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.
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.
Cooperative Research Centre for Catchment Hydrology.
Export rate is automatically installed with Source.
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
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. Model parameters
Fixed rate of export of a constituent from a land use
Constituent load in kg per time-step.
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.