HK1HWAY ;X)\STI{i;(TK)N -II 



stream; (2) by measuring, preferably at time of high water, a cross- 

 section of the stream at some narrow place; and (\\) determining the 

 height of high water as indicated by drift and the evidence of the 

 inhabitants of the neighborhood. 



On mountain roads or roads subjected to heavy rainfall culverts 

 of ample dimensions should be provided wherever required, and it 

 will be more economical to construct them of masonry. In localities 

 where boulders and other debris are likely to be washed down during 

 wet weather, it will be a good precaution to construct catch pools at 

 the entrance of all culverts and cross drains for the reception of 

 such matter. In hard soil or rock these catch pools will be simple 

 well-like excavations, with their bottom two or three feet below the 

 entrance sill or floor of the culvert or drain. Where the soil is soft 

 they should be lined with stone laid dry; if very soft, with masonry. 

 The size of the catch pools will depend upon the width of the drainage 

 works. They should be wide enough to prevent the drains from 

 being injured by falling rocks and stones of a not inordinate size. 



The use of catch pools obviates the necessity of building culverts 

 and drains at an angle to the axis of the road. Oblique structures 

 are objectionable, as being longer than if set at right angles and by 

 reason of the acute- and obtuse-angled terminations. to their piers, 

 abutments, and coverings. 



Materials for Culverts. Culverts may be of stone, brick, vitri- 

 fied earthenware, or iron pipe. Wood should be absolutely avoided. 



For small streams and a limited surface of rainfall either class 

 of pipes, in sizes varying from 12 to 24 inches in diameter, will serve 

 excellently. They are easily laid, and if properly bedded, with the 

 earth tamped about them, are very permanent. Their upper surface 

 should be at least 18 inches below r the road surface, and the upper 

 end should be protected with stone paving so arranged that the water 

 can in no case work in around the pipe. 



When the flow of water is estimated to be too great for two lines 

 of 24-inch pipes, a culvert is required. If stone abounds, it may be 

 built of large roughly squared stones laid either dry or in mortar. 

 When the span required is more than "> feet, arch culverts either of 

 stone or brick masonry may be employed. For spans al>ove 15 feet 

 the structure required becomes a bridge. 



