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Does PondPack use TR-20 or TR-55 for the SCS Unit Hydrograph calculations?
TR-55 was a simplified procedure that was used when engineers didn't have computers that could properly crunch the numbers for them. It was simplified from TR-20. TR-20 is typically preferred in modeling software.In PondPack, the SCS default approach uses a hybrid of the strengths of HEC-1 and TR-20. To choose to strictly use HEC-1 or TR-20, change the method under Tools > Options.The curve number tables PondPack uses were taken from TR-55.Further references in the PondPack help documentation:1) The section titled "Overview of the SCS Unit Hydrograph Method" (location may differ depending on your PondPack version, so I would suggest doing a search).2) The section titled "CN Weighting", which discusses how the CN information is based on TR-55.