102 



THE IRRIGATION AGE. 



of the Hydrographic Division of the Geological 

 Survey.* 



The runoff map is intended to show at a glance the 

 wide difference in condition between the rivers and 

 creeks of different portions of the United States. It 

 is obviously impossible to show minute details, but it 

 is none the less important to those considering the 

 resources of different parts of the country to have 

 broad views concerning the physical conditions. 

 These the map attempts to give, and doubtless does* 

 when one looks at it from that standpoint. It is to 

 be hoped that in the future more detailed facts will 

 be obtained, and that this preliminary sketch may be 

 improved here and there until every locality is shown 

 with great exactness. 



As far as possible, data have been obtained for 

 each drainage basin, but there are large areas for 

 which it is impossible to obtain more than crude esti- 

 mates. The need of more extensive work in ascer- 

 taining the exact quantity of water available in each 

 stream, both east and west, is being more generally 

 appreciated, and it is hoped that within a few years 

 the different States, and possibly the United States, 

 may take up this investigation and maintain it con- 

 tinuously on a more extended scale. The results ob- 

 tained by the State Engineers of California and 

 Colorado, the U. S. Geological Survey, the State Ge- 

 ologist of New Jersey, and by other officials, have 

 demonstrated that investigations of this kind can be 

 carried on to reach definite ends at comparatively 

 moderate expenditures. 



DATA FOR RUN-OFF MAP, EASTERN HALF. 



In order to bring out more clearly the strength or 

 weakness of this graphic presentation of water 

 supply, the following figures are introduced, these 

 being condensed from voluminous computations of 

 daily and monthly discharge. First will be given the 

 mean annual discharge in depths in inches over the 

 basins of the Connecticut, Potomac and Savannah 

 rivers, these being representative of the heavily 

 shaded portion of the runoff map, marked 20 inches 

 and upwards, and covering the eastern and south- 

 eastern part of the United States. 



The figures for the Ohio, upper Mississippi and 

 Missouri basins are not yet reduced to compact 

 form; but in general it maybe said that the runoff 

 from the basin of the Ohio river is taken at about 25 

 inches, that of the upper Mississippi at 12 inches, and 



* Attention should be called to the fact that the title of the 

 map referred to is in error, the mistake probably arising while in 

 the hands of the printer from its similarity to the rainfall map 

 prepared by Mr. Gannett. 



Depth of annual runoff 

 eastern United States: 



from three large rivers of 



Year. 



1872 

 1873 

 1874 

 1875 

 1876 

 1877 

 1878 

 1879 

 1880 

 1881 

 1884 

 1885 

 1886 

 1887 

 1888 

 1889 

 1890 

 1891 

 1892 

 1893 



Connecticut, 

 inches. 



26.41 

 30.62 

 30.81 

 23.95 

 29.15 

 22.09 

 27.51 

 24.91 

 18.25 

 23.88 

 27.30 

 23.45 



Potomac, 

 inches. 



Savannah, 

 inches. 



15.30 

 14.50 

 18.83 

 37.06 

 26.13 

 32.57 

 17.37 

 18.45 



19.84 

 18.27 

 23.41 

 18.14 

 31.07 

 23.02 

 16.26 

 25.66 



Average, 25.69 22.53 21.95 



Computations by Cyrus C. Babb, in Transactions of American 

 Society of Civil Engineers, Vol. XXVII, et seq. 



of the Missouri at 3 inches. A comparison of these 

 three great rivers which unite to form the lower 

 Mississippi shows that the Ohio, draining the smallest 

 area, discharges by far the most water; the Mis- 

 sissippi, draining a larger area, discharges less; and 

 the Missouri, from an enormous basin, carries down 

 comparatively little water, so that, per square mile of 

 area drained, the quantity is only about one- eighth 

 or even one-tenth of that from the Ohio basin. 



The above facts illustrate the futility of sugges- 

 tions seriously made even lately, and upon the floor of 

 Congress. It has been urged that storage of the flood 

 waters of tributaries of the Mississippi, rising in the 

 Rocky mountains, would not only be of benefit to ir- 

 rigation but would diminish the disastrous floods of 

 the lower Mississippi valley. A study of the data, 

 however, such as given above, brings out the fact 

 that the flood waters from the Rocky mountains are 

 insignificant in relative proportion to those from the 

 Ohio and other tributaries. Further than this, they 

 usually come at another time of year and cannot be 

 said to have any perceptible influence on the destruc- 

 tive floods in the States of Arkansas, Mississippi and 

 Louisiana. 



