A monitoring system of a combined cycle power plant having a topping cycle performed by a gas turbine and a bottoming cycle performed by a steam turbine, the monitoring system. The monitoring system includes a processor that receives a first set of data indicating a first measurement value of an operating parameter of the combined cycle power plant. The processor determines a baseline efficiency of the process based on the first measurement value using a bottoming cycle performance (BCP) model. The processor determines a threshold based on the baseline efficiency. The processor receives a second set of data indicating a second measurement value of the operating parameter. The processor compare the threshold to an operational efficiency based on the second measurement value using the BCP model, and provides an indication of a decrease in efficiency of the process if the operational efficiency is below the threshold.