The Constant Monthly baseflow method allows the specification of a constant baseflow for each month of the year.
Unless parameters are carefully chosen, this method is not guaranteed to conserve mass (e.g., precipitation losses < baseflow volume).
This method is primarily intended for continuous simulation in subbasins where the baseflow is easily approximated by a constant flow for each month.
Required Parameters
Parameters that are required to utilize this method within HEC-HMS include the rate of baseflow for all twelve months throughout the year [ft3/sec or m3/sec]. These constant monthly baseflow rates are best estimated empirically using measurements of channel flow when storm runoff is not occurring. In the absence of such records, field inspection may help establish the average flow. For large watersheds with contribution from groundwater flow and for watersheds with year-round precipitation, the contribution may be significant and should not be ignored. On the other hand, for most urban channels and for smaller streams in the western and southwestern US, baseflow contributions may be negligible.
A tutorial describing an example application of this baseflow method, including parameter estimation and calibration, can be found here: Applying the Constant Monthly Baseflow Method.
