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Introduction

The mass-balances module determines the inflow, outflow and storage change within a give polygon from available flow fields. The various parts of the mass balance are computed separately and result in a scalar timeseries:

• To compute the horizontal inflow and outflow, you need to have timeseries of the flow in x- and y-direction defined on a rectangular grid.
• To compute the vertical flow, you need to have timeseries of the flow coming in through the lower face of the grid cells and the flow coming in through the upper face.
• To compute the storage change, you need either the storage change per grid cell or the water table per grid cell. In the first case, the computation consists of summing the values over all grid cells within the given polygon, in the second case, the change over time must be computed as well.

The polygon for which the mass balance is determined is defined via the location set of the output timeseries: the locations defined in that set are taken as the vertices of the polygon. Grid cells are considered to be inside the polygon if their centre is.

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The input for determining the horizontal flux consists of:

• The flow velocity in the x-direction
• The flow velocity in the y-direction

The timeseries must be defined on the same rectangular grid for the same times.

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The input for determining the vertical flux consists of:

• The flow velocity at the lower face of each grid cell
• The flow velocity at the upper face of each grid cell

The timeseries must be defined on the same rectangular grid for the same times.

The output consists of a timeseries of the nett in- and outflow, where the flow rate through the faces faces is computed as the flow velocity times the length and width of the grid cell. The result is a flow rate in m3/s (assuming the flow velocity is given in m/s and the grid size in m). Effects of porosity are not taken into account.

description

An optional description

exportTypeStandard

This type specifies which reader should be used to read the file. The type must be one from the enumeration. Presently (2007/02) only bfg and pi are included in this list.

exportType

This type specifies which reader should be used to read the file. It may be any string as long as this type is supported by the TimeSeriesExport module. The list of supported types is given below.

folder

Folder (directory) in which to store the exported files.

exportFileName

This elements describes how to construct the filename(s) of the exported file(s).
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If only the name element is given a fixed name is used for each export. The prefix and suffix elements describe how to create a filename prefix and/or suffix. The temporaryPrefix is used to generate a prefix for the temporary file as it is being written. After that the fine is renamed.
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validate

Optional element. Only applicable if the data are exported to the xml-file. This option activates the validation of the exported file against a XML schema.

idmapId

Id of IdMap to be used for parameterId and locationId mapping

unitConversionsId

Id of UnitConversions to be used for unit mapping

flagConversionsId

Id of flagConversions to be used for flag mapping

exportMissingValue/exportMissingValueString

Missing value definition for this time series. Either a string or a number. Defaults to NaN if not defined.

omitMissingValues

If set to true records with missing values are not exported

exportTimeZone

TimeZone in which to export the data. Can either be a string (timeZoneName) or an offset (timeZoneOffset).

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Storage change

The input for determining the storage change consists of either:

• The storage change rate per grid cell (that is, the change in the water table per time step)

or

• The water table or water level per grid cell

The timeseries must be defined on the same rectangular grid, and in the latter case there must be at least two times.

The output consists of a timeseries of the nett change in storage, where the stored volume per grid cell is computed as the water table times the length and width of the grid cell. The result is the change in the volume of water present within the area delimited by the polygon. Effects of porosity are not taken into account.

Remarks

While the above description refers to volume or mass balances, the module is more generally applicable to any parameter that represents a mass balance, for instance, if instead of flow velocities, you specify the flux of nutrients (concentration times flow velocity), you can compute the nett inflow/outflow of nutrients through the given polygon.

Porosity is not taken into account in the module, but you can correct for that via the transformation module.