Infiltration excess overland flow is when there is flow of water hitting a spot that cannot handle the rate of water impacting it, the water then runs off since it cannot percolate into the soil. In this case, concrete has a very very low infiltration rate, so the water dripping from melting snow on the roof hits the concrete then runs off. FYI this does have real world implications, highways and urban environments definitely change the hydrology of streams due to concrete's lack of infiltration
2/1/2021