HYDRAULIC DESIGN OF PAVED AREAS

Significant increases in car and air travel have resulted in a corresponding increase in the number and size of paved areas in the UK. These large areas can produce considerable amounts of surface water runoff in heavy storms. A 28-month study into the design of drainage for large paved areas was conducted. A numerical program was developed for the calculation of water depths on pavements, site data was collected for the validation of the program, and design guidance was developed. The monitoring sites were an aircraft stand at Heathrow Airport (rigid pavement) and a prupose-built pavement representative of a car park (flexible pavement). Data from an earlier laboratory study jointly carried out by HR Wallingford and TRL limited was also used. For the railfall/runoff model a good agreement was found between the model predictions and site measurements when a 'loss model' was applied, in which the rainfall profile is reduced by subtraction of a constant loss rate. Critical storm durations were determined for the four pavement surfaces studied. For impervious surfaces the largest flows were during heavy short-duration storms. Mean rainfall intensity was simulated for three characteristic UK rainfall locations. Design guidance was produced for 2-dimensional catchment lengths from 10-100m and slopes of 1/150 to 1/50 as these values constitute an envelope of the conditions for which paved areas are likely to be designed in the future. Tables of data are provided.