Framework for morphodynamicmodeling in alluvial estuaries

2010 ◽  
pp. 1-28
Keyword(s):  
Alluvial Estuaries

scholarly journals Salt intrusion in multi-channel estuaries: a case study in the Mekong Delta, Vietnam

2006 ◽  
Vol 10 (5) ◽  
pp. 743-754 ◽  
Author(s):  
A. D. Nguyen ◽  
H. H. Savenije
Keyword(s):  
River Discharge ◽  
Single Channel ◽  
Mekong Delta ◽  
Salt Intrusion ◽  
Predictive Equations ◽  
Alluvial Estuaries ◽  
Tidal Characteristics ◽  
Mixing Behaviour ◽  
Sloping Bottom

Abstract. There is a well-tested theory for the computation of salt intrusion in alluvial estuaries that is fully analytical and predictive. The theory uses analytical equations to predict the mixing behaviour of the estuary based on measurable quantities, such as channel topography, river discharge and tidal characteristics. It applies to single-channel topographies and estuaries that demonstrate moderate tidal damping. The Mekong delta is a multi-channel estuary where the tide is damped due to a relatively strong river discharge (in the order of 2000 m3/s), even during the dry season. As a result the Mekong is a strongly riverine estuary. This paper aims to test if the theory can be applied to such a riverine multi-channel estuary, and to see if possible adjustments or generalisations need to be made. The paper presents salt intrusion measurements that were done by moving boat in 2005, to which the salt intrusion model was calibrated. The theory has been expanded to cater for tidal damping. Subsequently the model has been validated with observations made at fixed locations over the years 1998 and 1999. Finally it has been tested whether the Mekong calibration fits the overall predictive equations derived in other estuaries. The test has been successful and led to a slight adjustment of the predictive equation to cater for estuaries that experience a sloping bottom.

scholarly journals Maximum power of saline and fresh water mixing in estuaries

2019 ◽  
Vol 10 (4) ◽  
pp. 667-684
Author(s):  
Zhilin Zhang ◽  
Hubert Savenije
Keyword(s):  
Fresh Water ◽  
Dispersion Coefficient ◽  
Saline Water ◽  
Maximum Power ◽  
Estuarine System ◽  
Natural Systems ◽  
Gravitational Circulation ◽  
Advection Dispersion ◽  
Physically Based ◽  
Alluvial Estuaries

Abstract. According to Kleidon (2016), natural systems evolve towards a state of maximum power, leading to higher levels of entropy production by different mechanisms, including gravitational circulation in alluvial estuaries. Gravitational circulation is driven by the potential energy of fresh water. Due to the density difference between seawater and river water, the water level on the riverside is higher. The hydrostatic forces on both sides are equal but have different lines of action. This triggers an angular moment, providing rotational kinetic energy to the system, part of which drives mixing by gravitational circulation, lifting up heavier saline water from the bottom and pushing down relatively fresh water from the surface against gravity; the remainder is dissipated by friction while mixing. With a constant freshwater discharge over a tidal cycle, it is assumed that the gravitational circulation in the estuarine system performs work at maximum power. This rotational flow causes the spread of salinity inland, which is mathematically represented by the dispersion coefficient. In this paper, a new equation is derived for the dispersion coefficient related to density-driven mixing, also called gravitational circulation. Together with the steady-state advection–dispersion equation, this results in a new analytical model for density-driven salinity intrusion. The simulated longitudinal salinity profiles have been confronted with observations in a myriad of estuaries worldwide. It shows that the performance is promising in 18 out of 23 estuaries that have relatively large convergence length. Finally, a predictive equation is presented to estimate the dispersion coefficient at the downstream boundary. Overall, the maximum power concept has provided a new physically based alternative for existing empirical descriptions of the dispersion coefficient for gravitational circulation in alluvial estuaries.

scholarly journals Thermodynamics of saline and fresh water mixing in estuaries

2018 ◽  
Vol 9 (1) ◽  
pp. 241-247 ◽  
Author(s):  
Zhilin Zhang ◽  
Hubert H. G. Savenije
Keyword(s):  
Potential Energy ◽  
Fresh Water ◽  
River Flow ◽  
Maximum Power ◽  
Gradual Transition ◽  
Mixing Processes ◽  
Advection Dispersion ◽  
Alluvial Estuaries ◽  
New Equation ◽  
A Minor

Abstract. The mixing of saline and fresh water is a process of energy dissipation. The freshwater flow that enters an estuary from the river contains potential energy with respect to the saline ocean water. This potential energy is able to perform work. Looking from the ocean to the river, there is a gradual transition from saline to fresh water and an associated rise in the water level in accordance with the increase in potential energy. Alluvial estuaries are systems that are free to adjust dissipation processes to the energy sources that drive them, primarily the kinetic energy of the tide and the potential energy of the river flow and to a minor extent the energy in wind and waves. Mixing is the process that dissipates the potential energy of the fresh water. The maximum power (MP) concept assumes that this dissipation takes place at maximum power, whereby the different mixing mechanisms of the estuary jointly perform the work. In this paper, the power is maximized with respect to the dispersion coefficient that reflects the combined mixing processes. The resulting equation is an additional differential equation that can be solved in combination with the advection–dispersion equation, requiring only two boundary conditions for the salinity and the dispersion. The new equation has been confronted with 52 salinity distributions observed in 23 estuaries in different parts of the world and performs very well.

Conditions for tidal bore formation in convergent alluvial estuaries

2016 ◽  
Vol 172 ◽  
pp. 121-127 ◽  
Author(s):  
Philippe Bonneton ◽  
Andrea Gilberto Filippini ◽  
Luca Arpaia ◽  
Natalie Bonneton ◽  
Mario Ricchiuto
Keyword(s):  
Tidal Bore ◽  
Alluvial Estuaries

scholarly journals The physics behind Van der Burgh's empirical equation, providing a new predictive equation for salinity intrusion in estuaries

2017 ◽  
Vol 21 (7) ◽  
pp. 3287-3305 ◽  
Author(s):  
Zhilin Zhang ◽  
Hubert H. G. Savenije
Keyword(s):  
Empirical Equation ◽  
Saline Water ◽  
Predictive Equation ◽  
Residual Circulation ◽  
Saline Water Intrusion ◽  
One Dimensional ◽  
Feasible Range ◽  
Physical Foundation ◽  
Alluvial Estuaries ◽  
New Equation

Abstract. The practical value of the surprisingly simple Van der Burgh equation in predicting saline water intrusion in alluvial estuaries is well documented, but the physical foundation of the equation is still weak. In this paper we provide a connection between the empirical equation and the theoretical literature, leading to a theoretical range of Van der Burgh's coefficient of 1∕2 < K < 2∕3 for density-driven mixing which falls within the feasible range of 0 < K < 1. In addition, we developed a one-dimensional predictive equation for the dispersion of salinity as a function of local hydraulic parameters that can vary along the estuary axis, including mixing due to tide-driven residual circulation. This type of mixing is relevant in the wider part of alluvial estuaries where preferential ebb and flood channels appear. Subsequently, this dispersion equation is combined with the salt balance equation to obtain a new predictive analytical equation for the longitudinal salinity distribution. Finally, the new equation was tested and applied to a large database of observations in alluvial estuaries, whereby the calibrated K values appeared to correspond well to the theoretical range.

scholarly journals Maximum power of saline and fresh water mixing in estuaries

2018 ◽  
Author(s):  
Zhilin Zhang ◽  
Hubert Savenije
Keyword(s):  
Fresh Water ◽  
Dispersion Coefficient ◽  
Saline Water ◽  
Maximum Power ◽  
Dissipated Energy ◽  
Estuarine System ◽  
Natural Systems ◽  
Gravitational Circulation ◽  
Advection Dispersion ◽  
Alluvial Estuaries

Abstract. Natural systems evolve towards a state of maximum power (Kleidon, 2016), leading to higher levels of entropy production by different mechanisms, including the gravitational circulation in alluvial estuaries. Gravitational circulation is driven by the potential energy of the fresh water. Due to the density difference between seawater and riverwater, the water level on the river side is higher. The hydrostatic forces on both sides are equal, but have different working lines. This triggers an (accelerating) angular moment, providing rotational kinetic energy into the system, part of which drives mixing by gravitational circulation mixing; the remainder is transferred into dissipated energy by friction while mixing. With a constant discharge over a tidal cycle, the density-driven gravitational circulation in the estuarine system performs work at maximum power, lifting up saline water and bringing down fresh water against gravity. The rotational flow causes the spread of salinity, which is mathematically represented by the dispersion coefficient. Accordingly, a new equation for the dispersion coefficient due to the density-driven mechanism has been derived. Together with the steady state advection-dispersion equation, this resulted in a new analytical model for gravitational salinity intrusion. The simulated longitudinal salinity profiles have been confronted with observations in a myriad of estuaries worldwide. It shows that the performance is promising in eighteen out of twenty-three estuaries, with relatively large convergence length. Finally, a predictive equation is presented for the dispersion coefficient at the boundary. Overall, the maximum power concept has provided an alternative for describing the dispersion coefficient due to gravitational circulation in alluvial estuaries.

scholarly journals Frictional interactions between tidal constituents in tide-dominated estuaries

Ocean Science ◽  
2018 ◽  
Vol 14 (4) ◽  
pp. 769-782 ◽  
Author(s):  
Huayang Cai ◽  
Marco Toffolon ◽  
Hubert H. G. Savenije ◽  
Qingshu Yang ◽  
Erwan Garel
Keyword(s):  
Iterative Procedure ◽  
Underlying Mechanism ◽  
Hydrodynamic Equations ◽  
Tidal Amplitude ◽  
Tidal Constituent ◽  
Friction Term ◽  
Southern Portugal ◽  
Tidal Constituents ◽  
Alluvial Estuaries ◽  
Effective Friction

Abstract. When different tidal constituents propagate along an estuary, they interact because of the presence of nonlinear terms in the hydrodynamic equations. In particular, due to the quadratic velocity in the friction term, the effective friction experienced by both the predominant and the minor tidal constituents is enhanced. We explore the underlying mechanism with a simple conceptual model by utilizing Chebyshev polynomials, enabling the effect of the velocities of the tidal constituents to be summed in the friction term and, hence, the linearized hydrodynamic equations to be solved analytically in a closed form. An analytical model is adopted for each single tidal constituent with a correction factor to adjust the linearized friction term, accounting for the mutual interactions between the different tidal constituents by means of an iterative procedure. The proposed method is applied to the Guadiana (southern Portugal–Spain border) and Guadalquivir (Spain) estuaries for different tidal constituents (M2, S2, N2, O1, K1) imposed independently at the estuary mouth. The analytical results appear to agree very well with the observed tidal amplitudes and phases of the different tidal constituents. The proposed method could be applicable to other alluvial estuaries with a small tidal amplitude-to-depth ratio and negligible river discharge.

Sign in / Sign up

Export Citation Format

Share Document