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Zinke P.,Sintef | Bogen J.,Norwegian Water Resources and Energy
Hydrology Research | Year: 2013

Water level changes resulting from a hydropower regulation have influenced water flow, gradients and sediment processes in the Lake Øyeren delta for about 150 years. They are reflected in the morphology of the islands on the delta plain. Under current regulation practices, water levels during the mean annual flood are maintained at about 1 m lower than during the previous regime prior to 1978. As the channels continue to mature, the recently deposited tongues and levees in the southern part will therefore probably maintain a distinctly lower elevation than that of the older islands. The influence of flood regulation on levee deposits during the extreme 1995 flood was estimated by comparing simulated overbank deposits resulting from different flood regulation schemes. The simulations showed that reduced water levels during floods in the presence of older islands extend the period of in-channel flow and promote the development of levee-like deposits in the lower part of the delta plain. This explains some of the characteristics observed in the morphological development, most notably the increased number of lagoons resulting from a higher number of levees. © Centre for Ecology and Hydrology 2013. Source


Dyrrdal A.V.,Norwegian Meteorological Institute | Saloranta T.,Norwegian Water Resources and Energy | Skaugen T.,Norwegian Water Resources and Energy | Stranden H.B.,Norwegian Water Resources and Energy
Hydrology Research | Year: 2013

Observed trends in annual maximum snow depth (SD) in Norway are analyzed and examined in the context of changes in winter climate from 1961 until today. Trends are evaluated for the 50-year period (1961-2010) and for three 30-year periods (1961-1990, 1971-2000, 1981-2010). The analyzed dataset is the most extensive and geographically representative for the country so far, and the analysis gives an up-to-date picture of the recent development in snow accumulation. In regions characterized by colder winter climate long-term trends are found to be positive in general, while short-term trends shift from strongly positive in the first period to predominantly negative in the last period. Variation in SD is here mainly linked to variation in precipitation. In regions of warmer winter climate variation in SD is dominated by temperature, and long-term trends are mainly negative. Short-term trends start out weak overall in the first period but become strongly negative most places in the last period. It is likely that, although more and more regions in Norway will experience declining maximum annual SD in a projected wetter and warmer future climate, some inland and higher mountain regions may still accumulate more snow in the coming decades. © IWA Publishing 2013. Source

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