:
22
123. The following may be taken as the objects which have been aimed at and attained, and which we have kept in view in forming our conclusions ----
1. The improved facility for the propagatian of the tidal wave up the river. 2. The better direction of the ebb currents.
3. The improvement effected from a navigation standpoint.
124. The first of these points requires little explanation since, as is clear from an inspection of the plan, the tidal wave is now propagated through a single comparatively straight channel instead of through two channels, the deeper one of which was sinuous. In this connection it must be borne in mind that, at the date of the commencement of the works, the curvature of the Ship Canal was rapidly increasing, under the eroding influence of the tidal currents, and the disadvantages due to such curvature were becoming correspondingly accentuated.
125. The second point, viz., the better direction of the ebb currents, is also a matter of the greatest importance. Under the scheme as carried out, the ebb currents, after rounding the curve at the upper end of Gough Island, pass directly along the Astræa Channel to the Woosung curve, their energy being thus preserved and concentrated on the river outlet, instead of, as formerly, being largely dissipated in the mischievous erosion of the concave bank of the Ship Channel and in traversing the sharp reverse curve and the old Inner Bar. This sharp training and directing of the ebb currents should have the best possible effect in improving the Astraca Channel and in maintaining and increasing the depths already obtained at the Outer Bar.
126. From a navigation standpoint the advantages of the Astrava Channel over its predecessor are very apparent. The new reach is now one of the easiest in the whole river for navigation, and ocean-going steamers, which previously experienced such difficulties and danger from confused currents and ebb tides, at the low turn into the Ship Canal, can now pass up the river with perfect ease.
Relative Cost of Ship and Junk Channel Routes.
127. The chief ground on which those who favoured the Ship Channel, as the principal route for the river to and from Shanghai, based their arguments appears to have been that, by its adoption, a considerable saving in expenditure would have been effected. We have looked into this aspect of the question and cannot find that there would have been any substantial reduction in the quantities of the work to be executed, had the Ship Channel route been adopted, basing the calculation on the condition of the river as it existed at the time the operations were commenced---- in 1907.
128. By the adoption of the Ship Channel course it would no doubt have been practicable to have prolonged the period for the execution of the works, and thereby to have reduced, to some extent, the sum which was paid for interest, consequent on the raising of a loan for the more rapid carrying out of the Junk Channel works, speed being essential for the successful accomplishment of the latter undertaking.
129. We consider, however, that even in the cost of the works so involved in the opening out that and formation of the Astræa Channel were somewhat greater than that necessary for the development of the Ship Channel, the superiority of the former route fully justifies the additional outlay.
Cross Dams at Upper End of Ship Channel.
130. With regard to the exception which has been taken to the number of cross dams at the upper end of Ship Channel, as shown on drawing No. 2, the present state of progress of which has been referred to in paragraph 70, M. de Rijke las explained that in constructing the main parallel dam required for closing the Ship Channel he was extremely anxious lest damage or accident should occur in consequence of excessive scour at the foot of this dam, during constructions, and the more so having regard to the exceedingly soft nature of the bottom. In order to obviate this scour, which might have endangered the safety of the dam, he considered it advisable to provide the series of cross dams as shown on drawing No. 3, their object being, as previously described by M. de Rijke, to "subdivide the fall of the water," and so diminish the scour.
131. We think this view was a sound one in principle, but apparently M. de Rijke does not now consider, in the light of experience, that all the dams which he
* Not reproduced.
23
proposed will be necessary. Thus only four out of the six suggested have been commenced, and of these four, it is, as we understand, proposed to complete two only, known locally as I and C, and so indicated on drawing No. 2. In this decision.
we concur.
132. We fully appreciate his anxiety for the safety of the main parallel dam, during the difficult and delicate operations of diverting the course of so large and important a river as the Whangpoo, in constant use by ocean traffic to and from one of the largest shipping ports in the world. Any accident to the dam might have led to such disastrous results, that we consider the magnitude of the interests at stake fully justified the precaution which was adopted.
Woosung Fort Jetty Works.
133. We understand that before proceeding with the Fort Jetty works at Woosung M. de Rijke made careful inquiries with regard to the wave-stroke to which such works would be exposed, and that he designed the cross-section of the structure accordingly. Mr. Wilson and Mr. Matthews, when at Shanghai, were informed by the harbour-master that, in addition to typhoons, which occasionally occur, considerable "seas" were sometimes experienced at the entrance to the Whangpoo, and that lightering operations in connection with vessels lying in the roads had in consequence to be frequently suspended.
134. Having regard to these facts, and seeing that the "fetch" in the Yang-tsze, at high water, is very considerable, we can fully realise that the work may at times be exposed to a heavy wave-stroke, and therefore we cannot endorse the criticisms which have been raised with regard to there being any excessive strength in the Fort Jetty.
The Mode of Construction adopted for the Training Works.
135. During the progress of this investigation we have been much impressed by the successful manner in which various forms of fascine work have been employed in the construction of the training banks, cribwork groins, and other similar structures,
136. By the employment of zinkstuks, gabbioni, and corresponding forms of construction in the training works, M. de Rijke has been enabled to carry out his proposals with a rapidity and economy which would have been quite impracticable by the adoption of any other method.
137. In illustration of the rapidity of construction, we may observe that, from the commencement of the training works in February 1907 to the end of 1909, a period of thirty-five months, about 60,000 lineal feet of works had been put in hand, and well advanced, or on an average, say, 1,700 lineal fect per month. These figures, no doubt, include a large number of shallow cribs, of a light character, constructed across mud flats, but combined therewith heavy structures such as Fort Jetty, the main dam at Upper Gough, and the training works at Lower Gough and Kajow, have also been carried out.
138. In the appendix hereto* we give, in detail, a description of the mode of construction which was adopted in forming the different types of fascine work to which we have referred, and of the procedure which was observed when placing the same in position.
The Effects produced by the Works Executed.
139. We have already described, in section IX hereof, the results which have been produced by the works already executed, and which appear, on the whole, to be of an entirely successful character. The accumulation of silt between the cribs, which extend from the "normal lines" shorewards is, we understand, very noticeabic, and forms a satisfactory feature in the undertaking.
XIV. THE NECESSITY FOR CAREFUL MAINTENANCE OF THE WORKS. 140. It is necessary that we should here allude to, and emphasise, the absolute necessity for the due and proper maintenance of the works after completion. During the progress of the undertaking there has been no difficulty in keeping a watchful eye on the various works which had been previously constructed, but we are strongly of opinion that provision should be made for systematic and periodical * Not printed.
405