The Passaic Flood of 1903

by Marshall Ora Leighton

FLOOD CATCHMENT.

Among the highland tributaries of Passaic River there are three principal areas where storage reservoirs for flood catchment may be placed: (1) The Ramapo, Wanaque, and Pequanac drainage basins, from which the waters are carried into the central basin by Pompton River; (2) the Rockaway drainage basin, and (3) the upper Passaic drainage basin. The remaining principal tributary of Passaic River, the Whippany, is not well provided with storage reservoir sites. The combined capacity of catchment reservoirs which could be constructed in these drainage areas is considerably more than the volume of the heaviest known rainfall, that of October 8-11, 1903.

In the description of reservoir possibilities in the following pages the data with reference to many of the basins are computed from planimeter and other measurements, the United States Geological Survey topographic maps being used as a base. The measurements are therefore not of refined accuracy but suffice for the purpose in view—that of showing flood catchment possibilities.

POMPTON RESERVOIR.

There are in the Pompton system several sites on Ramapo, Wanaque, and Pequanac rivers which, if utilized, would afford sufficient storage for flood catchment purposes, but the entire flow of the river system may be conserved in what has been described as the Pompton reservoir. This project was first presented by Mr. C. C. Vermeule in the year 1884, the details being described at some length in the Engineering News, of April 12 of that year, pages 169-171. In this article Mr. Vermeule presented the possibilities of Pompton reservoir for use as an additional water supply for the city of New York, at the time when the Quaker Bridge reservoir on the Croton watershed was being considered. A few pertinent quotations from this article may be of interest:

This basin, subdivided by minor ridges which cross it, furnishes several admirable sites for large storage reservoirs, with catchments from 50 to 400 square miles in area, lying above on the primitive rock of the Highlands. About 6 miles of the northeastern end of the basin is cut off by Hook Mountain, a small ridge of trap which crosses it from east to west, inclosing a basin 21 square miles in area, known as Pompton Plains, having its outlet at Mountain View, 5 miles west of Paterson, at a pass in Hook Mountain, through which the Pompton River flows to join the Passaic, 2 miles below. This pass is the gateway by which the Delaware, Lackawanna and Western Railroad, the New York and Greenwood Lake Railway, and the Morris Canal enter the plains. The basin is also crossed near its head, above Pompton, by the New York, Susquehanna and Western Railroad. Pg032

The Pompton River has a drainage area above Mountain View of 420 square miles. It is formed near the head of the basin by the confluence of the Pequanac from the northwest, the Wanaque from the north, and the Ramapo from the northeast. * * *

The entire flow from this watershed may be stored by building a dam across the gap at Mountain View and converting Pompton Plains into a great lake covering an area of 21 square miles. The elevation of the river at the gap is 168 feet. The slopes in the basin being gentle up to an elevation of 220 feet and abrupt beyond it, it will be advisable to take this as the minimum or low-water level of our reservoir. It is generally estimated that 25 per cent of the volume of the mean annual rain on a given catchment is sufficient reservoir capacity to fully utilize the flood flows. We have long series of observations of rainfall at three points, which may be taken to fairly represent the Passaic catchment. At Newark the mean annual rainfall is 46.2 inches, at Paterson, 50 inches, and at Lake Hopatcong, 42. The last being on the Highlands, like most of our watersheds, is perhaps the safest to use. Now, 25 per cent of 42.5 inches, 10.62 inches, which, on 420 square miles, give a volume of 10,362,000,000 cubic feet, the necessary capacity of reservoir.

By raising our reservoir to 240 feet when full we secure a capacity of 10,493,000,000 cubic feet, or ample to utilize the heaviest floods of the watershed. This gives a beautiful sheet of water 21.1 square miles in area, with bold, rocky shores, and a depth at dam of 72 feet. We secure the above capacity by uncovering but 22 per cent of the reservoir bottom; and, as we shall presently see, we shall rarely need more than half this storage, and probably not oftener than once in ten years will we expose over 10 per cent of the area. By building side dams to keep certain flats always flowed this may be reduced to 5 per cent; and this area will be pretty evenly distributed around 36 miles of uninhabited shore line, leaving the reservoir open to no valid sanitary objections. On the contrary, by relieving the remainder of the Passaic Basin of the flood waters of the Pompton, which now flow large areas of flat land during wet seasons, the sanitary condition of the valley would be much improved.

In constructing this reservoir Mr. Vermeule stated that the following work would be necessary: