Lesson4undergroundwater地下水.doc

Lesson 4 underground water 地下水 Of all the earth’s water 97% is found in the oceans, 2% in glaciers and only 1% on land. Of this 1% almost all (97%) is found beneath the surface and called sub-surface or underground water. Most of this water eventually finds its way back to the sea either by underground movement or by rising into surface streams and lakes. 地球上的总水量中，97%在海洋，2%在冰川，只有1%在陆地上。陆地上的水几乎全部（97%）埋藏在地面一下，称为地下水。大部分地下水或通过地下流动，回到海洋；或先进入河流或湖泊，最终又回到海洋。 These vast underground water deposits provide much needed moisture for dry areas and irrigated districts. Underground water acts in similar ways to surface water, also performing geomorphic work as an agent of gradation. 这些广阔的地下含水层为干旱地区和灌溉区域提供了迫切需要的水分。地下水的作用和地表水的作用类似，也以均夷作用塑造着地貌。 Even though man has been aware of sub-surface water since earliest times, its nature, occurrence, movement and geomorphic significance have remained obscure. Recently, however, some answers have been found to the perplexing questions about underground water’s relationship to the hydrological cycle. 尽管人类自古以来就知道地下水，但对它的特性、发生、运动和地貌意义还不清楚。然而，近来关于地下水和水文循环关系的这些错综复杂的问题已找到了一些答案。 1 source of underground water地下水资源 Since the days of Vitruvius at the time of Christ, many theories have been presented to explain the large volume of water underneath the earth’s surface. One theory was that only the sea could provide such large quantities, the water moving underground from coastal areas. Vitruvius was the first to recognize that precipitation provided the main source of sub-surface water, although his explanations of the mechanics involved were not very scientific. 自从公元维特鲁维亚时代以来，为了解释在地面以下存在大量的地下水，已经提出了许多理论。一种理论认为 ： 只有海洋能提供大量的地下水，地下运动的水来自海岸带。维特鲁维亚是第一个认识到降水是地下水的主要来源，尽管他所涉及的力学方面的解释很不科学。 His theory, now firmly established, is termed the infiltration theory, and states that underground water is the result of water seeping downwards from the surface, either directly from precipitation or indirectly from streams and lakes. This form of water is termed meteoric. A ve