The opportunity to detect, analyse intensity and forecast development of filtration and erosion processes is one of the key issues in monitoring earth dams. These processes pose the major danger to the safety of such structures. Thermal analysis of the distributed fibre optic temperature measurements carried out in the dam's body is currently the most effective monitoring method. This method requires application of models for analysing temperature measurements enabling the reading of information contained in thermal signal transmitted through the soil medium, including data on water filtration and erosion processes relating thereto. The IRFTA (impulse response function thermal analysis) model is one of such models developed by the Authors of this article. The model parameters have physical definition. They allow the expert concerned with dam surveillance to identify a leakage in its early development phase, to determine precisely by parametric physical description the intensity of the filtration process, and also to analyse its time-variability. The opportunity to use this model for analysing filtration processes in the event of placing the temperature sensors in the dam downstream toe is a specific advantage of the IRFTA model. This article includes description of the model and effective application examples of two earth hydraulic structures equipped with distributed temperature fibre optic measurements networks. Besides, the Authors present the opportunity to determine water filtration velocity on the basis of scientific equations derived for the IRFTA model parameters.