Analysing the results of the New Zealand national hydrological model for estimating design floods

Kling, D.J. (2016) Analysing the results of the New Zealand national hydrological model for estimating design floods.

Abstract:For use in design of bridges, levees and other civil structures design floods are needed. These floods can be estimated by hydrological models. The National Institute of Water and Atmospheric research is delivering efforts in improving flood modelling in ungauged catchments. A way of doing this is testing if the national hydrological model, TopNet, is fit for use on ungauged catchments on a national scale. To answer whether or not TopNet is fit for flood estimation in ungauged catchments, the mean annual floods have been analysed at first. For evaluation the relative bias and the root mean square relative error were used. Furthermore, the time series of TopNet and observations were statistically compared mean ranks, variance and distribution. Because of the vast difference in geology in New Zealand spatial patterns in model performance are to be expected. To evaluate this expectation, the model error and statistical tests are visualised on maps and summarised per island. Explanations for model behaviour are investigated. This is done by calculating Spearman’s correlation coefficient for catchments characteristics. Another effort to explain checking whether or not TopNet simulates the flood event at the same dates. Lastly TopNet is compared to the empiric model currently in use and its recently improved version. To do this the relative bias and Root Mean Square Relative Error are compared. Another performance parameter is introduced, the Root Mean Square Weighted Error. This parameter weights the errors by using both the observation and model record lengths. TopNet has a significant error in estimating mean annual floods. The maps and comparison between islands did not show any clear spatial patterns nor significant differences between areas. No strong correlation between catchment characteristics and error can be found. The channel area, slope and elevation however have the strongest correlation to the error. The TopNet model seems to do a decent job at the timing of the flood events for about half of the cases. Comparison with the empiric models points out that TopNet in its current state produces worse results. All in all, TopNet is promising and may after improvement be a better way for flood estimation in ungauged catchments than using an empiric model but in its current state it is unfit.
Item Type:Essay (Bachelor)
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering BSc (56952)
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