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Ground Water [1]:![Ground Water [1]](img/ground-water-[1]-.jpg) When the river reaches the sea the sediment it is carrying is deposited. In some areas tidal currents are strong enough to remove it and the river ends in an estuary. Where more sediment is brought down than can be removed by the sea a delta is formed [10].
Heavy and prolonged rain may make level ground water [1] waterlogged. But once the rain has stopped, the ground water [1] will dry out as the water sinks into it. In hot weather standing water will evaporate and plants will absorb water through their roots, transpiring it from their leaves. Sloping ground water [1] drains quickly, for the water that cannot Sink into the ground water [1] flows downhill in rills, then in streams and finally in rivers. That part of the rain that has percolated into the ground water [1] will emerge later, at a lower level in the terrain, as a spring and flow away as a stream or river.
In many limestone areas, including chalk downlands, there is a complete valley system, but most of the valleys are now dry with no flowing streams in them. Limestone is a highly permeable rock, so that any rain quickly seeps into it to add to the ground water [1] water at depth. That is the position under the present climatic conditions, but in the past rainfall may have been much greater. The level of the ground water [1] water would then rise and springs break out higher up the valley sides. During glacial episodes, rainfall or meltwater could not seep into the frozen ground water [1], but must have flowed away, carving the valleys.
Another recently discovered method involves measuring the amount of water the rocks contain. Under strain, the pores in the rock enlarge, allowing more water to enter. Because of the importance of ground water [1] water in producing earthquakes, knowledge of the water level in wells in earthquake-prone areas is extremely valuable. |
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