Shelter for juvenile Atlantic salmon: availability and prediction in rivers with and without hydropower regulation.

It is assumed that river regulation in general and hydropeaking in particular, cause elevated degrees of fine sediments in river beds which affect negatively habitat quality for juvenile salmon. Finstad et al. (2007) developed a method to measure interstitial spaces (shelter abundance for fish) in running waters. Shelter availability is a candidate mechanism for the survival of juvenile salmon due to the reduction of predation risk and is influenced by the degree of fines. The first goal of this study is to find better relationship between shelter abundance measured with the method by Finstad et al. (2007), and grain size distribution. This relationship will be based on a dataset by (Jocham, 2010) and own data gathered from the river Gaula in Norway. The second goal of the study is to implement the new relationship into the one-dimensional hydraulic model HEC-RAS, in order to predict the development of shelter over time. Here, two main flow scenarios will be investigated at two river sites, Lundesokna and Nidelva streams from Middle-Norway. As a forerunner before the main simulations, sensibility tests will be run to estimate differences between several empirical sediment transport equations, sorting methods, computational time steps and an extreme flood event s effect on river bed. In the case of main flow scenarios, the first hydrograph consists of an average yearly runoff without the hydropower regulation. The second hydrograph will be in correlation with the yearly energy production of the regulation power company. The comparison at the end of the study contains the main differences between the two type of hydrograph related to chosen and calculated parameters. These variables proved their worth to play key factors in the differentiation between operated and natural type of hydrographs with their effects on river bed morphology. Nevertheless, major differences cannot be observed among the cases, some anomalies are occurred in details, which are going to be explained at the evaluation of the results