mainly for storage projects the stations are so located that both the high-water and the low water conditions can be studied with equal accuracy. The equipment at the stations consists of a gage for measuring heights of the water surface, and some support from which the meter measurements can be made. The gage is either a fixed wooden staff or is of the standard chain type. Gage heights are read daily by some person living in the vicinity, who is employed for the purpose, and the records are transmitted to the resident hydrographer on postal-card forms prepared for that purpose. Measurements of the flow or discharge are made with current meters from a bridge, boat, cable, or by wading. (See Pl. VII.) Whenever possible, stations are established at bridges, where stations can be equipped at little expense. The measurement, which is usually made by the resident hydrographer or an assistant, consists in dividing the cross section of the stream at the gaging station into an arbitrary number of parts and determining the area and mean velocity for each part; the product of these two factors gives the discharge for each part, and the total discharge is the sum of these partial discharges. An effort is made to take the measurements at different stages, so that when they are plotted on cross-section paper enough points will be had to construct a discharge curve that will extend from extreme high to extreme low water. Aside from the meter stations, a few determinations of flow are made by small weirs and at mill dams. The current meter is an instrument for determining the velocity of flow of streams. In general it consists of a wheel carrying a series of cups which rotate about a horizontal or a vertical axis. Connected with this axis is either an electric or an acoustic appliance for counting the number of revolutions. The velocity per second is indicated by the number of revolutions per second. This relation is determined separately for each meter by drawing the meter through still water. The length and time of the run and the number of revolutions are recorded by automatic devices, and from these factors the velocity in feet per second, to correspond to any number of revolutions, is determined. Pl. VIII, A, shows the equipment at meter-rating stations. In operation the meter is held in the water and headed against the current, which causes the wheel to rotate. Since the organization of the work five types of meters have been used-Fteley, Ellis, Haskell, Bailey, and Price. Each of these has its good points, but the Price meter best fulfils the demands of the work and is in general use. The Price meter is made in two sizes. It consists of a wheel containing five conical cups, rotating about a vertical axis, which is connected by a copper-wire cable to a small battery buzzer, and is so arranged as to make and break contact with each revolution of the wheel. (See Pl. IX.) This is indicated by a buzz. The cable serves the double purpose of supporting the meter and of transmitting the current from the battery. A tail keeps the meter headed against the current, and leaden weights hold it at the proper depth. With the exception of the conical cups the various parts and appliances of this meter have been modified by hydrographers of the Geological Survey. The data collected by this division have formed the basis of all reclamation investigations, and the success of the reclamation service is largely dependent upon the hydrographic studies of the last fifteen years. In the East, where the data are principally used in estimates for water-power developments, power plants costing in the aggregate millions of dollars have been built, based upon information furnished by the hydrographic division. The records of the division have been of great value in estimating available water supplies for large cities, and the data have proved of great importance in lawsuits or arbitration for settling satisfactorily the relative rights of various claimants on the basis of the physical facts. Information in regard to floods is a later but no less important feature of its investigations. For publications prepared by this division see the Survey's list of publications. DIVISION OF HYDROLOGY. Eastern and Western Sections. The division of hydrology deals with underground waters, in the same manner that the division of hydrography deals with surface waters, the aim being to obtain and publish for the benefit of the people information relating to the occurrence, movements, methods of obtaining, and uses of artesian and other underground waters, including those reaching the surface both in wells and in springs. As underground waters are intimately connected with many geologic features, more or less attention has been given to them throughout the existence of the Survey, but mostly in connection with the investigation of other problems. Two special reports, one on the conditions of artesian wells and another on the hot-spring deposits of the Yellowstone National Park, were published in the Fifth and Ninth annual reports, respectively; and papers on potable waters and on natural mineral waters appeared in the Fourteenth Annual Report. To carry out the provision of the act of October 2, 1888, previously quoted (p. 75), the hydrographic work of the Survey was organized, and during the first year some progress was made in the investigation of underground water supplies. Every year since 1888 more or less hydrologic work has been done, by field investigations in both the West and the East. These have yielded a number of reports on underground-water resources, and a large collection of data is preserved in the office for future reference and elaboration. |