Popular Science Monthly 



739 



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 



