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Footing Drains

Footing Drains

Footing Drains

Is there any methods to calculate/estiimate the flow from footing drains... we have a storm sewer system that does not have any surface water inlets, and are trying to predict the peak flow.


RE: Footing Drains

You need to know what the possible variables are and determine which is controlling the flow:

1.  You can probably get your footing drain size from the design plans, perforation size and distribution from the manufacturer.  Calculate the length of pipe it would take for full flow to occur if the flow was only restricted by the perforations.

2.  Is there a sock on the drain?  Manufacturer can probably tell you what the max/avg flow rate is through a square foot of material.  Calculate the maximum flow allowed to the pipe for the square footage of sock you have if there were no other restrictions.

3.  Was the trench backfilled with gravel?  Use darcy's law to estimate the possible flow to the sock if there were no other restrictions.

4.  Estimate the possible flow from the soil on the edge of the trench to the gravel in the trench using darcy's law.

Use this info to determine what the controlling variable is

Or just try Manning's equation wih a minimal slope, that is your peak flow.

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