阿斯旺水坝的影响和三峡大坝

埃及的阿斯旺水坝修建于1970年。它建成之后，产生了许多事先预料不到的结果。水利和地质学家们在课本上总结说：

The Aswan High Dam of the Nile provides a good example of the many consequences of modifying a river system. For centuries, the Nile River has been the sole source of life in Egypt. The principal headwaters of the Nile are located in the high plateaus of Ethiopia. Once a year, for approximately a month, the Nile used to rise to flood stage and cover much of the fertile farmland in the Nile Delta area. The Aswan High Dam, completed in the summer of 1970, was to provide Egypt with water to irrigate 1 million acres of arid land and generate 10 billion kilowatts of power. This ,in turn, was to double the national income, and permit industrialization. The dam, however, destroyed the equilibrium of the Nile, and many unforeseen adjustments in the river resulted. This is what happened.

The Nile is not only the source of water for the delta. It is also the source of sediment. When the dam was finished and began to trap sediment in a reservoir, Lake Nasser, the physical and biological balance in the delta are was destroyed. Without the annual “gift of the Nile”, the delta coastline is now exposed to the full force of marine currents, and wave erosion is eating away at the delta front. Some parts of the delta are receding several meters a year.

The sediment previously carried by the Nile was an important link in the aquatic food chain, nourishing marine life in front of the delta. The recent lack of Nile sediment has reduced plankton and organic carbon to a third of the former levels. This change either killed off or drove away sardines, mackerel, clams, and crustaceans. The annual harvest of 16000metric tons of sardines and a fifth of the fish catch have been lost.

The sediment of the Nile also naturally fertilized the flood plain. Without this annual addition of soil nutrients, Egypt’s 1 million cultivated acres need artificial fertilizer.

The water discharged from the reservoir is clear, free of most its sediment load. Without its load, the discharged water flows downstream much faster and is vigorously eroding the channel bank. This scouring process has already destroyed three old barrier dams and new barrier dams between Aswan and the ocean must be built at a cost equal to one-fourth the cost of the Aswan Dam itself.

The annual flood of the Nile was also important to the ecology of the area, because it washed away salts that formed in the arid soil. Soil salinity has already increased, not only in the delta, but throughout the middle and upper Nile area. Unless corrective measures are taken (at a cost of over $1 billion), millions of acres will revert to desert within a decade.

The change in the river system has permitted double the cropping, but there are no periods of dryness. The dry seasons previously helped limit the population of bilharzias, a blood parasite carried by snails, which infects the intestinal and urinary tracts of humans. One out of every two Egyptians now has the infection, and causes a tenth of the deaths in the country.

Problems have also occurred in the lake behind the dam. The lake was to have reached a maximum level in 1970, but it might actually take 200 years to fill. More than 15,000,000 m³ of water annually escaped underground into the porous Nubian Sandstone which lines 480 km of absorbing an almost unlimited quantity of water. Moreover, the lake is located in one of the hottest and driest places on the earth, and the rate of evaporation is staggering. A high rate was expected, but additional losses from transpiration by plants growing along the lakeshore and increased evaporation from high winds have brought the total loss of water from the lake to nearly double the expected rate. This loss equals half the total amount of water that once was “wasted”, flowing unused to the ocean.

W Kenneth Hamblin：The Earth’s Dynamic systems (Four Edition) 1985版.第10章River Systems

我选择了几段（有的段没有翻译），大意翻译如下：

尼罗河不仅是三角洲水的来源，也是沉积物的来源。当大坝完工后，开始拦截沉积物在水库中，三角洲的物质和生物上的平衡机制被打破了。没有了一年一度的“尼罗河礼物”，三角洲的海岸线完全暴露在强劲的洋流面前，三角洲某些地方的海岸线每年后退数米远。

以前尼罗河带来的沉积物是水生物食物链的重要环节，滋养了三角洲附近的海生物。最近缺少尼罗河的沉积物，已经导致了浮游生物和有机碳减少到了过去三分之一的水平。这样的变化不是灭绝了或者赶走了沙丁鱼、mackerel 、贝类和甲壳类生物。年捕捞16000吨的沙丁鱼和五分之一的鱼类捕捞量已经消失了。

尼罗河的沉积物也给泛洪平原施肥，没有了这些每年的额外肥料，埃及1百万英亩的农田需要人工施肥。

尼罗河每年一度的洪水泛滥对于该地区的生态也是非常重要的，因为洪水冲刷走了在干旱土壤里沉积的盐分，现在三角洲的盐分已经增加了，并且还在上部和中部尼罗河地区也是一样的。除非采取适当的措施（代价超过10亿美元），1百万英亩的农田将在未来几十年内重新返回成荒漠。

河流系统的变化使得农业收成翻倍，但也使得干旱季节消失了。以前干旱季节限制了一种携带血吸虫的螺的数量。这种血吸虫感染人的肠道和泌尿系统。现在每两个埃及人中就有一个感染了血吸虫，这占了全国死亡原因的十分之一。

问题也发生在大坝后面的库区。湖面在1970年达到最高水平，在未来200年的时间内，库区会被淤平。库区西岸480公里长的地区是多孔的怒比亚砂岩。每年有一千5百万立方米的水渗到这些地下砂岩里。这些砂岩吸水的能力几乎是没有限制的。另外，库区是位于地球上最干旱和炎热的地区之一，蒸发率是令人吃惊得高。现在湖边生长的植物的蒸腾作用和高速的风增加的蒸发量使得湖区水的损失超过了原来期待值的一倍。这个数量等于该河每年注入海洋的流量的一半。人们通常认为那是“浪费掉了”的水量。

这些知识在1985年就写入了课本。这些后果，当时已经很清楚了。人们通常会说“当事后聪明人很容易（It is easy to be wise after the event）”，而中国在修建三峡水库前吸取了这些教训吗？根本没有！何况，中国人自己早就搞清楚了大型水库会诱发地震，加剧库区某些地区的山体滑坡，等等，等等。

对此，中国人去搞什么重新发现！就算如此，那些知识也是根本不起任何作用的。

既然任何知识对于中国人来说，几乎不起作用，那么，他们遭到大自然的报复，就是一种报应了。怪谁呢？“吾谁欺？欺天乎？”2000年前刘秀的话，用到此处，不是很合适吗？