【2009.09.22 地球观象台】当日图片：人类活动导致三角洲地区下沉

rhapsody

【中文标题】人类活动导致三角洲地区下沉
【原文标题】Sinking deltas due to human activities
【标题说明】这里用的是文中介绍的一篇相关论文的题目，原文用的是下边的配图标题。
【登载媒体】地球观象台（Earth Observatory）
【来源地址】http://earthobservatory.nasa.gov/IOTD/view.php?id=40257
【译者】rhapsody
【声明】本译文供Anti-CNN使用，未经AC或译者许可，谢绝转载，谢谢合作

Sinking River Deltas — Irrawaddy River: Image of the Day

配图：下沉的河流三角洲——伊洛瓦底江（当日图片）

Rivers flow across the world’s continents, picking up soil as they grow and move towards the ocean. When rivers pour into the sea, the dirt and rocks sink as fresh water disperses into salt. Over time, rich flat land, a delta, builds around the river mouth, usually forming a triangular shape. Deltas are rich agricultural land and provide easy access to water and water-based transportation. As a result, many of the world’s largest deltas are heavily populated. Nearly half a billion people live on or near deltas, and that could be an increasingly serious problem, says James Syvitski, a researcher at the University of Colorado, and his collaborators.
江河流经世界各大洲，在成长和奔向大海的同时也夹带了沙土。当江河倾注入大海时，淡水散入盐中而松土和沙石沉积下来。日积月累，在江河口堆积成了肥沃的平原，通常呈现出三角形的形状——也就是所谓的三角洲。三角洲是肥沃的耕地，并且提供了便利的用水及水路运输。因此，世界上最大的三角洲大多人口密集。近五亿人口生活在三角洲及其周围地区——而根据科罗拉多大学的研究人员詹姆斯·西维茨基与其同僚的说法——这可能成为一个日益严重的问题。

In a paper published in Nature Geoscience on September 20, 2009, Syvitski and his colleagues warn that deltas throughout the world are sinking, largely because of human activity. One of the deltas in danger is the Irrawaddy River delta in Burma (Myanmar), shown in this image. The image is an elevation map, made from data collected by the Shuttle Radar Topography Mission. Higher elevations are white, while lower elevations are depicted in green. The Irrawaddy Delta is clearly flat, much of it below five meters in elevation. This low elevation makes the delta particularly prone to flooding from storm surges. In April 2008, Cyclone Nargis flooded much of the delta, killing thousands. As deltas sink, storm surges can move farther inland, affecting more people.
在登载于2009年9月20日出版的《自然地理科学》杂志的一篇论文中，西维茨基和他的同事们警告说世界范围内的三角洲正在下沉，而这很大程度上是人类活动所导致的。其中一个面临威胁的三角洲就是上图所示的，缅甸境内的伊洛瓦底江三角洲[1]。上图是一张高低立位图[2]，根据航天飞机雷达地形测绘计划[3]采集的数据而制成的。高地用白色表示，而低地则用绿色标出。伊洛瓦底江三角洲显然相当低平，多数地方海拔都在5米以下。低海拔使得该三角洲特别容易受到风暴潮引发的洪水的侵袭。2008年4月，纳尔吉斯台风引发的洪水淹没了该三角洲大部分地区，导致数千人死亡。而由于三角洲的下沉，风暴潮侵袭的范围可能向内陆进一步延伸，影响到更多的人。

Syvitski and his colleagues used shuttle radar topography data compared to historic maps to assess the condition of 33 of the world’s largest deltas. They found that many of the deltas were sinking, and as a result, the delta area vulnerable to flooding could increase by 50 percent in the twenty-first century. Disastrous storm surge flooding like that seen in the wake of Cyclone Nargis or Hurricane Katrina could become more common.
西维茨基和他的同事们利用航天飞机雷达地形测绘数据与历史地图进行比较，评价了世界最大的33个三角洲地区的状况。他们发现其中多数三角洲地区正在下沉，因此在21世纪，受到洪涝灾害的三角洲地区面积可能上升50个百分点。纳尔吉斯台风或卡特琳娜飓风中出现过的灾难性风暴潮洪水，亦可能变得更为常见。

The deltas are sinking for a number of reasons. Deltas grow when they receive new sediment, often during seasonal floods. Rivers split into many channels that wander across the delta, distributing sediment. In this image, small dark green channels reveal where the Irrawaddy once meandered across its delta before finding its current path, which is marked in blue. Higher-elevation white squiggles are probably the canopy of trees growing along small water channels. But wandering rivers are very inconvenient for people, who build canals to divert the water and prevent flooding in cities built on the delta. People also build dams along major rivers to control flooding and generate power. The sediment in the river water gets trapped behind the dams. In the end, less sediment reaches the deltas, so they are not regenerated. Even during severe floods, the authors found that little sediment was being added to many of the deltas.
造成三角洲地区的下沉有几个原因。三角洲的成长需要吸收新的沉积物，而这通常是在季节性泛滥的时候。江河分成众多支流淌过三角洲，带来沉积物。在上图中，小型的暗绿色渠道展示了伊洛瓦底江曾经蜿蜒流淌过的轨迹，而现时的流向渠道则是以蓝色标出。高海拔的白色短线可能是沿着小水道的树木形成的树冠层。但蜿蜒曲折的河流对于人们来说相当不便，于是人们建造运河来改变水流方向，并防止洪水侵袭建在三角洲上的城市。人们还在大江大河上建造大坝来控制洪峰和进行发电。江河水中的沉积物也就被大坝给挡住了。最终，抵达三角洲的沉积物变少了，三角洲也就没能得到补给。甚至于在严重洪涝时期，诸位作者也难以观察到三角洲中沉积物的增加，对于其中的多数三角洲而言都是如此。

Even as the deltas are not being replenished with fresh soil, sediment in the delta is compacted or erodes away, naturally causing the delta to sink. The delta may sink farther if oil, gas, or water are pumped out of the delta. If the delta sinks faster than it gets new soil, it becomes increasingly prone to floods, both from the river itself and from storm surges. Even if the delta is building, it must build faster than sea levels are rising, or it will, in effect, sink.
由于三角洲得不到新土壤的补充，其沉积物受到固结或侵蚀，自然会引起三角洲的下沉。如果油、气或水被抽出三角洲，它可能下沉得更厉害。如果三角洲下沉速度快于其吸收新土壤的速度，它会变得更容易受到洪涝灾害，洪水可能来自河流本身，也可能来自风暴潮。即使三角洲在成长，其成长速度也必须比海平面上升速度更快才行；否则，实际上，它还是相当于在下沉。

【相关论文题目和摘要】

Sinking deltas due to human activities

Many of the world's largest deltas are densely populated and heavily farmed. Yet many of their inhabitants are becoming increasingly vulnerable to flooding and conversions of their land to open ocean. The vulnerability is a result of sediment compaction from the removal of oil, gas and water from the delta's underlying sediments, the trapping of sediment in reservoirs upstream and floodplain engineering in combination with rising global sea level. Here we present an assessment of 33 deltas chosen to represent the world's deltas. We find that in the past decade, 85% of the deltas experienced severe flooding, resulting in the temporary submergence of 260,000 km2. We conservatively estimate that the delta surface area vulnerable to flooding could increase by 50% under the current projected values for sea-level rise in the twenty-first century. This figure could increase if the capture of sediment upstream persists and continues to prevent the growth and buffering of the deltas.

http://www.nature.com/ngeo/journal/vaop/ncurrent/abs/ngeo629.html

【译注】
[1]伊洛瓦底江从德耶谬以下是下游河段，德耶谬至缅昂是下游谷地，缅昂以南，伊江呈伞形分成多支汊河流入安达曼海，形成著名的伊洛瓦底江三角洲。三角洲从勃生河口以东至仰光河口，宽约242公里，面积为32400平方公里。
[2]这个词按照专业术语应译为“高程图”，取这样的名称是为了更直观易懂。
[3]航天飞机雷达地形测绘计划（英文简称SRTM）的数据主要是由美国太空总署(NASA)和国防部国家测绘局(NIMA)联合测量的。2000年2月11日上午11时44分，美国“奋进”号航天飞机在佛罗里达州卡那维拉尔角的航天发射中心发射升空，“奋进”号上搭载的SRTM系统共计进行了222小时23分钟的数据采集工作，获取北纬60度至南纬56度之间，面积超过1.19亿平方公里的9.8万亿字节的雷达影像数据，覆盖全球陆地表面的80%以上，该计划共耗资3.64亿美元，获取的雷达影像数据经过两年多的处理，制成了数字地形高程模型。

trsita

沙發 做了

中国平凡人

是不是长三角就有这样的问题存在？

rhapsody

是不是长三角就有这样的问题存在？
中国平凡人 发表于 2009-9-23 19:52

不止。。。据报长江三角洲、珠江三角洲及黄河三角洲根据该项研究的说法都处于“最严重级别”。。。{:10_402:}
参见消息：http://bbs.m4.cn/thread-197767-1-1.html

curiouspuppy