Popular Science Monthly
��ing the dry season. The ancients had great works of this kind on the Nile and the Euphrates. We have the largest in the world in the United States today.
The chief point of interest about many of the works of this kind built in Germany is the manner in which the interests bene- fited cooperate in paying for their construc-
��water users was formed to cooperate in financing works to increase the low-water flow of the Ruhr. This was called Ruhrtalsperren-Verein or Ruhr Reservoir Association.
In 1904 an exceptionally dry year made it apparent that additional storage on a large scale was necessar\- to prevent a
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��In the valleys of the Miami and Scioto Rivers, near Dajrton and Columbus, several conservation districts for preventing floods have been formed under the Conservancy Law of Ohio, passed in 1914 as a result of the great flood of March, 1913, which almost destroyed the locality
��tion and maintenance. This cooperation is effected under the provisions of a law passed in 1879, which provides for the organization of water users' associations.
The most important of these associations is the one made up of the water users of the Ruhr Valley. The Ruhr is a large tributary entering the Rhine not far below Diisseldorf. It is about one hundred and forty miles long, and drains an area of a little over two thousand square miles. It flows through the great iron and steel manufacturing center of Germany, around Essen (the home of the Krupp works), and is extensively used for domestic and in- dustrial water supply and for water power. In 1899 a voluntary' association of the
��disastrous water shortage in the valley. ^ After e.xhaustive investigations the Ruhr Association decided to build at its own ex- pense a great reservoir on the Mohne River, one of the principal tributaries of the Ruhr. Work was begun in January, 1908, and the reser\oir was completed in December, 1912, in exactly four years.
The Mohne Reservoir is the largest on the Ruhr basin, and the second largest in Europe. It has a capacity of about 4,600- 000.000 cubic feet and controls the run-off from about one hundred and sixty square miles. The dam is built of rubble masonry, arched upstream, and is one hundred and thirty-two feet high, twenty feet wide on top, one hundred and twelve feet wide at