By Marshall O. Leighton.

INTRODUCTION.

In the following pages is given a brief history of the disastrous flood which occurred in the Passaic River Basin in October, 1903. In the report by George Buell Hollister and the writer, entitled "The Passaic Flood of 1902," and published by the United States Geological Survey as Water-Supply and Irrigation Paper No. 88, are discussed the principal physiographic features of the drainage basin and their general relations to the stream flow. This report will not repeat this information, and the discussion will be confined to the flood itself. References to local features will be made without explanation, the presumption being that this publication shall accompany the earlier one and be, as it is, a continuation of it. In the present report more attention is given to an estimate of damages than in the earlier work, and remedies by which devastation may be avoided are briefly considered.

Passaic River overflowed its banks on October 8, 1903, and remained in flood until October 19. Between these dates there occurred the greatest and most destructive flood ever known along this stream. Ordinarily the channel of the lower Passaic at full bank carries about 12,000 cubic feet of water per second, but at the height of this flood it carried about 35,700 cubic feet per second.

The flood period for the entire stream can not be exactly stated, as the overflow did not occur at the same time in different parts of the basin. For example, the gage-height records at Dundee dam show that the flood began to rise on October 8 at 6.30 a. m., and reached a maximum of 9-1/2 inches over the dam crest at 9 p. m. on October 10. Similarly, on Beattie's dam at Little Falls the flood began to rise at midnight on October 7, and reached its maximum at 2 p. m. on October 10, or about thirty-eight hours after the initial rise, the height of the water being 1.29 inches over the crest of the dam.

The flood rose on the highland tributaries as follows: On Ramapo River the flood crest passed Hillborn at about 10 a. m. on October 9 and reached Pompton, at the mouth of the river, shortly after noon of the same day.

The highest reading recorded on the Geological Survey gage at the feeder of Morris Canal, in Pompton Plains, was 14.3 feet, at about 6 o'clock on the morning of October 10. As this gage is read only once daily it is probable that this reading does not represent the height of the flood crest. Evidence shows that it passed this point on the previous day. Records of the Newark water department show that the flood on Pequanac River began to rise at Macopin dam on October 8 at noon, and rose rapidly to the maximum of 6,000 cubic feet per second at 4 p. m. on October 10.

No records are available with reference to the rise of flood on Wanaque River.

Observations made on Pompton Plains on the morning of the 11th show that Pompton River was well within its banks at that time; therefore the Ramapo, Wanaque, and Pequanac must have discharged their flood waters some time previous to this hour. The fact is important when considered in connection with the height of water in the main stream at that period. This observation was made only eighteen hours after the maximum height over Beattie's dam at Little Falls, and twelve hours after the flood crest passed Dundee dam. The conditions here outlined illustrate the rapidity with which flood waters are discharged from the Pompton drainage area, and the deterring effect of Great Piece Meadows upon the flood.

The rise of the flood on Rockaway River at Old Boonton was almost coincident with that on Pequanac River at Macopin dam. The maximum flow occurred fourteen hours later than the maximum on the Ramapo at Pompton.

The flood crest did not reach Chatham on upper Passaic River until the morning of October 11, or about twenty-four hours later than the flood heights in Pompton and Rockaway rivers, and about twelve hours later than the maximum over Dundee dam.

Adequate reasons for these differences in flood periods between neighboring points are abundant. They are apparent after a review of the physiographic conditions described in Water-Supply Paper No. 88.

The flood of 1903 was the immediate result of an enormous rainfall, and not, as is often the case in north temperate latitudes, the combined effect of rainfall and the rapid melting of accumulated snows. The records of weather-observation stations in northern New Jersey and New York fail to show, throughout their entire observation periods, as great an amount of precipitation in so short a period. The storm which was the immediate cause of the flood occurred principally between October 8 and 11. During that interval rain fell to an average depth of 11.74 inches over the Passaic Basin.

The Passaic Basin is fairly well supplied with storage facilities, which, under ordinary circumstances, would temper the severity of floods by holding back a large amount of water. In this case no such effect was produced, as the reservoirs, lakes, and ponds on the drainage area were filled, or practically so, at the beginning of the storm, and there was consequently no available space in which to hold back even an appreciable part of the run-off water. Over some of the dams in the highland region a comparatively small amount of water was being discharged at the beginning of the storm. Therefore, while these storage basins may have had a certain deterring effect upon the rate of flood accumulation, they could not, in the end, assist materially in preventing damages in the lower part of the drainage area.

PRECIPITATION.

The precipitation records for June, July, August, and September are given below:

Precipitation, in inches, in Passaic Valley and vicinity, June to September, 1903.

An examination of the above table shows that throughout the summer of 1903 the precipitation was considerably above normal. The records for June and August indicate extremely wet months, and the July figures are slightly above while the September figures are somewhat below normal. The important fact shown by this table is that disastrous floods may occur after long periods of abundant rains. It has been observed that heavy precipitation may be expected after protracted periods of drought. Such a belief is not altogether fanciful. In the northeastern part of this country the total amount of precipitation is approximately uniform from year to year. The variations, comparatively speaking, are not very wide, and we are therefore led to expect that there are in operation influences which serve to compensate for excesses or deficiencies in our annual rainfall. Therefore after the abundant precipitation of the summer of 1903, an observer might have had some measure of justification in predicting a normally or abnormally dry fall. In view of the actual events the fact must be emphasized that in adopting measures to prevent floods the margin of safety must be extremely wide. The extraordinary rainfall of those three October days can not with assurance be accepted as the maximum.

Precipitation, in inches, in Passaic Valley and vicinity, October 7 to 11, 1903.

The extremely rapid rate of precipitation during the crucial part of the storm is shown by the recording gages placed at observation stations in Newark and New York City.

Hourly records of precipitation at New York observation station, October 8 and 9, 1903.

Hourly record of precipitation at Newark observation station, October 8-11, 1903.

From the above tables it may be seen that the maximum rate of precipitation per hour was 1.38 inches at New York and 1.2 inches at Newark. Comparison of the tables on pages 11 and 12 gives an excellent idea of the intensity of the storm. The amount of water falling in a single storm is nearly equal to the total for June, a month of unusual precipitation.

The average of the total amounts of precipitation recorded at the various stations in the Passaic area is 11.74 inches. These totals are fairly uniform, none of them varying widely from the average. Therefore the figure 11.74 represents a conservative mean for a calculation of total amount of water over the drainage area. Assuming this as the correct depth, the amount of water which fell on each square mile of the Passaic drainage area during the storm was 27,273,000 cubic feet, or for the whole Passaic drainage area over 27,000,000,000 cubic feet, weighing about 852,000,000 tons. This amount of water would, if properly stored, fill a lake with twenty times the capacity of Greenwood Lake, would cover Central Park in New York City, which has an area of about 1.5 square miles, to a height of 645 feet, and, at the present rate of water consumption in the city of Newark, N. J., would supply the city with water for twenty years.

DESCENT OF FLOOD.

HIGHLAND TRIBUTARIES AND CENTRAL BASIN.

A description of the descent of flood waters from the highland tributaries into the Central Basin has been given in Water-Supply Paper No. 88. It has been shown that the lands of the Central Basin are covered even in ordinary freshets, and that in the event of a great flood the waters merely rise higher, being, for the greater extent, almost quiescent, and beyond the flooding of houses and barns and the destruction of crops, little damage is done. In other words, the flood along this portion is not torrential in character.

During the flood of 1903 the water fell so quickly all over this basin, and was collected so rapidly by the small tributaries, that a lake was formed at once which served as a cushion against which the raging torrent of the highland tributaries spent itself without doing extraordinary damage in that immediate region. Bridges which might have been lost in a smaller flood like that of 1902 were actually standing in slack water by the time the mountain torrents appeared in force. These streams caused much destruction higher up in the mountains, but in the Central Basin their energy became potential—a gathering of forces to be loosed upon the lower valley. A discussion of the effects of this will be taken up under the heading "Damages."

In Water-Supply Paper No. 88 is given the proportion of flood waters contributed to the Central Basin by each of the tributaries. These figures were computed from the results of gagings maintained for a period sufficient to afford this information within a reasonable approximation. In the case of the storm which resulted in the flood of 1903 it is probable that data referred to can not be safely applied.

The flood of 1902 was the result of abundant rains following upon and melting a heavy snow. Weather Bureau records show that neither the depth of the snow nor the amount of subsequent rainfall was uniform, or even approximately so, over the Passaic drainage area. Indeed, so marked was the variation that it was believed that the mean rainfall for all the observation stations on the basin did not bear sufficient relation to observed run-off to allow of any reliable deductions. In the case of the October storm, however, the distribution of rainfall was more nearly uniform, and the run-off from the highland tributaries into the Central Basin must have been proportionately different in amount from that indicated in the upland tributary tables in the report of the previous flood. The data given for the 1902 flood can not, therefore, in the case of the highland tributaries, be applied to the conditions which obtained in the flood of 1903.

FLOOD AT MACOPIN DAM.

Mr. Morris R. Sherrerd, engineer of the Newark city water board, has furnished flow computations over Macopin intake dam, which is the head of the Newark pipe line. As about 73 per cent of the Pequanac drainage area lies above this intake, the table on page 16 shows roughly an equivalent percentage of the flow contributed by Pequanac River to the Central Basin of the Passaic. In consulting this table it should be borne in mind that the entire run-off of the drainage area above Macopin is about 25,000,000 gallons per day more than the amounts presented in this table. All reservoirs and ponds connected with the conservancy system of the Newark water supply were filled except that at Oakridge, which was about 1.5 feet below the crest of the spillway.

Flow of Pequanac River over Macopin dam, October 7-24, 1903.

[From Newark water department.]

FLOOD AT BEATTIE'S DAM, LITTLE FALLS.

The flow over Beattie's dam at Little Falls, has been calculated according to coefficients used for the same dam in Water-Supply Paper No. 88. Recorded gage heights show that over the main dam there was a maximum depth of 11.12 feet, which continued from 2 to 8 p. m., on October 10, representing a maximum flow of 31,675 cubic feet per second. (See Pl. I, A.) In the following table is set forth the flow of the river over Beattie's dam during the flood, and for purposes of comparison, the figures for the flood period of March, 1902. It should be borne in mind in consulting this table, that in the case of the flood of 1903 exact dates and hours are given, while the figures for the 1902 flood represent flow determinations at six-hour intervals, beginning with the initial rise of that flood.

A. BEATTIE'S DAM, LITTLE FALLS, N. J., IN FLOOD.

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.

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.