. Railroad structures and estimates . l gap. Ifplaced close to the dam, care must be taken to prevent the spillfrom endangering the dam from washing, saturation, or erosion, by 204 RAILROAD STRUCTURES AND ESTIMATES. building aprons and wings to prevent the water from passingaround or under the dam. For safety, waste water should alwaysbe discharged at a distance from the dam. Top of levee should be at least 6 feet wide and level with top ofdam, with slopes or waste side not steeper than 1 to 3, riprappedwhen possible. Difference in elevation between top of dam andbottom of waste way should not
. Railroad structures and estimates . l gap. Ifplaced close to the dam, care must be taken to prevent the spillfrom endangering the dam from washing, saturation, or erosion, by 204 RAILROAD STRUCTURES AND ESTIMATES. building aprons and wings to prevent the water from passingaround or under the dam. For safety, waste water should alwaysbe discharged at a distance from the dam. Top of levee should be at least 6 feet wide and level with top ofdam, with slopes or waste side not steeper than 1 to 3, riprappedwhen possible. Difference in elevation between top of dam andbottom of waste way should not be less than 4 feet, with slope ofdam side at angle of repose. A deep fall waste should have checks so as to form a series ofsmaller falls. The waste way may be constructed of timber as shown in sketch,though permanent material is more desirable. Crib and Masonry Dam. — When the location is convenientand only a gap or small length of dam is necessary a masonryor concrete wall or crib as illustrated in Figs. 93 and 94 is **) H M M\ .•*~>s ^fvV *) <j*} 4*1 CRIB DAM FSff. 93. Fis:. 94. With the masonry dam it would be necessary to have a wasteway at some natural point around the storage reservoir or a DAMS. 205 sluice with gate valves to let out the over surplus water in timeof floods or severe storms. The crib dam is built with three offsets so as to form a spillway in itself. The approximate cost of dams will vary greatly, depending onlocal conditions. Approximate cost. — Earth dams 12 feet high, per lineal foot,$5 to $15. Wood and crib 25 feet high, per lineal foot, $40 to$60. Stone dam 25 feet high, per lineal foot, $80 to $150. APPROXIMATE ESTIMATE GRAVITY WATER SUPPLY PIPE LINE 2500 FEETLONG (300 FEET IN DOUBLE WOOD BOX). Crib dam: 3000 lineal feet cedar logs at 15 cts $450. 00 6000 feet board measure timber at $50 200 cubic yards boulder fill at 50 cts 100. 00 Waste channel and fixing up gulley for overflow. ... $ Pipe line: 180
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