Frequency curves for water quality as support for the framework of water bodies from mathematical modeling under unsteady regime

ABSTRACT

Water quality models have been used as tools for planning and water resources management in many countries. Generally, in rivers the simulations are based on flow conditions under steady regime. However, urbanized basins have an intense dynamics, the consequence of land use and soil occupation mechanisms, able to induce pollution processes that require representation of physical, chemical and biological processes. The unsteady regime approach provides a better description of these characteristics, and a more consistent association of water quality and quantity interactions, based on a hydrodynamic representation of the system. This paper aims to contribute to this understanding using as case study the Iguaçu river, located in the metropolitan region of Curitiba, analyzing possible impacts of quality evaluations based on an analogy between steady and unsteady regime conditions as a manner of supporting water management elements. The proposed model (SIHQUAL), developed in traditional modules, uses explicit finite difference methods to solve the Saint-Venant equations integrated with the mass transport equation, for biochemical oxygen demand (BOD) and dissolved oxygen (DO) concentrations. The frequency curve concept was used to analyze the water quality. It was observed mainly that water quality models under unsteady state offer more flexibility and a different perspective for management, especially regarding the implementation of water resources management instruments, like the framework.

Keywords:
Water quality model; Saint-Venant equations; Water resources management; Iguaçu river