The stage-storage relationship defines the physical topographic conditions of the proposed asset.

Extended detention depth

It is important when creating a new custom stage-storage relationship that the user first enters the correct extended detention depth in the treatment properties dialogue. MUSIC requires sufficient stage-storage data above the adopted extended detention depth to complete hydraulic calculations. Designers should confirm the current software requirements applicable to the version of MUSIC being used.

Stage-storage

The stage-storage relationship should be entered prior to defining the stage-discharge relationships for pipe and weir flow.

A stage value of 0 represents the wetland NWL and the corresponding storage volume at NWL represents the wetland permanent pond volume. The specified stage-storage relationship must be consistent with the submitted functional design.

Where 1 is the Height increment and decimal places settings, 2 is the option to open data from a text file and 3 is the option to paste copied data from a text file.

The data output from the earthworks model should be saved with a *.csv file extension. It is recommended the data is viewed in a text editor (e.g. Notepad) to ensure the data does not contain additional formatting or formulas. The data must be presented in the following format for input to MUSIC:

• No header line
• Comma or space delineated
• Set Height increment (m) to 0.1 m and Decimal places to at least 4 decimal places (Recommended) 
• Stage-Storage relationship must extend at least 2.0 m above the extended detention level (rounded up to the nearest 100 mm) – to ensure significant changes in storage are recorded and rounding errors avoided
• Use standard number format (MUSIC will convert these to scientific format)
• A starting height of 0.00 m represents NWL of the wetland
• Starting volume is the storage below NWL (i.e. permanent pool volume)

Once formatted correctly, the *.csv file containing the earthworks model data can be imported using the open button or copied to the clipboard and pasted using the paste button

In the example provided in Figure 10, an extended detention depth of 0.35 m was adopted and therefore the stage-storage relationship must be defined to at least 2.35 m above NWL (0.35 + 2.0 = 2.35 m).

Often the data from the associated earthworks model will not contain storage values for all stages up to 2.35m above NWL, unless the wetland is located within a retarding basin. Generally, the stage-storage curve can be extrapolated linearly from the highest two stage-storage data points to the target stage value (2.0 m + EDD), see Figure 11. Since the wetland should rarely reach these water levels this should usually be a reasonable approximation.

Stage-Discharge Relationship

The stage-discharge relationship defines the outflow behaviour in terms of both outflow (pipe flow) and overflow (weir flow).

In its calculations, MUSIC interpolates between the stage (water level) and total discharge, which is the sum of pipe and weir discharges. To support this, all possible combinations of stage and total discharge should be unique and the total discharge should always increase with stage. The curve cannot be flat or increase then decrease as there would then be two possible stages which have the same discharge.

Figure 12 and Figure 13 show example stage discharge curves for low (‘pipe’) flows and high (‘weir’) flows, respectively.
Where 1 denotes whether the imported data will replace or add to the pipe flow based on the equivalent pipe diameter in MUSIC (usually use replace), 2 denotes the stage-discharge table and 3 denotes the settings for Height increment and decimal places.
Where 1 denotes whether the imported data will replace or add to the pipe flow based on the equivalent pipe diameter in MUSIC (usually use replace), 2 denotes the stage-discharge table and 3 denotes the settings for Height increment and decimal places.

Inputs for the stage-discharge curves can be calculated using standard orifice and weir equations. Weirs and orifices should use accepted equations for weir and orifice design as prescribed on the Melbourne Water website. The designer must consider the type of outlet structure and the resulting outflow behaviour and adopt the appropriate equations accordingly.

The Custom High (Weir) Flow in must be set such that the calculated outflows replace standard flows (Note 1, Figure 12 and Figure 13).

The adopted relationships for low and high flows can be verified by observing the curves of the respective data and noting changes at the stage corresponding to the adopted EDD of the wetland (Note 2, Figure 12 and Figure 13).

For the high (weir) flow relationship, it is expected that the outflow will be zero up to EDD, then increase at an increasing rate as the stage increases above the EDD level.