Abstract. -Meso-scale classification of rivers has been used for decades in hydrology and ecology. Recent research has demonstrated a large potential for using this in ecohydraulics. Habitat modellers have to look at complex systems (e.g. catchments), where problems inherent in applying models developed for small scales applied for larger scales need to be overcome. The use of hydro-morphological units linked to meso-habitats extends the information and helps bypassing the problems arising from scale alteration. The process is called upscaling. This paper presents a physical approach for mesohabitat assessment in small to medium sized rivers, with the purpose of serving as a scaling tool for physical habitat information from micro-scale to macro-scale. Results of the assessment are to be used for population modelling of juvenile Atlantic salmon (Salmo salar). The system has been tested in Norway and in Great Britain on rivers of various sizes, has a flexible structure, so that it can be adapted to different situations and problems and is also rapid regarding habitat mapping.

There is a need to estimate design floods for areal planning and the design of important infrastructure. A major challenge is the mismatch between the length of the flood records and needed return periods. A majority of flood time series are shorter than 50 years, and the required return periods might be 200, 500, or 1,000 years. Consequently, the estimation uncertainty is large. In this paper, we investigated how the use of historical information might improve design flood estimation. We used annual maximum data from four selected Norwegian catchments, and historical flood information to provide an indication of water levels for the largest floods in the last two to three hundred years. We assessed the added value of using historical information and demonstrated that both reliability and stability improves, especially for short record lengths and long return periods. In this study, we used information on water levels, which showed the stability of river profiles to be a major challenge.