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Macomb as to his views upon the improvements that could be effected in the way of deepening the above river, except that our confidence in the maintenance of a 15-foot channel by the erosive power of the current was not as great as his. We also concurred as to the use of the north jetty to remove the bar in the Delaware at the mouth of the Christiana, with the following changes:
First. That the jetty be built at the present time only as far out as the 12-foot curve. It was thought quite probable that the erosion would extend a little beyond the jetty's end, but whether it would or would not it seemed very suitable to let its extension be dependent upon the successful maintenance of 15 feet depth of channel to Wilmington.
Second. To make the jetty more effective it was proposed to raise it to high-water (mean high-water).
Third. As the portion above low-water would be alternately immersed and exposed to the sun's rays, this Board suggested that the pile structure of Colonel Macomb's project should be terminated as near the ordinary low-water as "economy of construction will admit, and to put on a superstructure of crib-work rising to high-water. This last when decayed can be removed." Now the ordinary rise and fall of the tide at this place is 5 feet 6 inches. As the finished pile structure will rise about 1 foot 6 inches above mean low-water, the superstruct ure will be but 4 feet high. A method of construction in conformity with our design is exhibited on accompanying sketch. By the change thus indicated the Board thought that oak might be dispensed with and much saving effected.
Fourth. It was also suggested that while the width of the jetty as originally designed by Colonel Macomb would endure all ordinary pressures it might be insufficient as against ice floes. The widening by the Board bore reference to the possibility of its being subjected more or less to ice piled upon it or borne down against it by reason of rising river, excessive currents, and high storm winds. The experience on the Hudson was the Board's guide in suggesting additional width of sec tion to jetty at the mouth of the Christiana. The question was fully discussed whether to make a return as a protection against ice or to widen the jetty. It may not be necessary to widen the inshore portion where the ice grounds. If the constructing officer, however, knows, from his own experience, that there is no danger to his jetty from ice floes, there seems to be no reason why he should not build it with the width shown in his project. Stone is in our opinion altogether preferable to mud for filling between the piles.
We submit the following as an approximate estimate:
One thousand four hundred and seventy feet long and extending to 12-foot curve, and rising to level of mean high-water.
1,286 feet 1-inch bolts, 1,960 feet 1-inch tie rods, 10,800 pounds, at 6 cents...
Stone, 12,675 cubic yards, at $1.75..
648 00 22,988 27 22, 181 25
45, 169 52
The timber, piles, &c., are at the contract prices for the Savannah River. The price of stone is assumed at 75 per cent. greater than contract prices on Long Island Sound, and more than twice as great as those paid on the Hudson River.
The Board presents the annexed sketch to accompany its estimate and to show how its results were obtained. Respectfully submitted.
Z. B. TOWER,
Colonel of Engineers, Bvt. Maj. Gen.
Colonel of Engineers, Bvt. Maj. Gen., U. S. A.
Lieutenant-Colonel of Engineers, Bvt. Brig. Gen.
Brig. Gen. H. G. WRIGHT.
Note: 20% more stone than shown in this
IMPROVEMENT OF BROADKILN RIVER, DELAWARE.
In the last Annual Report a full exhibit was made of the condition and circumstances of the Broadkiln improvement, and recommendation was made that the application of the available balance of the appropriation be deferred until further action of Congress. Such action not having yet been taken, the matter remains as last reported, no reasons having presented themselves for altering the recommendations then submitted and approved.
This work is in the collection district of Delaware, Wilmington being the nearest port of entry, the revenue collected there during the past fiscal year amounting to $50,530.
The nearest fort and light-house are, respectively, Fort Delaware and Delaware Breakwater light.
Total amount appropriated to June 30, 1882..
Total amount expended to June 30, 1882.
July 1, 1881, amount available.....
July 1, 1882, amount available..
Amount aopropriated by act passed August 2, 1882..
Amount available for fiscal year ending June 30, 1883...............
Amount (estimated) required for completion of existing project......
IMPROVEMENT OF MISPILLION CREEK, DELAWARE.
11, 022 42
13, 977 58
The improvement of this stream was begun in 1879, with an appropriation of $3,000, and continued with the further appropriation of $4,000 in 1880. The general plan was to remove the shoals in succession downward from the head of navigation to a depth of 6 feet at lowwater, and a width of 40 to 50 feet.
The details of operations are given in the Annual Reports of the Chief of Engineers for 1880 and 1881.
During the past year, with the appropriation of $3,500 in the act of March 3, 1881, the work has been continued in accordance with the project. Contract was made and the work begun May 26, 1882, and continued until July 1, 1882.
During this time a channel of the prescribed width and depth was made through the "Mushpot Shoal," a distance of 950 yards, requiring the removal of 5,550 cubic yards of mud which were deposited upon the bank. A similar channel was made through the "Fork Shoal," and an additional 793 yards removed, making a total of 6,343 cubic yards.
In addition to appropriating for the improvement, the act of March 3, 1881, provided for a survey of the mouth of the stream, report of which has already been submitted, and will be found elsewhere, herewith.
In the case of the Mispillion, as in that of most of the minor streams in Delaware tributary to the bay, the entrance is shallow, and its deepening both the most costly and important part of any valuable improve
The work already done in the stream itself has had, however, a cer
tain beneficial effect in relieving the vessel-builders from the annoyance and expense of the delays heretofore encountered in getting their vessels down to the bay. These delays, in frequent cases, absorbed the profits of the builders, and seriously limited the dimensions of the vessels for which contracts could be made. Ship-building at Milford has during the last two years shown a considerable increase, and several vessels of from 400 to 1,000 tons were built during the last year. Three more are constructing, and several others are under contract. The business of the stream is reported to have increased about 25 per cent.
For the completion of the present project of a 6-foot low-water navigation to the mouth, there will be required the sum of $6,500. It will always remain, however, to open the mouth of the stream to such extent, at least, as will admit of the entrance and exit of loaded vessels near the period of high-water. In this connection attention is invited to the accompanying report of the survey of February 20, 1882.
To secure an available entrance depth of 4 feet at mean low-water would cost about $55,000, or for a 3-foot low water entrance, which with the rise of the tide would admit vessels drawing 7 feet, about $49,000.
Mispillion Creek is in the collection district of Delaware, Wilmington being its nearest port of entry, the revenue collected there during the past fiscal year amounting to $50,530.
Mispillion Creek light is the nearest light-house, and Fort Delaware the nearest
July 1, 1882, amount expended during fiscal year, exclusive of
outstanding liabilities July 1, 1831.
July 1, 1882, outstanding liabilities.
July 1, 1882, amount available..
Amount appropriated by act passed August 2, 1882.
Amount available for fiscal year ending June 30, 1883..
Amount (estimated) required for completion of existing project....
Amount that can be profitably expended in fiscal year ending June 30, 1884. 3,500 00
Abstract of contract entered into during fiscal year ending June 30, 1882, for improvement of Mispillion Creek, Delaware.
UNITED STATES ENGINEER OFFICE,
SIR: The following report on the examination of the mouth of Mispillion Creek, Delaware, is submitted, in compliance with the requirements of the river and harbor act of March 3, 1881.
With a navigable length of about 18 miles, and discharging into the Delaware Bay about the same distance north-northwest from Cape Hen
lopen, Mispillion is one of the more important of the Delaware streams, by reason of its considerable ship-building industries and the high repute of its native white-oak timber.
The original examination of this stream was made in 1878, and the report printed in Annual Report Chief of Engineers, 1879, pp. 467–470. The improvement of the navigation, in progress since 1879, in accordance with a project of that date, under small annual appropriations, aggregating $10,500, has been confined to the removal of shoals in the creek, beginning at Milford, the head of navigation and the site of numerous saw-mills and ship-yards, where vessels of over 1,000 tons are built. The details of operations are given in Annual Reports Chief of Engineers, for 1880, pp. 587-589, and for 1881, pp. 785 and 786.
As is the case with nearly all the streams tributary to Delaware Bay, the most serious obstruction to navigation is found at the entrance, the chart of which, from a survey of last season, is forwarded herewith.
It will be seen that the low-water contours of 2, 4, and 6 feet in the bay lie approximately parallel to the shore, at distances, respectively, of about 3,000, 4,000, and 5,000 feet, without any indication of a channel across the intervening shoals. The trend of the shore line is about north by east. All winds from the northward and eastward, therefore, tend to supplement the action of the ebb-tide of the bay in the gradual transfer of sand and mud southward along the shore.
Under these circumstances, the effluent current from the creek is deflected, and by the loss of power from constant choking is able to maintain an entrance depth of from 1 to 13 feet only at low water, by following the shore half a mile southward.
The short line of pile dike, shown on the chart above the entrance, is the evidence of an ineffectual attempt by the local authorities, some twenty years ago, to guard against further encroachments due to the littoral movement of sand.
The design was correct in theory, but the dike, both in development and construction, was manifestly inadequate to modify the action of the forces in operation.
For the maintenance of a channel entrance of any desired depth, it is necessary not only to prevent the intrusion of sand at the mouth, but the transporting and distributing action of the waves and tidal currents. of the bay as well.
For these purposes, after determining the line, a jetty should be built, starting from the north side of the entrance, with a reliable shore connection, and extending out into the bay to at least the depth desired. Along this jetty the channel may be dredged to such depth and width as shall make it available for the vessels which are to use it.
The low-water navigation in the Mispillion is about 6 feet, and under ordinary circumstances it would be desirable to continue this depth into the bay, but the rise of tide in the bay is about 4 feet, while at Milford the rise does not exceed 23 feet.
The entrance depth, therefore, might be reduced to 4 feet at low-water without serious disadvantage and with a large saving in the cost of the necessary works.
The distance from the shore to the 4-foot low-water contour in the bay is about 4,000 feet, and a jetty of this length will be required. Its posi tion and plan are shown on the tracing.
The jetty should be built to about high-water, with its shore end suitably secured by riprap or loaded brush.
The inner 2,500 feet of length may be straight, the outer 1,500 slightly curved southwardly.