愚公移「砂」?

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1992 / 3月

文‧張靜茹


不只是清水溪,今天東部河川有一個共有的「特殊景觀」,且愈往下游愈明顯——河床「鶴立雞群」,不僅高過堤防、高過橋面、甚至高過兩岸住家。一位住花蓮的居民甚至誇張的說:「馬太鞍溪有一小段河床快與光復糖廠的煙囪一樣高了。」


東部河川砂石多,肇因於脆弱的地質。「東部砍一棵樹等於西部砍三棵樹」,植物學者常如此形容。

這前因後果還得由台灣的誕生追溯起。

台灣在一百八十萬年前,因為地球板塊擠壓才「有幸」露出海面,至今則仍以每年約五公分的速度在拔高。不斷抬高的地殼,使河流反覆下切,斷層縱橫交錯。山高谷深再加上頻繁的颱風、暴雨切割,土壤反覆風化,地質結構因此先天「積弱不振」。

東部缺乏生態緩衝帶

「地力資源難保持,生界舞台不穩定」,植物學者陳玉峰如此描述台灣的大地。所幸「綠色生命前來填皮補肉,整個后土才算是開了光」。

原生植物在貧瘠的土地上緩慢、艱困地演替,往往歷經千萬年,再三崩解與重建,才成為高度複雜、穩定的森林生態系,也才能擔負土地保全作用。陳玉峰解釋,克服台灣惡地成長的森林,植物學上稱為「長期適應高度不穩定基質的特殊植群」,它重要的特徵之一就是「受毀損後復原困難,也將引發長期激烈的連鎖反應」。

今天的清水溪水土流失、危及下游居民生命財產,正是植被與地表遭破壞後產生的連鎖反應。

尤其中央山脈偏東,東部人群、聚落最主要的散佈地——花東縱谷寬只有三到七公里,以三民地區為例,向西八.四公里內,就由海拔五百公尺陡升至三千三百公尺,平均每西行三公尺就升高一公尺。東部平均坡度達四十多度,「地勢陡峻世所罕見」,「台灣綠色傳奇」一書如此形容。

河底隧道

急劇的落差,使溪流沖蝕更劇烈,而花東縱谷腹地有限,幾乎沒有生態緩衝帶可言,水土直接就氾濫在山腳下的部落與谷地上的市鎮,前年的銅門村與去年紅葉村整個淹沒,都是慘烈的例證。

花東縱谷東邊矗立的海岸山脈,則阻礙沖蝕物流出外海,不斷堆積在下游,河床日益填高,連溪床上的鐵軌也因此每年被砂石淹沒,得年年重新加高。鐵路局不堪其擾,為百年計,遂鑿通壽豐、馬太鞍兩條溪流河床,讓火車由「河底隧道」而過。

這也是學者均認為開發東部應更謹慎、更完善地全盤規劃的原因。只惜東部地表的傷害至今並未停止。主管花蓮治山防洪工作的台灣省水土保持局第六工程所所長趙國昭頗傷腦筋的說,上游「舊疤」未癒,如今中、下游山坡地卻新傷——濫墾——累累。

多山的特質,使過去東海岸農業一直欲振乏力,今天坡地副產物則大行其道,「民眾常自己叫怪手開產業道路,上山種金針、香菇、檳榔、茶葉……,抓不勝抓」,趙國昭說。如今沿花東海岸一路而行,放眼兩側盡非「宜林樹種」的檳榔樹。

曾來過台灣的一位美國華盛頓大學土木工程教授認為,台灣水土保持工程技術並不輸給西方;但台灣水患卻頻傳,除了先天的地形條件,「主管單位沒有嚴格管制山坡濫墾、人民也不守法」,趙國昭坦言今天的問題癥結。去年位在秀姑巒溪東岸、發源海岸山脈的阿眉溪,就因為山坡地濫伐、濫墾,下游氾濫成災,今年中央與省、縣政府準備花一億多元整治這條全長不到十公里的小溪。

愚公移「砂」?

如何處理滔滔而下的砂石,是個迫在眉睫的事。「總不能和河床比高般年年加高堤防,僅花蓮縣就有大小廿七條河川!」趙國昭說,幾十年伐木累積的結果,使東部河川幾乎無一倖免於水土大量流失。

把東部河床上「取之不盡」的砂石,運往西部幾個大城市做建材,已成為東部人的共同心願。但「東砂西運」陸路運費過於可觀;前任的省主席邱創煥在位時,曾提議在台北八里設砂石碼頭,由花蓮港以船運舶過去,卻遭八里人以破壞景觀為由反對而胎死腹中!

由於東、西海岸構造迥異,東海岸外幾公里就是八、九千公尺的海溝,整個中央山脈切割下來也填不滿,因此把砂石都搬棄於太平洋,也無法產生海埔新生地。「這樣做太浪費砂石了!」礦務局東部辦事處主任黃大邦說。

即使真的把砂石丟到太平洋,水土保持工作人員直接的難題是,要像「愚公移山」,把東部河川的砂石全換個位置,恐怕不是徒有愚公的耐力就能做到。愚公不過想搬動一座山,但若要疏濬花蓮河川的砂石,「恐怕廿七條大小河川當中,有百分之九十不能倖免」,趙國昭說。

〔圖片說明〕

P.90

東部地質脆弱,使水土流失加遽。圖為前年遭到砂石掩埋的銅門村一戶人家。(邱瑞金攝)

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EN

The Foolish Old Men Who Moved Mountains?

Chang Chin-ju /tr. by Phil Newell

Not only the Chingshui River, but all the rivers and streams in eastern Taiwan have one "special feature" in common, which becomes more obvious the farther downstream you go: The river beds are as high as "a crane standing among chickens," higher than the dikes, higher than the bridges, even higher than the homes on the two sides. "There is even one section of the Mataian riverbed that is almost as high as the smokestack on the Kuangfu Sugar Factory," says one Hualien homesteader.


There are many rocks in the riverbeds in eastern Taiwan, a result of the brittle quality of the land. "To cut down one tree in the east is equivalent to cutting down three in the west," is how botanists often describe it.

This cause and effect relationship can be traced back to the birth of Taiwan.

About 1.8 million years ago, Taiwan "fortuitously" popped through the surface of the ocean as a result of the pressures of the earth's plates. Even today it continues to rise at a rate of about five centimeters per year. The continually rising earth's crust has left the rivers correspondingly lower, cutting back and forth across geologic layers. With high mountains and deep gorges, plus frequent typhoons and harsh storms cutting away, the soil has been repeatedly eroded, so the geologic structure is inherently "extremely brittle."

The East Lacks an Ecological Protection Belt: "It's difficult to retain the resources of the land," says botanist Chen Yu-feng, thus describing in a nutshell Taiwan's terrain. Fortunately, "flora has come and fleshed it out, giving the soil new life."

Natural vegetation grows slowly in barren soil, which makes it difficult for the land to renew itself, and, over tens of millions of years, it repeatedly collapses and is reconstituted, only then becoming a complex, stable forest ecological system. And only then is it capable of fulfilling the function of land preservation. Chen Yu-feng explains that the forests which have been able to overcome Taiwan's harsh land are called "special flora which has adapted to an unstable ground quality over a long period of time." in botany. One of its most important features is that "it is very difficult to restore an area to the original condition after the surface has been stripped away, and this will initiate a long-term, intensive chain reaction."

Today's erosion of the bed of the Chingshui river, threatening the lives and property of downstream residents, is precisely this kind of chain reaction following the destruction of the plant life and surface of the land.

This is especially the case in the main area of human settlement east of the Central Mountain Range, the Hua-Tung (Hualien-Taitung) Valley, which is a mere three to seven kilometers wide. Taking the Sanmin area for example, within 8.4 kilometers to the west, the land rises from 500 meters above sea level to 3,300 meters, or an average of a rise of one meter for every three meters west that you go. The average incline in eastern Taiwan is over 40 degrees: "A topographic slope the likes of which is rarely seen" is how Taiwan's Green Legend describes it.

A Riverbed as High as a Smokestack? The dramatic drop in elevation causes the rivers and streams to erode the land more rapidly, and the HuaTung Valley has a limited hinterland, giving it almost no ecological protection belt to speak of. The soil is thus simply sloshed down around the villages and towns in the valley at the foot of the mountains. The complete eradication of Tungmen Village two years ago and of Hungyeh Village last year are tragic testimony.

The Coastal Mountain Range to the east of the Hua-Tung Valley blocks the eroded soil from flowing out to the sea, so it continually accumulates downstream, building up the riverbeds ever higher. Even the railroad tracks are annually displaced by the sand and stone, and must be raised every year. The Taiwan Railroad Administration has got tired of the problem, and, planning for the long haul, is calling for a tunnel through the riverbed.

This is the reason why scholars unanimously argue that much more careful and comprehensive planning should be set out before developing the eastern part of the island. Unfortunately, the harm done to the land in the east has still not been brought to a halt. Chao Kuo-chao, director of the Sixth Work Office of the Mountain Agricultural Resources Development Bureau, which has responsibility for land management and flood control in Hualien, says perplexedly that even before the "old wounds" can be healed upstream, new injuries--excessive deforestation--are being incurred on the slopes midstream and downstream.

The special nature of a mountainous area in the past made it difficult for agriculture to get a foothold on the east coast. But a by-product of the slopes today is to open up the road for them: "People often open production roads, and go up the mountains to plant day lilies, mushrooms, betelnuts, tea . . . so that they can never get ahead," states Chao Kuo-chao. For example, going along the Hualien-Taitung coastal road today, both sides are covered with betelnut trees.

A professor of civil engineering from the University of Washington in the US who has been to Taiwan believes that Taiwan's land and water protection engineering technology is by no means inferior to the West's. But the high frequency of water and flood related disasters in Taiwan are because, besides innate geographic conditions, "the authorities do not strictly control mountainside-over-development, and the people don't obey the law." Chao Kuo-chao frankly admits that today's problems are a tough nut to crack indeed. Last year the Amei River, located to the east of the Hsiu-kuluan River, and which originates in the Coastal Mountain Range, flooded over because of excessive silt buildup downstream. This year, the central, provincial, and county governments are preparing to spend NT$100 million to deal with this tiny, lessthan-10-kilometer-long stream.

The Foolish Old Man Who Moved the Mountain? How to deal with the cascading flow of soil and stone is an urgent problem. "You can't just keep making the dikes correspondingly higher every year. Hualien alone has 27 streams and rivers of various sizes!" exclaims Chao Kuo-chao. The cumulative impact of decades of logging is that virtually not a single stream in the eastern part of Taiwan has been fortunate enough to avoid massive erosion.

The common desire of the people of eastern Taiwan is to transport the rocks to the major cities in west Taiwan to be used as construction materials. But the transportation costs of transporting the east's stone and soil west are extravagant. In his term of office, former provincial governor Chiu Chuang-huan suggested building a stone pier at Pali in Taipei, moving the rocks by boat from Hualien Harbor. But this met the resistance of Pali residents who said it would destroy the scenery, and the plan died in the womb.

The geologic structure of the east and west coasts is vastly different, and just off the east coast there is a sea trench eight or nine thousand meters deep--so deep it couldn't be filled even if the whole Central Mountain Range could be sliced off and dumped in. Thus there is no hope of generating new land or reclaiming land from the sea by casting the rocks into the Pacific. "To do it that way would be too much of a waste of the stone and soil," says Huang Ta-pang, director of the Eastern Regional Office of the Provincial Bureau of Mines.

Even if they do just dump the rock into the Pacific, a direct stumbling block for soil and water protection workers is that they will be like "the foolish old man who moved the mountain." To move all of the soil and stone from east Taiwan's rivers elsewhere will unfortunately take not only as much patience as the old fool, but the old man only wanted to move one mountain, and if you want to move all the sediment from Hualien's waters, "I'm afraid you'd have to do it for 90% of the 27 rivers and streams," warns Chao Kuo-chao.

[Picture Caption]

The east coast geology is weak, making the erosion problem even more serious. The photo shows a home in Tungmen Village after it was buried in sand and rocks the year before last. (photo by Diago Chiu)

 

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