JOURNAL

OF

THE FRANKLIN INSTITUTE

OF THE

State of Pennsylvania,

AND

MECHANICS' REGISTER.

DECEMBER, 1841.

Civil Engineering.

Description of the Bear Trap Sluice Gates of the Lehigh Descending Navigation. By ELLWOOD MORRIS, Civil Engineer.

The public are indebted to the inventive genius of Josiah White, Esq., President of the Lehigh Coal and Navigation Company, for the admirable hydrostatic contrivance which has received the singular name of Bear Trap.*

These sluice gates were devised under the following circumstances: in the year 1818, Messrs. White, Hauto, Hazard, and others, associated themselves under the style of the "Lehigh Navigation Company," for the purpose of improving the Lehigh river by means of wingdams, &c., so as to form a descending navigation suitable for the transportation of coal from the Anthracite mines, near Mauch Chunk, to the city of Philadelphia.

This work was commenced upon the 10th of August, 1818, as appears by the "History of the Lehigh Coal and Navigation Company, published by order of the board of managers in 1840," and did not originally contemplate the use of sluice gates as a primary expedient; the residents upon the margin of the Lehigh river having pointed out "a certain mark in a rock at the Lausanne landing," as the low-water level of the stream, Messrs. White & Co. were induced to

* The writer is indebted to Josiah White and Erskine Hazard, Esqs., for the opportunity of examining the drawings in the office of the Lehigh Company, and for the personal expla nations which have enabled him to draw up, for the Journal of the Franklin Institute, the present account of the Bear Trap Sluice Gate.

VOL. II, 3RD SERIES.-No. 6.-DECEMBER, 1841.

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believe that there would always be a sufficiency of water for their purposes, if it were "confined by wing-dams in its passage over the ripples, or shoals, from pool to pool," and under this impression the work was begun; but in the autumn of 1818 "the water in the river fell by an unparalleled drought, as was believed, fully twelve inches below the mark which has been mentioned as shown by the inhabi tants to be the lowest point to which the river ever sunk. Here was a difficulty totally unanticipated, and one which required a very essential alteration in the plan. Nature did not furnish enough water by the regular flow of the river, to keep the channels at the proper depth, owing to the very great fall in the river and the consequent rapidity of its motion. It became necessary to accumulate water by artificial means, and to let it off at stated periods, and let the boats pass down with the long wave thus formed, which filled up the channels. This was effected by constructing dams in the neighbourhood of Mauch Chunk, in which were placed sluice gates of a peculiar construction, invented for the purpose by Josiah White, one of the managers, by means of which the water could be retained in the pool above, until required for use. When the dam became full, and the water had run over it long enough for the river below the dam to acquire the depth of the ordinary flow of the river, the sluice gates were let down, and the boats, which were lying in the pools above, passed down with the artificial flood."

It was to meet the exigency created by the discovery above mentioned, that Mr. White contrived the beautiful sluice gate, which we are about to describe, and upon the successful operation of which, the whole enterprise very much depended.

At that day the scene of the company's operations was almost a perfect wilderness, and the carpenters having been set at work to frame a sluice gate for trial, it became an object of great curiosity to the settlers; who being far more familiar with the implements used in the chase and capture of the beasts of the forest, than with the hydraulic works of a flash navigation, either in jest, or from some fancied resemblance of the sluice gate to a Bear Trap, quickly gave to it this cognomen, which it ever since has borne.

The Bear Trap Sluice Gate, which is exhibited in plan and section in the annexed diagrams, consists of two leaves or shutters, reclining against each other so as to present a triangular vertical section, and contain beneath them a space capable of being filled with water from the superior level and emptied thereof at will; the contained angle at the vertex when the gates are up being rather more than 100°, in order that the leaves may slide easily, one over the other, which they evidently would not do if the vertical angle of the uplifted gate were

either a right or an acute angle; this sluice gate is raised and depressed by hydrostatic pressure, applied and removed upon the principle of that well known philosophical instrument called the Hydrostatic Bellows; in its usual form, as applied upon the Lehigh, it will not work in dead water, but requires the action of a head more than sufficient to overcome the weight and friction of the gates, to enable it to be manœuvred with facility.*

By an inspection of the diagrams it will be perceived that the leaves of the gate are hinged horizontally with hollow quoin joints, at some distance above the floor; the hinge of the upper leaf being higher than that of the lower, by something more than its thickness, so that even when the gate is down there is a vacant space into which the aperture opens from the well C, because the height of the hinge of the lower leaf is fixed at about the same level as the tops of the openings communicating with the well.

Catch blocks on the underside of the upper leaf determine the height to which the rise of the gate is limited; the well C is constantly in communication with the vacancy beneath the gate; the water chamber B, is constantly open to the water from the upper level, whilst that of the lower level flows freely into the chamber D; it will be observed that both these chambers communicate by suitable wickets with the well C; now it will be evident from inspection that if the wickets F, between C and D are shut, whilst the wickets E between C and B are opened, the water from the upper level will enter beneath the leaves with the upward hydrostatic pressure due to the head, and the gate will consequently rise; now on the other hand if the wickets E are closed, whilst those at F are opened, the downward and lateral hydrostatic pressure of the water in the upper level, acting then upon the top surface of the upper leaf, will force down the gate; and thus by simply putting the vacancy beneath the leaves of the sluice gate, in communication separately with the upper and lower levels alternately, the gate is elevated, depressed, or arrested at any stage of its movement, by hydrostatic pressure alone; the only manual labour or attention needed for the highest and widest gates, being that which

* Mr. English, formerly a contractor upon some of the works of the Lehigh navigation, having for many years observed the action of the Bear Trap Sluice Gates, has conceived the idea of rendering them applicable as the upper gates of Lift Locks, by placing a large air vessel under the lower leaf, which by its buoyancy enables the gates to rise in dead water: and he has exhibited at the Franklin Institute a working model of a lock having the Bear Trap Gates with his attached air vessel applied as upper gates; and, though liable to some objec tions there is reason to believe that for the upper, if not for both, gates of Lift Locks only, they will prove to be a valuable improvement, though it is evident that the same object may be attained; by the application of counter weights, but not perhaps as well as by an air vessel.

is requisite to manœuvre the wickets E or F, a duty for which a mere boy would be physically competent.

The sluice gates used upon the Lehigh descending navigation, as there is no necessity of making them perfectly water tight, are allowed a play on each side of half an inch or more, which effectually prevents lateral friction; they are generally twenty-four feet wide, formed by spiking together three successive layers of thick plank, and the lower leaf is strengthened by bolting upon its back a few heavy beams, (as may be seen in the sketch annexed,) which rest their extremities against suitable stops when the gate is up.

Where the water, violently descending the sluice, leaves the platform, it usually excavates the bed of the stream and forms deep water, the sudden entrance into which, of boats shooting down the sluice, would prove very injurious to, or even destroy, them, if it were not for the ingenious device called fingers; these consist of the trunks of trees placed side by side, and bolted to heavy subsills, with their butts up-stream, the tops freely projecting over the lower sill some twenty feet or more; they receive in part the shock of the boat in its plunge into the deep water, and by their elasticity ease off its momentum so that it glides down with the swift stream uninjured; this dexterous mode of avoiding concussion, is found in practice fully to answer the end for which it was designed.

For the purpose of guarding the horizontal hinges of the leaves of the sluice gates against obstruction from the deposition of gravel, a glove of plank is ingeniously secured across the hinge by a curved spring, as shown at G, and in contact with this plank glove, the leaf revolves upon its hinges, without the possibility of being impaired in its action by the lodgment of hard substances.

From the above description and the annexed sketches, which are designed more to develope the principle of the sluice gate, than to display all the details of its construction, it is hoped that the plan and mode of action of the Bear Trap Sluice may be gathered without further explanation, and we will now proceed to make a few remarks upon the great usefulness of this invention.

Utility of the Bear Trap Sluice.

This skilfully devised hydraulic machine, continued in use upon the lower Lehigh-giving perfect satisfaction in practice-from the year 1821 until 1829, when the descending navigation upon the main part of the river, was abandoned for an improvement which admitted of transit in both directions: though a section upon the former plan, with its Bear Trap Sluices, still forms the navigation for the lumber trade between Whitehaven and Stoddartsville, a distance of twelve and one