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Fig. 4: Left – an orthophoto image with the developments in the HPP Brežice construction pit site; right – the same site captured using the numerical mesh of the 2D hydraulic model [4] A physical model in a scale of 1:45 was also built for this case and the conditions in the plant’s immediate area were analysed to an extent allowed for by the characteristics of the installations at the Institute for Hydraulic Research. It comprised the area of the entire HPP construction pit with a diversion channel and the Sava River reach 600 m downstream the envisaged dam location. Flow and velocity fields, water levels for dimensioning cut-off barriers at the construction pit and erosive action in riverbanks and the channel during the construction [6]. Fig. 5: Physical model of the HPP Brežice construction pit (Hidroinštitut, 2011). In the diversion channel the remains of the sand left from studying sediment transport capacity are evident The coupling of physical and numerical modelling is reflected both in determining the boundary conditions for the physical model from investigating the wider area and the additional calibration of the numerical model to analyse the 1140