張彝

站在錢塘江邊海寧古海塘上，面對眼前奔騰而過、萬馬齊喑的錢塘江涌潮，不禁生出“何以海寧潮”的感嘆！在這顆藍色的星球上，入海河流以數(shù)萬計，何以獨獨錢塘江有此景象？北宋陳師道有詩《十七日觀潮》，滿足了我們無窮的好奇之心：“漫漫平沙走白虹，瑤臺失手玉杯空。晴天搖動清江底，晚日浮沉急浪中?！蔽覍幵赶嘈旁娭谐錆M無邊暇想的演繹，就是眼前一切的答案，錢江潮就是那碧空之上神仙居住的瑤臺邊，仙女玉手偶失灑落的玉液瓊漿。人間勝景絕景也不過如此了吧。

百尺樓前越王愁

在今天杭州蕭山國際機場的西北面，有三座小山。吳越爭霸之時，越王勾踐于此修筑有樓，樓名“百尺”。南宋《咸淳臨安志》記載：“鹽官縣百尺浦，在縣西四十里?！遁浀刂尽吩疲骸酵跗鸢俪邩怯谄稚希?，因以為名今廢?！?/p>

公元前489年，戰(zhàn)敗入?yún)侨倘枞昊貒墓篡`，時刻不忘復仇于吳，召計倪問伐吳之事。《越絕書》錄勾踐之言：“西則迫江，東則薄海，水屬蒼天，下不知所止。交錯相過，波濤浚流，沈而復起，因復相還。浩浩之水，朝夕既有時，動作若驚駭，聲音若雷霆。波濤緣而起，船失不能救，不知命之所維?！惫篡`為伐吳之事什么都愁，愁山、愁林、愁江、愁海、愁水、愁濤、愁船，愁吳有備，愁越糧道不通，愁謀不成或致不能勝。盡管當年的越國水上航運技術(shù)已經(jīng)非常發(fā)達，跨越錢塘江已不是難事，但仍對喜怒無常的涌潮心有余悸。這是歷史上第一次有關(guān)錢塘江涌潮的文字記載。

今天的錢塘江涌潮是聞名天下的自然奇觀，是浙江最珍貴的旅游景觀資源。但是，歷史上，它曾經(jīng)就是一個“禍害”，給沿海地區(qū)帶來了諸多洪潮災害，造成巨大損失。

《宋史·五行》記載較為詳細：“嘉定十二年（1219），鹽官縣海失故道，潮汐沖平野二十余里，至是侵縣治。蘆洲港瀆及上下管、黃灣黃岡等鹽場皆圯，蜀山淪入海中。聚落田疇失其半，壞四郡田，后六年始平。”宋嘉定十五年（1222），專任鹽官海塘事的浙西提舉劉垕上書都省：“大海元與縣治相去四十余里，數(shù)年以來水失故道，早晚兩潮奔沖向北，遂致縣南四十余里盡淪為海。近縣之南元有捍海古塘亙二十里，今東西兩段并已淪毀，侵入縣兩旁又各三、四里，止存中間古塘十余里。”

元泰定元年（1324）十二月，海水大溢，壞堤塹，侵城郭;二年（1325）八月，大風海溢，捍海堤崩廣三十余里，徙民居千二百五十余家避之;四年（1327）正月，海潮大溢，捍海塘崩二十余步，四月復崩十九里。

明代自永樂至萬歷時期（1403-1620），海寧發(fā)生了五次較大的潮災，造成大量房屋田地沖毀，居民大規(guī)模向北遷徙，史稱“海凡五變”。清代順治二年（1645）至乾隆二十三年（1758），錢塘江主槽在寬達20多公里南北岸線之間的“南大亹”“中小亹”和“北大亹”三條江槽通道上反復擺動，史稱“三亹變遷”。不僅造成新的災害，還引發(fā)了海寧與蕭山行政區(qū)域的調(diào)整，江走“北大亹”安流后，江南原屬海寧的土地于清嘉慶十八年（1813）轉(zhuǎn)隸蕭山。

江底沙坎催潮生

潮汐，是海水在月球和太陽引力作用下發(fā)生的周期性運動，地球上凡是海洋與陸地的交界處都存在這一現(xiàn)象。

涌潮，是潮差較大的喇叭形入海河口或者海灣出現(xiàn)的一種潮水暴漲的現(xiàn)象。如果沒有其他特定的條件，按理說，全世界4萬多條入海河流河口都會出現(xiàn)涌潮。實際情況卻不是這樣的，全世界只有16個國家、60余處河口和海灣存在或出現(xiàn)過涌潮，絕大多數(shù)的入海河口沒有涌潮。其中最為著名的巴西亞馬遜河、印度胡格利河、英國塞文河、加拿大芬迪灣等處，它們有和錢塘江河口一樣的喇叭形狀入?？?，有比錢塘江更高的潮差，但是在涌潮的絕對高度、潮流速度、治理難度和觀賞度等方面綜合對比，唯錢塘江涌潮居首位。

錢塘江是浙江省最大河流，以北源新安江起算，河長588.73千米;以南源衢江上游馬金溪起算，河長522.22千米。自源頭起，流經(jīng)今安徽省南部和浙江省，流域面積55058平方公里，經(jīng)杭州灣注入東海。

錢塘江河口形狀為喇叭型。其外口段杭州灣，上海南匯與浙江寧波鎮(zhèn)海之間的灣口寬98.3千米，向內(nèi)85千米至浙江海鹽縣澉浦與余姚、慈溪交界之間的灣頂寬僅19.4千米，東海潮波從臺灣海峽北上經(jīng)過舟山群島進入杭州灣，隨著江面迅速縮小，潮波能量集聚，潮差增大。

錢塘江河口屬強潮型河口。平均潮差4米以上的河口為強潮型河口，實測錢塘江澉浦多年平均潮差5.57米，最大記錄8.93米，比外口增加一倍。每潮進潮量35-50億立方米。潮流流速強勁，最大流速12米/秒。高潮差、大潮量和強流速，加劇泥沙上下搬運運動，由于河口段泥沙主要由分選良好的細粉沙組成，極易淤積。

錢塘江水下有巨大的沙坎。錢塘江上游來沙少，年輸沙量600-800萬噸，比每潮進出河口的沙量（1000萬噸）還少。在海寧段觀測到，潮差3.6米時，一次全潮內(nèi)，漲潮輸沙量180萬噸，落潮輸沙量僅90萬噸，凈輸入90萬噸。大量泥沙隨潮流行進而淤積，日積月累，自平湖乍浦至蕭山聞家堰，形成長130千米、體積達425億立方米、與河流同向的“沙坎”?！吧晨病笔购哟惭杆偬钭儨\，潮流前鋒受阻遠較波峰為大，速度為慢，前坡逐漸變陡，到一定程度潮波破裂，于是錢塘江涌潮就出現(xiàn)了。（見林炳堯《錢塘江涌潮的特性》）

早在1964年，中國工程院院士、國內(nèi)外著名河口海岸學家陳吉余在《錢塘江河口沙坎的形成及其歷史演變》一文發(fā)表其研究結(jié)論 ：“沙坎的形成以漏斗狀河口為基本條件，涌潮形成又以沙坎為根據(jù)?！本扌蜕晨?，就是錢塘江涌潮產(chǎn)生的特殊條件。

潮起海寧越千年

海寧人稱錢塘江涌潮為“海寧潮”，是因為它的起潮點在海寧，最佳觀潮地在海寧。

南宋《咸淳臨安志》記載 ：“今觀浙江之口，起自纂風亭，北望嘉興大山，水闊二百余里?！迸c紹興纂風亭相對的位置大概在今天海寧大、小尖山處。

1888年9月，英國皇家海軍“逍遙者號”（RAMBLER）艦艇指揮官摩爾（MORRE）中校主持錢塘江涌潮的觀測和沿江訪問，在《錢塘江（杭州灣）涌潮》報告中，他認為，“完全可以得出下列一般結(jié)論：月圓和月相轉(zhuǎn)變時，10時0分至10時30分之間，錢塘江涌潮形成于海寧東南方向12海里處的一個突出岬角尖山附近”。

1920年，上海開浚黃浦河道局在錢塘江北岸海寧段高陽山至鹽官縣城之間設置6個涌潮觀測點，每分鐘記錄一次潮位，從各站潮位過程線的變化情況，判斷大潮期間，涌潮大致在鹽官以東21千米的小尖山附近形成。

20世紀60年代以前，錢塘江涌潮的起潮點基本沒有變化，都在海寧尖山附近。60年代以后，隨著大規(guī)模治江圍涂，錢塘江江道縮窄，起潮點、觀潮點和涌潮形態(tài)都發(fā)生了變化。從20世紀80年代中期開始，起潮點往東移至高陽山一線。此后錢塘江的治理同時落實保護涌潮的理念，治理措施所致的江道岸線變化，給自唐宋以來盛行的錢塘江觀潮增添了意外的驚喜，海寧更是呈現(xiàn)出“全線可觀潮、處處有潮景”的狀態(tài)，最佳觀潮點遠不止“一潮三看賞四景”，自東向西依次如下：

嘉紹大橋。江道開闊，潮流速度快，因江中沙洲影響，形成東、南兩股潮，大潮汛期間有“波紋潮”“兩股潮”或“交叉潮”出現(xiàn)。

塔山壩。清代修建的塔山壩，壩頂伸向江心。西向潮流先折北至此，再折西而行，大潮汛時可見東潮、南潮、交叉潮和碰頭潮等多種潮景，壩頂則有亂潮環(huán)繞景象。

大缺口。觀看“碰頭潮”的傳統(tǒng)最佳景點。潮流至此被江中中沙截成兩段，北段沿海塘繼續(xù)西進，南段沖向南岸撞擊海塘后北返，與東潮在江面上匯合碰撞，形成“碰頭潮”或“交叉潮”。

八堡。觀看“交叉潮”的最佳景點。若南潮速度快會沖上海塘，速度慢會形成“二度潮”。

鹽官景區(qū)。觀看“一線潮”的最佳地段。潮流至此融合西進，呈現(xiàn)齊頭并進景象，稱為“一線潮”。

老鹽倉。觀看“回頭潮”“沖天潮”的最佳景點。潮流至此撞擊長650米的南北向丁字壩，潮頭騰空而起形成水墻，折身返回與西涌潮流相互激蕩著一路向東，在東面約600米處的海塘凹口處沖天而起，潮頭高達10余米。

自標準海塘建成后，海寧海塘全線交通方便，設施完備，視線良好。農(nóng)歷每月初一至初五、十五至二十日大潮汛期間，每天白天、夜間均“兩潮”可觀，全線皆可觀潮。

筑塘護城終安瀾

對抗破壞力巨大的涌潮，最有效的手段是修筑海塘。海寧地處太湖流域最南端，海塘修筑關(guān)乎整個流域的安危，故歷代均極其重視。因生產(chǎn)力水平所限，千年以來，人們與涌潮的斗爭經(jīng)歷了從潮進人退到潮止塘下，從攻守相當?shù)今Z服涌潮、人潮共生的過程。

自唐至宋、元、明各代，古代海塘修筑的狀況是屢筑屢毀，不斷后退，以空間換取防御效能。

海寧古代海塘的修筑是從唐代開始的?！缎绿茣さ乩碇尽酚涊d：“鹽官……有捍海塘堤，長百二十四里，開元元年（713）重筑?！贝撕蟾鞔窌?、方志多有述及大海、海塘與縣治的距離：

“海水，在縣南七里?！保ㄌ啤对涂たh圖志》）

“大海元與縣治相去四十余里?！保ㄔ端问贰罚?/p>

“縣南去海一里余。”（元《宋史》）

“在縣東南一十里。”（南宋《咸淳臨安志》）

“鹽官州去海岸三十里，舊有捍海塘二。”（明《元史》）

“海在縣治南一十里?！保鳌冻苫贾莞尽罚?/p>

“大海在縣治南一十里?！保鳌都尉负幙h志》）

“縣治南即海，海之上即塘?！保髡勥w《海昌外志》）

海寧古代海塘的塘型，也經(jīng)歷了從土塘、柴塘、竹籠石塘、斜坡式石塘到直立式石塘的演變過程。

唐開元元年重筑的捍海塘即為土塘。宋代未見有石塘的修筑記載，宋仁宗延祐年間，有議筑石塘，卻并未實施，應仍為土塘。南宋《咸淳臨安志》中有《鹽官縣境圖》一幅，圖上縣治與大海之間有“捍海塘”“范蠡塘”各一條。元代改進五代十國時期吳越王錢镠修筑杭州捍海塘使用的“竹籠石塘”，用石囤木柜搶險抵御涌潮。天歷元年（1328）潮患漸息，石囤木柜基本完好，于是改“鹽官州”為“海寧州”。明代仍沿用石囤木柜救急，未修筑石塘。清代，錢塘江江槽發(fā)生重大改變，康熙五十九年（1720）江槽走“北大亹”，浙江巡撫朱軾改進明代嘉靖年間浙江僉事黃光升發(fā)明的“五縱五橫魚鱗石塘”，主持修筑老鹽倉魚鱗大石塘500丈，這是海寧歷史上首次修筑石塘。此后雍正、乾隆兩朝，全力修筑海寧石塘，至乾隆四十九年，海寧海塘均已建成魚鱗大石塘。自此，潮水終于止步于塘下，錢塘江涌潮的治理進入攻守相當?shù)碾A段。

清代乾隆以后，海寧海塘基本處于修損補缺的狀態(tài)。民國時期，采用混凝土等新技術(shù)修筑海塘的工程量很小，一線抵御錢塘江涌潮的重任仍由清代古海塘支撐，加上戰(zhàn)亂失修，工程老化，塘頂偏低，難以抗御洪水強潮的侵襲。

新中國成立以后，錢塘江河口進入了系統(tǒng)化治理的新時代，特別是海寧標準海塘工程建設，按抗御一百年一遇洪潮高水位和12級臺風標準，自1996年11月至2005年底，55.66公里全線完成建設。錢塘江涌潮第一次聽從我們的指揮，成為今天人們喜聞樂見的旅游景觀資源。

今天的人們，若想重睹錢江潮走龕赭兩山間的景象已不可能，唯有詩文畫作或想象可聊作寄托。清代鹽官城北白馬寺僧達受觀《潘松墅月夜觀潮圖》，觸景生情，遂題詩曰：

赭龕兩點影朦朧，卷起銀濤浴碧空。

惟有月輪推不去，定光還在浪花中。

Haining Tidal Bore： Past and Present

By Zhang Yi

Standing on the ancient seawall in Zhejiangs Haining city along the Qiantang River， and facing the surging tidal waves of the river， one cant help but wonder： why Haining tidal bore？ Tens of thousands of rivers are flowing into the sea on this blue planet， but why is it only in Qiangtang River that this specular scene can be found？ Some clues might be discovered in “Watching the Tidal Bore on the Seventeenth Day of the Lunar Month”， a poem written by the Song （960-1279） poet Chen Shidao （1052-1102）：

On the endless beach， come up the tides like a white rainbow.

The nectar from the fairies jade cup they are， accidentally poured to this mortal world.

The blue sky is swinging in the bottom of river，

and the setting sun is bobbing in the rapid waterflow.

Imaginations aside， the Haining tidal bore goes back a long way. “On the west lies the big river， and on the east lies the great sea…when the tides surge up， they are so horrifying that they sound like thunders， and once the ships are lost in the tides， there is no way to recover them as well as the lives，” said Gou Jian （ca. 520-465 BC） in 489 BC， when the king of the State of Yue （2032-222 BC） asked one of his advisors for the possibility of military campaign on Yues archenemy， the neighboring State of Wu （ca. 12th century-473 BC） to the north. Back then， Goujian just returned to Yue after being imprisoned for three years in Wu. Among Goujians many concerns for possible defeat in his revenge， the unpredictable tidal waves weighed heavily on him， despite the fact that Yue had already been leading the way in water transport technologies and there was no difficulty in crossing the Qiantang River.

Goujians concern， documented in the Yuejueshu， or the Glory of Yue， ?is believed to be the first written record of the Qiantang River tidal bore， which is now one of the most stunning natural wonders in the world. While it is undoubtedly Haining citys most valuable tourism resource， the tidal bore was once considered a major scourge， causing much damage.

“In 1219， the tidal waves flooded into Yanguan county [in present-day Haining] for over 20 li [10 kilometers]…destroying half of the fields along the way， the recovery of which took six years，” according to the History of Song. In 1222， a local official reported： “The county seat was originally 40 li away from the sea， but the changing water course and the tidal bore have flooded the area， with sea water now running 40 li to the south. The seawall， which was originally 20-li long， has only the middle section of about 10 li left， while the other parts are all breached and destroyed.”

In the 12th lunar month of 1324， seawater ran over the embankment and went all the way to the city walls; in the eighth lunar month of 1325， heavy winds and overflown seawater breached the embankment for over 30 li， more than 1，250 households had to relocate; and in the first lunar month of 1327， some 20 li of embankment was destroyed by the rising seawater and another 19 li ?was destroyed in the fourth month.

From 1403 to 1620， five major tidal disasters hit Haining， shattering houses and damaging fields， and a large number of residents had to migrate to the north. In the 23 years between 1645 and 1758， the course of the Qiantang River oscillated repeatedly along a section that was 20 kilometers wide from north to the south， which brought not only fresh destruction but also administrative redrawing between Haining and Xiaoshan.

Tides are the periodic movement of sea water caused by the combined effects of the gravitational forces of the Moon and the Sun， and the rotation of the Earth. Wherever the sea meets the land， tides can be seen.

A tidal bore， on the other hand， is a tidal surge occurring in a horn-shaped estuary or bay with a large tidal range. Theoretically， the estuaries of more than 40，000 rivers entering the sea around the world should have tidal surges. In fact， that is not the case： ?tidal bores can only be seen in 60 estuaries and bays in 16 countries. Among the most well-known are the Amazon River in Brazil， Hooghly River in India， River Severn in the UK and Bay of Fundy in Canada. While they all share a similar horn shape as the Qiantang River estuary， have larger tidal ranges， their tidal bores are dwarfed by the Qiantang tidal bore in terms of absolute tidal height， tidal speed and spectacle.

As the largest river in Zhejiang province， the Qiantang River runs a total length of 688 kilometers and covers an area of 55，558 square kilometers. The formation of the tidal bore results from the unique features of the Qiantang River. For one thing， its mouth is horn-shaped： at the inward side where the river mouth starts， the width stands at 19.4 kilometers while， flowing for 85 kilometers， at the outward end where it meets the Hangzhou Bay， the width increases to 98.3 kilometers. When the sea waves crash down from the East Sea into the Hangzhou Bay， the tidal energy builds up and the tidal range increases rapidly as the Qiantang River shrinks as quickly.

Although widely known as the Qiantang River tidal bore across the world， the tidal wave is called the “Haining tidal bore” by Haining people， as it is from Haining where the tidal bore starts. For example， Annals of Linan during the Reign of Xianchun， written in the Southern Song （1127-1279） period， put the forming of the tidal bore at somewhere near Hainings big and small Jianshan Mountains. “…I feel justified in submitting to you the following general conclusions. At full and change of the moon the Bore of the Tsien-tang Kiang originates between X. h. and X. h. 30 m. in the neighbourhood of the meridian of Chi-san [Jianshan]， a conspicuous hill 12 miles E. by S. 1/2 S. from Haining，” wrote Captain William Moore （1849-1918） in Report on the Bore of the Tsien-tang Kiang， the first detailed description of the Qiantang River bore by a Western observer. Indeed， successive surveys and investigations before the 1960s all put the area near Jianshan Mountain as the place where the tidal bore originated， before it moved eastwards to Gaoyang Mountain when extensive management and reclamation measures on Qiantang River were instituted.

While Haining has historically boasted the best watching spots for the tidal bore， visitors now can appreciate the tide even more conveniently， thanks to the construction of a “standard seawall”. Throughout centuries， Haining people have built all sorts of embankments， causeways and dams to try to tame the waves， with varying degrees of success. The founding of the Peoples Republic of China has ushered in a new era of systematic governance for the Qiantang River estuary. Of particular note is the Haining Standard Seawall， running 55.66 kilometers and built between November 1996 and the end of 2005， which can withstand not only strong waves but Category 12 typhoons.

Now， rather than an affliction to be avoided， Haining tidal bore has become a veritable tourist spectacle. From the first day to the fifth day， from the 15th to the 20th day of every lunar month， when sea waves are most active， people are able to watch the tidal bore along the Standard Seawall twice， once at daytime and once at night， with a wide range of facilities and amenities provided.