Subject: Rules for NRSCS Unit Hydrographs in InfoSWMM
Rules or Guidelines for NRSCS Unit Hydrographs if used as the Hydrology Option in InfoSWMM and H2OMAP SWMM:
1. The Unit Hydrograph CN comes from the Subcatchment Table and the NRCS_CN Column
2. Time of Concentration is from the TC column in the Subcatchment Table
3. The Infiltration Model should be from the CN infiltration Model Column in the Subcatchment Database Table
4. The CN in the Soil Database Table should be the same as the CN in the Subcatchment Database Table
5. If the Depression Storage is zero in the Subcatchment Database Table then the Initial Abstraction in inches will be calculated as 0.2*(1000/CN-10) internally in the engine
6. Initial Abstraction or IA in US Units = 0.2*(1000/CN-10) in American Units
