| OCR Text |
Show GOOD j; HIGHWAYS j PROTECT ROADS FROM RAINS Where Flood Spreads Out Over Val. ley, It Is Big Problem to Secure Proper Drainage. (Prepared by tho United States Department of Agriculture ) During July und August, cloudbursts, cloud-bursts, which are practically very heavy thunderstorms, cause serious problems in road construction In Nevada Ne-vada and Utah. The bureau of public roads of the United States Department of Agriculture has worked out several effective methods of protecting roads from these Immense sudden flows of water after long dry spells. Where the drainage channels are well defined de-fined no great difficulty Is Involved In the design of the road drainage structures struc-tures ; but whore the flood spreads out over a delta or a valley It Is a problem prob-lem so to locate the line and drainage structures that the latter will save the road from destruction. In sectious where the flood tends to spread out, a wide berm on each side of the roadway makes a substantial protection. The borrow pit provides 3: v I , I T - " . " , K J , L . ( v t Water-Soaked Roadway In Nevada. material for the embankment and serves as a diversion drain. Sometimes Some-times a short concrete dip is used for the purpose of passing the water over the road in a comparatively wide and shallow flow Instead of under it. A dip is simply a pavement extending the full width of the roadway and protected at each edge against undermining under-mining by a cut-off wall extending 18 Inches below the bottom of the pavement pave-ment Instead of attempting to build up a grade for this pavement, so as to raise it above the flood water, the dip follows the grade of the wash, and the water passes over it in time of flood. Where the deltas are so wide and the country so undevelojed as to make the cost of a concrete dip excessive, exces-sive, the dips are surfaced with gravel grav-el and the downstream edge Is protected protect-ed by a concrete cut-off wall. In connection con-nection with these drainage dips a V-shaped V-shaped system of dikes and ditches Is used, converging toward the road if it is desired to lead the flow from two or more washes to a single dip, and diverging toward the road when It Is better to split the flow of a single stream to more than one dip. |
