the nile river is egypt's lifeblood. ople here cling to its path through the desert and cluster in its broad delta. our case explores human modification of the environment as humans harness the mighty nile through projects like the aswan dam, lake nasser and the new toshka canal; the move from subsistence to commercial agriculture; and how an expanding population in the nile river delta is encroaching on the area's remaining precious farmland. from space, the earth can seem an abstract pattern of color and shape, but as we look closer, environmental processes come into view. here the rain of east-central africa collects in the giant lake victoria. its waters drain to the north, giving rise o of the world's great rirs, the nile descending from the african highlands, the nile winds through one of earth's most arid landscapes. coursing through the vast desert of northern africa, the waters of the nile nourish a ribbon of green across the sun-baked terrain. and 4,000 miles from its source, the nile puts forth its greatest gif

the source of all this water, many early philosophers theorized that the waters of the nile, as well as all other rivers, originated from a system of boundless underground fountains. then in the 17th century, french scientist pierre perrault conducted a simple experiment that would yield a startling discovery. perrault reasoned that rivers transport snow and rain from the land to the oceans. to test this hypothesis, he compared rainfall with the flow, or discharge, of a river. he first measured the amount of water flowing annually in the river seine in france. then he calculated rainfall for the upstream drainage basin surrounding the river. perrault found to his surprise that rainfall was six times as large as the flow of the river. so early speculation about rivers actually addressed the wrong question. the problem was not... where does river water come from? but...where does all the excess rainfall go? only about 1/4 of earth's annual precipitation flows in rivers. the rest seeps underground to become ground water or is stored as glacial ice or soil moisture or is returned to the atmosphere by evapor