ed by road builders, but during recent years constantly increasing attention has been given to this phase of road construction. It is unfortunate

ct or minimize the importance of drainage in connection with either earth roads or any class of surfaced roa

tes, which are, roughly, those portions east of a north and south line passing through Omaha and Kansas City, together with the northern part of the Pacific slope, precipitation is generally in excess of 30 inches per year and fairly well distribute

year and its effect as an agent of erosion is of greatest significance, although in re

ent, and, to do so, a study must be made of all factors that have any bearing on the drainage requirements and the probable effect

iable thickness under the traveled part of the road. This layer should probably never be less than two feet thick and for soils of a structure favorable to cap

ion. Very frequently, deterioration of a road surface is directly attributable to failure to provide adequately for the removal of the storm water or water from the melting of snow that has fallen on the road, or water that flows to the road from land adjacent thereto. Surface water can usually most cheaply and expeditiously be carried a

o several feet, but may be well distributed throughout the year with an absence of excessive rainfall for short periods, that is, flood conditions may rarely occur. In other areas, the annual rainfall may be comparatively small but t

nd that drains to the road ditches will soak into the soil and therefore not reach the ditches along the road. The extent to which the water is taken up by the soil will vary with the porosity and slope of the land and the character of the growth thereon. Cultivated land will

considerable absorption of storm water. Surfaces such as sandclay, gravel and macadam do not absorb to exceed 10 per cent of the prec

ore, all of the water will run off, as the soil will reach a state of saturatio

ined, the character of the soil, the slopes and the rainfall char

ith an increase in the grade of the ditch. If the surface water must be carried along the road for distances exceeding five or six hund

to great refinement in the design of the side ditches for the ordinary case where the water is carried along the road for only a few hundred feet. The ditches are made of ample capacity by using the commonly accepted cross section for a road, which will be discusse

epth may be decreased one foot, and for grades of four per cent and upward, the depth may be still less. These general rules for depth are susceptible of variation but are believed to be the minimum except in arid or semi-arid climates. It is far better to be too liberal in

to account. Sometimes such water can be diverted by ditches well back from the road, and thus prevented from flowing into the side ditches along the roadway. It is esp

ally if the gradient is less than one per cent, and the construction work should be checked to insure that the ditch is actually constructed as planned. A few high places in the ditch will greatly reduce

disturbed natural soil, five feet or more from the toe of the slope of the fill, and along the filled portion of the ro

arger part being absorbed by the soil. The water thus absorbed flows downward through the pores in the soil until it is deflected laterally by some physical

hers. If a cut is made in grading the road, the road surface may actually be lower than the ground water level in the land adjoining the road. As a result, the water will seep out of the side slopes in the cut and keep the ditches wet, or even furnish enough water to occasion a flow in the ditch. Si

ghway. The impervious stratum may not actually outcrop but may lie only a few feet under the surface of the road, in which case, the road surface will be so water soaked as to be unstable. The so-called "seepy places" so often noted along a road are generally the result of this condition. This condition can be corrected by t

water rising to a level not far below the road surface, the ground water level is lowered by means of tile underdrains. The fun

ound water level well down. They must be carefully laid to line and grade. A good outlet must be provided and the last few joints of pipe should be bell-and-spigo

ration of surface water to the tile. In other instances, it is advantageous to place catch basins about every three or four hundred feet. These may be of concrete or of tile placed on end or may be blind catch basins formed by filling a section of the trench with broken st

rely a matter of size. Generally, structures of spans less than about eight feet are classed as culverts,

e extent and physical characteristics of the drainage area. Sometimes there is sufficient evidence at the site to indicate quite closely the size required, but this should always be checked by run-off computations. The drainage area contributing water to the stream passing through the culvert under consideration is computed from contou

Formula

ge area above culvert. C a factor varying from 1 for flat country to 4 for mountainous cou

Area of waterway

inage area

according to ci

is longer in proportion to the area, decrease C. In districts not affected by accumulated snow, and where the length of valley is several times its width, 1/5 or 1/6 or even less may be used. C should be increased f

of Pipe Culve

ditches. This is a minimum of 20 feet for secondary roads and ranges from 24 to 30 feet for main roads. The headwall to the cu

These culverts are usually about 16 feet along, and should be of a size adequate to take the flow of the side ditch. The farm

of C

ecause of the rectangular form of the cross section. Culverts of pre-cast pipe

cal Concrete

is known that the pipe made from uncoated, light sheet steel is not very durable. Sheet iron and sheets made from alloy iron coated with spelter have been extensively used and seem to be durable, especially when laid deep enough to eliminate possibility of damage from hea

, preferably on a concrete cradle and the joints filled with cement mortar. Culverts of this type have a tendency to break under unusual loads, such as traction engines or trucks. T

ed. The pipe should be carefully laid on a firm earth bed with earth carefully back-filled and tamped around th

coming choked with earth and to retain the roadway at the culvert. It also indicates to the drivers the location of the end of the culvert. The endwall extends a foo

ypes of Drop

but especially for the larger ones. These are usually constructed with endwalls integral with the barrel of the culvert. Culverts of this type must be designed for the

Drop Inl

floor of the culvert. This is a reason for placing the culvert as high as the roadway will permit, so long as the area above the culvert will be properly drained. Considerable reclamation of land

, as would sometimes be the case on side hill roads, the culvert barrel would follow the gen