What is a Watershed?

In simple terms, it is a drainage basin or an area of land that drains all of its water to a specific body of water like a river, lake or bay.
Simple Diagram of a Watershed

Generalized Watershed

The boundary of a watershed is defined by the ridges of highest elevation that surround a given network of streams. A drop of rainwater falling outside this boundary enters a different watershed and will flow to a different body of water.

Large watersheds contain smaller watersheds, sometimes referred to as sub-watersheds or sub-basins.

The Raritan Watershed

The Raritan Watershed, which is commonly known as the Raritan Basin, is the largest watershed located entirely within the State of New Jersey. It encompasses 1,100 square miles of land drained by the Raritan River into the Raritan Bay and is about the size of Rhode Island. It is comprised of three smaller watersheds — the Upper Raritan, the Lower Raritan and the Millstone. Centrally located in New Jersey, the Raritan Basin is bounded by the Passaic River Basin to the north, the Delaware River Basin to the west, the Atlantic Coastal Basin to the South and the Hudson River Estuary to the northeast.

The Upper Raritan Watershed

In our region, water drains into a 470 square-mile area known as the headwaters of the Raritan River, and the watershed is therefore known as the Upper Raritan Watershed. This headwaters region is made up of two smaller watersheds – the North Branch and the South Branch. These two watersheds include 52 sub-watersheds.