VI.—River Curves Round Alluvial Plains

Extract

In the Geological Magazine for October, 1902, Dr. Callaway mentions the explanation of these curves that I gave in a paper printed twenty-one years ago. His quotation should be read with the immediate context—”These [the tributary streams] keep open a channel into which the larger stream falls.” This is the essence of my argument.

Professor Phillips and Sir A. Geikie have remarked that an alluvial plain in the course of a river may be regarded as an old lake-bottom, now drained; the lake-like appearance being renewed in times of flood. Let us suppose ABCB (Fig. 1) to represent such an area with a river flowing through it in a straight line, and, on one side, a tributary stream, or, to use a shorter and more expressive term, an affluent, coming in at an angle. Such a condition, if it existed, would not continue even in consolidated alluvial soil; it is still less likely to have existed in the soft mud when the area was first drained. A succession of floods would certainly wash away the bank where the affluent, coming through it, had caused a break in its continuity. By this the river-bed opposite the affluent would be expanded beyond its requirements when at low water. At every flood the whole of the bed of the river and the adjoining area of land will be covered with water, the ordinary river channel being effaced. From this water suspended matter falls and forms a deposit, visible after the flood has subsided, but in greater quantity on the banks by the sides of the low-water channel than on the adjoining land.