Storage node

In regulated river systems, storages control the supply of water to consumptive and non-consumptive users, and may also provide flood mitigation, social and environmental services. In a river model, they represent places where water is stored along the river, such as dams, reservoirs, weirs and ponds. Storages operate by maintaining water mass balance. 

In Source, the storage node operates by calculating the minimum and maximum discharge based on current inflows and user defined discharge, gain and loss relationships. They maintain water balance and assume that the change in storage height across a time-step is small compared to the storage fluxes. Additionally, it assumes that any flows fluxes into or out of the storage are distributed throughout the time-step. Flows and changes in storage volume are calculated by integrating across the time-step.  

For all storages in Source, four aspects must be configured as a minimum in the node’s feature editor:  

• Details of the storage such as its dimensions and capacity;
• Inflows to storages such as stream flow from upstream catchments, rainfall over the storage surface area, recharge from groundwater, and runoff from the catchment surrounding the storage;  
• Outflows from the dam, which could be initiated either through controlled releases (to fulfill downstream demand) or uncontrolled flows; and
• Losses that constitute evaporation from the storage surface area and seepage to groundwater.  

The editor’s main window (Figure 1) allows you to specify storage details, which are outlined in Table 1. You are recommended to use the same units as those in Dimensions, but you can change them by clicking on their respective units buttons.

Figure 1. Storage node

Table 1. Storage node, details

Releases from storages are normally assumed to be constant through the time-step (limited by volume to the minimum or maximum release curves). Enabling the Adaptive Storage Release Method check box generates a release curve based on the orders combined with the outlet curve. With this option, the storage would release at maximum release rate where the storage couldn’t release at ordered rate. The storage would release at minimum release rate when it was greater than the order. The adaptive storage release method will generate small artifacts when switching between the order and maximum/minimum release rates. However, it should provide better handling of releases when there are multiple outlets with big operating ranges. 

Both Minimum operating level and Maximum operating level are only used when the storage is configured as a weir. Outlets MUST be configured correctly, and an ungated spillway must NOT be configured as the default outlet. The storage will not release water to satisfy downstream requirements if this results in the water level dropping below the minimum operating level. Likewise, water will be released to prevent the storage rising above the maximum operating level.

Operating target is the level that the system will attempt to maintain in a downstream storage by transferring water from an upstream storage.

Storage dimensions

Select Dimensions (Figure 2) to specify the dimensions of the storage node using level, volume and surface area. It can be entered manually as a piecewise linear relationship or imported as a comma-separated file (format shown in Table 1). The graph displays a relationship between Level vs Volume or Level vs Surface Area, which can be changed using the drop down menu. You can also export the relationship for use in another scenario.

Figure 2. Storage node, Dimensions

Table 2. Storage node, Dimensions (data file format) 

Constituents

These inputs are required for water quality constituents, and can be specified by selecting Constituents. Ensure that constituents have been defined prior to configuration (using Edit » Constituents). The dialog for configuring constituents is the same as for links. Hence, refer to Links for details.

Gauged Level

The Apply Unaccounted Difference to Storage level calculation check box allows you to enable modelled values to be overridden by observed values. The storage level forces the parameter to equal the observed value. You can link the source data to a time series, an expression, or the output of another scenario, as shown in Figure 3.

 Figure 3. Storage node, Gauged level

Gauged Releases

This item shows a list of storage releases that are forced to be equal to observed releases. Click on the disclosure triangle to view these. Then, right click to enable the required release. For each outlet path, you can source observed release from either a time series, an expression, or the output of another scenario, as shown in Figure 4.

Figure 4. Storage node, Gauged releases 

Outlets

Outlets (Figure 5) define how water is released from the storage and must be added to allow for spills. In Source, you must specify the following: 

• Outlet path – the path (out of the storage node) taken by the outlet. To choose an outlet path, click on the disclosure triangle to open a list of links connected to the node. You can choose the link that is associated with an outlet by right-clicking and choosing the outlet type;
• Outlet types – right-click on Outlets and choose the outlet type from the contextual menu.You can add more than one outlet type per storage. These are shown in Table 3. Storage Outlet Types; and  
  You can enter a relationship between storage level and discharge for each outlet as a piecewise linear relationship (format shown in Table 4.).You can also see a piecewise linear relationship accounting for all the release types (eg if you have a gated spillway and a culvert) in the table for Total Outlet Capacity.

Table 3. Storage Outlet Types

Table 4. Storage node, Seepage (data file format)

Note that when there are multiple outlets configured, water will flow down the outlet path assigned to the default spillway. Also, when a minimum flow requirement node is connected downstream of the storage node, water will flow through the path that links it to the storage.

Figure 5. Storage node, Outlets 

Rainfall

Rain falling directly over the storage reservoir can be input as a time series, using the expression editor (such as adding a daily or monthly pattern), or linking to the output of another scenario, as shown in Figure 6. It is assumed to occur only on the surface area. Daily rainfall data near the storage is required and can be obtained from managing agencies, SILO or the Bureau of Meteorology. 

Figure 6. Storage node, Rainfall

Evaporation

Evaporation directly from the storage surface can be input as a time series, an expression, or linking to the output of another scenario (Figure 7).

Figure 7. Storage node, Evaporation

Seepage

Water can infiltrate into the ground where the soil is not fully saturated. Where groundwater intercepts the surface, water can seep from groundwater into the storage, where infiltration can occur wherever there is a ground/water interface. Seepage (Figure 8) is specified using a piecewise linear relationship between storage level and infiltration volume/time. Note that you cannot specify negative values. The data file format for seepage is shown in Table 4.

Figure 8. Storage node, Seepage

Weirs 

You can specify whether this storage will operate as a weir by right-clicking Storage and selecting Convert to Weir to enable Upstream Reach (Figure 9). This feature can only be defined if the storage is configured as a weir. The upstream reach represents the storage relationship in the stretch of river that the weir inundates. You can define the storage in the same manner as a link, which may be important for constituent modelling. If you do not want to configure storage routing through a weir, you can define the upstream storage relationship as 0. Refer to Links for configuring groundwater, loss/gain etc.

The weir-related data entered for the storage node refers to the volume of the upstream reach that is inundated for a given operating level of the weir. The outlet relationships of the weir allow you to define a default outlet, which represents the main downstream flow path from the weir. For a re-regulating weir, this should be a Gated Spillway. Ensure that you incorporate the rating curve further downstream of the default outlet to constrain the maximum outlet capacity of the Gated Spillway.

Figure 9. Storage node, Upstream reach

Ordering storages

If your model uses optimised ordering, you should leave the priority level of each link at its default value of 1. Refer to Figure 10 for details on configuring ordering for the storage node.

Figure 10. Storage Node, Ordering

Ownership in storages

In ownership, observed values may not be available for every time-step. Additionally, observed values cannot include negative numbers, as ownership of storages can potentially result in negative shares when you support borrow and payback. Refer to Figure11 for details.

   Figure 11. Storage node (Ownership)