HEC HMS Unit Hydrograph generation problem

[mary]

Hello to everyone,
I am a new user of HEC-HMS and I can’t figure out the following
problem:
I have one rainfall gauge station on my study area. The data is daily
(i.e. one record per day).My flash flood spans for 12 days. I would
want to generate the hydrograph on the basis of this rain data, using
the Loss SCS Curve Number method and the SCS Unit Hydrograph
Transform method. I determined the CN by following the Purdue
university tutorial, along with all the hydrologic parameters needed.
I also determined the Basin Lag and the Time of Concentration
according to the HEC HMS users’ manual. My problem is that the
hydrograph generated has values 10 to 15 times smaller than the
streamflow measured data, hence giving significant calibration errors.
I have no idea at all what do I do wrong, considering that a few
months ago, on the same river basin, with the same type of data, I
managed to generate a hydrograph that fitted the measured streamflow
hydrograph.
Any suggestions would help a lot.
Thanks,
Mary