1. Structures

2. Structures Structure Types: Weirs, spillways Culverts Pumps
Reservoir operations
Advanced controllable structures
Dambreak
Bridge module

3. Structures in NWK11 file Structure Types: Weirs Culverts Regulating
Tabulated
Energy Loss

4. General Structure Features
Structures are located at Q-points
Flow equations substituted by energy equation Q H Q H Q

5. General Structure Features
Upstream and downstream cross sections must exist in database at a distance < dx-max from the structure, preferably about half a channel width upstream and downstream of structure
Valve regulation to allow flow in one direction only - e.g. for flap gate operation
Group structures in parallel to describe complex geometries (eg combined overflow and throughflow). These can be placed at same Branch, Chainage and differentiated by the ID.

6. Internal Conditions Structures impose internal boundary conditions:
a) due to a control somewhere in the structure Qstr = f (Hu/s)
b) due to energy losses through the structure, Qstr = f (Hu/s, Hd/s )
MIKE 11 looks at both cases and decide which is the governing mechanism.
Replace momentum equation with control equation (a) or local energy balance (b).

7. Upstream Control Control somewhere in the structure, Qstr = f (Hu/s)
Egs:
- Weir; Free flow over the weir
- Culvert; Inlet critical
Outlet critical
Orifice flow at inlet

8. Upstream or inlet controlled
Upstream Control
Zero flow,
Upstream or inlet controlled

9. Downstream Control
Energy losses through the structure, Qstr = f (Hu/s, Hd/s )
Egs:
- Weir; Drowned flow over the weir
- Culvert; Drowned flow through the culvert

10. Downstream Control
Downstream or outlet controlled

11. Downstream Control
Qstr = f (Hu/s, Hd/s) comes from energy equation which gives the headloss as a function of flow.
Hlost is a function of Q and is due to:
Eddy losses / vortices / turbulence
Contraction / expansion of streamlines

12. Head Loss in Structures

13. Loss Coefficient,  Contributions from inflow and outflow: Note!
As < A1 and A2

14. Total Headloss Contributions from:
inflow (note As1, str.area at inlet)
friction (for culverts, note Asa, average str. area)
bend (for culverts, note Asa, average str. area)
outflow (note As2 , str. area at outlet)
subject to min specified in the HD11 file, default values page.

15. Specifying Loss Coefficients
Defaults:
in = 0.5
out = 1.0
Determine from:
Flume tests
Field measurements
Model calibration
Function of :
Degree of smoothness of entry, exit

16. Free Overflow Q = ac Qc For culverts and weirs
Qc is tabulated, ac is applied during simulation
Irregular sections: H not horizontal, v not uniform.
To be used when known, otherwise ac = 1
ac > 1, for non-parallel flow (curved streamlines) over weir as in the case of a sharp-crestred weir
ac < 1, for side effects.

17. Weirs

18. Weirs
Broadcrested Weir
Level-Width relationship

19. Weirs
Special weir
Same geometric input as for a broadcrested weir except that the Q/h relationship can be inserted manually

20. Weirs
Weir Formula 1 (Villemonte)

21. Weirs
Weir Formula 2 (Honma)

22. Culverts

23. Culverts Rectangular Circular Irregular H-B Irregular h-B
Cross-section DB

24. Weir cf. Culverts Weirs and culverts are very similar, except:
Culverts have a length, therefore a friction loss
Culverts have a length, therefore an outlet critical plus friction loss control mechanism
Culverts have a soffit therefore a possible orifice control mechanism
Culverts have a bend loss option

25. Regulating Structures
Q = f (t)
eg pumps, reservoir outlet, historical release
breaks branch into two
specified in boundary (BND11) editor
Q(t) specified in timeseries (DFS0) file

26. Regulating Structures
Q = A Za
where:
Za is H or Q at location a
A is a coefficient given by A = f (Zb)
Zb is H or Q at location b
Examples: Bifurcation, Qbif = f (Qu/s)
Reservoir, Qout,res = f (Qin, Hres)
Dummy branch Q = 1  Q = f (Zb)

27. Regulating Structures
Regulating structures are part of standard MIKE 11 HD
Some pumps can be modelled as a regulating structure with Q = f (H)
For more complex functionality, for example in control cases, the user may need to use a control structure, which is an add-on module, with moveable underflow (including radial gates) and overflow gates, which can be controlled by a hierarchical list of control strategies / control and target points / PID control / logical operands, etc.
Pumps are best modelled as a control structure

28. Tabulated Structures Defined as: Qstr = f (Hu/s, Hd/s)
Hu/s = f (Qstr, Hd/s)
Hd/s = f (Qstr, Hu/s)
Some pumps can be modelled as a tabulated structure with Qpump = f (Hu/s, Hd/s)

29. Local Energy Losses Abrupt change in river alignment
Gradual change in river alignment,
User defined energy loss
Flow contraction loss
Flow expansion loss
where,  = 0.1 to 0.2

30. (In)Stability at Structures
Ensure there is sufficient headloss through the structure. A very small headloss leads to an ill-conditioned solution  Increase energy loss or remove structure
Ensure a monotonically increasing Q/h-relation
 Edit the Q/h-relation by hand or change structure geometry
Ensure gradual variation in structure area
 Alter structure area slightly
Also play with Delta, Delhs, Zetamin and Inter1Max in the HD11 file, default values page

31. MIKE-11 Bridge Structures

32. Bridge Module Simplifies approach to bridges
Specific menu for including bridges
Uses recognised approaches for estimating head loss at bridge structures

33. Bridge Module - Approach
User specified physical bridge parameters and user selected approach.
Bridge module pre-calculates a rating table.
Uses rating table in fully dynamic model mode to calculate bridge flow impacts

34. Eight Bridges Types FHWA WSPRO USBPR Bridge Method
Fully Submerged Bridge
Arch Bridge (Biery and Delleur)
Arch Bridge (Hydraulic Research)
Bridge Piers (D’Aubuisson Formula)
Bridge Piers (Nagler)
Bridge Piers (Yarnell)