The Planet Earth is a wet place, with 71% of the surface being covered with water, compared to 29% being land. Most of this water, about 97%, exists as saltwater from oceans, leaving just 3% freshwater. And of this 3% freshwater, 2% is stored as glacier and polar ice, leaving just 1% as available, ready to use freshwater.

In this lesson, students will learn and process this information through the creation of models and graphs. The lesson will build on 4th and 5th grade math standards by relating percentages to decimals and fractions and using 100ths grids to represent the distributions, a visual aid with which students are familiar from math instruction. Students will build upon this knowledge to create pie graphs and scale models of water distribution.

With these visual aids, students will be able to draw conclusions about the importance of water stewardship.

We know water is important for all living things, but often we are unaware of the sources of water in our city. Where is freshwater in the city and how does it flow?

We all live in a watershed. Natural watersheds are those where land has not been developed by humans, but where water supports all organisms that live on the land. A watershed is the land that water travels over or under as it makes its way to a stream, river, lake, or other body of water. Whether frequently or infrequently, all land catches water from precipitation, and so all land is a watershed. Watersheds play an integral role in the water cycle, catching, using and distributing the water that does not fall directly into larger bodies of water.

Not all water flows directly to the sea, however. When rain falls on dry ground, it can soak into, or infiltrate, the ground. This groundwater remains in the soil, where it will eventually seep into the nearest stream. Some water infiltrates much deeper, into underground reservoirs called aquifers. In other areas, where the soil contains a lot of hard clay, very little water may infiltrate. Instead, it quickly runs off to lower ground.

Rain and snowmelt from watersheds travel via many routes to the sea. [ In cities like Philadelphia] during periods of heavy rain and snowfall, water may run onto and off of impervious surfaces such as parking lots, roads, rooftops of buildings, sidewalks and other structures because it has nowhere else to go. These surfaces act as “fast lanes” that transport the water directly into storm drains. The excess water volume can quickly overwhelm streams and rivers, causing them to overflow and could possibly result in floods unless the city collects and manages the water before it goes down the storm drain. Philadelphia has something we call “green infrastructure” which is a system of plants, trees and shrubs all planted in soil that is designed and engineered to retain and absorb the overflow of water

Watersheds can be classified as natural or urban. Natural watersheds are those where land has not been developed by humans, but where water supports all organisms that live on the land. Urban watersheds, on the other hand, are lands that have been altered by human development, where people live in communities, travel on paved roads, sleep in constructed homes, and visit stores, places of worship, playgrounds, and more. Here, water also supports life, but is managed in a way that considers both the community and the ecosystems around it. Humans have found great success in their endeavors to manage water in urban watersheds, but these endeavors sometimes have unintended consequences.

The city of Philadelphia is part of the Delaware River Watershed. However, because there are many tributaries of the Delaware River and Schuylkill Rivers, there are several subwatersheds, or smaller watersheds within the larger Delaware River Watershed. Thus, Philadelphia includes several smaller watersheds: Poquessing, Pennypack, Tookany/Tacony-Frankford Wissahickon, Schuylkill, Darby-Cobbs, and Delaware Direct. After this lesson, students will be able to map the parameters of their local watershed and identify its characteristics. They will be using website applications such as Google Earth and Model My Watershed.

In the early settlement of Philadelphia, people relied on its abundant stream flowing downhill to also drain its wastewater off the streets, its privies and industrial factories. Once these streams became too polluted, the solution was to encapsulate them in a pipe system– a network of underground tunnels is our sewer system that we have to this day. Once created, the pipes were buried under new landfills that built up the landscape to be flat and buildable– row houses popped up everywhere and the built environment of Philadelphia that we see today came to be.

Natural surfaces, now covered with hard, impervious surfaces, were not only suitable for buildings, but for roads and transportation. With all of these changes, the land no longer had the natural ability to drain itself but now drained as part of an engineered infrastructure that manages the sanitary waste and stormwater in the city. This infrastructure functions at the smallest level of a single row home and spans the entire city connecting homes, schools, workplaces and shopping centers in a network of 3,000 miles of pipes underneath our streets to keep water flowing to our wastewater treatment plants, where it is cleaned and returned to the river.

Humans have drastically changed the landscape of Philadelphia over the last 300 or so years. Many creeks and streams once flowed over the land and into the Delaware and Schuylkill rivers. Many of these waterways in the city have been covered over and used as sewers. These changes have shaped the way people interact with the local waterways and environment and have resulted in intended and unintended consequences that we will explore in the Unit. In the end, students will envision a future that is sustainable for all living things and helps us thrive over time.