Tabular exhibit of trials of the crushing strength of ice under conditions, as regards temperature, &c.—Continued.

F 21.

DELAWARE BREAKWATER HÅRBOR.

The history and character of this harbor, and its value in particular to the coasting trade of the United States, have been explained and dwelt upon in numerous Annual Reports, special attention baving been given it in the Annual Report for 1879, and subsequently.

The constantly progressing diminution in depth from the gradual rise of the bottom, and the relative decrease in the available area in proportion to the amount of commerce seeking shelter, demand that remedial measures shall be applied for the protection and reclamation of the harbor, unless it is to be surrendered to the destructive action of natural forces, and the expenditure hitherto made upon it be abandoned. The two works sheltering the anchorage and composed of massive piles of pierres perdues are in about the same condition as when left in 1869, since which time no expenditure has been made upon them. Their partially unfinished condition, however, does not impair to any serious extent the service which they were designed to render, and their completion may well be deferred until more important measures shall have been inaugurated.

The act of March 3, 1881, ordered a survey of the Delaware Breakwater Harbor and of the entrance thereto. This survey was made during August and September, 1881, and the chart, plotted on a scale of 800 feet to the inch, is submitted herewith. The area covered is about 18 square miles, and includes both the inner and outer roadsteads, and the shoal known as "The Shears," under the cover of which the large vessels now usually anchor.

In comparing the present hydrography north of the break water with that shown on the Coast Survey chart of 1843, no changes of magnitude are observed. The position of the fathom contours exhibits no notable variation. The "Shears" have about the same position and development as in 1843, with their outer points at about the same distance from the breakwater works. So also the 12 and 18 foot contours off the mouth of the Broadkiln appear to have undergone little change.

In the interior of the harbor, however, the filling, particularly between the breakwater and the shore, exhibits a considerable shoaling, which is a measure of the physical deterioration of the harbor. The decrease in depth varies from 3 to 5 feet, with an average of about 4 to 4 feet. The 24-foot curve which formerly, and even so lately as 1877 (see comparative chart accompanying my report of May 15, 1878, Annual Report Chief of Engineers, 1879, page 457 et seq.), penetrated from the cape nearly to the head of the government pier, now curves from the cape to the east end of the breakwater without connecting with the isolated pool, which is in process of filling up. The shoals under the breakwater and off the Old Dominion Pier have attained to large dimensions and the anchorage has become suitable only to the lighter class of vessels. In other words, the processes hitherto reported have been in regular and steady operation, and their effects serve only to emphasize the necessity for the adoption of counteracting measures.

In the river and harbor bill now under consideration by Congress, provision is made for beginning these by closing the "gap" between the ice-breaker and the breakwater, and should appropriation be made there can be no doubt as to the desirability of completing this work as rapidly as possible.

The arguments for its construction are mainly two, viz:

1. The necessity for increasing the area protected against northeast gales which now enter freely through the "gap."

2. The prospect of checking the shoaling behind the breakwater by compelling the large portion of the ebb which now escapes through the "gap" to traverse the harbor and pass out by its eastern entrance.

The effect of the former provision is positive in at once doubling the useful frontage of the work. The results to be anticipated in retarding shoaling between the breakwater and the shore are less clear.

If, as is suggested in my former reports, the material in course of deposit in the harbor is derived not from the deep water outside and to the eastward, but from the less depths to the west and north under the disturbing influences of the winds and tides from that quarter, an increased flow of the ebb tide, while it may reasonably be expected at first to reduce the shoaling near the breakwater and even temporarily to remove a portion of the material already there, may eventually serve to increase the deposits by augmenting the transporting forces.

However this may be, and whatever the ultimate remedies to be applied to meet this difficulty, the closing of the "gap" must under any circumstances constitute an indispensable part of any project for the improvement of the harbor, and time will thereafter be afforded for further operations, to be based upon frequently renewed examinations and careful study.

The wrecks which for some years have obstructed the western portion of the harbor and made its use dangerous have been removed, as elsewhere reported. It is proper to say that if the work of closing the gap be seriously entered upon, the annual appropriations therefor should be such as to enable the Engineer in charge to prosecute the work without intermission, and have such amount of funds at his disposal as to secure contracts for the delivery of large quantities of material required at favorable economical prices. The annual sum available ought not to be less than $150,000 yearly for four years, and the work could be done to much better advantage in three years with appropriations of $200,000 each.

A project and drawings showing details of the means proposed for closing the "gap" accompany this report.

This work is in the collection district of Delaware, Wilmington being its nearest port of entry.

Fort Delaware and Delaware Breakwater light are respectively the nearest fort and light-house.

Total estimated cost of project (for closing the "gap").....

$675,000

Money statement.

Amount appropriated by act passed August 2, 1882..

Amount (estimated) required for completion of existing project..

$125,000

550,000 Amount that can be profitably expended in fiscal year ending June 30, 1884. 200,000

GENERAL PROJECT FOR CLOSING THE "GAP" IN THE DELAWARE

BREAKWATER HARBOR.

The width of the "gap" or opening between the "ice-breaker" and the "breakwater" is about 1,390 feet, and the depth at mean low-water on the line joining the two varies from 25 to 43 feet.

The tidal currents through the gap have velocities of from 2 miles to 4 miles per hour, and the seas from the northeast traverse it freely. With appropriation sufficient in amount to warrant the commencement of the work-say, $150,000 to $200,000, to be yearly repeated