Part 6

U. S. GEOLOGICAL SURVEY WATER-SUPPLY PAPER NO. 92 PL. IV

U. S. GEOLOGICAL SURVEY WATER-SUPPLY PAPER NO. 92 PL. V

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away. This structure was built to conform to the established grades of streets on both sides of the river and was completely inundated, forming a barrier for floating debris and practically making a dam in the river. Main street bridge is a 3-span, steel-arch structure, which was completely covered during the flood, but was only slightly injured. Arch street bridge, built in 1902 to take the place of a structure carried away by the March flood, was a concrete-arch bridge of three spans. It was undermined at the north pier and collapsed, being practically destroyed. The original cost of this bridge was $34,000. Its piers presented a serious obstruction to the flow of the stream, especially as the channel is very narrow at this point. In addition to this, the bridge was of low grade and admirably adapted for deterring flood flow. Below Arch street bridge all the other structures crossing the Passaic were of iron and were carried away, with the exception of Sixth avenue and Wesel bridges. Those destroyed were designated as follows: Straight street, Hillman street, Moffat, Wagaraw, Fifth avenue, East Thirty-third street, and Broadway bridges. All these structures were built too low, and were inundated during the early stages of the flood.

The damage to real property, stock, and household goods in the city of Paterson amounted, according to certified returns, to about $2,700,000. It is impossible to secure correct figures, because merchants and manufacturers refuse to give details of losses, fearing that the publication thereof would affect their credit. General ideas concerning the destruction by the flood can be gathered from Pls. I, B, III, IV, V, and VI.

Passaic and vicinity.--Below the city of Paterson destruction was as complete as in Paterson, although the damage was not as great because the improvements were not as valuable. Damage to property, exclusive of public works, in this region, amounted to about $1,250,000. This estimate does not take into consideration losses by manufacturers arising from destruction of raw materials or finished products. The flood was about 4-1/2 feet higher than that of 1902. (See Pl. VII, A.)

On the right bank of Passaic River, in the city of Passaic, the damage was severe, especially to manufacturing plants. In addition to the flood in the Passaic itself, the bursting of Morris Canal, a few miles east of Passaic, flooded Wesel Brook, which in Passaic is used as the tail-race of the Dundee Power Company. The capacity of Wesel Brook channel is limited, and the extraordinary amount of water which was turned into it carried away all culverts and bridges from Richfield to Passaic.

Below Passaic, along the river front of Essex County, the damages to bridges amounted to $50,000. (See Pl. VII, B.) The loss due to washouts in roads throughout the county amounted to $15,000. The effects of the flood were apparent along the entire length of the river and into Newark Bay. The damage from inundation in Newark and vicinity amounted to $753,199.

The figures above given with reference to damage along Passaic River are uncommonly accurate, being for the most part the result of a house-to-house canvass by the northern New Jersey flood commission. As has been stated above, tradesmen are reluctant to give full details with reference to their losses through fear of injured credit. Roughly estimating the damage as a whole, and taking into consideration factors which were given to the writer confidentially, the damage throughout the drainage area from this flood will amount to not less than $7,000,000.

PREVENTIVE MEASURES.

GENERAL DISCUSSION.

In the consideration of means of preventing damages by floods every plan proposed falls under one of two general heads--the storage of flood waters or an increase in the capacity of the streams.

The first plan involves the construction at selected localities of reservoirs of sufficient size to hold all or a greater part of the waters which run over the surface during and after storms. This plan is not practicable except where valleys or plains are inclosed by high ridges and these ridges approach sufficiently near each other to admit of the economical construction of a bank or dam across the gorge or bed of the stream which flows through, so that the inclosure will be complete and form a water-tight basin. Where such a reservoir exists the water can be held back and gradually let down through properly provided gates so that the channel will not be flooded.

For flood purposes alone it would be necessary to provide reservoirs of sufficient capacity to contain the run-off waters resulting from the largest storms. With such provisions it would be necessary to entirely empty the reservoir as soon as possible after a storm had passed and leave its full capacity available for the next storm. It is therefore better, wherever possible, to provide a reservoir capacity considerably larger than that represented by the run-off from the heaviest storms, so that water may be stored for use as power or domestic supply. With such provision it is necessary merely to draw from the reservoir water to a depth equivalent to the stream run-off in the drainage area above.

The second plan for prevention of flood damages involves provisions for letting the flood water out rapidly by removing obstructions to its flow by straightening and deepening the channels and providing long embankments, dikes, or levees which rise above the ordinary river level to a height exceeding that of the stream during its highest floods. This plan is most generally followed in the case of large rivers like

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U. S. GEOLOGICAL SURVEY WATER-SUPPLY PAPER NO. 92 PL. VI

U. S. GEOLOGICAL SURVEY WATER-SUPPLY PAPER NO. 92 PL. VII

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the Mississippi, where the contributing area is enormous and the conservation of the waters would be impracticable even if the nature of the country would admit of the construction of reservoirs. In Switzerland, where the torrents occasioned by the rapidly melting snows are especially destructive, the flood waters are confined by a series of parallel dikes on each side of the river, which have the effect of dividing the flow into several parallel streams. As the main river channel fills and overflows the inner dikes, the overflow water collects into the first series of parallel channels, and when a height is reached at which the second dikes are overflowed the water collects into the third, and so on. This gives an enormous carrying capacity, the limit of which is approached slowly, and therefore abundant opportunity is afforded for preparation upon the part of the riparian owner.

The drainage basin of Passaic River is admirably adapted to the development of the conservation system. At its headwaters in the mountains of northern New Jersey are numerous sites for reservoirs. The comparatively limited area draining into Passaic River makes such a scheme relatively inexpensive. On the other hand there is abundant opportunity for effective work in removing obstructions and straightening and deepening the channel of the lower river. So that, all things considered, the prevention of flood damages in the Passaic Basin can be best accomplished by a combination of the two general methods above outlined.

LOWER VALLEY IMPROVEMENTS.

The channel of Passaic River below Great Falls, at Paterson, is of limited capacity. To anyone making an inspection, especially within the city of Paterson, it is readily apparent that the river bed has for years been considered a legitimate field for encroachment. Owners of lands fronting on the river have increased their holdings by filling in beyond the channel line. Buildings have been erected upon these tracts and the builders have not hesitated to extend retaining walls still farther into the river bed. Refuse from the city's streets, light and unstable in character, has been freely deposited upon the bank to be carried out into the river. Thus the channel has been constricted laterally, the bottom raised, and there is left for the flood waters no alternative than that of extending themselves in the upward direction. It would seem that this, at least, should have been unobstructed. Such, however, is not the case.

The bridges across the Passaic have apparently been erected without reference to channel capacity. The authorities have evidently considered it more important to retain established approach levels than to provide proper capacity for river water. As an example the following instance may be cited: During the flood of 1902 a steel truss bridge across the river in Paterson was carried away. The point of crossing was one of the narrowest places in the stream and it should have been clear to everyone that the space beneath the bridge was not large enough to carry flood waters. It should have been apparent that a new bridge, if erected at that point, must be higher than the old one, to be thoroughly safe. Notwithstanding, the new bridge was erected at the level of the old one, and in addition to this, it was a concrete arch structure, and the great piers and low arch springs reduced the former channel capacity about 15 per cent. This new bridge, as might be expected, collapsed during the October flood.

Along the entire course of the stream in the lower valley we find a continuation of instances of unreasonable encroachment and ill-considered bridge engineering, and there is opportunity for relieving a large part of the purely local obstructions by straightening the channel at chosen points.

Although this matter has not been thoroughly investigated it is readily apparent to one traversing the river bank that considerable relief may be secured in this manner. Damage, however, can not be prevented by this means alone. It would, of course, be possible to erect high and resistant levees along the entire course of the river, but this would be extremely expensive and would destroy the water front for commercial purposes. In fact, such a plan is quite visionary. At the present time there are no obstructions in lower Passaic River the removal of which would give relief in the event of floods like those of 1902 and 1903. When one considers the amount of water which was carried into the lower valley, the heights which it reached, and the area which it inundated, the futility of any local improvement except levee construction is emphasized. The present channel of the river will not carry without damage the amount of water recently thrown into it, and while it is important to provide regulations which will in the future prevent encroachment, and which will correct the evils now present along the channel, these measures can not, operating of themselves, give relief from flood devastation. Immunity from flood destruction in the Passaic must come, if it ever comes, from the construction of flood-catchment reservoirs in the uplands.

It is not necessary to spend any great amount of time in determining the cause of floods upon the Passaic. A review of the flood history of this river shows that in every case floods arise from extraordinary precipitation. High waters occur through the melting of snows and during periods of abundant rain. The heavy floods which have been regarded as extraordinary are clearly the result of unusual conditions of precipitation. The river carries the usual flood waters, and no damage is done until the water poured into it is far beyond its carrying capacity. Therefore the provisions which are made for preventing damage by floods must, if they be effective, be designed to meet extraordinary conditions, and means which would prove effectual in ordinary cases will not stand the test. In order to appreciate the extent of the flood in the lower valley it is necessary to visit the flooded area and observe the points of flood height. Unless one does this he will be very readily deceived when he considers means of flood prevention.

FLOOD CATCHMENT.