Structures Data
- 01 Nov 2022
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Structures Data
- Updated on 01 Nov 2022
- 1 Minute to read
- Print
- DarkLight
Article Summary
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The unit simulates the extra reaeration due to flow over and under hydraulic structures.
Description
When using the DISSOLVED OXYGEN module, the user may wish to allow for extra reaeration at specific hydraulic structures such as weirs and sluices. This is done in the STRUCTURE module. The additional reaeration is a function of the type of hydraulic structure and the head loss across it. The type of structure is represented by a reaeration coefficient which the user specifies. If the user wishes to use the same coefficient at all structures in the model area this can be done in the DISSOLVED OXYGEN module. Coefficients which need to differ from this uniform value are specified in the STRUCTURE module.
Equations
Extra reaeration due to flow over structures is simulated by the following equation:
(1)
Where:
| Field | Description |
|---|---|
Cu | Dissolved oxygen concentration upstream of the structure (kg/m3) |
Cd | Dissolved oxygen concentration downstream of the structure (kg/m3) |
Cs | Saturated dissolved oxygen concentration (kg/m3) |
r | Reaeration coefficient |
The reaeration coefficient is defined by the following equation (Bowie et al, 1985):
(2)
Where:
| Field | Description |
|---|---|
k | Factor specified in the STRUCTURE module |
Δh | Head loss across the structure (m) |
T | Water temperature (oC) |
a | Coefficient which depends on the quality of the water:
|
A value for k of 0 will lead to no additional reaeration at the structure. The value of k will increase in relation to amount of disturbance that the structure causes to the flow. Some values of k for various structures are given below:
Structure type k
Rock barrier 0.70
Flat broad crested regular step 0.70
Flat broad crested irregular step 0.80
Flat broad crested vertical face 0.80
Flat broad crested straight sloping face 0.90
Flat broad crested straight sloping face 0.90
Flat broad crested curved face 0.75
Round broad crested curved face 0.60
Sharp crested straight sloping face 1.05
Sharp crested vertical face 0.80
Sluice gates with submerged discharge 0.05
General
The STRUCTURE module may only be run in conjunction with the DISSOLVED OXYGEN module. Additional reaeration may only be specified at structures which are simulated in Flood Modeller. The module checks that all the specified nodes are at structures.
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