EE8 and EFDC+ can simply and quickly setup up hydraulic structures (HS) such as culverts, weirs, sluice gates, and orifices with the physical dimensions of the structures and use the corresponding HS equations (Dill, 2012), as well as the previous option of defining a flow series for the structure. EE allows the user to view summary of the type of the hydraulic structure and the equation definition (i.e. parameter definition) as shown in Figure 1.

Figure 1  Boundary condition groups for Hydraulic Structures.

Using the Edit button shown in Figure 1 the user may load the Hydraulic Control Structure Boundary Conditions form as shown in Figure 2. On this form, there is a drop-down selection of all available Flow Control Type (NQCTYP). When the user has defined a hydraulic structure the EFDC.INP file creates the card C32A to handle these variables. Some of the parameters in C32A are not used, depending on which equation has been selected.

Figure 2  Boundary condition editor.

The drop-down list defines the flow derived control structure (NQCTYP < 5) and the new hydraulic control structures (NQCTYP > 4). Based on what the user selects the "Head Lookup Equations" and the "Cell Options" frames are updated based on the selection. The Multiplier is used to adjust computed flows by a user defined factor. This serves as a control knob for calibration.

Selecting the Edit button shown in Figure 2 opens the equation editor for the flow control type selected. Each hydraulic structure type is described further below. Note that for every equation, there is a check box to indicate whether or not to allow reverse flows. In terms of vertical layering, EFDC draws equally from all the layers not impacted by the structure.

Culverts

To assist the user define the input parameters for the culvert, a Definition Editor is provided as shown in Figure 3. This form can be accessed by clicking on Edit button in Figure 2. Here the user may define the Equation ID, allowing various culverts dimensions and type to be defined.

The user should select the Hydraulic Structure Type from the drop-down menu. In this case, the option chosen is "culvert". The user should then select the Cross-section type. Depending on the options chosen the image of the culvert will change to match the user's selection. The user can then specify the culvert dimensions in meters, including upstream and downstream elevations of the pipe, length of the pipe, Manning's roughness coefficient and diameter of the pipe as shown in Figure 3. The user may also import 3D structures to better visualize the hydraulic structures in EE8 as shown in Figure 4. An animation of an example culvert may be seen here.

Figure 3   Hydraulic Structure Equation Editor: Culverts.

The methods for determining flow through culverts are based on the culvert flow type classification and analysis from Chow (1959). This methodology describes six different types of culvert flow based on the location of the control section within the culvert and the relative elevations of the headwater, tailwater, and culvert invert and crown elevations in meters. The discharge is primarily computed using Manning's equation which can be expressed as:

Q= KS^1/2

Where conveyance, K= (A/n)R^(2/3) and where A = cross-sectional flow area (m); n = Manning's roughness coefficient, and R = hydraulic radius (m).

Figure 4  Image of culvert in View3D.

Sluice Gates

The sluice gate hydraulic structure boundary has been enhanced to simulate the opening and closing of gates.  Currently two types of sluice gate operation are supported: operational time series, and operational rules.

With the operational time series option, the gate is opened or closed during the simulation based on a defined time series of the operational state and settings such as rate of gate opening, and maximum opening height.  Examples of the types of gates may be shown in Figure 5.

a) Structures with upward opening
b) Structure with downward opening	c) Structures with sideward opening

Figure 5  Operation for different types of gates.

When using the equation based hydraulic structures, if the user selects Equation: Sluice Gate, the Time Control dropdown menu will be displayed as shown in Figure 6. 

Figure 6  Hydraulic Structures: Sluice gate controls.

The options available in this menu are as summarized in the table below and the final three options described in detail in the following sections.

Time-Series Control of Sluice Gates

When the flow control type of Controlled using Time-Series is selected for sluice gate, the user can select which time-series will be used for the structure by selecting the corresponding item in the Table dropdown list in Time Variable Hydraulic Structure Control group (Figure 7).  To create new time series, or edit an existing one, the user can click on Edit button beside the Table dropdown list to edit the control time-series which is shown in Figure 8.

Selecting the Show Params button provides the user with more control over which parameters from the time series will be used to control the gate. Parameters that can be selected for the sluice gate include the initial opening height, opening width, sill level change, number of units, flow discharge and rating curve.  A setting of “1” means that this parameter is used in control calculations. A setting of “0” means this parameter is ignored.  In this example only gate height is set to 1.  Other parameters are left to 0, meaning only the opening height of the gate will change with time.

Figure 7  Sluice gate control using a time-series.

Figure 8  Data Series: Time series for sluice gate control.

Control Rules from Upstream Elevation or Head Difference

When the flow control type of "Controlled based on Upstream Level" or "Controlled based on Head Difference" is selected, the user can select which control rules will be used for the structure by selecting the corresponding item in the Control Rules dropdown list in Time Variable Hydraulic Structure Control group shown in Figure 9.

To create a new set of control rules, or edit an existing set, the user can click on Edit button beside the Control Rules dropdown.

Figure 9  Hydraulic structure: Sluice gate control using operational rules.

The hydraulic structure control rules are shown in Figure 10.  Here the user can configure the number of sets of rules with Number of Rules, and then scroll between the sets with Current Rule menu.  For each set of control rules, the user must configure which parameters the rules are to be set for: opening height, opening width, and sill level (height above bottom of structure) change.  The actual rules require the following settings:

• Control value: the elevation or (head difference) which will trigger the gate to start to open or close
• State: the direction of the opening or closing. Opening is configured with a “1” and closing is configured with “0”
• Height: opening height to which the structure can rise or fall
• Width: the opening width (m) of the gate at (for sideward opening).
• Sill Level Change: the sill level change (m) of the gate. Default is zero.
• Rate: the rate of increase or decrease of the gate opening.

EE uses the “state” of the structure to allow the user the high level of control required to simulate realistic scenarios.  The logic of the process is that if the state of the structure is “1” then it is currently opening, and the rate of opening determined by the Rate.  This will occur from that trigger level until it reaches another trigger level, or it reaches the Height assigned (presumably the maximum opening).  Once it reaches the maximum opening the rate no longer applies and the final flow rate is maintained.  When a trigger is reached with state of “0” the gate will close, and flow decrease at the set Rate. This continues until it reaches the Height assigned (presumably fully closed). 

Figure 10  Operational rules configuration for sluice gate.

Figure 11 shows the form for setting the initial condition of the hydraulic structure.  As described above, the location of the hydraulic structure trigger does not have to be in the same cell as the actual structure.  Here the user can configure the upstream and downstream locations of the control triggers in the Time Control Locations frame.  The user should also configure the initial conditions: whether the gate is opening or closing, and the initial height width and sill level change, if any.

Figure 11  Initial Conditions for gate operation.

Sluice Gate Equation Editor

To assist the user define the equation parameters for the sluice gate, a Definition Editor is provided as shown in Figure 12. The user should define the Equation ID, for various sluice gates to be defined.

The user should select the Hydraulic Structure Type from the dropdown menu, in this case it is "sluice gate". The user should then enter the sluice gate dimensions, including sill elevation, height, width, super-critical weir flow, sub-critical weir flow, free sluice flow and submerged orifice flow parameters as shown in Figure 12. The user may also import 3D structures to better visualize the hydraulic structures in EE8 as shown in Figure 13. An animation of an example sluice gate may be seen here.

Figure 12  Hydraulic Structures Equation Definition: Sluice gate.

Flow through a sluice gate can be characterized by two basic parameters: the tranquility of the flow (i.e., subcritical or supercritical flow) and the water depth (i.e., gate submerged or not).

The equation for free sluice gate flow is:
 

Where C3 and C4 are discharge coefficients for free flow and submerged orifice flow respectively, W is the width of gate, Hu and Hd are headwater and tailwater, respectively.

Figure 13   Image of sluice gate in View3D.

Weirs

To assist the user define the equation parameters for a weir, a Definition Editor is provided as shown in Figure 14. The user should define the Equation ID, for various weirs to be defined.
The user should select the Hydraulic Structure Type from the dropdown menu, in this case it is "weir". Four cross-section types are available to the user: rectangle, v notch, trapezoid and broad crested. This example shows a broad crested weir definition form which requires the crest elevation, width of the weir, and the co-efficient of discharge.

An imported 3D structure image (COLLADA file), used to better visualize the hydraulic structure in View3D is shown in Figure 15.

Figure 14  Hydraulic Structures: Weir definition form.

The equation to define the flow for weirs are as follows:
 
Where a is the ratio, C discharge coefficient and β is a exponent coefficient depending on the shape of flow cross-section.

Figure 15   Image of broad crested weir in View3D.

Orifices

To assist the user define the equation for an orifice, a Definition Editor is provided as shown in Figure 16. The user should define the Equation ID, for various orifices to be defined.

The user should select the Hydraulic Structure Type from the dropdown menu, in this case it is "orifice". Six cross-section types are available to the user: circle, half-circle, ellipse, half-ellipse, rectangle, v notch, and trapezoid. This example shows an orifice with a half circle cross section. The user should send the upstream elevation, diameter of the cross-section in meters, coefficient of discharge for a weir, and coefficient of discharge for an orifice.

An imported 3D structure image (COLLADA file), used to better visualize the hydraulic structure in View3D, is shown in Figure 17.

Figure 16  Hydraulic Structures: Orifice definition form.

The flow equations for the submerged orifice as defined as follows.

Figure 17   Image of half circle orifice in View3D