For students that have already been introduced to the water cycle this lesson is intended as a logical follow-up. Students will learn about human impacts on the water cycle that create a pathway for pollutants beginning with urban development and joining the natural water cycle as surface runoff. The extent of surface runoff in an area depends on the permeability of the materials in the ground. Permeability is the degree to which water or other liquids are able to flow through a material. Different substances such as soil, gravel, sand, and asphalt have varying levels of permeability. In this lesson, along with the associated activities, students will learn about permeability and compare the permeability of several different materials for the purpose of engineering landscape drainage systems.

Landscape engineers and civil engineers must consider the permeability of the ground around major construction projects when designing drainage systems. Carefully planned systems can reduce pollution due to runoff and prevent flooding. porosity permeability storm water runoff hydrology Students will be able to: Identify different materials based on their level of permeability Identify which materials (permeable vs. impermeable) would be better for development or agriculture in various (urban vs. rural, coastal vs. inland) settings and why Describe how pollutants concentrate and runoff over non-permeable surfaces Describe some human impacts on environment Learn how to link anthropogenic pollutants and contaminants to local environmental issues such as water quality and estuary health Describe how non-permeable surfaces cause runoff and affect the health of local watersheds Hook the students by showing a picture of a large commercial parking lot (e.g. Wal-Mart), focusing on the detention ponds. Ask them what they see in the picture, and what they think the purpose of the ponds is. They may come up with esthetic reasons and practical reasons. Encourage all of their answers, and suggest that they think about why they are there from an engineering perspective if the students are only considering esthetic reasons. The purpose of the ponds is to collect and treat runoff. More information on detention ponds in general is available from the EPA (Wet Detention Ponds) Show pictures of flooding to aid in explanation of permeability, and ask questions to encourage students to think about why flooding occurs. Permeability is the degree to which water or another liquid is able to flow through a material. Different substances such as soil, gravel, sand, and asphalt have varying levels of permeability. Materials that are densely packed are less permeable than those that are loosely packed. The porosity of the material enables permeability: the more gaps, the more permeable the material. As the population of the Earth increases and as more development and urbanization occur, more of the Earth's surface is replaced by impervious or non-permeable surfaces such as roads, houses, parking lots, and buildings that reduce seepage of water into the ground and accelerate runoff to ditches, streams, and detention basins. Increases in imperviousness, removal of vegetation and soil, gradation of the land surface, and construction of drainage networks all result in higher runoff volumes and shortened runoff time into streams from rainfall and melting snow (www.usgs.gov). Over time, this new and human-induced movement of pollutants through an area creates the "other" water cycle. This cycle is a way to describe the journey of rainfall from the atmosphere to the surface of the earth, over land, and eventually into the terrestrial water system (groundwater, rivers, ocean, or estuary). In this way, pollutants accompany the natural water cycle and are inadvertently spread and able to contaminate other water sources. the degree to which water or another liquid is able to flow through a material the ratio of the volume of gaps of a material to the volume of its mass material deposited by water, wind, or glaciers the portion of precipitation on land that ultimately reaches streams, often carrying dissolved or suspended material a brownish-black solid or semisolid mixture of bitumens obtained from native deposits or as a petroleum byproduct, used in paving, roofing, and waterproofing an arm of the sea that extends inland to meet the mouth of a river What Trickles Down What is permeability? Permeability is the degree to which water or another liquid is able to flow through a material. Why is runoff a problem? Runoff leads to the introduction of pollutants and excess nutrients into the water cycle and leads to the contamination of bodies of water. How can runoff be prevented? Runoff can be reduced by using more permeable materials in engineering designs and by taking advantage of the natural ability of wetlands to capture and filter water. The students should be actively involved in the discussion and should be able to explain which materials are more permeable than others. List materials and ask the class which material is the most permeable. Ask students to give an example of runoff.