Water quality modelling for small river basins

Abstract

Water quality modelling in small rivers is often considered unworthy from a practical and economic viewpoint. This paper shows instead that a simple model structure can be set up to describe the stationary water quality in small river basins in terms of carbon and nitrogen compounds, when the use of complex models is unfeasible. In short rivers point and nonpoint sources play a key role in shaping the model response, being as important as the self-purification dynamics. Further, the varying river characteristics, in terms of morphology, hydraulics and vegetation, require the introduction of variable parameters, thus complicating the originally simple model structure. To determine the identifiability of the resulting model an identifiability assessment was carried out, based on sensitivity analysis and optimal experiment design criteria. The identifiable subset was determined by ranking the parameters in terms of sensitivity and computing the associated Fisher Information Matrices. It was found that the inclusion of the nonpoint sources as piecewise constant parameters affected the identifiability to a considerable extent. However, the combined parameteresources calibration was made possible by the use of a robust estimation algorithm, which also provided estimation confidence limits. The calibrated model responses are in good agreement with the data and can be used as scenario generators in a general strategy to conserve or improve the water quality.

Dilution and volatilization of groundwater contaminant discharges in streams

“…Incorporating varying river characteristics such as morphology and vegetation into the model would require site specific data, which are often not available and the introduction of variable parameters (Guymer 1998;Marsili-Libelli and Giusti 2008), thus complicating the simple model structure.…”

A parsimonious dynamic model for river water quality assessment

“…A Monte Carlo procedure was used to generate large numbers of sets of parameters for both sub-models, each parameter value being drawn from ranges (Table 1) thought feasible for the Savena River on the basis of physical argument and previous experience (Brown et al 1970;Willems 2000;Cox 2003;Radwan et al 2003;Marsili-Libelli & Giusti (2008)). …”

“…When employing such models, the goal is to reduce the complexity and effort spent on computation and analysis. Tailoring a model type for a certain application depends on the project objectives and the data availability (Marsili-Libelli & Giusti 2008). Detailed models are very useful for short-term simulations of representative events (Radwan et al 2003).…”

A hydrodynamic water quality model for propagation of pollutants in rivers

“…However, especially for small rivers, some problems hamper a straightforward application of the model due to data scarcity, lack of major investments because of their minor importance, and the large number of diverse inputs, especially if they flow through densely populated areas (Marsili-Libelli & Giusti 2008). These facts constitute the major complexities for applying water quality models, such as those provided by the US Environmental Protection Agency; QUAL2E (Brown & Barnwell 1987), QUAL2K (Chapra & Pellettier 2003), WASP6 (Wool et al 2001), or the IWA River Quality Model No.…”

“…To avoid this source of subjectivity, the parameter variation ranges used in this study were estimated by calibration using multiple events(Beven & Binley 1992). Concerning the model calculation grid, for the present application, a Dx equal to 25 m and a dt equal to 1 s have been employed.RESULTSA Monte Carlo procedure was used to generate large numbers of sets of parameters for both sub-models thought feasible for the Savena River on the basis of physical argument and previous experience(Willems 2000;Cox 2003;Radwan et al 2003;Marsili-Libelli & Giusti 2008; …”