Weirs¶
Weirs, like orifices, are used to model outlet and diversion structures in a drainage system. Weirs are typically located in a chamber of a manhole, along the side of a channel, or along the top of a storage unit. MIKE+ SWMM represents a weir as a link connecting two nodes, where the weir itself is placed at the upstream node. A flap gate can be included to prevent backflow.
The Weir editor organizes the related input data into the following groups:
- Identification. General identification and connectivity information
- Geometry. Geometric data
- Hydraulic Properties. Hydraulic parameters
- Description. Optional descriptive information about the element. Also includes an option for adding images of the structure.
Figure: The SWMM Weirs editor
Identification¶
The identification group box holds element ID and connectivity information. Use the Insert or Delete buttons to add or remove records from the editor, respectively.
Figure: Weirs Identification groupbox
| Edit field | Description | Used or required by simulations | Field name in datastructure |
|---|---|---|---|
| ID | Id of the Weir | Yes | MUID |
| From Node | Node location of Weir | Yes | FromNodeID |
| To Node | Receiving Node | Yes | ToNodeID |
| Description | |||
| Description | Descriptive information for the element | No | Description |
| Data Source | Reference to an external data source from which the record was imported | No | DataSource |
| Asset ID | Id in the asset management system | No | AssetName |
| Status | Status according to a user-specified list in the Status Code editor | No | Element_S |
| Network Type | Network type describes the type of network i.e Stormwater, Combined or separate. The list of network types can be extended by user. Network type can be specified for each hydraulic element. | No | NetTypeNo |
| Tag | Optional label used to categorize or classify the weir | No | Tag |
Table: Edit fields in the Weirs Identification groupbox and Description tab (mss_Weir)
Figure: Weirs Description tab
Geometry¶
Specify weir geometric properties on the Geometry tab.
| Edit field | Description | Used or required by simulations | Field name in datastructure |
|---|---|---|---|
| Type | Type of weir from a predefined list | Yes | TypeNo |
| Opening | Height of weir | Yes | Height |
| Crest Height/Elevation | Offset of weir crest above invert elevation of location node | Yes | CrestHeight |
| Length | Length of weir | Yes | Length |
| Side Slope | Side slope of weir | If Type = V-NOTCH or TRAPEZOIDAL | SideSlope |
Table: Edit fields in the Weirs Geometry tab (mss_Weir)
The following weir types are available, each with a slightly different formula for computing flow as a function of area, discharge coefficient and head difference across the weir:
- TRANSVERSE (rectangular shape)
- SIDEFLOW (rectangular shape)
- V-NOTCH (triangular shape)
- TRAPEZOIDAL
- Roadway
Weirs attached to storage units are active under all types of flow routing. Those attached to other types of nodes are active only under Dynamic Wave flow routing; otherwise the flow through them is zero.
The height of the weir crest above the inlet node invert can be controlled dynamically through user-defined control rules. This feature can be used to model RTC controlled Weirs and inflatable dams.
Roadway weir types model roadway overtopping using the FHWA HDS-5 (Hydraulic Design Series 5) method and would typically be used in parallel with culvert conduits.
Hydraulic Properties¶
Define weir hydraulic parameter values on the Hydraulic Properties tab.
Figure: Weirs Hydraulic Properties tab
| Edit field | Description | Used or required by simulations | Field name in datastructure |
|---|---|---|---|
| Flap gate | Option to add a flap gate preventing backflow | No | FlapGateNo |
| Can surcharge | Option for allowing weir surcharge where upstream water level can go above height of opening | No | CanSurchargeNo |
| Discharge Coeff | Weir discharge coefficient | Yes | DischargeCoeff |
| No. End Contraction | Number of end contractions for Transverse and Trapezoidal weirs | Yes, if weir type is TRANSVERSE or TRAPEZOIDAL | NoEndContractions |
| End Coeff | Discharge coefficient for triangular ends of trapezoidal weir | Yes, if weir type is TRAPEZOIDAL | Cd2 |
| Coefficient Curve | Optional weir curve that relates discharge coefficient to head | No Does not apply to ROADWAY weirs | CoeffCurveID |
| Road Surface | Type of road surface, PAVED or GRAVEL | Yes, if weir type is ROADWAY | RoadSurf |
| Road Width | Width of the road lanes and shoulders | Yes, if weir is ROADWAY | RoadWidth |
Table: Edit fields in the Weirs Hydraulic Properties tab (mss_Weir)