Transcript 2_MIKE21_FloodPlains..

MIKE 21 Flood Plain Modeling
MIKE 21 flow velocity and depth
MIKE 21 provides detailed information on
• Flow pattern
• Flooding Depth
• Duration of flooding
• and Flow velocity
(eroding forces)
MIKE 21 Flood Modeling
Data Requirements :
• Topographical data
• Boundary data
• Roughness coefficients
• Structure Data
MIKE 21 Advantages and Limitations
+ Flow pattern is not pre-scribed, i.e. the model
predicts the direction of flow in contrast to 1-D
model with defined channels
- Computational expensive to solve St. Venant
equations in all grid points. Therefore, 2-D model
particularly suited for local flooding studies
Handling of dried/flooded areas
+ Flooding and drying is an efficient algorithm to
reduce the effective number of computational points
where only submerged grid points included in solver.
This approach is used in MIKE 21.
- Sloth-technique as applied in MIKE11 requires
that momentum and continuity equation is solved in
all grid points. On the other hand, this can provide
better and more continuous description of the
transition from dry land to flooded land
In both cases, mass balance is important. This is
preserved in MIKE 21 by keeping track of
remaining water in dried grid cells
Structures
- Such as culverts, dikes, roads (acting as a weir)
etc. are vital geometrical features influencing the
flow.
- “Discrete” structures like culverts can be included
via MIKE11 coupling with 1-D description of flow
through the structure.
- “Continuous” structures like river embankments
can be described using MIKE21s weir formula.
Extension of this expected so e.g. a dike can be
described as a line (x,y,z) cutting across the 2-D
area.
2D flood modelling (USBR) - MIKE 21
Dam break (USBR)
Embankment breach (USBR)
Embankment breach - 3D view
MIKE 21 Adv. & Lim. Summary
- 2-D flow simulated dynamically without pre-scribing
flow patterns -> Useful for detailed local studies
- Flood and drying handled with module which
excludes dried grid cells from computations
- Supercritical flow at the edge of the wave front is
handled now in MIKE21, but more experience/
development required for accurate modelling of wave
front celerity
- Structures are important in flood modelling. Some
exists in MIKE21, but more are available when
coupling to MIKE11
MIKE 21 Flood Modeling
When should a two-dimensional model (MIKE21) be
used for flood modeling ?
• For local flood studies where detailed velocity and
depth pattern are important
• For studies with significant two-dimensional flows
and where a one-dimensional model can not address
the problem
• For studies where the flow paths are not well
defined