Abstract
The Ou River, a medium-sized river in southeastern China, is selected to study the lateral flow response to rapidly varied river discharge, i.e., peak river discharge (PRD). A three-dimensional model based on the Finite-Volume Community Ocean Model is validated by in situ measurements from 15 June to 16 July 2005. PRD, which considers the extra buoyancy and longitudinal momentum in a short time, rebuilds the stratification and lateral flow. PRD, compared with low-discharge, generally makes stratification stronger and lateral flow weaker. PRD mainly rebuilds lateral flow by changing lateral advection, lateral Coriolis, and lateral-barotropic pressure gradient terms. After PRD, the salinity recovery time is longer than that of the flow because the impact on buoyancy lasts longer than that on longitudinal flow. Longitudinal flow is mostly affected by the momentum transferred during PRD; therefore, the recovery time is close to the flooding duration. However, the lateral flow is affected by the buoyancy, and its recovery time is generally longer than the flooding duration. The lateral flow recovery time depends on transect width, flow velocity and the variation caused by PRD. PRD occurs widely in global small-/medium-sized river estuaries, and the result of this work can be extended to other estuaries.
Highlights
The North Channel, as a main channel, is further divided into the northeastward Sha-Tou Passage (STP) and the Middle Passage (MP); it stretches along the North Submerged Dike (NSD), Ling-Ni Dike (LND), and several islands, including Da-Men Island (DMI), Ni-Yu Island (NYI) and Zhuang-Yuan-Ao
Without a loss of generality, a typical ebb–flood cycle during spring tide is described to show how the peak river discharge (PRD) changes the stratification in the OR Estuary (ORE)
The isolines are distributed asymmetrically between the ebb (Figure 6b) and flood (Figure 6c) tides at the DNC under the low-discharge condition (Run 2), indicating difference in mixing between ebb and flood tides; the ebb–tidal-averaged isolines are tilted more than the flood–tidal-averaged isolines, which are nearly vertical in the lower layer
Summary
River discharge plays a crucial role in estuarine circulation and material transport [1]. Due to a lack of connected lakes and tributaries (small drainage basins) acting as sponges, the fluvial flow of small-/medium-sized rivers is likely to form peak river discharge (PRD), i.e., a rapidly varied large-volume flux during a short period under natural conditions (e.g., heavy rainfall or snowmelt) or anthropogenic conditions (e.g., sluice floodwater) [10]. The Ou River in China, which has a drainage basin area of ~1.80 × 104 km2 [43], is categorized as a medium-sized river [12,44] and frequently suffers PRD from spring to summer It is used as a case study to explore the response of lateral flow to a PRD.
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