Water In Our World

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.