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second. This flows through Sabine Pass. At two places in the pass where it is narrow-one opposite the upper end of the town and the other opposite the light-house—the two places being about 4 miles apart, care. ful cross-sections were made, and in these sections numerous current observations were made. The area of the upper or hotel section was 28,112 square feet, wbile that of the lower or light-house section was 27,376 square feet. A mean of the two would be 27,744 square feet. If, now, we assume that the tidal flow was regular and uniform, the rate per second of the flood-tide through this mean area would be 2.3 feet, while that of the ebb-tide would be 2.83 feet. Our observations in the two sections show current velocities on the ebb.tide varying from 0 to 47 feet per second, which was the maximum observed. Current observations made on the crest of the bar in 1878 give the strongest ebb sur. face current at 1.7 feet per second; at a depth of 2 feet the velocity fell to nine-tenths of 1 foot, and at 4 feet depth (the water being but 6 feet deep on bar) the velocity was only one-half foot per second.
Of the flocd currents observed on the bar, the greatest observed velocity was 1.1 feet per second.
From nearly two months' observations it was found that the flood-tide in its first qnarter, and sometimes extending nearly through the second quarter, came in on the Louisiana side, gradually widening until, when running at its strongest, it seemed to concentrate from the Gulf toward the throat of the pass; the current would frequently run out on the Texas side for two hours after the tide had commenced to run in on the Louisiana side. The ebb-tides acted almost exactly opposite. The first of the ebb-current was always on the Texas side, then this thread began to widen and extend toward the Louisiana shore, until finally the entire current over the bar was an ebb-current. We also observed that after southerly winds, when the water was banked up in the Sabine Lake and the Sabine and Neches rivers were high, there would be a surface current running out during an entire flood-tide, and that this water was fresh enough to drink.
Outside of Sabine Pass there is an undoubted littoral current whose general direction is from the east towards the west. This is variable, depending on the wind, and runs with a velocity of from 1 to 3 miles per bour. This current is appreciable for at least nine months in the year. During and after a strong southeaster this current pushes in toward the pass, mostly towards the Texas shore, but this is ordinarily of but two or three days' duration.
We now liave the results of several surveys of Sabine Pass and its bar, know something of its tides and currents, have made sufficient borings to determine the character of the bar, and also know that there is a variable littoral current here, and have had the experience of at least two dredged channels across the bar. With this information, it is required to project a plan and make an estimate for the improvement of Sabine Pass and the bar at its mouth.
The dredged channels were not maintained; the conditions for selfmaintenance were unfavorable, and were mentioned on pages 4-5 of this report. Dragging the channel with a large harrow attached to a steamtug was tried, and the experiment showed that the channel could not be improved by this method. Would protecting works on either or both sides of the cut have maintained iti Possibly; but such works of themselves would have been of the nature of jetties, and they would probably have to extend the entire length of the cut. The problem to be solved at the time the cut was made was to get a channel through the bar. This was done in the quickest and cheapest manner, by dredg.
ing. It was not known whether the channel would be maintained or not. Had there been many steam vessels using the channel, the contin. uous cutting of the bottom and stirring of the mud might have helped to longer maintain the channel, but there was no commerce there for vessels of this class, hence no vessels worth mentioning. The few ves. sels (steam) that went there were on government business, drew less than 8 feet of water, did not know where the narrow cut was, and would, in consequence, get ashore, and do more damage than benefit to the cut. The experience gained from dredging here was valuable. It proved that a channel could be dredged, that it was expensive work, and that such channel, if let alone, would fill up again.
With this experience before us, to resume dredging now without some means of protecting the work done or to be done would be worse than a most serious error.
In the pass itself, where the pass is narrow (1,800 to 1,900 feet in width), we have good channels self-maintaining the bottom of the entire pass, excepting here and there where a few small oyster reefs are scattered about, is of precisely the same nature; that is, soft, blackish blue mud, as that found on the bar. In these narrow gorges of the pass we find channels 25 feet deep and over 500 feet wide. Where the pass is much wider, we have of course the same volume of water, but less depth and a wider channel. That this depth, its production, and maintenance, is due principally to the velocity of the tidal flow, there is no doubt, and therefore, if similar conditions can be reproduced on the Sabine Pass Bar, there is no good reason why similar results should not be obtained there.
We can only hope to produce similar conditions by means of jetties. If we can concentrate a sufficient quantity of water on a limited portion of the bar, we get over that portion of the bar an increased current. This, if it produces a scour, makes and maintains the channel. The pass itself is sufficiently wide and deep, with its funnel-shaped mouth, to offer but little obstruction to the free movement of the flood-tide; the banks of the pass are the jetties wbich concentrate and confine the water through them, and the Sabine Lake is the reservoir into which the waters flow. If jetties be built, they must therefore be constructed in such a way as to offer the least resistance to an inflow of the tides, and yet control the outflow and direct it in a certain fixed direction.
Their distance apart, direction, length, height, cross-section, composition, and, finally, their cost, are matters of the greatest importance.
They should be far enough apart to secure them against serious subsidence that may occur from the excavation of a deep channel between them, and their direction should be such as to direct the current pass. ing out between them with or across the littoral current, and certainly not against it. The nearer they be placed together with the same volume of water flowing between them, the deeper ought to be the channel which they should produce, and the consequent greater danger of their undercutting and final loss. In the pass, at its narrowest place (opposite hotel), the banks are 1,820 feet apart, and there we have depths of 39 feet. At the light-bouse the banks are 2,145 feet apart, and the greatest depth in this section is 27.7 feet, having a channel through it 500 feet in width, of 22 feet in depth. As the waters of the pass form an *18-foot deep channel, except over a few small oyster reefs mentioned, we ought to try to get 22 to 25 feet depth of channel over the bar. The mean of the areas of cross-sections at hotel and light-house is 27,744 square feet, the respective areas are 28,112 and 27,376 square feet, differ
from the mean only 1.3 per cent., while their mean depths are re
spectively 15.4 and 12.7 feet, and this difference of mean depths is due to the difference of the widths of the two sections.
On the chart I have projected the lines of the jetties parallel to each otherand 1,800 feet apart, with the following object in view: As there must be but little obstruction to the inflow of the tides, we must either build low (drowned) jetties or leave openings near the shore; but the same conditions which permit of easy inflow of the tides may permit the escape of so much of the ebb-tides as to destroy their scouring power. I therefore assume that the jetties to be built are high jetties, the inner portion of each jetty being drowned. We know that the flood-tides come in for two hours or more from the east or Louisiana shore before reaching the Texas side; therefore the east jetty should be a low one or else have a large opening near its shore end. The ebb-tides incline toward the Texas shore; therefore the west jetty should be a high one with a smaller opening near its shore end, to prevent as much as possible the escape of the ebb-tide.
If both jetties be built high with shore openings to permit the fullest inflow of flood-tides, we approximate more nearly to the condition of things in the pass. We have the funnel shape formed by the jetties and the shore lines, and we more certainly control the action of the ebb-currents than we could with low jetties; but the objection to high jetties is that they cost much more money to build and are more liable to injury by heavy seas than low jetties. Leaving out the question of difference of cost and maintenance of high and low jetties, let us see what we may expect with high jetties. We have already said that the mean area of the cross-sections in the pass was 27,744 square feet. If we leave openings near the shore ends of the jetties, protecting the openings by a sill (mattress) to prevent scour there, the aggregate area of the two openings below high-water, representing 20 per cent. of the mean area of the gorge above referred to, and make 15 per cent. of this aggregate opening on the Louisiana side or east jetty, I think we shall get nearly as full an inflow of tides as at present, but we shall get less discharge through the jetties than now, for the reason that fully 5 per cent., probably much more, must escape through the opening on the Texas side, and some, perhaps more than another 10 per cent., from the Louisiana opening. Therefore, with this loss of ebb volume through the jetties, they, to produce the same depth as we get in the gorge, should be closer together than the width of the pass at the gorge. We have shown, by a very rough calculation, that the volume of discharge of an ebb-tide, if flowing uniformly, would average about 77,727 cubic feet per second.
The jetties at South Pass of Mississippi River have a volume of water flowing through them varying from 26,688 to 78,410 cubic feet per second, and though only 1,000 feet apart are not sufficient to produce and maintain a channel such as we have in the gorge at Sabine Pass. Many inferences may be drawn from this, but the most plausible one is that, assuming my calculation of discharge for Sabine Pass to be approximately correct, then, with jetties 1,800 feet apart, we shall not get such a channel as the South Pass jetties now have. With the Sabine Pass jetties 1,000 feet apart (both high jetties) we might get 26 feet and more of depth, but fortunately Sabine Pass bar does not require this depth.
Whether the jetties be placed 1,800 feet apart or less, it will make but a very small difference in their aggregate cost. Neither will tho direction taken by the jetties make much difference in their cost, as the bottom on the bar, to the eastward and westward of the lines projected, is of the same character and has the same depth of water on it as is found on the lines indicated. The line selected has some advantages;
it reaches deep water (the 20-foot curve) in about as short a distance as can be found. It covers or incloses what is left of the dredged chan. nel, directs the ebb-discharge across, and very slightly with the littoral current; and during southeast storms, which are generally the most severe in that vicinity, the jetties would take the storm and consequent sea at an acute angle, instead of broadside on, as would be the case were they deflected more to the westward.
A single jetty at Sabine Pass would probably produce much deeper water over the bar than is now found. Such jetty, if built, should be on the west side of the present channel, and should follow approximately the line laid down for the proposed west jetty shown on the chart. The reason for this side being preferable to one on the east side of the channel, is in consequence of the pressure or inclination of the ebb-tides toward the west. In consequence of the jetty we might get a scour on the east side of it from both tides, and as it would check the spread of the ebb in a westerly direction, we should get increased velocity and probably scour.
At all events, in the construction of jetties at Sabine Pass, one jetty would have to be commenced first, for reasons given; in my judgment, it should be the west jetty. The foundation course of this jetty should be built nearly or quite its full length, before a second course is placed upon it. On the crest of the bar, where the water is only 6 feet in depth, the foundation course of the jetty will probably make some scour, which will continue to increase as the jetty is raised. As soon as a foundation mattress is laid and loaded with its stone to secure it, it should be covered with mud pumped on with a centrifugal pump. This will add to its weight, compact the stone, and possibly prevent the attack of the teredo; at all events, it will save quantities of stone, which is the most expensive ingredient of the jetty. When the jetty has been raised sufficiently high, the scour ought to be well remarked as well as the channel which it produces; this will then determine whether or not this jetty is to be raised higher or the other jetty to be commenced. As the difference between high and low water is only 1.4 feet, a high jetty will not very greatly exceed the cost of one reaching to low-water level.
The jetty or jetties, built or to be built, should have a sufficiently broad foundation, depending upon the depth of water in which they are placed, to be able to withstand the pounding of the seas without danger of overturning. The foundation mats, at least the outer ones, should be partly flexible rather than stiff or rigid, so that in the event of a close scour the outer portion will drop, and modify and possibly prevent further scour. In the estimates and designs submitted, I have estimated for a top 15 feet wide, with side slopes of 1 on 2, and always a berme 15 feet in width at the foot of this slope.
With regard to the kind of mattresses to be used in the jetties, we have on the Sabine and Neches rivers, within 50 miles of the pass, any amount of brush and logs, and at about 100 miles distant from the pass there are immense quantities of hard sandstone in the vicinity and on the line of the Eastern Texas Railroad where it crosses the Neches River. We can, therefore, have a choice of mattress material. Those constructed by Mr. Eads in the jetties of the Mississippi River consisted of willows and brush, confined by parallel layers of plank at top and bottom, the hamber being held together by hickory pins passing through the mattress and planks and then wedging the ends of the pins. This mattress is patented, and even were it not, it is probably no better and costs fully as much or more per cubic yard (in the history of the jetties by
Mr. Corthell it is given as $8.97 per cubic yard in place) than the Dutch mattress now being used by Colonel Mansfield on the Texas coast.
The next mattress to be considered is that designed by General Gillmore for use in the jetties at Charleston. Its detailed construction is not known to me, but taking the simple log raft composed of 12 inches diameter, logs each 30 feet long, and using poles for binders, and iron drift-pins for fastenings, taking the cost of the logs at the prices the mills are paying for them, we get the following as the cost of a mattress 30 by 60 feet in plan by 18 inches deep, loaded with stone: 60 logs, each 30 feet long = 1,800 feet, at 5 cents per foot ....
$90 00 300 feet of 6" poles, at 3 cents
9 00 300 drift-pins=198 pounds, at 4 cents per pound, driven.
7 92 64.4 cubic yards of stone to sink it, at $4 per yard....
257 60 Total
364 52 Making a volume of stone and logs of 3,600 cubic feet, or 1334 cubic yards, at a cost of $2.73 per cubic yard.
The Dutch brush and fascine mattress, as constructed by Colonel Mansfield at Galveston, assuming the cane to cost $5.25 per cord, brush $4.50 per cord, and stone $4 per cubic yard, which, I believe, are the prices now being paid, would cost about, for Wiepens
$24 09 Brush..
94 95 Labor and ropes..
65 00 44 cubic yards stone, at $4
360 04 Volume=30 X 6 X 21 feet=166.66 cubic yards=$2.16 per cubic yard.
The length of the west jetty projected on the map is 18,120 feet, its cubic contents to mean high-water level=374,141 cubic yards; if built to 6 inches below mean low-water its contents will be about 304,578 cubic yards. The east jetty, measured on the straight line, is 19,800 feet long; measured on the curved line, its length is 19,180 feet. Th contents of the straight jetty to mean high-water line=407,877 cubic yards; to 6 inches below mean low-water=336,468 cubic yards.
In the construction of jetties here it is probable that hearting mattresses can be used to within 3 or 4 feet of the surface of the water. If such be the case after the plant is available it is probable that they can be built in place at a cost of about $3 per cubic yard. At this price the West high jetty would cost.
$1, 122, 423 West low jetty would cost.
$913, 734 East high jetty would cost
1, 223, 631 East low jetty would cost.
1,009, 404 Totals ....
2, 346, 054 1,923, 138 To the above amounts, whether we build one or more jetties, should be added the cost of plant, consisting of a good tow-boat, scows, piledriver, powerful steam-pump and mattress-way, aggregating about $50,000. We shall also have to do considerable piling to compact the jetties, for which I estimate 3,103 piles, each 30 feet (average) in length, at $3 éach, driven = $9,309. It may also be necessary to dredge a channel between and above the jetties. The following estimate is for dredy. ing so that the channel shall be 20 feet deep by 100 feet bottom width, with side slopes of 1 on 2, which will carry us into the 18-foot channel inside the bar. The estimate is only a rough approximation, and is about 800,000 cubic yards; this at 20 cents would cost $160,000.