On characteristic hydraulic times through hydrodynamic modelling: discussion and application in Patos Lagoon (RS)

Abstract

Although the analyses of characteristic hydraulic times are important diagnostic tools for studying water mass exchanges and identifying areas prone to stagnation that are potentially subjected to eutrophication effects, their concepts and uses are often misinterpreted. This paper compares similarities and differences between widely used characteristic hydraulic times, CHT, known as Residence Time, Times of Water Renewal Rates and Water Age. A proper definition for each of these characteristic hydraulic times is stated to avoid the existing confusion with multiple concepts in the literature. Methodologies to compute these CHT through hydrodynamic modelling systems are presented and, in order to enhance understanding, applied to three idealized cases in steady flow channels: (1) Channel with uniform flow; (2) Channel with a lateral inflow; and (3) Channel with a lateral embayment. Finally, a practical example is discussed by applying the methodologies to the Patos Lagoon (RS). The results for the idealized channel cases are non-intuitive and this theoretical discussion clarifies the interpretation and uses of different timescales and outlines the Water Age as the more versatile and multifunctional timescale if compared to the others addressed here. The results for the Patos Lagoon exemplify the valuable information that CHT can offer for environmental management in natural water bodies.

Meteorological and potential climatic influence on high cyanobacterial biomass within Patos Lagoon (southern Brazil): A case study of the summer of 2019–2020

“…The wind pattern also shifts due to ENSO, with La Niña showing more S-quadrant winds, which can contribute to reducing seaward flow. Because of this low discharge and S-quadrant winds, PL has a higher residence time (Fernandes et al, 2002;Aguilera et al, 2020), which might allow the development of freshwater algae and cyanobacteria, such as Microcystis aeruginosa complex (Souza et al, 2018) or Microcystis spp., Spirulina sp. And Anabaena (=Dolichospermum) spp.…”

“…For instance, the alternation between flood and drought events can impact the structure and dynamics of cyanobacterial populations, since floods might produce high export rates of nutrients and organic material to adjacent coasts (Souza et al, 2018). On the other hand, dry periods can result Meteorological and climatic influence on cyanobacteria Canever et al in high phytoplankton biomass (Michalak et al, 2013;Ho and Michalak, 2017) and an increase in residence time (Fernandes et al, 2002;Aguilera et al, 2020), which can promote the development and extension of cyanoHABs in lagoons, such as in the main PL waterbody.…”

Seasonal Hydrodynamics and Transport Timescale of a Coastal Island

“…Eulerian approaches are commonly used in numerical models to assess water transport timescales (Huguet et al, 2019;Aguilera et al, 2020). These transport timescales are applied to quantify the efficiency of water renewal and transport processes in coastal areas, especially regarding water quality (Lucas & Deleersnijder, 2020;Tang et al, 2021) To provide useful information, this paper aims to describe the coastal hydrodynamics and assess the transport timescales of Santa Catarina Island, including the North and South Bays.…”