The aims of this study are to fully describe the nature of turbulent flow over an artificial redd built in gravel in an hydraulic flume. The study will identify the detail of the flow pattern around the redd and locate zones of high and low pressure at the gravel surface which promote intragravel flow. The main flow paths through the gravel will be delineated and the rate of intragravel flow will be determined at critical locations throughout the redd structure. The software SIDO will be recalibrated for use with UK salmonid fishes and graphical output will be produced of the predicted changes within the redd environment of such parameters as dissolved oxygen, egg survival and fish emergence. In summary the aim is to fully understand the physical environment around a salmonid redd and to test the recalibrated software SIDO for potential use by agencies within the UK.