Pennsylvania Watersheds (original) (raw)

Definition:

A watershed is an area within which all water that enters as precipitation will exit via the same stream or river. The water may reach that river as overland runoff, as groundwater flowing within soil and/or bedrock layers, or as storm sewer flow via urban/suburban stormwater collection systems, piped straight into streamflow. Smaller tributaries also contribute to the watershed's outflow. The watershed's name is that of the outflow stream or river for the small and major watersheds, but may include the names of significant tributaries within the large watersheds.

If you zoom in on this map and examine the watershed boundaries, you will see that the more detailed watersheds do not line up with the more general ones. The reason is that these separate maps came from different sources compiled at different times, and were probably based on different original maps of the streams and elevations.

Discussion:

Waters exit the state via six routes:

• Lake Erie: flows eastward through Lake Ontario to the Atlantic Ocean
• Ohio River: flows westward toward the Mississippi River which flows south to the Gulf of Mexico
• Genessee River: flows north through New York State into Lake Ontario and on to the Atlantic
• Susquehanna River: flows south through Maryland into the Chesapeake Bay
• Potomac River: (labeled "Maryland" on the map above), flows south through Maryland and then eastward into the Chesapeake Bay
• Delaware River: flows south along the eastern boundaries of Pennsylvania and Delaware into the Delaware Bay and on to the Atlantic Ocean

The land uses reported in the table below are based on apparent uses of the land interpreted from aerial photography.