A wetland is a complex hydrological unit with features including a hydraulic connection between a water source and a water body or storage. Wetlands may have ecological, recreational, cultural or consumptive requirements and, thus, behave in a similar way to some functions of the Water User node. In some systems, wetlands consist of several storages that are connected using wetland links. In others, a wetland can connect directly to a main river channel.
Cells model
Source uses a cells model that represents each wetland as a wetland cluster, that is, a number of storage cells with the movement of water between them described by a set of functions and boundary conditions.
In Source, a wetland cluster consists of one (or more) Storage nodes connected by Wetlands links to each other or to Wetlands Hydraulic Connector nodes. The hydraulic components of elements within a wetland cluster interact with each other.
Cells are wetland compartments in which water can be stored. They have a relationship between water surface elevation (reduced level) and surface area that represents the spatial distribution of water in a wetland. In Source, a cell is represented by a wetland Storage node, that is, a Storage node that is connected to at least one Wetland link.
Boundary conditions are points at which water can flow in to or out of the cells model. In Source, boundary conditions occur either at a Wetlands Hydraulic Connector node or at a wetland Storage node with at least one standard inlet or outlet connection.
Figure 1 illustrates some types of wetland that may be represented in Source by nodes in a wetland cluster:
A wetland without river flow (green box). Examples include upland swamps, or spring fed wetlands on a floodplain.
A wetland with a single water body (purple box). Examples include billabongs and oxbow lakes.
A complex wetland with multiple water bodies (grey box). There are multiple paths of river flow through this type of wetland. Examples include the Macquarie Marshes, Hattah Lakes and Menindee Lakes.
Boundary conditions in the Source model shown in Figure 1 occur whenever the clusters (boxes) intersect with a non-Wetland link (dashed line).
Figure 1. Example wetland clusters
For further information on the Cells model and its use in Wetlands, refer to Wetlands SRG.
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The Wetlands Hydraulic Connector node connects wetlands directly to the main river network (ie. not at a storage), and is used when the inflows and outflows are too small to have an effect on the water surface elevation in the river. This node distributes flows between the main river system and the wetland system. It represents a boundary condition for the connected wetland cluster with a configured relationship between the river's water surface elevation and flow rate (Figure 2). You can import this relationship as a .csv file or enter it manually.
Figure 2. Wetlands Hydraulic Connector node
Just like the inflow node, you can forecast flows in the Wetlands Hydraulic Connector node (Figure 3). In a rules-based ordering system, this accounts for return flows from a wetland on the receding limb of the hydrograph, thus reducing orders placed upstream.
Figure 3. Wetlands Hydraulic Connector node, Forecast
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Wetland links use a hydraulic model and are used to connect storages within a wetland, or a wetland to a river. They are represented by a green line with a black arrow, and are created by using the side anchor point from a Storage node or Wetlands Hydraulic Connector node (Figure 4).
Figure 4. Wetland link, Schematic Editor
Note that a conveyance link is the type of wetland link used in Source. The discharge across the link depends on the Modified Conveyance function and the hydraulic head difference between the two ends of the link. The Modified Conveyance is dependent on the hydraulic conveyance and the channel length. The weighting configuration controls the point in the channel at which the hydraulic head difference is applied (see Wetlands SRG).
Wetland links can be either regulated or unregulated, uni- or bidirectional, and you can configure which end of the link will have a higher water surface elevation (reduced level - RL). Use the Wetland link feature editor to configure each of these parameters.
Configuration
This tab (Figure 5) is used to specify the direction type of flow in the link, weighting, and the Modified Conveyance Relationship.
The Direction Type allows Wetland links to be either uni- or bidirectional. If unidirectional is chosen, flow along the link will only be in the default direction. The default flow direction is set when the modeller selects one node before the other when creating the wetland link. The flow direction is indicated by the direction of the arrow on the link in the Schematic Editor (Figure 5). When bidirectional is chosen, flow can go in both directions along the link. Flow that moves in the default direction is represented by a positive number, while flow in the other direction is represented by a negative number.
The Weighting applies to the head difference between each end of the Wetland link, and adjustments to this value are important if there is a significant head difference between the wetland and river water surface elevations. For example, if there is a Wetland link from a wetland Storage node to a Wetlands Hydraulic Connector node (as in Figure 5), and the water surface elevations of the Storage and Connector are RL1 and RL2, respectively; then a weighting of 0.5 gives a weighted water surface elevation that is the average of RL1 and RL2. If a weighting of 0 were used instead, the weighted water surface elevation is equal to RL1, and if a weighting of 1 were used, the weighted water surface elevation is equal to RL2.
The Modified Conveyance Relationship allows the user to enter the relationship between Elevation, which is the weighted water surface elevation, and the Modified Conveyance.
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Note: The Modified Conveyance Relationship table requires an entry with a Modified Conveyance of 0. Also, it accepts negative water surface elevations (used to model a wetland link with a weighted water surface elevation below sea level). |
Figure 5. Wetland link, Configuration
Target Flow
This tab (Figure 6) is used to specify whether the link is regulated or not (using the Flow Regulated checkbox) and to allocate a time series to the flow.
Figure 6. Wetland Link, Target flow
Ordering at wetlands
In the order phase, wetland clusters can both generate orders (directly or indirectly) and supply them:
- Direct order generation
- Each storage in a wetland can have a target level or range and place orders to ensure the storage remains at the level or within the range; or
- Indirect order generation
- Water users may be used to generate demands for a wetland cluster that are translated into orders at supply point nodes. For example, a water user may use an ecological demand model to generate a demand. The order associated with this in-stream requirement would enter the system at a supply point node immediately downstream of a wetland cluster.
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| Note: Wetland clusters may be an order delivery source if they are connected to downstream ordering nodes (such as the supply point node) via standard links. However, the ordering system will bypass/ignore wetland links. |
Viewing wetland results
In the Results Manager, select the following results to view the output of the different components of a wetland:
- Cell: Storage » Storage Level for a wetland Storage node;
- Boundary condition: Wetlands Hydraulic Connector » Average Reduced Water Level for node-related results; and
- Wetland link ('connector'): Wetland Link » Average Flow Rate
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Note: There are detailed wetland recorders that can be useful for debugging, which can be turned on in the Project Hierarchy under Miscellaneous » Wetlands. The individual recorder names do not show up in the Parameters window, but the wetland recorder results can be viewed in the Results Manager. |
In Figure 7, the bidirectional link (red) shows that as the storage level decreases, there is an increase in the water flow through the wetland link from the connector to the storage. There is also a flow back to the connector from the storage if the head level in the storage is higher than the head level at the connector. The unidirectional link (blue), shows that the flow is one way, ie. there is a flow only into the storage from the connector and no flow from the storage to the connector. Hence the values are all above zero.
Figure 7. Wetland link, Results
Figures 8 and 9 show how water level for a wetland Storage node, Wetland link and the Wetlands Hydarulic Connector node differ between a unidirectional and bidirectional link, respectively. For a unidirectional link, as the level in storage increases, there is a gradual drop in the average reduced water level (average water surface elevation), which in turn reduces the amount of water flowing through the link into the storage. This process is gradual because the water can also go from the Storage side to the Wetlands Hydraulic Connector side if there is a drop in the Connector's head level.
In a bidirectional link, the drop in average reduced water level of the connector and the wetland is steeper because a reduced head in the river level will stop water flowing into the wetland but will also stop water from flowing back into the river from the wetland due to the wetland link being unidirectional. The wetland link water level gradually reduces after a steep fall as the head level in the storage reduces.
Figure 7. Wetland results, Unidirectional
Figure 8. Wetland results, Bidirectional
