Comparação entre ferramentas computacionais de modelagem da qualidade da água em ambiente lótico

Abstract

The increased pollutant load released into watercourses over time leads to significant changes in water quality standards. These changes impact the quality, the diversity of the biota and the various uses of the waters. Water quality modeling through computational tools has proved to be an important tool in planning and managing water resources. The use of mathematical models allows the efficient management of water resources, as it allows the joint analysis of the quality and quantity of water. In general, an accelerated development of water quality models was observed, increasing their applications regarding the number of dimensions represented, the number of modeled constituents, interface with GIS and its interaction with aquatic ecosystems. Thus, the models diversity varies both because of the application purpose, and the complexity of their use, representation of the medium and its constituents. This master's thesis compares three computational tools for water quality modeling in a lotic environment: QUAL-UFMG, QUALI-TOOL and HEC- RAS, pointing out potentialities and limitations with a focus on the creation of water topology, data input procedures (geometric, hydraulic, fluviometric, water quality and coefficients of physical and biochemical processes). It also analyses the results in simulations of dissolved oxygen, biochemical demand for oxygen, organic nitrogen, ammonia, nitrate and total phosphorus. It has been used a watercourse with an average annual water capacity of 4.8 m3/s and punctual release of high pollutant load (528.8 kgDBO/day, 163.8 kgNO/day and 6.2 kgP/day during the dry season), specifically Jordão River, the hydrographic basin of Dourados River, Triângulo Mineiro, Brazil. The simulations were carried out in the dry and rainy season, data extracted from De Paula (2011) and Salla et al. (2013). Comparing all three tools, longitudinal profiles of the quality parameters kept the same trend, except for dissolved oxygen in the QUAL-UFMG tool during the dry and rainy season and nitrogen series in the HEC-RAS tool for the rainy season. Also, the methods for calculating the net depth and flow velocity directly interfered in longitudinal profiles of dissolved oxygen and nitrogen series. In addition, upon an operational analysis, QUAL-UFMG and QUALI-TOOL tools were similar because they were developed in Excel spreadsheet formats and used the same mathematical equation.

For more simplified studies, on a reduced scale, QUAL-UFMG and QUALI-TOOL tools provide sufficient results, and they also have an user-friendly interface, are of free distribution, and of an easy access to the user. The HEC-RAS tool proved to be more complex due to the greater amount of input data required in hydraulic and water quality modeling. HEC-RAS also has a connection with GIS. In contrast, HEC-RAS has the limitation of non-variation of the coefficients of the biochemical reactions model. Also, the need to include a cross section to feed the pollutant loads in the main river limits its use in studies with financial limitations for fieldwork.