A. BEATTIE'S DAM, LITTLE FALLS, N. J., IN FLOOD.
A.BEATTIE'S DAM, LITTLE FALLS, N. J., IN FLOOD.
B. FLOOD-WATER LINES IN RESIDENCE DISTRICT, PATERSON, N. J.
B.FLOOD-WATER LINES IN RESIDENCE DISTRICT, PATERSON, N. J.
Flood flow over Beattie's dam during floods of 1902 and 1903.
FLOOD FLOW OVER DUNDEE DAM.
The flood, as indicated by gage heights at Dundee dam, lasted from about 6.30 p. m. October 8 to about midnight October 18. Although the maximum recorded gage height was 19 inches higher than during the flood of 1902, the actual time during which the river was out of its banks was forty-five hours less than at the earlier flood. Examination of fig. 1 shows that the flood of 1903 was decidedly more intense than that of 1902, the maximum height being reached in 1903 in about sixty hours, while in 1902 the maximum was not reached until the expiration of about one hundred and twenty hours.
At Dundee dam the familiar break in the progress of the flood took place about thirty-five hours after the initial rise. It occurred before the time of the maximum gage height at the mouth of Pompton River, and there is nothing to indicate that it was caused, as has been claimed, by slack water from the Pompton flood being forced back into Great Piece Meadows. There is no doubt that a part of the Pompton flood was so diverted, but there was maintained throughout at Little Falls a steady pressure, which constantly increased to maximum. This flood check, at Dundee dam was observed in 1902, but it could not be shown to arise from the frequently mentioned phenomena at the mouth of Pompton River. It is important to prove or disprove this hypothesis.If it were found to be true, it could be advantageously taken into consideration in connection with measures for the prevention of flood damages. As the Pompton had no such effect upon the flood flow at Dundee dam in two consecutive historic floods, the writer is inclined to believe that the idea is entirely erroneous.
1.--Comparative flood run-off at Dundee dam, March, 1902, and October, 1903.
Fig.1.—Comparative flood run-off at Dundee dam, March, 1902, and October, 1903.
Since the flow curves in fig. 1 were drawn it has been found by careful observation that the depressions which occur in the rise of every flood over Dundee dam are probably due to the carrying away of the flashboards which are placed upon the dam crest in times of low water. A review of the gage heights recorded by floods for several years past shows that the break occurs when the height of water over the dam crest reaches from 40 to 60 inches. The flashboards used upon this dam are usually 18 inches wide, and as they are supported by iron rods, which are of approximately the same strength and are placed upon the dam by one crew of workmen, it may be safely assumed that they are of approximately equal stability and might be expected to fail almost simultaneously along the length of the dam crest. So sudden a decrease in the effectual height of the dam must lower the water on the dam crest markedly, and as every other probable cause has been eliminated in the case of the recent flood, the explanation of the check in the progress of floods over this dam may be safety accepted as due to carrying away of flashboards. This effect should be apparent in the gage-height records only.
In the flow diagrams (figs. 1 and 2) the effect would not be the same, but the curve would rise more sharply. Similarly, the measurements at the beginning are not correct, as they are calculated according to gage heights measured from the stone crest of the dam. Therefore, a true flood curve at this point would be much flatter at the beginning and rise sharply at a period coincident with the carrying away of the flashboards.
An important difference between the two floods is that the earlier continued longer, but the later one was much higher. The flood of 1902 was caused by the turning of an equivalent of approximately 6 inches of precipitation into the main channel during a period of six days. In the deluge of 1903 there fell 11.74 inches of rain, the greater part of which was precipitated in 36 hours. Thus it is seen that there was in the flood of 1903 a larger rainfall during a much shorter period than in the flood of 1902. Computation shows that the total run-off from the drainage area above Dundee dam during the earlier flood was 13,379,000,000 cubic feet, and that on account of the frozen condition of the ground at that time this amount of water represented practically all of the precipitation. During the flood of 1903 there was a total run-off for the same area of 14,772,000,000 cubic feet, which represents about 66 per cent of the observed precipitation. According to these figures the total amount of run-off in the 1903 flood was only 10 per cent greater than that in 1902, while the actual flood height during the 1903 flood was 27 per cent higher than during the flood of 1902. The above comparison shows, in a striking manner, the effect of the condition of the surface. In the case of the later flood we had, as has been stated in previous pages, an area which had been well watered during the previous summer, and the observed ground-water levels were fairly high. There was, however, sufficient storage capacity in the basin to retain about 34 per cent of the precipitation occurring between October 7 and 11. This water must have been largely absorbed by the earth. The general relations of the floods of 1903 and 1902 can therefore be briefly stated as follows:
General relations of floods of 1903 and 1902.
In the following table and fig. 2 are recorded gage heights taken at hourly intervals during the crucial part of the flood and the amount of water expressed in cubic feet per second flowing over the crest of the dam at each gage height.
Fig.2.—Diagram of flood flow at Dundee dam, flood of 1903.
Flow of Passaic River at Dundee dam, 1903.
GENERAL STATEMENTS.
Estimates of flood damages are always approximations only. It is possible to determine with a fair degree of assurance the cost of replacing structures which have been carried away, to estimate the value of goods destroyed—especially if they be commodities stored in shops or warehouses—to calculate the amount of operatives' wages lost, and in the case of general mercantile business to estimate the damages incurred through consequent reduction of trade. Destruction by flood, however vast, is incomplete. It differs materially from destruction by fire, for often destructible property is of value after floods have passed. Buildings which are inundated still retain value, and many kinds of merchandise are not totally destroyed. Therefore when the amount of damages is calculated there is always to be taken into consideration the fact that a part of the material which has been flooded can be reclaimed, and retains some proportion, at least, of the value which it had previously possessed. Furthermore, damages by flood enter into practically every detail of social and business affairs. There are losses which are severe to one or more persons, and which can not be appreciated except by those whom the floods have actually overtaken. Therefore estimations of flood damages can be only approximate, and while a measure of accuracy may be reached with respect to a part of the losses, there remains a necessity for approximation which can not be classed with carefully computed damages along other lines.
HIGHLAND TRIBUTARIES.
Along the three northern tributaries, the Ramapo, Wanaque, and Pequanac, and at their confluence with the Pompton, the destruction by flood waters was far greater than along the Rockaway, Whippany, and upper Passaic, or in that area described as the Central Basin. In the drainage areas of the three tributaries last mentioned the waters were higher than in the flood of 1902, but the general effects were of the same nature, and consisted principally of flooded lands, houses, and washouts. There were few radical cases of complete destruction like those which marked the course of the flood in the northern tributaries. The principal interest is therefore confined to the Pompton and the three highland tributaries which discharge into it.
Ramapo River.—The greatest destruction was along the Ramapo. It is the largest of the upland branches, and was therefore the heaviest contributor to the main stream. Throughout the flood period the stream was especially violent, causing great apprehension in the lower valley.
The destruction along several stretches of the valley was almost complete. Nearly all the dams failed, and every bridge across the river, with one exception, was carried away. Some small villages were swept bare, and the damages to realty value and personal property were excessive.
It was only by strenuous measures that the dam impounding the waters of Tuxedo Lake was saved. If this had failed the destruction along the entire course of the river, even to the cities in the lower valley, would have been enormously increased.
The dam at Cranberry Pond, in Arden, failed in the early part of the storm, the flood waters disabling the Tuxedo electric-light plant and inundating the Italian settlements along the river below. The failure of the dam conserving the waters of Nigger Pond, which lies at the head of a small tributary emptying into the Ramapo below Tuxedo, resulted in the inundation of Ramapo village. The village of Sloatsburg was practically obliterated.
The damage at Pompton Lakes was especially severe. During the early part of the flood the timber dam of the Ludlum Steel and Iron Company, which raised the water to a height of 27 feet, and afforded 7.04 horsepower per foot fall, was carried away with a part of the headrace. (See Pl. II,A.) This sudden emptying of Pompton Lake, an expanse of 196 acres (see Pl. II,B), was extremely destructive to Pompton Plains, and the destruction of the dams above on Ramapo River, which followed some time after the bursting of the lower dam, refilled Pompton Lake above its former level, and caused greater damage than that which resulted from the failure of Pompton dam itself. The large iron bridge just below the dam was carried away, with the stores of the Ludlum Steel and Iron Company. The river front along this company's property was destroyed, along with coal docks at the head of Morris Canal feeder. The channel of the river below the dam is filled with débris, which will raise the height of the water in the tailrace, and unless it is cleared will diminish the available power at the iron works. It has been authoritatively announced, however, that the power facilities will not be restored, as the Ludlum Steel and Iron Company is preparing to use steam power exclusively.
Pequanac and Wanaque rivers.—Along Pequanac River the principal damage consisted of washed-out roads and destroyed bridges. The large ponded area in this basin was practically full at the time of the flood, and, as measurements at Macopin dam show, the run-off per square mile was extremely large. In the Wanaque drainage area the storage facilities afforded at Greenwood Lake were probably useful in holding back a part of the water for a brief period, but the damages along the stream are comparable to those of the Pequanac.
The effect of the flow from these two streams, added to that of the Ramapo, was particularly disastrous over the Pompton Plains. Three