38 HIGHWAY CONSTRUCTION 



it is necessary that water should cross the road a culvert should be 



built. 



g 



On the side hill or mountain roads catch-water ditches should 

 be cut on the mountain side above the road, to cut off and convey the 

 drainage of the ground above them to the neighboring ravines. The 

 size of these ditches will be determined by the amount of rainfall, 

 extent of drainage from the mountain which they intercept, and by the 

 distances of the ravine water courses on each side. 



The inner road gutter should be of ample dimensions to carry 

 off the water reaching it; when in soil, it should be roughly paved with 

 stone. When paving is not absolutely necessary, but it is desirable 

 to arrest the scouring action of running water during heavy rains, 

 stone weirs may be erected across the gutter at convenient intervals. 

 The outer gutter need not be more than 12 inches wide and 9 inches 

 deep. The gutter is formed by a depression in the surface of the 

 road close to the parapet or revetted earthen protection mound. The 

 drainage which falls into this gutter is led off through the parapet, 

 or other roadside protection at frequent intervals. The guard stones 

 on the outside of the road are placed in and across this gutter, just 

 below the drainage holes, so as to turn the current of the drainage 

 into these holes or channels. On straight reaches, with parapet 

 protection, drainage holes with guard stones should be placed every 

 20 feet apart. Where earthen mounds are used and it may not be 

 convenient to have the drainage holes or channels every 20 feet, the 

 guardstones are to be placed in advance of the gutter to allow the 

 drainage to pass behind them. This drainage is either to be run off 

 at the cross drainage of the road, or to be turned off as beiore by a 

 guard stone set across the gutter. 



At re-entering turns, where the outer side of the road requires 

 particular protection, guard stones should be placed every 4 feet. 

 As all re-entering turns should be protected by parapets, the drainage 

 holes through them may be placed as close together as desired. 



Culverts are necessary for carrying under a road the streams 

 it crosses, and also for conveying the surface water collected in the 

 side ditches from the upper side to that side on which the natural 

 water courses lie. 



Especial care is required to provide an ample way for the water 



