HYDRAULICS OF RUNOFF FROM DEVELOPED SURFACES

RUNOFF PRODUCED BY RAINFALL ON A DEVELOPED SURFACE, SUCH AS A HIGHWAY PAVEMENT OR AIRFIELD RUNWAY, TAKES PLACE AS "OVERLAND" FLOW IN A THIN SHEET ACROSS THE SURFACE. USUALLY THIS OVERLAND FLOW IS COLLECTED IN A LONGITUDINAL GUTTER. THE FIRST PART OF THIS PAPER DEALS WITH THE HYDRAULICS OF OVERLAND FLOW AS DEVELOPED FROM A COOPERATIVE EXPERIMENTAL PROJECT. A METHOD IS GIVEN FOR COMPUTING THE HYDROGRAPH OF RUNOFF RESULTING FROM GIVEN RATES OF RAINFALL TAKING INTO CONSIDERATION THE ROUGHNESS, SLOPE, AND LENGTH OF THE SURFACE. THE SECOND PART OF THE PAPER IS BASED ON AN ANALYTICAL STUDY OF THE HYDRAULICS OF FLOW IN A GUTTER COLLECTING RUNOFF ALONG THE EDGE OF A PAVEMENT. THE STUDY SHOWS HOW STORAGE IN THE GUTTER CAUSES THE OUTFLOW HYDROGRAPH TO LAG BEHIND THE INFLOW HYDROGRAPH. AN APPROXIMATE METHOD IS GIVEN FOR COMPUTING THE HYDROGRAPH OF OUTFLOW TAKING INTO CONSIDERATION THE ROUGHNESS, GRADE AND LENGTH OF THE GUTTER AS WELL AS THE CHARACTERISTICS OF OVERLAND FLOW. AS A PRACTICAL APPLICATION CURVES ARE DEVELOPED GIVING THE MAXIMUM RATE OF RUNOFF ON A GIVEN ROADWAY CROSS-SECTION FOR VARIOUS LENGTHS OF ROADWAY AS LIMITED BY THE INTENSITY-DURATION RAINFALL FREQUENCY CURVES FOR A GIVEN LOCALITY. /AUTHOR/