Gates may be used whenever structure flow is to be regulated by the operation of a movable gate forming part of the structure. The Gates menu contains the physical properties of the structures, while the control rules regulating it are defined under the Control menu.
Under the General tab the following types of information must be specified.
Location
ID. String identification of the gate. ID will be used in structure results and hence makes it easier to identify a specific structure if setup contains many structures, or if multiple structures are defined at the same location.
Branch name. The Branch name of where the gate is located can be chosen from the drop down list.
Chainage. Chainage at which the gate is located.
Type. The location type may be defined as Regular, Side structure or Side structure with storage. See Structure types definition (pg. 114) for details.
Graphics
Horizontal offset from marker 2. The horizontal position of the gate within the cross section can be defined. By default the centre of the gate is positioned at marker 2. Note that the position is used only to plot/display the gate and has no impact on the simulation.
Attribute
Gate Type. The following options are available to define the gate type:
· Overflow: This gate type corresponds to a variable crested weir.
· Underflow: This gate type corresponds to a vertical sluice gate.
· Radial gate: This gate type corresponds to a Tainter gate. In contrast to the other gate types a radial gate does not need any information about head loss factors. Instead a number of radial gate parameters must be entered, see the Radial gate parameters section.
· Sluice gate: This gate is physically the same as an underflow gate but instead of using the energy equation a set flow formulas are applied, see the Sluice gate parameters section.
Max speed. Defines the maximum allowable change in gate level per time.
Max speed represents the physical maximum speed of the gate, and may be used to avoid very rapid changes in gate level. Such rapid changes could appear from some control rules but in case they are not realistic they would potentially create instabilities in the computation.
Initial level. The value specified will be used as initial gate level at the beginning of the simulation.
Contraction coef. This is the contraction coefficient used for underflow gates only. The default value is 0.63.
Geometry
Here, the geometry of the gate is defined. The exact content of the dialogue window depends on the type of the gate.
No. of gates. The number of identical gates is entered here. This variable is used when a series of identical gates are simulated. When multiple gates are simulated, they will always have the same gate level and obey to the same control rules.
Gate width. The width of the gate.
Sill level. The level of the sill just upstream of the gate.
Max level. The highest possible gate level.
Gate height. Parameter specified for radial gate and sluice gate. Height of the overflow crest above sill level when the gate is closed. See Figure 6.20 for radial gate.
Trunnion. Parameter specified for radial gates only. Height of the centre of gate circle above sill level, see Figure 6.20.
Radius. Parameter specified for radial gates only. Radius of gate, see Figure 6.20
Figure 6.31 Definition of a radial gate
Head loss
Head loss variables are included in the calculation of the energy loss occurring for flows through hydraulic structures. These are specified for overflow and underflow gates and may be distinguished according to the flow direction.
Positive/Negative flow. Head loss factors are defined for Inflow, Outflow and Free overflow. Different loss factors can be applied depending on the flow direction across the structure.
In MIKE 1D, radial gates are automatically divided into an underflow part and an overflow part. When specifying gate levels for a radial gate, the user should specify the level for the underflow part, i.e. the level of the bottom of the gate. The gate level for the overflow part is then calculated based on geometric considerations.
Flow through a radial gate is calculated as a function of the flow regime of the gate (either; ‘Free’, ‘Submerged’ or ‘Transition’). Free and Submerged flow regimes are calculated individually as described in ‘Hydraulic Aspects - Radial Gates’ in the MIKE 1D Reference Manual and flow in the transition zone is calculated as an interpolated value between the calculated Free and Submerged flows.
Tune factor. Discharge calibration factor. The Tune factor is applied as a multiplication factor solely on the part of the discharge that flows below the radial gate (not applied to eventual overtopping gate flow).
Weir coeff. Coefficient used in the calculation of eventual flow above the top of the radial gate (considered as weir flow above the top of the radial gate).
Weir exp. Exponent used in the calculation of eventual flow above the top of the radial gate (considered as weir flow above the top of the radial gate).
Tran. depth. The Tran. depth parameter is used to define the depth (or height) of the transition zone between free flow and submerged flow regimes and consequently is used to define the level where the flow regime changes to submerged flow. Corresponds to yTran,Depth as defined in ‘Hydraulic Aspects - Radial Gates’ in the MIKE 1D Reference Manual.
Tran. Bottom. The Tran. bottom parameter is an offset used to define the level where a free flow regime for the gate changes to a transition zone between free flow and submerged flow regime. It corresponds to yTran,Bottom as defined in ‘Hydraulic Aspects - Radial Gates’ in the MIKE 1D Reference Manual.
With this gate type the flow under the gate is divided into four flow regimes, the choice of which depends on the upstream and downstream water level. The four flow regimes are:
· – Controlled submerged
· – Controlled free
· – Uncontrolled submerged
· – Uncontrolled free
Additionally flow over the top of the sluice gate is taken into account when the water level up stream and/or downstream exceeds the gate level plus the gate height.
The parameters to specify for the four flow regimes are:
Coef. a. Coefficient a of the flow equation for the four different flow regimes.
Exp. b. Exponent b of the flow equation (it does not apply to the uncontrolled free flow).
High limit and Low limit. High limit and low limit parameters used to smoothen the transitions between flow regimes (they do not apply to the uncontrolled free flow).
Please refer to the chapter ‘Hydraulic Aspects - Sluice Gates’ in the MIKE 1D Reference Manual for further details on the flow at sluice gates and to see the equations used in the computations.
Flow blockage
Apply flow factor
When this option is active, the discharge computed through the gate is multiplied by a flow factor. This factor's value is specified in the Flow factor field. The factor is a dimensionless factor, and a value of 1 means that no change is applied to the computed discharge. A value lower than 1 can typically be used to describe the reduction of the flow through the structure due to obstacles, like debris, restricting the flow area in the structure.
