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<br />DISCHARGE MEASUREMENTS AT GAGING STATIONS <br /> <br />27 <br /> <br /> <br />Fi9ure 43.-Bridge board in use. <br /> <br />4. A life preserver for each hydrographer. <br />5. A bailing device. <br />Figure 49 shows the equipment assembled <br />in a boat. <br /> <br />Icrt equipment <br />Current-meter measurements under ice cover <br />require special equipment for cutting holes in <br />the ice through which to suspend the meter. <br />Cutting holes through the ice on streams <br />to make discharge measurements has long been <br />a laborious and time-consuming job. The <br />development of power ice drills, however, has <br />eliminated many of the difficulties and has <br />reduced considerably the time required to cut <br />the holes. <br />Holes are often cut with a commercial ice <br />drill that cuts a 6-inch-diameter hole. (See <br />fig. 50.) The drill weighs about 30 pounds and <br />under good conditions will cut through 2 feet <br />of ice in about a minute. <br />Where it is impractical to use the ice drill, <br />ice chisels are used to cut the holes. Ice chisels <br />used are usually 4 or 4~ feet long and weigh <br />about 12 pounds. The ice chisel is used when <br /> <br />first crossing an ice-covered stream to deter- <br />mine whether the ice is strong enough to support <br />the hydrographer. If a solid blow of the chisel <br />blade does not penetrate the ice, it is safe to <br />walk on, providing the ice is in contact with <br />the water. <br />Some hydrographers supplement the ice <br />chisel with a Swedish ice auger. The cutting <br />blade of this auger is a spadelike tool of hard- <br />ened steel which cuts a hole 6-8 inches in <br />diameter, by turning a bracelike arrangement <br />on top of the shaft. <br />When holes in the ice are cut, the water is <br />usually under pressure owing to the weight of <br />the ice, and it comes up in the hole. In order to <br />determine the effective depth of the stream <br />(see p. 42), ice-measuring sticks are used to <br />measure the distance from the water surface <br />to the bottom of the ice. This is done with a <br />bar about 4 feet long, made of strap steel or <br />wood, graduated in feet and tenths of a foot <br />and having an L-shaped projection at the lower <br />end. The horizontal part of the L is held on the <br />underside of the ice and the depth to that point <br />is read at the water surface on the graduated <br />part of the stick. The horizontal part of the L <br />is at least 4 inches long so that it may extend <br />beyond any irregularities on the underside of <br />the ice. <br />When the total depth of water under ice <br />cover is greater than 10 or 12 feet, a sounding <br />reel or handline is usually used. The sounding <br />reel is mounted on a collapsible support set <br />on runners. (See fig. 51.) <br />A special ice-weight assembly is used for <br />sounding under ice because a regular sounding <br />weight will not fit through the hole cut by the <br />ice drill. (See fig. 51.) The weights and meter <br />are placed in a framework that will fit through <br />the drilled hole. <br /> <br />V elocity-c zimuth-depth-assembly <br /> <br />The velocity-azimuth-depth-assembly, com- <br />monly called V ADA, combines a sonic sounder <br />with a remote-indicating compass and Price <br />current meter to record depth, indicate the <br />direction of flow, and permit observations of <br />velocity at any point. <br />In figure 52, the azimuth-indicating unit is <br />shown mounted on the four-wheel crane. <br />Incorporated within the remote-indicator box <br />