Sharing Experiences of Flood Modelling Using MIKE 21
1. 1
The 15th MIKE by DHI UK User Group Meeting
Sharing Experience of Flood Modelling
Using MIKE 21
Dr Lei Yang
Arup
4 Pierhead Street Capital Waterside Cardiff CF10 4QP United Kingdom
d +44 29 2026 6686
www.arup.com
2. 2
Case study 1
Port Talbot
A harbour
A brook
Trash screen and
buried culvert
West End
Industry site
Historical flooding
3. 3
Case study 1
As Build
A highway project
Distributor road
4.8km link Port
Talbot and docks to
M4
Funding £106m
FRA - a part of the
development
Permission grant
from EA
6. 6
Case study 1
As Build
model
• Ditches
along
back road
• Highway
culvert in
West End
• Extended
open
channel
to the
brook
7. 7
Case study 1
Application of weir structure
• Weirs (definition of contracted weir)
• Brick / concrete Wall
• Field Embankment
• Flood bund
L-W table
• W2 = W1
• L2 = L1 +3m glasswall
L1
W1
8. 8
Case study 1
Headlosses of the culvert structure
3 arch culverts, L-W table, manning 0.013, L 28m, IL 6.5 to 6.4 mOD.
Q
(m3/s)
V
(m/s)
D
(m)
HWL
(mOD)
Headloss
(mm)
Mike 21 11 1.0 0.87 7.94 670
CulvertMaster 11 1.63 0.87 7.54 270
9. 9
Some discussions
Structures in 2D
• Conservative computation of headloss of culvert structure
• Model build features
(currently culvert in Mike 21 is specified as a cross-section, suggesting to
develop it as two cross-sections for inlet and outlet locations therefore the
culvert could be placed through under a barrier)
• Construction (sandbag bund, speed humps, ramp)
(weir structure (line structure in 2D), block structure (large geometry
structure in 2D?)
• Output functions for Q, V, D and headloss of structure
(currently no output specifications for structure rather retrieving data from
2D horizontal field; suggesting to add output functions for structures such
as discharge of culvert, spill of weir etc)
11. 11
Case study 1
Mitigation
• New open channel
diverting flood
• Flood free up to
Q100CC for the
industry site
• Restriction of
invert levels
• Overtopping
• New culvert under
highway releasing
flood
• Reduced flood risk
to West End area
12. 12
Case study 2
Brize Norton
• Infrastructure design
• Historical flooding
• Three brooks
• Buried culverts
• FRA
• Full planning
application
• 2D overland flood
flow modelling