HYDRAULICS.] HYDROMECHANICS 479 diameter, and the greatest head above the fixed orifice is 1 metre. The use of this module involves a great sacrifice of level between the canal and the fields. The module is described in Lieutenant Scott Moncrioff s Irrigation in Southern Europe. 56. Reservoir Gauging Basins. In obtaining the power to store the water of streams in reservoirs, it is usual to concede to riparian owners below the reservoirs a right to a regulated supply through- - . out the year. This compensation water requires to be measured in such a way that the millowners and others interested in the matter can assure themselves that they are receiving a proper quantity, and they are generally allowed a certain amount of control as to the times during winch the daily supply is discharged into the stream. Figs. 72 and 73 show an arrangement designed for the Manches ter Water Works. The water enters from the reservoir a chamber A, the object of which is to still the irregular motion of the water. The admission is regulated by sluices at b, b, I. The water is dis charged by orifices or notches at a, a, over which a tolerably con stant head is maintained by adjusting the sluices at I, b, b. At any time the millownsrs can see whether the discharge is given and whether the proper head is maintained over the orifices. To test at any time the discharge of the orifices, a gauging basin B is Fig. 72. Scale provided. The water ordinarily flows over this, without entering it, on a floor of cast-iron plates. If the discharge is to be tested, the water is turned for a definite time into the gauging basin, by suddenly opening and closing a sluice at c. The volume of flow can be ascertained from the depth in the gauging chamber. A mechanical arrangement was designed for securing an absolutely constant head over the orifices at a, a. The orifices were formed Fig. 73. Scale in a cast-iron plate capable of sliding up and down, without sensible leakage, on the face of the wall of the chamber. The orifice plate was attached by a link to a lever, one end of which rested on the wall and the other on iloats/in the chamber A. The floats rose and fell with the changes of level in the chamber, and raised and lowered the orifice plate at the same time. This mechanical
arrangement was not finally adopted, careful watching of the sluices
