Coupling Watersheds, Estuaries and Regional Oceanography through Numerical Modelling in the Western Iberia: Thermohaline Flux Variability at the Ocean-Estuary Interface

Abstract

The characterisation of the water and properties exchanges at the estuary-ocean interface is a key information to understand the estuarine plume influence on coastal circulation and in the generation of haline fronts. In this work, the largest eight Portuguese estuaries were modelled using the MOHID Water numerical model for the period 2010-2016. Water fluxes and associated properties were computed numerically at each of the estuary mouths. These results served to estimate the tidal prisms, tidal flows and to describe the annual evolution of water temperature and salinity. Those fluxes could serve to improve the land boundary conditions for regional ocean models. Moreover, the numerical analysis of the estuarine fluxes allow for the better characterisation of the studied systems, as two neighbouring estuaries could present very different fluxes and water properties. Where available, modelling results were compared with stations near the estuary mouth.

Coupling Rivers and Estuaries with an Ocean Model: An Improved Methodology

“…Offline upscaling through momentum discharges in MOHID was first developed in Campuzano et al [38], where a full description of the flow and tracer properties computation is provided. The difference to the offline upscaling methodology proposed herein is procedural only, and the reader is referred to [38] for additional details.…”

“…Offline upscaling through momentum discharges in MOHID was first developed in Campuzano et al [38], where a full description of the flow and tracer properties computation is provided. The difference to the offline upscaling methodology proposed herein is procedural only, and the reader is referred to [38] for additional details. In both methodologies, the flow rate, velocity, and tracer properties are computed from the output of the schematic rivers and estuaries domains (Figure 2) through the definition of a cross-section perpendicular to the flow direction of the local domain in a suitable location, such as the mouth of the river or estuary.…”

“…In both methodologies, the flow rate, velocity, and tracer properties are computed from the output of the schematic rivers and estuaries domains (Figure 2) through the definition of a cross-section perpendicular to the flow direction of the local domain in a suitable location, such as the mouth of the river or estuary. However, while in the detached methodology, the discharge properties are obtained through an external tool [38], where the user must define the location of the cross section, and one discharge file (time series containing flow, velocity, and tracer properties) is produced for each vertical layer of the estuary model application; in the integrated methodology the discharge properties are obtained directly in run-time by the MOHID model, where the user only needs to provide the HDF (or netCDF) outputs of the schematic rivers and estuaries along with the coordinates of the regional model numerical cell where the discharge is to be made (Figure 2-blue cell). In this case, MOHID will automatically detect the schematic river or estuary model cells that are required for the computation of the flow, velocity, and tracer properties and apply them to the userspecified regional model cell(s).…”

“…The methodology presented in this work provides a solution to this problem by using schematic representations of the main freshwater sources in the western Iberian Peninsula-Minho, Douro, Mondego, Tagus, Sado, Guadiana, and Guadalquivir-which mix fresh and salt water before being discharged into PCOMS. The first upscaling approach follows the methodology proposed by Campuzano et al [38] (hereafter detached methodology), and the second is an improved methodology proposed in this article (integrated methodology). Schematic rivers and estuaries have the advantage of a very simple representation of the river channels and estuaries-easy to update over time-but the new upscaling methodology allows for a simpler implementation of the freshwater discharges into the regional model, which only needs to receive an HDF or NetCDF from each separate estuary.…”

Model-Observations Synergy in the Coastal Ocean

“…COFS must thus resolve interactions between nearshore, estuarine and shelf processes (target resolution: 10-100 m) and open ocean processes (target resolution: 1 km), preferably in a two-way mode. Approaches include downscaling and multi-nesting (e.g., Debreu et al, 2012;Kourafalou et al, 2015b;Trotta et al, 2017), upscaling (Schulz-Stellenfleth and , and unstructured-grid models (e.g., Zhang et al, 2016a,b;Federico et al, 2017;Stanev et al, 2017;Ferrarin et al, 2018;Maicu et al, 2018), and coupling with watersheds (Campuzano et al, 2016(Campuzano et al, , 2018. These features make those COFS more relevant to the interpolation and interpretation of sparse observations.…”