4.12. Storage node

In pegulated 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 (Feature Editor 14) allows you to specify storage details. These are outlined in Table 8. You are recommended to use the same units as those in Dimensions, but you can change them by clicking on their respective units buttons.

Releases from storages are normally assumed to be constant through the time-step (limited by volume to the minimum/maximum release curves). Enabling the Adaptive Storage Release Method checkbox 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.

The maximum operating target refers to the full supply level where a maximum target level/volume has been defined based on an operating and management decision, such as to maintain airspace for flood mitigation. Note that you can only specify either the level or volume, although only the level is retained.

Storage dimensions

Select Dimensions (Feature Editor 15) 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. The graph displays a relationship between any two of the three parameters, which can be changed using the drop down menu. You can also export the relationship for use in another scenario.

Where: level is the level of water in the storage in metres
volume is the storage volume for the associated storage level in megalitres
surface area is the surface area of the associated storage level in hectares

Constituents

These inputs are required for water quality constituents, and can be specified by selecting Constituents (Feature Editor 16), then Inlet Channel Mixing (Feature Editor 17) tabs.

Gauged Level

The Apply Unaccounted Difference to Storage level calculation checkbox allows you to enable modelled values to be overridden by observed values. Depending on whether storage level or volume is used, it forces the parameter to equal the observed value. You can link the source data to a file, an expression editor, or the output of another scenario, as shown in Feature Editor 18.

Gauged Releases

This tab includes:

• A checkbox enabling model releases that are forced to be equal to observed releases;
• Drop down list of all outlet paths downstream of the storage; and
• For each outlet path, you can source observed release from either an external file, an expression editor, or linking to the output of another scenario, as shown in Feature Editor 19.

Note that the default value is no forecast release model. If you configure a forecast model, releases in the forecast period can be forecast using the same method as for the Inflow node.

Outlets

Outlets (Feature Editor 20) 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, select Outlets, which opens 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 9; and
• You can enter a relationship between storage level and discharge for each outlet as a piecewise linear relationship (format shown in Table 10).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.

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.

Rainfall

Rain falling directly over the storage reservoir can be input as a time series (format shown in #anchor-21-anchor), using the expression editor (such as adding a daily or monthly pattern), or linking to the output of another scenario, as shown in Feature Editor 21. 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.

Evaporation

Evaporation directly from the storage surface can be input as a time series (format shown in #anchor-21-anchor), an expression editor or linking to the output of another scenario (Feature Editor 22). Appropriate units include mm/h, mm/day, mm/month and m/s.

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 (Feature Editor 23) is specified using a piecewise linear relationship between storage level and infiltration volume/time. Note that negative values refer to a gain into the storage from groundwater. The data file format for seepage is shown in Table 11.

Weirs

You can specify whether this storage will operate as a weir by right-clicking Storage and selecting Weir to enable Upstream Reach (Feature Editor 18)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 the river that the weir inundates. You can define the storage in the same manner as a link. As a result, you can configure storage routing through the weir storage, 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.

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.

Forecasting in storages

You can configure forecasting for various parts of the storage node using the following tabs:

• Evaporation forecasting
• Rainfall forecasting
• Release forecasting

Refer to Forecasting for more details.

Ordering in storages

If your model uses optimised ordering, you should leave the priority level of each link at its default value of 1.

Ownership in storages

Select Ownership to configure various aspects of 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.

Where: level is the storage level measured in metres
discharge is the associated discharge measured in megalitres per day

Where: level is the storage level measured in metres
seepage is the associated seepage measured in millimetres per day