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# Export rate - SRG

The Export Rate model applies a fixed constituent generation rate to a functional unit (FU) to calculate total constituent load. It requires only a single parameter so is quick to use and therefore useful for exploring sensitivity.

## Scale

This model is applied at the functional unit scale within a sub-catchment.

The model is a scaling factor and is independent of the basic time-step of the model. It is therefore more appropriate for estimating long term loads.

## Principal developer

Cooperative Research Centre for Catchment Hydrology.

## Version

Source v4.3

## Availability/conditions

Export rate is automatically installed with Source.

## Flow phase

The Export Rate model is a simple area-based scaling factor for constituents from a functional unit. It defines a value between 0 and ∞, representing the physical amount of constituent exported per unit area per year.

For constituent *C*

Equation 1 |
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## Input data

A single value representing the export rate in units of tonne/ha/year is required. Area of the FU is taken from the model.

For export rates: Generic lookup tables of export rates are available but there can be large variabilit between areas, which can introduce considerable uncertainty (Fletcher et al, 2004). Long-term data is required to derive reliable local values. Robust estimation of export rates is particularly difficult in environments where most of the load is delivered in a few events (eg. Tropics). The export rate model can therefore be appropriate for estimation of mean annual loads over long periods but generally provides poor estimates over shorter time-steps (a few years or less). |

## Parameters or settings

The parameters for this model are summarised in Table 1.

###### Table 1. Model parameters

Parameter | Description | Units | Default Min | Default Max |
---|---|---|---|---|

Export rate | Fixed rate of export of a constituent from a land use | tonne/ha/year | 0 | ∞ |

## Output data

Constituent load in kg per time-step.

## References

Fletcher, T, Duncan, H, Poelsma, P & Lloyd, L 2004, Stormwater flow and quality, and the effectiveness of non-proprietary stormwater treatment measures - a review & gap analysis, Technical Report 04/8, Cooperative Research Centre for Catchment Hydrology.