H = 100 mm/h S= 300 m2 V = volume in litres/second to discharge H = intensity of rain in mm/hour S = surface of drainage area in m2 Knowing the intensity of the rain (H) and the surface to be drained (S), the volume of water to be channeled is determined (V) with the formula: V= H x S 3600 V= = 8,33 l/s 100 x 300 3600 m. 30 m. 10 8,33 is the volume of water to be discharged per second EXAMPLE: how to apply the formula for an area of 300 m2 with an average rainfall off 100 mm/h UNDERGROUND PRODUCTS DRAINING CALCULATIONS AND TECHNICS 8 The underground products of First Plast, such as the drain well boxes with grids or covers, gully traps or modular channels, are ideal for drainage of rainwater. The collection of water can be carried out with two systems: for areas (rectangular or square) or linear. DRAINAGE FOR AREA: The drainage system for areas can be suitable in case the water falls into a surface that can be divided into more slopes that decline towards a network of wells or gullies. LINEAR DRAINAGE: The linear drainage system is set up if the area to be drained is made up of a single slope (or double as in the picture on the right) that drives the water into a drainage channel, a functional and aesthetic water collection solution. DRAINAGE FOR AREA LINEAR DRAINAGE The simplicity of using PVC FIRST products allows the creation of drainage networks in any type of rain. If a system of evacuation is chosen for points (with traps, grilles, siphons) or for trenches (grilled channels) it is always indispensable to know exactly the volume of fallen rain water in order to plan adequate canalization. Having obtained the volume of water to be drained, the position of draining point is planned in the intervention area choosing between two possibilities: 1 - the model of grill well is chosen and the quantity of use is calculated 2 - the number of grill wells to be set is decided calculating which model is suited to the volume of water obtained.
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