The Watershed
and Hydrology
A watershed is a natural unit of land which collects precipitation and delivers it to a common outlet. The quantity and purity of water reaching that outlet depend on the net sum of a variety of factors: topography, soils, climate, vegetation, surface bodies of water and so on. Each of these factors varies in relative importance from watershed to watershed. Over time, they will vary even in the same watershed. But it is the net sum of their effects that counts.
A major watershed such as the Pequannock is made up of many smaller watersheds which in turn channel their water to Newarks' water supply system. These are classified, according to degree to which they are removed from the outlet of the system, as first, second and third order watersheds.
Thus, the Pequannock River and each of the reservoirs constitute first order watersheds. The watersheds of streams which drain into first order streams are called second order watersheds. In the Pequannock, watersheds of streams which drain into second order watersheds and their headwaters are called third order watersheds.
Third order watersheds in this case do not usually include normal streams but consist rather of drainage swales and intermittent streams. They do not have the capacity to handle wide variations in runoff because they literally have no way to hold the water.Thus any increase in runoff in the third order watersheds, such as would be occasioned by removal of vegetation or by construction activities, would bring about doubly high peak flows in the second order streams and contribute vast amounts of soil and other pollution to the water in those streams. Therefore, it is especially important to protect the headwaters of streams in the Watershed. By the same token the first order watersheds are least susceptible to damage, given adequate protection, since they have higher capacity to hold water and more opportunity to allow pollutants to settle out.
Marshes and wetlands slow water down on its way to the primary watersheds. As a result they provide an effective filter of silt and pollutants before the water actually reaches the reservoirs. The wetlands and flood plain soils around the reservoirs also provide a limited amount of filtering, but because of their clayey nature could not handle any unusual flooding or pollution. A minimum 500 to 1000 foot buffer free of development must be maintained around each reservoir.