E-proceedings of the 36th IAHR World Congress 28 June – 3 July, 2015, The Hague, the Netherlands
NUMERICAL SIMULATION OF FLOW AND SEDIMENT TRANSPORT DYNAMICS ON THE MAGDALENA RIVER SECTION OF BARRANCABERMEJA-LA COQUERA (COLOMBIA). JOSE OLIVEROS-ACOSTA(1), JORGE ESCOBAR-VARGAS(2), MOHAMED YOSSEF(3),JORGE SANCHEZ(4), CESAR CARDONA(5), CESAR GARAY(6) (1)
Corporación Centro de Investigación Científica del Río Magdalena “Alfonso Palacio Rudas”,Honda, Colombia,
[email protected] (2)
Departamento de Ingeniería Civil Pontificia Universidad Javeriana, Bogotá D.C, Colombia,
[email protected] (3)
Deltares, Delft, Netherlands,
[email protected]
(4)
Corporación Centro de Investigación Científica del Río Magdalena “Alfonso Palacio Rudas”, Honda, Colombia,
[email protected]
(5)
Corporación Centro de Investigación Científica del Río Magdalena “Alfonso Palacio Rudas”, Honda, Colombia,
[email protected]
(6)
Corporación Centro de Investigación Científica del Río Magdalena “Alfonso Palacio Rudas”, Honda, Colombia,
[email protected]
ABSTRACT Due to the strategic importance of river transportation on the Magdalena River at the current Colombia´s development plan, Cormagdalena, as managing entity of the Magdalena river basin in Colombia, is building an unsteady numerical model for the flow and sediment transport dynamics for the Magdalena River (Colombia). This work shows the recent advances of a case of study on the river section (Barrancabermeja - La Coquera). The numerical platform is the computer program DELFT 3D which solves the shallow water equations, and the sediment transport equation with a finite difference approximation in three dimensions XYZ. The model is constrained by four boundary conditions, one at the beginning of the computational domain, where a flow discharge is imposed, a second one being an outlet condition, where a free surface elevation is enforced, and two additional flow discharge conditions are imposed, as inlet conditions, to take into account the Sogamoso River, which acts as a tributary. On each case a hydrograph of ten years was developed based on field measurements of climatologic stations in Magdalena and Sogamoso Rivers. Two modeling scenarios, for flow and sediment transport, were established: the first scenario is the modeling of the river natural dynamics, and a second scenario involves the modeling of groynes for the future maintenance of the waterway. From the hydrodynamic results a morphological model was developed based on the Engelund& Hansen, and the Meyer-Peter-Müller equations. A grid independence test was done for each of the simulations, ensuring an optimum distribution of the cells within the computational domain. Results showed that the numerical model approximates qualitatively the current natural conditions for three different flow scenarios given by the flow duration curve, and additionally shows the hydrodynamic and morphological evolution of the river when groynes are present within it. Additional analysis are presented where the efficiency of the civil works on the river are assessed to ensure the navigability on that section of the Magdalena River. Keywords:Magdalena River, numerical model, DELFT 3D, sediment transport, groynes. 1.
INTRODUCTION
The Magdalena-Cauca basin covers 24% of Colombia continental extension (approximately 256.000 km²), andis in this region where 80% of the population of the country is established (Cormagdalena, 2012). Situations like anthropic activities and deposition of sediments coming from tributaries, produce particular conditions for the sediment dynamics in the Magdalena River. These conditions affect navigability because the water depth decreases and the morphology of the riverbed changes (Ochoa, 2011). Various studies have been developed for the Magdalena River with the aim of understanding the hydrodynamics on critical sections of the river, and to ensure navigability in these sections (PONER REFERENCIAS). In the most recent study, a design of groynes in the Barrancabermeja - Regidor section was done (Cormagdalena, 2013) with the goal of ensuring navigability in the river for that specific section during dry season, by concentrating the river flow in the main channel and maintaining stability of the river bank in specific locations where the flow can be dispersed when the water level is low. Due to the strategic importance of river transportation for the current development plan of Colombia, Cormagdalena is making a numerical model for the hydrodynamic, sediment transport, and groynes effects on the Barrancabermeja – La Coquera section. The computational platform is the software Delft3D, which solves the shallow water equations, and a 1
E-proceedings of the 36th IAHR World Congress, 28 June – 3 July, 2015, The Hague, the Netherlands
transport equation for the concentration of sediments with a finite difference approach. The resulting model will be the first step on developing a decision making system for the problems related with the Magdalena River. This work shows the development of that project. The document is structured in the following way: Section 2 shows a description of the area of study, and where the main hydraulic characteristics are presented. The following section describes a theoretical framework for the governing equations used by Delft3D. In section 4 the model set-up is explained in detail, followed by the results of all cases analyzed. Finally, the conclusions and future work is presented. 2.
DESCRIPTION OF THE AREA OF STUDY (BARRANCABERMEJA – LA COQUERA)
The area of study covers a section of 22 km that is located at the north-east of Colombia, between the municipalities of Barrancabermeja and Puerto Wilches (see Figure 1). Upstream of Galan port in Barrrancabermeja there is a floodplain with a hydraulic section approximately 3 km wide. Just at the port location, the river channel shrinks to 700 m wide, and downstream of it, the flow is divided in two branches due to the existence of a river island (see Figure 1). Around this island the river dynamics generated a small groups of islands with multiple secondary channels.
Figure1Area of study (Google Earth 2014)
At the height of Puerto de Galan, the dynamics of Magdalena River creates an important feature on the left bank, where a significant bifurcation is generated. In the left branch (La Rompida), downstream of the bifurcation, there is a sector, with flood plain material, where the river narrows, affecting the navigation at that point.The branch on the right is called Brazo Berlin, and it is the main navigation channel. Downstream of the island that generates La Rompida and Berlin branches there is the mouth of Sogamoso River, which is characterized by its large sediment load. That sediment load makes difficult to define the path of the main channel. It is important to mention that this is one of the main tributaries of the Magdalena River, where about 50 km upstream from the mouth, a hydroelectric plant was built and the operation will begin in 2018. Downstream of the mouth of the SogamosoRiver the main channel is clearly defined. It leans to the left side of the river and multiple islands appearon the right side. After this point, the main channel goes toward the right bank, and continues like that until the end of the section at La Coquera.
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E-proceedings of the 36th IAHR World Congress 28 June – 3 July, 2015, The Hague, the Netherlands
3.
GOVERNING EQUATIONS
The model used by the numerical platform Delft 3D is based on a shallow water approximation where it is assumed that the main process occur on the horizontal plane. This approach departs from a simplification of the incompressible NavierStokes equations with the assumption of a hydrostatic pressure distribution (Kundu,1990), and the viscosity diffusion terms are replaced by Manning’s approximation. The general form of the shallow water equations is given by
(
)
(
)
+
+
+
(
)
+
(
)
+
+
(
+
) (
= 0[1] )
+
=−
+
=−
[2]
+
[3]
whereu and v are the horizontal velocities, η is the free Surface elevation, H is the meanwater depth, g is the gravitational acceleration, and Fx, Fy, are the forcing terms. The model equation for the sediment transport, which is solved once the previous model is resolved on each time step, is given by (ℓ)
+
(ℓ)
+
(ℓ)
(ℓ)
+
!
(ℓ)
=
"#,
(ℓ)
(ℓ)
+
"#,
(ℓ)
(ℓ)
+
!
"#,!
(ℓ)
(ℓ)
!
[4]
Wherec (ℓ) is the concentration of a sediment mass fraction, (u, v, w)are the velocity components, given by the (ℓ) (ℓ) (ℓ) (ℓ) hydrodynamic model, ε),* , ε),+ , ε),, represent the values of the Eddy diffusivity in a sediment fraction(ℓ)andw) is the settling velocity of the of sediment particles in a fraction of it(ℓ). The module used by Delft3D to handle the sediment transport takes into account sediment loads at the bottom of the river, as well as the suspension load for cohesive and non-cohesive sediments (Yossef, 2005). Based on the morphological studies of the river section (Cormagdalena, 2013) is recommended to work with non-cohesive sediments. In this case the settling velocity can be calculated with the methodology proposed by Van Rijin (1993). This velocity is calculated as a function of the sediment grain diameter as
-#,. = (ℓ)
2 0 0 1 0 0 /
3# (ℓ) .
6
456
8
BC1 +
(ℓ)7
,
... 3# (ℓ)
7
456
(ℓ)E
− 1F ,
1.1C(G (ℓ) − 1) ?# , (ℓ)
65
