THE DEPTH OF RAIN WATER ON ROAD SURFACES
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THE DEPTH OF WATER RESULTING FROM STEADY RAINFALL ON PLANE ROAD SURFACES OF BRUSHED CONCRETE AND ROLLED ASPHALT WITH CHIPPINGS WAS STUDIED. THE SURFACES, WHICH ARE CURRENTLY USED ON MOTORWAYS IN THE UNITED KINGDOM, WERE STUDIED WITH THE AID OF A LARGE TILTING PLATFORM WHICH COULD BE SPRAYED WITH WATER TO SIMULATE RAINFALL OF VARIOUS INTENSITIES. THE DISTRIBUTION OF WATER ON THE SURFACES OF ROLLED ASPHALT WITH CHIPPINGS AND ON THE BRUSHED CONCRETE WAS SIMILAR, INDICATING THAT AS FAR AS THE HYDRAULICS OF RAIN WATER FLOW IS CONCERNED, THE SURFACES CAN BE CONSIDERED TO HAVE SIMILAR ROUGHNESSES. THIS IS PROBABLY DUE TO THE RAINDROP IMPACT BEING THE SIGNIFICANT FACTOR AFFECTING THE SHALLOW WATER FLOW. THE WATER DEPTH (D CM) IS RELATED TO THE DRAINAGE LENGTH (L M), RAINFALL INTENSITY (I CM/H) AND SLOPE (1/N) BY THE FORMULA D = 0.015 (L X I)TO THE 1/2 POWER TIMES N TO THE 1/5 POWER. INCREASING THE SLOPE OF A ROAD PAVEMENT FROM 1 IN 60 TO 1 IN 30 DECREASES THE DEPTH OF WATER ON THE ROAD BY ONLY 11 PER CENT AND IT IS CONCLUDED THAT THE MAJOR BENEFIT OF A STEEP CROSSFALL IS THE REDUCED VOLUME OF WATER WHICH CAN POND IN DEFORMATIONS OF THE PAVEMENT. /RRL/A/