Lawrence D.,Norwegian Water Resources and Energy
Hydrology Research | Year: 2016
This paper presents the regionalisation of the three parameter event-based PQRUT model, which is used for design flood analyses. The PQRUT model is used for the analysis of peak flows for which a sub-daily temporal resolution is required. The availability of high-resolution discharge data and disaggregated precipitation data have made it possible to re-evaluate the regional regression equations currently in use. We also assess whether the model parameters show spatial dependency. Event-based calibration was performed for the 45 highest flood events for each of 55 selected catchments across Norway, representing peak flows generated predominantly by rainfall. Due to the geographical heterogeneity of most areas in Norway, a statistically significant homogeneous region was only identified for catchments in southeastern Norway. Multiple linear regression and weighted regression were, therefore, used to develop a single set of equations, applicable to the entire country. The results for the weighted regression indicate a decrease in the median Kling-Gupta efficiency from 0.64 to 0.51 for calibration and regionalisation, respectively. The results also suggest that regression methods may perform better than methods based on spatial proximity in regions with varying topography when a parsimonious model is used. © IWA Publishing 2016 Hy.
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.
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.