Additional Drainage

Below is the research and calculations that went into designing the additional drainage system. The system will be in the style of a french drain which uses a corrugated pipe to reroute runoff to the weep berm. The system totals 1,230 feet of pipe with a 6" diameter pipe on both sides of the park, each installed with no flatter than a 1% slope. The following spreadsheet calculates the maximum flowrate through a 4 in, 6 in, and 8 in diameter pipe under open-channel, orifice, and pipe flow conditions. The calculated flowrates were compared to the target flowrates for the left and right side of the park to determine the necessary pipe sizes. The target flowrate is that of a 5 year-24 hour storm as determined in the precipitation analysis in Fall 2020 Milestones.

Below is the spreadsheet used to determine the size and number of pipes needed for outflow from the weep berm. The number of pipes is decided as that which will drain 60% of the stored water above the pipe invert within 24 hours and 100% within 72 hours (Warner, 2012). The total number of pipes was determined to be 6 for both weep berms. Flow was assumed to be orifice flow as the pipe inlets are submerged and the outlets are not submerged.