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A wetland is a complex hydrological unit with features including a connection between a water source and a water body or storage. Multiple storages can be interconnected to form a complex system. In some systems, wetlands consist of several storages connected using wetland links. In others, a wetland can connect directly to a main river channel. Wetlands may have ecological, recreational, cultural or consumptive requirements and thus behave in a similar way to some functions of the water user node.
Wetland cluster
A wetland cluster is a group of wetland storage nodes and hydraulic connectors connected by wetland links, bounded at a hydraulic connector node, or storage with either standard inlet/outlet connection(s) or a single wetland link. The hydraulic behaviours of elements within wetland cluster interact with each other. A cluster comprises of cells (wetland storages) and connectors (wetland links).
Source uses the concept of cells to represent various components of a wetland:
The hydraulic connector node represents a boundary condition; a wetland link is a connector; and a wetland storage is cell
A wetland link connects storages in a wetland, or a wetland to a river. These links use a hydraulic rather than hydrological model. There are different types of wetland link to reflect differences in hydraulic properties – e.g. conveyances, weirs, pumps and culverts.
A wetland storage is a special case storage node that takes into account the hydrological behaviours of a wetland including evapotranspiration, infiltration and vegetation response to change in hydrological conditions i.e. inundation.
Boundary conditions are 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 wetlands as a number of storage cells with the movement of water between them described by a set of functions and boundary conditions. Cells are wetland compartments in which water can be stored. They have a relationship between reduced level and surface area that represents the spatial distribution of water in a wetland. Boundary conditions are points at which water can flow in or out of the cells model. In Source, these points , these occur at either a hydraulic connector or storage inflow or outlet (connected to standard outflow links). The The method for determining outflow rate at the ‘boundaries’ boundaries of a wetland cluster will depend on the type of node that is at the boundary.:
- For hydraulic connectors, mass balance is calculated as: Outflow is the difference between inflow and conveyance flow.
- For storages:
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- If the storage has reached its target level, outflow must be set so that the storage remains at the same volume where possible
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- ;
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- Outflow is determined by unconstrained orders and spill, but also limited by the total outlet capacity of the storage (which varies with water surface elevation)
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- ; and
- There a minimum amount ‘spilled’ (
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- ie.
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- when there is at least one spillway).
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- This also varies with water surface elevation.
Wetland cluster
A wetland cluster is a group of wetland storage nodes and hydraulic connectors connected by wetland links, bounded at a hydraulic connector node or storage with either standard inlet/outlet connection(s) or a single wetland link. The hydraulic components of elements within a wetland cluster interact with each other.
Each wetland cluster component is represented in Source as follows:
- The hydraulic connector node represents a boundary condition;
- A wetland link is a connector; and
- A wetland storage is characterised as a cell.
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The wetland hydraulic connector node connects wetlands directly to the main river network (ie. not at a storage). 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 reduced level (surface water elevation) versus flow rate relationship. You can import this relationship . as a .csv file or enter it manually.
Figure 1. Hydraulic connector node
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Wetland storage
Essentially the , a wetland storage models a pool of water connected to one or more wetland links. In many cases a weir (modelled as a storage) connects directly to a wetland via a wetland link. Hence the existing storage node is used to implement wetland link connections.
To implement the wetland storage as a regular storage, it is assumed:
- All links are at the wall (storage is a level pool)
- Storage capacity volumes are > 0
Storage volumes, levels and flows are first estimated, then recalculated using the standard Source storage model. The aim of this additional storage model run is to interface between the cells model and the rest of the river system model. When running the storage model, accumulated wetland link flows to/from the storage will be are treated as a lateral flux – ie. in the same way as seepage and net evaporation. This has the same effect as treating the wetland link as an inflow, or a priority zero outlet (ie. an outlet with higher priority than all others). Storage releases that go down standard links will be are taken into account in cell model storage and wetland link calculations, but these will be are an approximation based on combined outlet capacity and orders. Outlet path priority is not considered for this purpose.
To implement the wetland storage as a regular storage, it is assumed that:
- All links are at the wall (storage is a level pool); and
- Storage capacity volumes are > 0.
In Source, re-regulating storages will generate orders to upstream storages to maintain target operating levels or meet downstream requirements. Forecasting supply is complex, and even more so where flow direction is not specified. If there is no upstream storage connected to the wetland storage inlet via standard links, it will be treated as a headwater storage. Hence when no inlets are connected, order generation and accounting functionality are not used.
Similarly, it will is only be possible for downstream water users to place orders on wetland storages where the water user is connected to the wetland storage outlet via a path of standard links. Owner shares, internal spilling/ceding, borrow and payback arrangements are only relevant in these cases.
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This link is Wetland links use a hydraulic model and are used to connect storages in within a wetland, or a wetland to a river and use a hydraulic model. There are different types of wetland link to reflect differences links available, each reflecting variations in hydraulic properties - eg. conveyances, weirs, pumps and culverts. Wetland links can be either regulated or unregulated. This link is both , uni- and or bi-directional and net evaporation, groundwater and other fluxes are not modelled.
Essentially the wetland storage models a pool of water connected to one or more wetland links. Functionality of standard storage nodes (which have an inlet and one or more outlets connecting to standard links) is retained, as well as the ability to model wetland link connections.
Storage volumes, levels and flows are first estimated using cell model equations, then recalculated using the standard Source storage model. The aim of this additional storage model run is to interface between the cells model and the rest of the river system model. When running the storage model, accumulated wetland link flows to/from the storage are treated as a lateral flux – ie in the same way as seepage and net evaporation. This has the same effect as treating the wetland link as an inflow, or a priority zero outlet (ie. an outlet with higher priority than all others). Storage releases down standard links are taken into account in cell model storage and wetland link calculations, but these are an approximation based on combined outlet capacity and orders. Outlet path priority is not considered for this purpose.
Once a wetland link has been specified, double click it to configure it using the wetland link feature editor (Figure 2).
Figure 2. Link (Wetland, Configuration)
Conveyance link is a type of wetland link used in Source. The discharge across the link depends on the hydraulic conveyance (relationship between reduced level and discharge) of the link and hydraulic head difference between the two ends of the link.
Weighting refers to the and you can configure which end of the link will have a higher reduced level.
Use the link's feature editor to configure each of these parameters:
- The Configuration tab (Figure 2) is used to specify the direction type and weighting. The latter refers to the head height at each end of the link. It is the weighting applied to the head height and adjustments to this value are important if there were a significant height difference between the wetland head height and the river head height.
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- If RL1 is the Connector side
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- and RL2 is the wetland side
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- of the link, a weighting of 0.5 is
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- the average of the head height of RL1 and RL2.
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- If 0 were used instead, the head height of the
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- connector would be used to work out the reduced level to determine the direction of the flow of water and if 1 were used, the wetland head height would be weighted; and
- The Target flow tab (Figure 3) 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 2. Link (Wetland, Configuration)
Note that a conveyance link is a type of wetland link used in Source. The discharge across the link depends on the hydraulic conveyance (relationship between reduced level and discharge) of the link and hydraulic head difference between the two ends of the link. The weighting
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| Note: Weighting uses the same principle as Muskingum x (detailed in storage routing), where x is the weighting factor denoting the importance of inflow relative to outflow |
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Figure 3. Link (Wetland, Target flow)
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In the order phase, wetland clusters can both generate orders (directly or indirectly, ) and also be used to supply ordersthem:
- 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.
In phase 2 of the implementation, the supply point node will be modified to account for orders placed on behalf of a wetland cluster. It will be possible to configure a method of deducting water user accounts associated with a supply point node for delivery of water (flow volume) at an upstream of the node (not just at the node as is the default case).
- Order source
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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 Recording Manager, select the following attributes to view the output of the different components of a wetland:
Cell: Storage > Storage Level for a wetland storage;
Boundary condition: Wetland Hydraulic Connector for node-related results; and
Connector: Wetland Link for