Popular Science Monthly/Volume 72/February 1908/A Visit to the Hangchow Bore I
|A VISIT TO THE HANGCHOW BORE|
CANTON CHRISTIAN COLLEGE
Unlike the bores seen elsewhere, which generally occur intermittently, the Hangchow bore ascends the river at every tide, though its magnitude and speed vary considerably with the general state of the tides, and semi-monthly maxima are attained at the third tide after each new and each full moon. The latter affords a better opportunity to witness the bore under the more impressive and majestic stillness of midnight and the light and shadow of a moonlit scene. These semi-monthly maxima themselves attain greatest intensity at the times of greatest tides. Of these the autumnal equinox is preferable because of the cool and most probably fair weather and the absence of mosquitoes. The eighteenth of the Chinese eighth month is
generally reckoned as the time of the greatest bore of the year. In the fall of 1906 the writer spent the first and second days after the seventh full moon (September 6 and 7) in close observation of one midnight and two noon bores.Although observers sometimes go to Kanpu beyond the mouth of the Ch'ien-tang Kiang, and others content themselves with a view from Hangchow, from the first of these places the bore is seen when not fully formed, its two initial sections not yet united, while at Hangchow the effect, though still fairly remarkable, has completely lost its grandeur; and the best and most easily reached vantage ground is at the Haining Pagoda, though it is likely that at a point some five miles below the pagoda the bore is of even greater grandeur. This is close to where the two branches of the furious "Serpent's Head," as the
Chinese call it, meet, and some observers have reported thirty feet for its height there as against nine feet reported at the pagoda for the same bore, though we suspect that they refer to the height of the temporary waves caused by the impact of the two branches, and not ±o the height of the bore-front proper.
The Journey to Haining
Haining lies within and near the northwestern side of the equilateral triangle formed by Hangchow, Ningpo and Shanghai, and is readily reached from the last named by means of a so-called canal "train," a steam-launch towing three to six boats of various kinds. One may hire a horse-boat, Chinese or foreign style, or, as we did, take a cabin on one of the native passenger barges operated by the launch companies. Small cabins for two cost five dollars, Mexican, from Shanghai to Hangchow, and a very large one, enough for a party of six or eight, may be rented for twelve dollars, Mexican, for the one way. House-boats cost upwards of five dollars, Mexican, a day, according to size and fittings, and towing is extra.
Two or three of these launch-trains leave Shanghai from their landings in Soochow Creek every afternoon about five o'clock and with fair weather and favorable tides reach Hangchow the next afternoon anywhere after three o'clock. Three companies are now running these trains, two Chinese and one Japanese. Everything is managed in a creditable and business-like fashion, and one can make a fairly comfortable trip at reasonable expense. It is possible, using this launch service, to leave Shanghai on Friday night, see the Saturday night and Sunday afternoon bores, and be back in Shanghai on Monday morning. By private launch even better time can be made and a record round-trip of sixty hours, allowing fifteen hours at Raining to witness both a day and a night bore, and five hours of shooting during the return, was made by some Shanghai enthusiasts in October, 1902. On the other hand, the pleasures of house-boating in the region traversed, especially during the fall months, should not be underestimated, and if one is not pressed for time a very comfortable and interesting trip on a private boat, propelled by yulow and pole and landing you at the Haining Pagoda at the end of the third day from Shanghai, will allow a full enjoyment of the various scenes which enliven the river and canal banks throughout the Yangtse's delta. A satisfactory compromise between these two plans may be effected by taking a cabin passage on a launch train as far as Samen on the Grand Canal, which is reached at noon of the day after leaving Shanghai, and then hiring a native boat to be yulowed along narrow, well-shaded canals to Haining, which under fair conditions should be reached by six or seven o'clock that evening.
Leaving the wharf in Soochow Creek, Shanghai, shortly before
sunset, we passed under the Garden Bridge, from which many pairs of curious eyes watched our departure, the sturdy little tug puffing continuously and tooting spasmodically as it entered the Whangpu River to pass along the length of the Bund and native city wharves, thus affording an unexcelled view of Shanghai's glory. After rounding a bend toward the southeast our course was southward up the river to Sankong, from there west as far as the walled city of Sungkiang, and further, winding around in a west by south direction, we passed out of Kiangsu province into Chehkiang and came to Kashing, a walled city with a customs station under the management of the Hangchow customs. Here we entered the Grand Canal and followed its southwesterly course through several unimportant but crowded places, at one of which Samen, or Shih Men, we left the launch-train and proceeded in a native boat southeasterly toward Haining by means of the by-way canals which traverse the delta as frequently as crossroads are found in the country districts of western lands. At Samen, the Grand Canal proper makes a right-angled turn to the west as far as Dongsi, or Tang Hsi, where another right-angled turn gives it a straight course southward to Hangchow, its terminus.
All along we found the canals full of life, large boats laden with firewood passing down to Shanghai, while smaller boats with market supplies and other articles were met plying between intermediate points. Large rafts of fir or bamboo, sometimes stretching as far as one could see, excited wonder as to how four or at most five men
succeeded in managing them so well. Curious foot-boats here take the place of the slipper boat so common in the Canton Delta as a rapid passenger craft. They are long narrow affairs and owe their name to the peculiar fashion in which they are propelled. A single boatman sits in the stern and yulows, or wiggle-waggles a large tail oar, and at the same time operates a long oar slung over the starboard side, by means of both feet placed on the inner end—one on the round handle of the oar, and the other on the flat side of a good-sized wooden block attached to the oar-end at right-angles. These boats carry passengers, mails and parcels between the intermediate places not served by the launch-trains or on the side canals.
On both sides of the canal, especially near Kashing, fine granite memorial arches and several pagodas stand conspicuous, having escaped or baffled the destroying hand of the Taipings, though most other things in this region suffered woefully. At one turning point we noticed three graceful pagodas standing side by side.
But the most frequent and most notable feature encountered during a trip on these canals is the really wonderful series of bridges under which the traveler passes. Wooden bridges, granite bridges, crude bridges, artistic and picturesque bridges, dilapidated bridges and bridges in good repair. Bridges with sloping approaches and high curving arches, bridges with one arch or with several, all devoid of prominent keystones. Bridges crowned with shops or pavilions. Bridges whose sides are covered with verdant vines and with small trees clumped at either end. Bridges from the tops of which expectant fishermen let down the great umbrella net and blame the passing boat for the non-appearance of a decent "catch." Bridges which sometimes by their massive piers and narrow arches so reduce the waterway and increase the stream's flow that the spice of danger is added for the voyager whose craft may be a little over normal size. Later, while returning from a side trip to Mokanshan on a dark and rainy night, the cabin loft for servants at the rear of the house-boat we were using was almost completely demolished by crashing into the corner of one of the side arches of the bridge at Dongsi.
On some of the straight stretches of the canal as many as three bridges were sometimes seen from a single position, for every village must have its bridge, and settlements are so frequent that a canal is a veritable "stringtown on the pike." When the canals pass through towns and villages, the natives seem to exercise their best ingenuity in obstructing the already narrow space to the utmost passable limits, bybuilding overhanging porticos and pavilions or by mooring their craft on either side without regard to the resulting constriction. In many cases these bridge arches have more than a half-circle of opening and are fine examples of the stonemason's art and skill. With regular and
solid granite approaches on either side, having sometimes a simple open rest house, washed red on the outside, or a small group of houses at one end, about which cluster a few large trees, they often present charming pictures, especially when a bright day allows every outline to be reflected from the water and the observer is sufficiently distant to miss the inevitable dirt of a Chinese rural dwelling place. So-called river "gunboats," usually tied up in a shady spot near a village and large mandarin family boats were frequently met with. The most curious of all the craft encountered, however, were the cormorant fishermen's boats or rafts, with the berumpled and rather miserable-looking black birds crouching upon them or swimming alongside. Usually the fisherman was stamping rhythmically upon a loose board in the stern and yulowing his boat at a fair pace, some of the birds swimming alongside with a bobbing kind of motion in unison with this stamping, and every now and then making a dive for fish which were no doubt expected to be attracted by the boatman's noise, though to judge from our observation the returns for all this scheming were very meager.
Occasionally a grating sound under the bottom of the boat told us that we were passing over the loose central portion of the reed and bamboo fish-traps or wires which frequently extended completely across the stream, but always with an apparently unoccupied reception or storage compartment at one corner. At other times the progress of our light craft was somewhat impeded by the heavy growths of water weeds and cresses.
The banks of the canal are everywhere green and restful, and in the case of the smaller by-ways are often completely overhung. We have seen nothing finer of the same sort anywhere, the famous Fenways of Boston not excepted. Bushes, great grasses, trees straight and tall, dwarfish and crooked trees, laurel, graceful weeping willow, flowering shrubs, and non-flowering covered with some blooming vine—the whole a beautiful fenway for mile after mile.
The predominant feature is the mulberry-tree, showing everywhere the importance of this region as a silk producer. In well-kept rows, their crooked and wide-spreading branches hid beneath rounded canopies of huge pale-green leaves, the ground everywhere clear of other growth, these little trees represent no small part of the material wealth of a region famous for the splendid silken garments produced in its chief cities.
These mulberry groves sometimes alternate with clumps of graceful bamboos or spicy odorous pines, which mark the burial ground of the near-by village. Or again there is only a fringe of mulberry trees along the bank, much as the lichee trees occur in the delta near Canton, with the paddy fields soon to become bean fields after the rice harvest, or the lotus ponds all white and pink in their September glory, lying behind this fringe or veil.Haining was reached at eight p.m. in the midst of a pouring rain. Passing around the wall on two sides, our journey came to an end in the cul de sac with which the canal abruptly terminates, near a somewhat picturesque gateway in the city wall. A five minutes' walk from our mooring at the canal's end brought us to the sea wall and
the pagoda, and after witnessing the bore which swept past us at about 1:15 a. m. we again crawled into our not overlarge boat and enjoyed a half-night's dozing on hard boards.
Some Considerations concerning Tides in General
Before describing the Hangchow Bore as we saw it at Haining, some preliminary remarks about tides in general, and especially about tidal currents in rivers, will enable the general reader to understand better the phenomenon we are about to consider, and to appreciate its proper place as compared with other more general and ordinary tidal phenomena. This must be our justification for presenting here much that can be found elsewhere and is already matter of common knowledge, but which needs to be correlated and reviewed in this present connection.
The discrepancies in the range of the tides at different places are due chiefly to the local conformations of coasts and sea-beds. Indeed, it seems, as Sir Robert Ball has pointed out, that if the whole earth were covered with a uniform and deep ocean of water, the tides would be excessively feeble, since barometric records give no very distinct evidence of tides in the atmosphere, which is a deep and vast ocean of air embracing the whole earth to a practically uniform depth.
Along the borders of land areas the range of the tide is found to vary from zero up to seventy feet. Few of us realize how small the range is in some places, where at first sight we should expect it to be considerable. In midocean, for instance, an island like St. Helena is washed by a tide only about three feet in range; an enclosed sea like the Caspian or the Black is subject to no appreciable tides whatever, and even the Mediterranean, notwithstanding its connection with the great Atlantic, is subject in general to inconsiderable tides, the range of water-level varying from eight inches at Brindisi to two feet four inches at Trieste. The Mediterranean tides are, however, more strongly developed in the Bay of Gibraltar (where the range is from five feet to six feet five inches), the upper Adriatic and the Gulf of Gabes.In the deep wide reaches of the ocean, the tidal elevation progresses at the tremendous rate of about five hundred geographical miles an hour. But as this is merely the passing of an oscillation whereby the particles of water are gently moved through a cycle of positions, there can be no appreciable effect upon the distant ocean bottom, on an average of two or three thousand fathoms below. When, however, the tidal wave enters a shallow sea, the friction of the bottom becomes more and more effective in decreasing the speed while it increases the height and effective force of the wave. Again, when the tidal swelling is increased in height by the convergence of the shores between which it moves, it is no longer a mere oscillation or pulsation of the great ocean, but the water acquires a true motion of translation, and rushes past headlands and through narrow channels with tremendous force and speed—a phenomenon well known along the west coasts of Scotland and Scandinavia. In some cases the advancing tide on entering a narrow inlet or estuary gathers itself into one or more large waves, and rushes up between the converging shores. Thus, owing to the gradual
called "bore." Professor G. H. Darwin noted on the banks of the Severn during the spring tide in September, 1897, that there was no proper bore, but only a succession of waves up-stream, and a rapid rise of water-level.
In the case of the River Seine, which has been dyked as far as Rouen to admit vessels of twenty feet draught, it is said that there is a bore (barre or mascaret) at every tide, ranging usually from eight to ten feet. This is probably accounted for by the fact that after Candebec and Quillebœuf, the estuary is set with extensive sand-banks between which flows a narrow navigable channel.
These bores are relatively small compared with that in the Ch'ientang Kiang, while the destructive bore of the great Amazon is robbed of its impressiveness because it can not be well observed on account of its very magnitude; moreover, with it as well as with the other rivers it is only at spring tides and with certain winds that the phenomenon is at all striking. On the other hand, the Hangchow Bore occurs at every tide to a remarkable extent in any season and at certain times assumes colossal proportions and is always easily observable. For comparison it may be interesting to note the following description of the Amazon's bore, or proroca, by La Condamine:
sometimes by a fourth. These watery mountains spread across the whole channel, and advance with a prodigious rapidity, rending and crushing everything in their way. Immense trees are sometimes uprooted by it and sometimes whole tracts of land are swept away.
Tidal Currents in Rivers
There is no appreciable tidal effect in rivers due directly to the tidal attraction of the sun and moon, but the tidal wave in a river is caused by the oscillation of the larger body of water into which the river empties. The sea resembles a large pond in which the water rises and falls with the oceanic tide, and a river is a canal leading into it. The rhythmical rise and fall of the sea generates waves which would travel up the river, whatever were the cause of the oscillation of the sea and quite independent of any direct action of the sun and moon on the water of the river itself.
There are four characteristics of tidal currents in rivers which are of cardinal importance in the present connection. Briefly treated, they are:
1. Dependence of Speed on the Depth Alone.—It may readily be shown mathematically that loner waves travel in shallow water at a speed which depends only on the depth of the water, and that waves are to be considered long when their length is at least twice the depth of the water. Now the tidal wave in a river is many hundreds of times as long as the depth, and consequently it travels at a speed dependent only on the depth of the river. Moreover, its speed is very slow compared with the motion of the great tide wave in the open sea.
2. Difference between Ebb and Flow in a River and along an Open Coast.—On the open seacoast ebb and flow are simultaneous with fall and rise, but in a river the case is quite different. On an open coast slack water occurs at high and low water, but in a uniform canal connecting with the sea, slack water, i. e. the time of no tidal current, is at mean water-level, the current being most rapid up-stream at the water-level, it ceases flowing before mean water-level is reached; and
moment of high water and most rapid down-stream at low water. Hence the tidal current "flows" for a long time after high water has passed and when the water-level is falling, and "ebbs" for a long time after low water and when the water-level is rising. But rivers gradually broaden and become deeper as they approach the coast, and tidal currents in actual estuaries are, therefore, intermediate between those of an open seacoast and those in a uniform canal.
3. Effect of Proper Current of the River Itself.—A river has also to deliver a large amount of water into the sea during a single oscillation of the tide, and its own proper current is superposed on the tidal currents. Hence in actual rivers, while the resultant current continues to flow up-stream after high water is reached, with falling water-level, it ceases flowing before mean water-level is reached; and while the resultant current ebbs down-stream after low water, it generally continues to ebb with the rising tide for some time after mean water is reached, the downward stream, in fact, lasting longer than the upward one. The moments at which currents change will differ in each river according to the depth, the time and the extent of the rise and fall at the mouth and the volume of water delivered by the river; but in every case the tide rises more quickly than it falls, so that the time-interval from low water to high water is shorter than from high to low.
4. Natural Change in Shape of a Wave Advancing into Shallow Water.—The demonstration is too technical to be included here, but it can be proved analytically that a wave progressing up a river must change its shape so that the front slope gets increasingly steeper, and the rear slope more gradual. If this steepening of the front slope be carried to an extreme, the wave would present the form of a wall of water, but the mere advance into shallow water would not by itself suffice to produce so great a change of form without the aid of the natural current of the river, which cooperates with this change in the shape of a wave as it runs into shallow water, so as to exaggerate the steepness of the front slope. When, as is the case for many rivers, the estuary contains broad flats or shoals of mud or sand which are nearly dry at low water, the tide sometimes rises so rapidly, especially if the mouth of the estuary be funnel-shaped, that the wave becomes a wall of water, and is then properly called a "bore". Let us note briefly the way in which Hangchow Bay affords typical circumstances of this sort, so that we there have a most striking case of this interesting phenomenon.
The Physiography of Hangchow Bay
Hangchow Bay, or the estuary of the Ch'ien-tang River, has a very marked funnel shape. From Yangtse Cape (the extremity of Pu Tung Peninsula) on the north to Ketau Point on the south is considerably over sixty miles, while the distance between banks at a point thirty miles farther west is approximately only half of this and in twenty miles more has again been reduced by half, so that along the meridian of Chapu it is only about eighteen miles wide. From Ketau Point in a line approximately northeast there extends for over eighty miles a chain of rugged islands, beginning on the south with Chusan, by far the largest, and ending on the north in the Saddle Group, North Saddle Island being in the same latitude as the low-lying and rounded corner of Yangtse Cape. The most westward group is comprised by the Volcano Islands, which lie approximately due south from Yangtse Cape and about midway across the mouth of the bay. We shall presently refer to this group as one of the places at which definite observations of changing water-level have been made in studying the birth of the bore. Westward of this meridian the bay shoals quite rapidly in the southern half, and at times of low water, west of 121½° longitude (east of Greenwich) the mud drys for two miles from the southern embankment. It was off the northeast corner of this extensive "flat" that H. B. M. ship Kite was lost.
But the most marked shoaling and constriction in the figure of Hangchow Bay has yet to be noted. As already stated, at Chapu the bay is about eighteen miles wide. From this point inward the general direction of the bay is southwesterly and safe navigation ends near Rambler Island, which is about eleven miles from Chapu. Here the width of the bay for water over six feet deep has narrowed to less than five miles, and from here on inward for quite a distance the whole estuary, with the exception of a very narrow region near the northern bank, is a sandy shoal. Between Rambler Island and Haining is a range of hills forming a promontory that extends well out, making the general direction of the bay take a quarter turn and bringing it to the northwestward. On this promontory is the town of Kanpu, and a little beyond the projecting point of land and well out in the middle of the channel is a group of low tide-washed islands. Just at the western end of this turn in the northern shore is a sharp indentation, protected by a good-sized hill, which forms Bore Shelter Bay. It is at these flats and along the meridian of this hill that an observer at the Haining Pagoda gets his first glimpse of the bore.
On account of the regular recurrence of the bore, junks going from Chapu road to Hangchow take three days, and shelter first in Bore Shelter Bay and second at Haining platform. Boats drawing over three feet can not be used. The return from Hangchow to Chapu road can not be safely accomplished under three tides in any boat. Thus in spite of being situated on the main tributary of the bay of the same name, the city of Hangchow, the capital of the rich and populous province of Chekiang, the center of a great silk-producing district and of the manufacture of the best silks, being the sole source of the silk fabrics supplied to the Imperial household, and a great center of Chinese culture and literature, has practically no direct connection with the sea. There is a small canal connecting it with Haining, but practically its whole export trade passes through Shanghai by way of the water-route we have already described. In 1905 the total trade of the port amounted to 17,496,980 Haikuan taels. Our interest in these facts in the present connection lies in this: that this ancient and important city, whose population is now about 350,000, owes its very existence toward the southwest to the construction of the great sea-wall, called by the natives the "bore wall."
It is probably true that some thousands of years ago the great flat area now forming a considerable part of the province of Chekiang and Kiangsu was under water and that the Yangtse, gradually increasing its delta, reclaimed the land. The inhabitants, to assist the river in its land-forming process, built sea-walls, using the various islands as corner-stones. The wall or dyke confining the waters of the Haining-Hangchow canal is probably one of these early structures, which has better withstood the ravages of time and tide. As these walls were multiplied and extended, they caused the projecting north point formed by the alluvial deposits of the Yangtse and the Ch'ien-tang Kiang to extend seaward, thus forming the present funnel-shaped mouth of the latter river, as already noted, and obstructing to a considerable extent the progress of the ocean tide, the northern promontory deflecting it inwards and the shoals causing it to heap up into an increasingly powerful wave—the forerunner of the present bore. Against this rush of water the poorly constructed dykes were insufficient and the people along the shores of Hangchow Bay, especially on the northern side, frequently suffered great losses.
- See G. H. Darwin, "The Tides," etc., Scribners, 1898. This contains also an account of the Hangchow Bore based on Captain Moore's survey, to which we shall refer later on.
- A tael is about five sixths of a gold dollar and is the unit of trade in China.