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Upper Gough Works.
67. At the upper end of Ship Channel the main parallel or longitudinal training work starts from the eastern bank at the lower side of Kajow Creek, crosses obliquely the upper end of the old Ship Channel, and continues along the western margin of Gough Island for a length of about 900 feet, following the "normal line" laid down for this bank of the river. It consists of a parallel dam of strong "zinkstuks" construction, The stone brought up to about low-water level, and covered with a stone bank.
work was, at the beginning of this year, brought up to high water for a distance of 3,200 feet from the upper end of Gough Island, up to low water for a further 300 feet, and up to 11 feet below low water over the remainder of its length. The formation of the upper portion of the work to high-water level was being actively prosecuted, and, we understand, at this date is practically completed.
68. A portion of the main parallel dam ät Upper Gough has been backed with dredged material to the extent shown by green colour on the drawings, the dredgings having been pumped into an area enclosed for the purpose of retaining dams of "zinkstuks" by two cross dams, into three parts, and the dredgings were pumped up to a level of about 17 feet above low-water ordinary spring tide.
Dams across Ship Channel.
69. In addition to the reinforcement of the main dam by the backing of the lower length as just described, M. de Rijke's scheme provided for the construction of a series of six cross dams athwart the Ship Channel near its upper end with a view, as described by himself, of "subdividing the fall" of the water flowing over them, and thus avoiding the scour of the bottom adjacent to the main dam by reason of an unbroken "overfall of the water.
70. During the construction of the works the foundations of only two of these cross dams have been deposited, two others have been omitted altogether, whilst the remaining two have, we are informed, been brought up to low water within the last few weeks.
Kajow Crib-work,
71. The work at Kajow consists of three strong cribs, connected at their outer ends by a parallel work 1,350 feet in length, composed of zinkstuks, finished above low water with a bank of rubble stone. The object of this structure is to initiate the diversion of the ebb current by leading the same clear of the upper end of the main parallel dam at Upper Gough.
Subsidiary Works.
72. Further works have been constructed, in this reach, on both sides of the river, consisting, as shown by green colour upon the drawings, of crib of varying dimensions, terminating with lengths of parallel work constructed on the "normal lines." These works are, for the most part, built with a foundation of zinkstuks and a superstructure of gabbioni and laagwork, the surface being protected with a covering of rubble stone. The parallel works are in almost all cases brought up to a level slightly above low water, the object being to retain the low-water flow within the "normal lines" without diminishing the tidal capacity of the right bank of Ship Channel during the construction of the works required for the opening out of Junk Channel, a few light revetments and other works were constructed, but these subsidiary works are not shown upon the drawings.
Dredging in Junk Channel.
73. The opening of the new deep-water track through Junk Channel was mainly accomplished by means of dredging. Bucket dredgers only were employed in the channel itself, as the material was found to be of too fine a nature to be deposited into barges or hoppers by sand pumps, and the depositing grounds were not so placed as to admit of the use of shore delivery pipes. One pump dredger was, however, specially equipped for reclaiming purposes by being adapted for pumping out hoppers which had been filled by the bucket dredgers.
* Not reproduced.
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74. The quantity of material dredged, and in process of being dredged at the commencement of the year, is as follows, the measurement being computed in hoppers :-
Original contract Extra work
++
New contract (in execution)
Total
(Say, 8,000,000 cubic yards.)
Cubic yards.
6,666,700
25,400
1,200,000
7,892,100
VIII-DESCRIPTION OF WORKS PROPOSED BUT NOT YET EXECUTED.
75. It is necessary that we should now refer to the works, shown by red colour on the drawings, which are considered necessary by M. de Rijke, for the full completion of his scheme for the improvement of the Whangpoo, but which have not yet been
commence d
Training Works opposite Woosung.
76. The works proposed to be constructed at the mouth of the Whangpoo, on the right bank, have for their object the further directing of the tidal flow across the site of the Outer Bar, and also, more especially, the prevention of the development of a separate flood channel, close inshore, to which reference has already been made in paragraph 32. As previously described, such a channel has at various periods developed from natural causes, to a greater or less extent, but manifestly to the detriment of the depth on the Outer Bar. At the beginning of the year there were indications of this inshore channel again opening.
77. The works proposed, in order to counteract this tendency, consist of a curved parallel bank 5,000 feet in length, to be constructed along the "normal line" at the mouth of the river on its eastern side, and connected with the shore by four cribs. The character of construction would be substantially the same as that of the corresponding works on the left shore, but without the concrete block-work protection. M. de Rijke, for purposes of economy, proposes, in the first instance, to carry out only the cribs and two short lengths of parallel work, relying on the game to break the inshore flow of the flood to which reference is made above.
Cutting Back of Pheasant Point,
78. After the training works described in the last section have been carried out, it is proposed to dredge the accumulation at, and in the vicinity of, Pheasant Point, to the extent shown on the drawings. We understand it is not intended to proceed with this dredging until the training works, described in the preceding paragraph, are completed, as otherwise it is considered that full advantage of the dredging would not be obtained, inasmuch as one of the alleged main causes of the accumulation at Pheasant Point, viz., the inshore flood current charged with silt from the Yang-tsze, as already described, would not have been cut off. The dredging proposed by M. de Rijke amounts to a total of 2,650,000 cubic yards, and would be removed in three belts, having depths of 9, 15, and 18 feet respectively, at low-water ordinary spring tide.
Training Works at Point.
79. Above Gough Island, training works are proposed for the left bank as far as Point, consisting of long cribs stretching from the shore out to the "normal line," connected at their outer ends with lengths of parallel work. The object of these structures is to confine the low-water flow to the main channel, and to prevent the further development of an inshore flood channel which already exists, with a depth of about 9 feet at low water.
80. On the right bank, between Kajow Creek and Cosmopolitan Dock, small cribs are proposed with lengths of parallel work on the "normal lines," for the preservation of the river bank which over this length is in places very insecure,
Accumulation opposite Cosmopolitan Dock.
81. Above Point and opposite Cosmopolitan Dock, there is a considerable accumulation forward of the "normal line" as shown on drawing No. 1,* which * Not reproduced.
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