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inspections now that the works are drawing towards completion. The requisite plant and facilities, and also a competent staff should be likewise provided, such as may be required for the speedy and effective carrying out of such renewals as may be required from time to time.
Prompt Repairs essential.
141. Works of this character will certainly require repairs and renewals, the more so as they are laid on a sandy and alluvial bed. It is essential that such repairs and reinstatements as are found to be necessary should be promptly under- taken, as otherwise damage might arise, causing the breaching of the banks, which would readily have been arrested, at trifling cost, by timely repairs. If neglected such damage might lead to serious results, and a possible loss of much of the good effect which has undoubtedly been secured. On these grounds, therefore, we would strongly recommend that the question of the adequate and continuous maintenance of these important works should without loss of time be duly considered, and suitable provision made accordingly.
142. The present depth along the face of the main parallel dam at Upper Gough averages about 25 feet, and nowhere, we understand, does it exceed 29 feet at low water. It is satisfactory to observe that there does not appear to be any tendency to scour along this length of the work of a character likely to endanger its safety.
As to the Maintenance of Depth in the Astrea Channel.
143. The present cross-sectional area in the Astrea Channel is considerably less than that at, or in the vicinity of, Black Point; the latter, as already stated, having been adopted as a standard when fixing the "normal lines." The respective sectional areas in December last were approximately 32,000 square feet in Black Point Reach, the values of the two sections from a point of view of conductivity being, at the We understand that same date, in the proportion of about 75 to 100 feet. M. de Rijke does not consider that the régime of the Astræa Channel is at present quite satisfactory, but we gather from his quarterly reports to the Conservancy Board that there was a steady increase in cross-sectional area up to the end of December in last year when, as stated in paragraph 92, there was a depth of 18 feet at low-water ordinary spring tides for a width of about 950 feet between the "normal line" for the full length of the channel.
144. We have very carefully considered what effect that natural scour of the river may be expected to have on the maintenance of this depth in the Astræa Channel and are of opinion that if, in the first place, a channel of adequate and properly proportioned cross-sectional area be provided by dredging, there is no reason to anticipate that any large amount of dredging will be required to assist the natural scour in maintaining it. The data available at present are insufficient to enable us to express a very definite opinion on this point, but we certainly incline to the view, from general experience, that the channel should maintain itself to the 18 feet depth with but little, if any, and from dredging. An important fact favouring this view is that referred to in paragraph 93 of this report, viz., that during the process of dredging the Astræn Channel large quantities of material have been removed by the current over and above that excavated by the dredgers, thus indicating that there is apparently surplus of scouring power for the maintenance of the channel.
145. The quantity of water, moreover, which now runs into the cul-de-suc formed by the old Ship Channel, should as this latter becomes filled by the process of natural silting be largely diverted through the Astræa Channel, thus adding to the tidal volume in the upper part of the river and forming an additional scouring medium for this channel. The silting process referred to will also be assisted by the depositing of dredging in the Ship Channel, which is a convenient site for that
purpose.
As to the Upper River and Creeks.
146. We strongly endorse the remarks by M. de Rijke on the serious results to be apprehended from the want of care and interests shown in the upper river and in the creeks subsidiary to the Whangpoo, to which the regrettable condition of affairs referred to in paragraphs 44 and 45 hereof is to be ascribed.
XV.-OPINION WITH RESPECT TO THE FURTHER WORKS PROPOSED BUT NOT YET COMMENCED.
147. We have now to investigate the further works which have been suggested for the training of the river and propose to deal with them under three heads, viz. :--
(1.) Works which we consider to be essential in order to permanently secure the benefits already derived from the undertaking as carried out to date, for which funds should be at once obtained.
(2.) Works of importance, for the construction of some of which, at all events, the necessary funds should be provided as early as possible.
(3.) Works which for the present need not be proceeded with, though ultimately some of them will be required.
Head 1.
148. Works which we consider to be essential in order to permanently secure the benefits already derived from the undertaking, as carried out to date, for which funds should be at once obtained. Under this head we would include the following:-
(a.) The final closing of the old Ship Channel by the completion of the main parallel dam above Upper Gough to the level of high-water level spring tide and the completion of the double-cross dam No. 1.
(6.) The full carrying out of the present dredging contract of 1,200,000 cubic yards.
Head 2.
149. Works of importance, for the construction of some of which, at all events, the necessary funds should be provided as early as possible.
Under this heading we would include the whole of the training works proposed by M. de Rijke on both sides of the river between the upper end of the Astræn Channel and Cosmopolitan Dock. It will be seen that the principal object of the works on the left bank is to fix the channel of the river within the "normal lines" as laid down, and thus to prevent the formation of an inshore or flood channel between Long Flat and Point. As previously mentioned in this report (paragraph 78), a shallow channel exists along this shore which, if it were to develop to any great extent, would be detrimental to the main waterway. The works shown on right bank of the river consist, as will be seen, of short cribs and parallel work, their object being to protect the river bank, which in many places over this length, and especially between Tung Kow Creek and Black Point, is in a wasting condition.
150. Under this head we place the training works on the right bank of the river below Pheasant Point. At the present moment we are not convinced of the desir- ability or necessity for these works, but if future experience indicates that the Fort Jetty is not sufficient by itself to maintain the deep-water channel at the confluence of the Whangpoo with the Yang-tsze, and that the formation of a channel on the oppo- site shore is followed by a loss of depth on the main channel, it may be necessary that that be constructed. As regards the dredging on the convex side at Pheasant Point, it may be noted that the channel there, for the full width required for navigation, has already a depth of 18 feet, so that, from this point of view, no addition is required. Moreover, it is very questionable whether this dredging would have any permanent result, as experience shows that shoaling rapidly recurs on the convex side under similar circumstances.
As to Works mentioned under Heads 1 and 2.
151. If the works above enumerated, under heads 1 and 2, be dealt with as suggested, the river may then be considered to be in a sufficiently satisfactory and stable condition from Shanghai to its mouth. In this connection we may add that all those interested in the river who have been consulted considered it was essential that the training of the river should eventually be completed up to the point to which it is proposed the works should be carried, i.e., Cosmopolitan Dock.
Η [2958 kh-1]
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