Transient events e.g. valve closures, initiate pressure oscillations in the pipeline with specific frequency and damping rate. It is known that a lateral disturbance of the flow such a leak causes a noticeable attenuation of transients. In this study we have experimentally tested if analyses of changes of transient damping rate and damping modes can be used for detection of intrusion location and size. Results showed that both the frequency and the decay rate were influenced by the intrusion. Opening of the intrusion port and pumping liquid into the system results in change of frequency, regardless of intrusion rate. However, intrusion flow rate also has an effect on damping of oscillations – they decay faster at higher intrusion rates.