You are looking at the land where I live. My home, the City of Philadelphia, is located on a broad, flat sandy expanse of land known as the Atlantic Coastal Plain.
Most of the city sits on this plain except for the northwest section. The northwest section (Chestnut Hill, Mt. Airy, West Oak Lane, Roxborough, Manayunk and Germantown) sits on the geological region known as the Piedmont Plateau.
Coastal Plain Extends to the Rio Grande
The Coastal Plain includes most of Philadelphia, southeastern parts of Bucks and Delaware Counties, all of southern New Jersey (from Newark to Cape May) and most of Delaware except a small area at the very top of the state.
The major cities along the plain are New York, Philadelphia, Washington, Baltimore, and Norfolk.
Stretching along the Atlantic Ocean, the Coastal Plain covers the Eastern seaboard from New York City to the Rio Grande. The plain widens as it extends southward.
The map above shows the portion of the Coastal Plain along the East Coast of the United States has 3 sections which cover parts of New York, New Jersey, Pennsylvania, Delaware, Maryland, the District of Columbia, Virginia, North Carolina, South Carolina, Georgia, and Florida. Not shown are the region’s 2 Gulf Coastal Plains and the Mississippi Alluvial Plain. (Wikimedia Commons map).
The Size of the Coastal Plain in Philadelphia
In Philadelphia, the plain is just five miles wide – the widest part in Pennsylvania. In Pennsylvania the plain runs along the Delaware river, from Levittown to Chester. The Delaware River flows in to the Atlantic Ocean.
You can row a boat from the Atlantic Ocean 98 miles up the Delaware and land in Philadelphia. Philly is the only city in Pennsylvania with access to the Atlantic Ocean.
Elevation on the Pennsylvania section of the Coastal Plain ranges from sea level to just 60 feet above sea level.
The Two Parts of the Coastal Plain
There are two parts of the Coastal Plain, the Continental Shelf Province and the Coastal Province.
The Continental Shelf is the submerged part of the Atlantic Coastal Plain. It is a broad belt sloping away from the land’s edge to a depth of 600 feet. This is the part that we don’t see. It is covered by the Atlantic Ocean.
The Coastal Province is the part that is above sea level. It was formerly sea bottom. This is what Philadelphia, south Jersey and Delaware lie on. The Coastal Plain meets the Piedmont Plateau, a broad area of gently rolling hills. The area where the two landforms meet is called the Fall Line.
The Fall Line is marked by waterfalls and rapids. When water flowing from the higher Piedmont Plateau drops onto the lower Coastal Plain, waterfalls are created. They can easily be seen along the Schuylkill River. Particularly, just below the Waterworks in Philadelphia.
The rolling Piedmont continues until it meets the Appalachian Mountains in Central Pennsylvania.
Philadelphia’s Natural Land
What did Philadelphia’s Coastal Plain look like before the building of the City? Probably, much like the wetlands and riverine forests at the John Heinz National Wildlife Refuge at Tinicum in South Philly.
Philadelphia Built to Escape Flooding
The City of Philadelphia was established on a raised area of the Coastal Plain. This helped the city escape some of the flooding of the Schuylkill and Delaware rivers. But, as the city spread, homes and buildings were built on places of lower elevation and the wetland area of the Delaware River. This is why Southwest Philly and West Philly flood during heavy rains.
I have stood in wetlands within the city limits that are lower than sea level. City Hall is about thirty feet above sea level.
Since, Philadelphia and the surrounding area is on such flat land, climate change and rising seas will directly affect the City.
The common phrase said around here, is that most of Philly will become beachfront property. I love the seashore. But, I think the seas rising up to meet me is a scary way to finally have the beach house I have always dreamed of having.
What physiographic region do you live in? Check here for Physiographic regions of the United States. (Wikipedia)
Further Information on the Atlantic Coastal Plain
Stream of Trouble Runs Though Region – Philly.com, May 06 2012. Again the Darby Creek Appears on the verge of flooding homes. “Philadelphia is the best case study in the United States for storm-water management.”
Atlantic Coastal Plain (Wikipedia)
Exploring: Atlantic Coastal Plain (Science Explorer, U.S. Geological Survey)
Philadelphia Nature: An Overview
Basic Information on Philadelphia Nature
More Water and Wetland Posts
Field Trip: Jenkintown Creek and a Not Quite Vernal Pool
Thank you for this terrific article Donna. It was very informative. I was confused by other information but you answered my questions.
Hi Heather – Thank you for your uplifting comment. I’m glad the info was useful. 🙂
This is a really clear and interesting explanation of the two regions and how they affect history and life in Philadelphia. It’s interesting to note that early water-powered mills were usually located in spots where the Piedmont drops off into the Coastal Plain, providing gravity-powered energy.
Hi, Steve
Yes, and look what happened to the Falls of the Schuylkill we both know so well. Wouldn’t it be great to have that waterfall in its’ natural glory? It has always bothered me that we aren’t taught about our local ecosystems and how they work. But, there would be an informed citizenry that refused to let their land be treated badly.