Reduced-complexity modeling of braided rivers: assessing model performance by sensitivity analysis, calibration and validation

This paper addresses an important question of modeling stream dynamics: how may numerical models of braided stream morphodynamics be rigorously and objectively evaluated against a real case study? Using simulations from the CAESAR Reduced-Complexity Model (RCM) of a 33km reach of a large gravel-bedded river (the Tagliamento, Italy) this paper aims to: (i) to identify a sound strategy for calibration and validation of RCMs; (ii) to investigate the effectiveness of multi-performance model assessments; (iii) to assess the potential of using CAESAR at meso spatial and temporal scales. The approach used has three main steps: firstly sensitivity analysis (with two steps - a screening method and a variance-based method), then calibration and finally validation. This approach allowed us to analyze 12 input factors initially and then to focus calibration only on the factors identified as most important. Sensitivity analysis and calibration were performed on a 7.5 km sub-reach, using a hydrological time series of 20 months; with validation on the full 33 km study reach over a period of eight years (2001 - 2009). CAESAR was able to reproduce the macro morphological changes of the study reach and gave good results as for annual bed load sediment estimates which turned out to be consistent with measurements in other large gravel-bed rivers, but showed a poorer performance in reproducing the characteristics of the braided channel (e.g. braiding intensity). The approach developed in this study can be effectively applied in other similar RCM contexts, allowing the use of RCMs not only in an explorative manner but also to obtain quantitative results and scenarios.

ZILIANI Luca;  SURIAN Nicola;  COULTHARD T. J.;  TARANTOLA Stefano; 

2014-02-18

AMER GEOPHYSICAL UNION

JRC84841

0148-0227,   

http://onlinelibrary.wiley.com/doi/10.1002/jgrf.20154/abstract,    jsessionid=B968477F3B4DD2F4B8425FE5934311DB.f01t04,    https://publications.jrc.ec.europa.eu/repository/handle/JRC84841,   

10.1002/jgrf.20154,