Uncertainty and sensitivity analysis of a travel‐time distribution‐based stream water electrical conductivity model

• Published in: Hydrological processes Vol. 38; no. 5
• Main Authors: Riazi, Zahra, Western, Andrew W.
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley & Sons, Inc 01-05-2024; Wiley Subscription Services, Inc
• Subjects: Age; Algorithms; Aquatic birds; Catchment area; Electrical conductivity; Electrical resistivity; Evapotranspiration; Hydrology; Parameter sensitivity; Parameter uncertainty; Parameters; Rainfall; Rivers; Sensitivity analysis; Solutes; Stream discharge; Stream flow; Stream water; Travel; Travel time; travel time distribution; Uncertainty; Uncertainty analysis; uncertainty and sensitivity analysis; Water quality; water quality model
• ISSN: 0885-6087; 1099-1085
• DOI: 10.1002/hyp.15168

In this paper, we analyse the uncertainty and parameter sensitivity of a conceptual water quality model, based on a travel time distribution (TTD) approach, simulating electrical conductivity (EC) in the Duck River, Northwest Tasmania, Australia for a 2‐year period. Dynamic TTDs of stream water were estimated using the StorAge Selection (SAS) approach, which was coupled with two alternate methods to model stream water EC: (1) a solute‐balance approach and (2) a water age‐based approach. Uncertainty analysis using the Differential Evaluation Adoptive Metropolis (DREAM) algorithm showed that: 1. parameter uncertainty was a small contribution to the overall uncertainty; 2. most uncertainty was related to input data uncertainty and model structure; 3. slightly lower total error was obtained in the water age‐based model than the solute‐balance model; 4. using time‐variant SAS functions reduced the model uncertainty markedly, which likely reflects the effect of dynamic hydrological conditions over the year affecting the relative importance of different flow pathways over time. Model parameter sensitivity analysis using the Variogram Analysis of Response Surfaces (VARS‐TOOL) framework found that parameters directly related to the EC concentration were most sensitive. In the solute‐balance model, the rainfall concentration Crain and in the age‐based model, the parameter controlling the rate of change of EC with age (λ) were the most sensitive parameter. Model parameters controlling the age mixes of both evapotranspiration and streamflow water fluxes (i.e., the SAS function parameters) were influential for the solute‐balance model. Little change in parameter sensitivity over time was found for the age‐based concentration relationship; however, the parameter sensitivity was quite dynamic over time for the solute‐balance approach. The overarching outcomes provide water quality modellers, engineers and managers greater insight into catchment functioning and its dependence on hydrological conditions.
Differential Evaluation Adoptive Metropolis and Variogram Analysis of Response Surfaces are used to analyse the uncertainty and sensitivity of age‐based and solute‐balance concentration models coupled with the StorAge Selection approach to water travel time distributions and stream electrical conductivity. The most important parameters are those directly related to the concentration algorithms, and the next most important are those related to the travel time simulation. Parameter uncertainty was found to play only a small role in the overall model uncertainty.