12 houses x 51 = 612 discharge units. Flow graph gives 150mm-dia. foul drain since the convergence of the two lines on the graph is between the pipe size 100mm diameter and 150mm diameter. Surface Water Pipe Sizing The following method is one way of sizing pipework. Choose a minimum gradient for all pipes, say 1:80 Use the table below to calculate the flow rate in each section. SURFACE TYPE AREA IMPERMEABILITY TOTAL FACTOR (f) (A) m2 (A x f) Road or 0.90 pavement Roof 0.95 Path 0.75 Garden 0.25 Access road, 0.90 parking Total The area of each surface is calculated from drawings. The impermeability factor allows for water, which runs off each surface. The flow rate (Q) for each house can be calculated from:
12 houses x 51 = 612 discharge units. Flow graph gives 150mm-dia. foul drain since the convergence of the two lines on the graph is between the pipe size 100mm diameter and 150mm diameter. Surface Water Pipe Sizing The following method is one way of sizing pipework. Choose a minimum gradient for all pipes, say 1:80 Use the table below to calculate the flow rate in each section. SURFACE TYPE AREA (A) m2 IMPERMEABILITY FACTOR (f) TOTAL (A x f) Road or pavement 0.90 Roof 0.95 Path 0.75 Garden 0.25 Access road, parking 0.90 Total The area of each surface is calculated from drawings. The impermeability factor allows for water, which runs off each surface. The flow rate (Q) for each house can be calculated from: