able to:

  • Describe the key soil mechanics and properties of media that determine infiltration rate and storage volume.
  • Calculate the storage capacity and infiltration rate of different types of media and media combinations.
  • Create a media layer that promotes infiltration, maximizes below-ground water storage, and provides an environment for healthy plants and microbial communities

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