Presentation by Anke Becker, Deltares, Netherlands, at the Delft3D - User Days (Day 2: Sediment transport and morphology), during Delft Software Days - Edition 2017. Tuesday, 31 October 2017, Delft.

1. 31st October 2017
Increased sedimentation in the Guayas
estuary, Ecuador
Dipl.-Ing. Anke Becker, Deltares

2. Background
Pedro Barrera Crespo MSc.

3. Background
Guayas

4. Background
Worries about sedimentation in the system Guayas - Daule - Babahoyo
 sediments blocking the outlets of drainage channels for rainfall water into the
river  risk of inundation in the city
 backwater effect because sediment blocks the river
 increase of the risk of river induced inundation
 problems for navigability
 prevention of illegal settlements

5. Background
Idea about the reason and about mitigation measures:
 increased sediment inflow from the catchment upstream due to deforestation
in the past decennia
 mitigation by better stabilization of the soil in the catchment
 and by dredging of the island

6. The model of the rivers Guayas-Daule - Babahoyo
The model of the rivers Guayas – Daule –
Babahoyo was constructed to explain
 Why there is a tendency for
sedimentation?
 Why the sedimentation has become
stronger in the past decades?
and to study mitigation measures.

7. Preferred grid structure: as much as possible curvilinear +
triangular cells where necessary
 the most computationally efficient
Unstructured grid

8. Unstructured grid
Preferred grid structure: as much as possible curvilinear +
triangular cells where necessary
 the most computationally efficient

9.  Quasi-3D model
 2D model + parameterisation of the relevant 3D
processes
 e.g. secondary flow in river bends:
 and effect of bed slope on transport direction
(Koch & Flokstra 1980, Talmon 1995)
 Important for good prediction of sediment
transport and bed patterns!
The model of the rivers Guayas-Daule-Babahoyo

10. River bed levels determined by Delft3D FM

11. The morphological processes in the estuary
tiempo
nivel
12h12h 0h0h
-1
0
1
2

12. sediment
transport
wash
load
bed
material
load
suspended
load
bed load
Sediment transport mode
fine
coarse

13. Sedimentation of fine sediments
in the outlets of drainage channels for rainfall water
 Amount of fine sediment depends on the sediment production in
the catchment
 and does not depend on hydrodynamics in the river system itself
 Sedimentation of fine sediments is not studied with the numerical
model

14. Mitigation measures:
 prevent dead zones
 create “depresiones de marea”
Sedimentation of fine sediments
in the outlets of drainage channels for rainfall water

15. Sedimentation of coarse sediments
 Palmar island: coarser material (sand)
 depends mainly of the hydrodynamics
 only influenced by the sedimdent production in the catchment
on the very long term
 This is studied with the Delft3D FM model.

16. System behaviour (coarse sediment)
Parameters that influence the estuarine dynamics:
 the tide and its asymmetry
 river discharges
 the dam upstream in the river Daule
 the El Niño phenomenon
 climate change

17.  Guayas estuary: flood tide is shorter than ebb tide
 net sediment transport into the estuary
 system is flood dominant
Tidal asymmetry
fast rise: high flow velocity
slower drop: lower
flow velocities
time
waterlevel
12h12h 0h0h
-1
0
1
2

18.  The impact of rhe river discharges
needs to be added to the influence
of the tide.
 Bigger discharges -> system less
flood dominant.
 Guayas: The discharges caused by
the tide are much bigger than the
river discharges
River discharges
10.000 m³/s
500-1.000 m³/s
 System is flood dominant, except at times of river floods

19. Sedimentation of coarse sediments

20. Sedimentation of coarse sediments
Increase of sedimentation in the past decades:
 Reduction of tidal flats due to shrimp
farms and mangrove reclamation 
increase of tidal asymmetry
 Decrease of river discharges due to
construction of Daule Peripa dam
 thus not because of deforestation in the
catchment

21. Other parameters of influence:
 El Niño  due to higher river discharges the
system becomes ebb dominant on average, even
though El Niño also increases the sea level
 Climate change  sea level rise makes the
flood dominant situation worse (without
considering a change in the river discharges)
Sedimentation of coarse sediments

22. Mitigation measures:
 Increase residual currents towards the sea
 Reduce tidal asymmetry
Sedimentation of coarse sediments

23. Mitigation measures:
 Increase residual currents towards the sea
 different operation of Daule-Peripa dam
 Reduce tidal asymmetry
 recuperation and reforestation of some of the
intertidal flats
Sedimentation of coarse sediments

24. Dredging:
 Locally improves navigability
 Does not significantly influence
(flood) water levels, because
these are mainly determined by
downstream:
 the confluence (backwater
effect)
 tide
Sedimentation of coarse sediments

25. El Palmar island:
 The apparition of the island is a local
effect caused by the widening of the river
Daule towards the confluence.
 Recommendation: redesign of the
confluence to reach a sustainable
situation in the future
 e.g. groynes
Sedimentation of coarse sediments