Part 7

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.

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:

The removal of the Delaware, Lackawanna and Western Railroad from the basin by changing the alignment for 6 miles. It may be done without increase of length or detriment to the alignment.

Three and one-fourth miles of the Morris Canal must be rebuilt. No engineering difficulties are involved.

Of the New York and Greenwood Lake Railway, 9 miles would have to be rebuilt.

The New York, Susquehanna and Western Railroad would be slightly shifted or raised for 3-3/4 miles.

A dam 2,400 feet long and 80 feet in height, with tunnels, wasteweir, and accessory works would be required at Mountain View. The situation is such that an ample wasteweir may be built at a low-side dam on the solid rock of Hook Mountain remote from the dam, and outlets may be had by tunneling the same ridge. Hence the dam may be a plain, heavy earthen embankment; built, of course, with every precaution but subject to less than the usual dangers of such works. However, a masonry dam might readily be substituted.

There would be 14,000 acres of arable land, swamps, and rough mountain land flowed.

The works are estimated to cost as follows:

Railroad and canal diversions $505,000 Dam and accessory works 1,162,000 Land damages 1,400,000 _________ Total 3,067,000

A recomputation of the drainage area above Mountain View, made by the northern New Jersey flood commission, shows that it is 380 square miles in extent. It was decided by this commission that the construction of this reservoir would be the most approved method of preventing disastrous floods in the lower valley of the Passaic. By raising a dam to a height of 202 feet above tide, 8 inches of water on the drainage area above might be held back, which, it was believed, would be a sufficient maximum for flood catchment. With this amount of storage the estimates of the flood commission showed that the remainder of the drainage area would not turn a sufficient amount of water into the lower valley channel to cause flood damages.

It was also demonstrated by the flood commission that by increasing the height of the dam an opportunity would be afforded for conserving water, and at the maximum height of 220 feet above tide sufficient storage capacity would be available to provide 5,000 horsepower at Little Falls, Great Falls, and Dundee dam throughout all dry seasons. The value of such a storage reservoir for municipal water-supply purposes is self-evident.

The cost of Mountain View reservoir would be about $3,340,000. Developed for flood catchment with the spillway of the dam at 202 feet above sea level the area of the reservoir would be 13.4 square miles, and the storage capacity 7,200,000,000 cubic feet.

RAMAPO SYSTEM.

Along the Ramapo Valley there are alternative propositions, one of which involves the construction of a dam below Darlington and another across the head of Pompton Lake.

In either case the water might be raised to the 300-foot contour, and if the dam across Pompton Lake were constructed a continuous lake would be formed extending 10-1/2 miles to Hillburn, N. Y. The improvement in either case would be positive, for as the country surrounding is hilly or mountainous it affords excellent opportunity for the location of summer homes and parks, the lake being a potent factor in beautifying the situation and increasing the value of the surrounding region. There are, nevertheless, several things to be taken into consideration, the most important of which are the improvements which have been made by wealthy residents along the valley where it has already been developed as a summer resort.

By the construction of a dam at Darlington 1,100 feet long and 70 feet high, the water would be raised to the 300-foot contour. The reservoir would have a water area of 2,064 acres, and the approximate storage capacity of 2,325,000,000 cubic feet.

A dam across the head of Pompton Lake 2,850 feet long and 100 feet high would raise the surface of the proposed lake to the 300-foot contour. This reservoir would have an area of 6.19 square miles and a capacity of 6,300,000,000 cubic feet, equal to 17.5 inches run-off from the drainage area. Here the measure of safety is wide, and if there were drawn from the lake an amount of water equal to 12 inches on the drainage area there would still be 5.5 inches which could be used for compensating purposes.

The construction of either one of the above-described reservoirs would involve interstate complications, as the 300-foot contour in Ramapo Valley includes a considerable part of the State of New York. This obstacle was deemed insurmountable by the northern New Jersey flood commission, and that commission directed studies to a reservoir which at the time of maximum flood would not back water into New York State to a greater height than it already rises during such floods. The following description is taken from the report of the engineering committee of the flood commission:

An admirable dam site is offered on Ramapo River about 2 miles above Oakland village. The drainage area tributary to this point is about 140 square miles in extent, the country for the most part being quick-spilling and upland. By constructing there a dam 700 feet long and 65 feet high a reservoir with a water surface of 2.8 square miles would be afforded, the flow-line elevation being 280 feet above tide. The capacity of such a reservoir would be 1,768,000,000 cubic feet, equal to about 5.5 inches on the drainage area.

WANAQUE SYSTEM.