Three variations of Thomas-Fiering log normal 3-parameter(TFLN3) model are fitted to the unregulated south-west monsoon-dependent monthly streamflows measured at Krishnarajasagara (KRS) on Cauvery, river in Southern India. The variations arise from the method of parameter estimation used in fitting the LN3 distribution. The validation is based on the preservation of the over-year drought characteristics using aggregated annual flows. It is observed that TFLN3 model with the moment estimator(MOM) is able to preserve the severe historical deficit volumes. However, none of the three estimators is able to preserve severe historical drought durations (at 90% truncation level). Further, the influence of monthly carry-over effects on drought characteristics is also investigated using historical flows.