1. The morphological factor
20 mei 2019
The morphological factor
Erik Mosselman
Bring Your Own Model to the RiverLab
Deltares, Delft, 9 May 2019

2. Long-term morphological developments
Strategies to speed up computations:
Hierarchical tree of processes
Cor Flokstra: Delft3D-MOR
Efficient computation of varying flow fields
Bert Jagers and Mohamed Yossef: case management tool
Morphological acceleration factor
Dano Roelvink: Delft3D-FLOW with sediment online
Now in Delft3D and Delft3D-FM

3. Hierarchical tree of processes (Flokstra)
Steering module:
Links modules for different processes
Process may be executed:
a fixed number of times
or for a given time span
or as long as a certain condition is not satisfied

4. Case management tool (Jagers, Yossef)
Efficient computation of varying flow fields:
Store flow fields for computed discharges in database
Use stored flow field from database as a starting point when discharge re-appears

5. Morphological acceleration factor (Roelvink)
Flow and morphology computed within the same module:
Calculate the flow field present during a time step Δt
Multiply the corresponding morphological changes by MorFac
Proceed in time over a period MorFac × Δt

6. Morphological acceleration factor
discharge
hydrodynamic time
discharge
x 2
morphodynamic time

7. Morphological acceleration factor
discharge
hydrodynamic time
discharge
morphodynamic time

8. Morphological acceleration factor
discharge
storage
hydrodynamic time
discharge
storage
morphodynamic time

9. Morphological acceleration factor
discharge
hydrodynamic time
discharge
morphodynamic time

10. Morphological acceleration factor
Squeezing of discharge hydrograph into shorter duration:
Acceptable for long, slowly varying hydrographs
quasi-steady flow
negligible flood wave attenuation
Caution for short, rapidly varying hydrographs
unsteady flow
significant flood wave attenuation

11. When does flood wave attenuation matter?
Chézy’s law:

12. When does flood wave attenuation matter?
Continuity:
Advection-diffusion equation with celerity c = 3u/2 and diffusion coefficient D = q/2iw
Linearization, co-ordinate system moving with celerity c and substitution of sinusoidal wave with length Lwave
Result: relaxation equation for water depth (and level)

13. When does flood wave attenuation matter?
Linear approximation:

14. When does flood wave attenuation matter?
discharge
time
acceleration factor 1
time

15. But there is much more …
Mart Borsboom

16. Thanks!