Estimation of the flushing capacity in estuaries

1. Estimation of the flushing capacity in
estuaries according to the temporal
variations of the main forcing and the
spatial variations of the geometry and
bottom topography
4th November, 2015
Javier F. Bárcena* (barcenajf@unican.es),
Javier García-Alba, Andrés García, César Álvarez

2. 2
CONTENTS
1. Motivations
2. Objectives
3. Methodology
4. Application
5. Conclusions
Suances Estuary

3. WHY THIS STUDY?
Flushing time
 The amount of time that it takes to effectively flush a confined
region, being the most important physical influence on water
quality in the system
 We have to analyze the water circulation for zoning the water
bodies and minimizing the environmental damage
anthropic pressures
Water management
Water monitoring
Development of
useful tools to
assess!
HOW?
Industrial
Urban
Overflow
Suances Estuary
¯Cantabria
1. MOTIVATIONS

4. 4
CONTENTS
1. Motivations
2. Objectives
3. Methodology
4. Application
5. Conclusions
Suances Estuary

5.  The final aim is to develop and apply a methodology for
the calculation of water renewal on estuaries in order
to use the obtained results for water management and
water monitoring
 The propose methodology has to:
o consider the temporal variability of the major forcing
o preserve the geospatial variations of the model
domain
o identify the major forcing in the study area
2. OBJECTIVES

6. 6
CONTENTS
1. Motivations
2. Objectives
3. Methodology
4. Application
5. Conclusions
Suances Estuary

7. FLUSHING TIME CALCULATION
 DELFT3D-FLOW
(Hydrodynamics)
 Local Flushing
Time described in
Jouon et al., 2006
·eCC γ·t
(o)(t)



1LFT 
3. METHODOLOGY
Local Flushing Time
Flushing Lag

8. 8
3. METHODOLOGY
t
%M(t)
M(t) = 37%
M(t)=37%=e-1
2) FT calculation 3) FT sensitivity analyses 4) Final FT
Velocity fields Boxes division
BOX 4
BOX 6
BOX 1
BOX 2
BOX 3
BOX 5
BOX 7
BOX 8
9BOX
8
1


i
iBOX
BOX 4
BOX 6
BOX 1
BOX 2
BOX 3
BOX 5
BOX 7
BOX 8
9BOX
8
1


i
iBOX
BOX 1
BOX 2
BOX 3
BOX 5
BOX 7
BOX 8
9BOX
8
1


i
iBOX
Spatial analysis Forcing analysis1) Hydrodynamic forcing analyses
River flow, tidal
amplitude, initial
phase and depth
 Approach described
in Bárcena et al., 2012
METHODOLOGICAL APPROACH

9. 9
CONTENTS
1. Motivations
2. Objectives
3. Methodology
4. Application
5. Conclusions
Suances Estuary

10. SU1
SU2
SU3 SU4
SU5
Shallow, narrow, macrotidal, intertidal flats  High
variability tide and different spatial behaviors
0.7 – 5.1 m tidal ranges
389 ha surface area
5.5 km long
150 m mean widthSaja-Besaya River Basin
Saja River Besaya River
Cantabric Sea
¯ Suances Estuary
Small surface area, short length, steep slope, reduced
time of concentration  High variability river flow
967 m2 catchment area
23 m3/s annual mean flow
<24 h time of concentration
4. APPLICATION
Cantabria
STUDY AREA

11. 11
PLAN VIEW SIDE VIEW
MESHGRID
4. APPLICATION
CELLSIZE INSIDE
ESTUARY=4-30 m

12. PHYSICAL PARAMETERS CALIBRATED VALUES
HZTAL EDDY VISCOSITY (VH) SIZE VARIABLE (k∙u∙∆x)
HZTAL EDDY DIFFUSIVITY (DH) SIZE VARIABLE (DH=VH/0.7)
VTCAL EDDY VISCOSITY (VV) k-EPSILON
VTCAL EDDY DIFFUSIVITY (DV) k-EPSILON
BOTTOM STRESSES DEPTH VARIABLE
LATERAL STRESSES FREE-SLIP CONDITION
MODEL SETUP
4. APPLICATION
WATER DEPTH (m) MANNING (n)
H≤-2.5 0.032
-2.5≤H<-2.0 0.028
-2.0≤H<-1.5 0.023
-1.5≤H<-1.0 0.020
-1.0≤H<-0.5 0.019
-0.5≤H<0.0 0.018
WATER DEPTH (m) MANNING (n)
0.0≤H<0.5 0.024
0.5≤H<1.0 0.026
1.0≤H<3.0 0.025
3.0≤H<-10.0 0.023
H>10.0 0.022
NUMERICAL PARAMETERS CALIBRATED VALUES
NUMERICAL SCHEME CYCLIC
TIMESTEP ∆t=0.1 min=6 s
NUMERICAL FILTERS VERTICAL ARTIFICIAL MIXING
WETTING AND DRYING THRESHOLD DEPTH < 0.1m

13. 13
CRITERIA NUMBER VALUES
DEPTH 10 σ-LAYERS
TIDAL PHASE 4
EBB/FLOOD = 0 m
HIGH/LOW = ±1.46 m
TIDAL RANGE 1 A50 = 1.46 m
RIVER FLOW 5
Q0=0.7; Q10=3.4; Q50=12.1;
Q90=51.6; Q100=561.2 m3/s
FLUSHING TIME CASES
4. APPLICATION

14. 14
CRITERIA NUMBER VALUES
DEPTH 10 σ-LAYERS
TIDAL PHASE 4
EBB/FLOOD = 0 m
HIGH/LOW = ±1.46 m
TIDAL RANGE 1 A50 = 1.46 m
RIVER FLOW 5
Q0=0.7; Q10=3.4; Q50=12.1;
Q90=51.6; Q100=561.2 m3/s
DEPTH
4. APPLICATION
AVERAGED!

15. 15
TIDAL PHASE
CRITERIA NUMBER VALUES
DEPTH 10 σ-LAYERS
TIDAL PHASE 4
EBB/FLOOD = 0 m
HIGH/LOW = ±1.46 m
TIDAL RANGE 1 A50 = 1.46 m
RIVER FLOW 5
Q0=0.7; Q10=3.4; Q50=12.1;
Q90=51.6; Q100=561.2 m3/s
4. APPLICATION
AVERAGED!

16. 16
RIVER FLOW
CRITERIA NUMBER VALUES
DEPTH 10 σ-LAYERS
TIDAL PHASE 4
EBB/FLOOD = 0 m
HIGH/LOW = ±1.46 m
TIDAL RANGE 1 A50 = 1.46 m
RIVER FLOW 5
Q0=0.7; Q10=3.4; Q50=12.1;
Q90=51.6; Q100=561.2 m3/s
4. APPLICATION
5 FT  OBJECTIVE  1 FT HOW?
NOT-AVERAGED!

17. 17
FINAL FLUSHING TIME
Annual Mean forcing FT=0.427 days=10.248 h
4. APPLICATION
SS4
SS2
SS3
SS1
SS4=0.126 days=3.024 h
SS3=0.267 days=6.408 h
SS2=0.797 days=19.128 h
SS1=0.349 days=8.376 h

18. 18
CONTENTS
1. Motivations
2. Objectives
3. Methodology
4. Application
5. Conclusions
Suances Estuary

19. 5. CONCLUSIONS
Methodology:
 Preserving the temporal variability of the major forcing and the
geospatial variations of the estuary
 Identifies the principal forcing in the study area
 Calculates a final FT which is more realistic than a FT evaluates with
mean annual conditions of the forcing
Applications:
 Results could be useful for water management (characterize, assess or
police)
 Results could be useful for water monitoring (design optimization)
Suances Estuary:
 River flow is the main forcing for water circulation in the Suances
Estuary and the main channel, becoming more significant in the
innermost part
 Tide is the main forcing for water circulation in the mouth and the
intertidal flats
 Water flushing time is almost independent of the forcing in the
estuarine reach

20. 20
THANKS FOR YOUR ATTENTION
Questions?
Suances Estuary

21. Estimation of the flushing capacity in
estuaries according to the temporal variations
of the main forcing and the spatial variations
of the geometry and bottom topography
4th November, 2015
Javier F. Bárcena* (barcenajf@unican.es),
Javier García-Alba, Andrés García, César Álvarez