Using Flux Output

Using FLUX Output as BATHTUB Input

The FLUX program (Walker, 1999, Chapter 2) can be used to develop the following BATHTUB inputs based upon monitored flows and concentrations in each tributary or outflow, as specified on the Edit Tributary screens:

Flow Rate (hm3/yr = cubic hectameters / yr = million cubic meters / year)
Flow weighted Concentration (ppb) for Each Nutrient
CV of Flow-Wtd Concentration (Relative Standard Error = Standard Error / Mean)

The time period analyzed in FLUX must correspond to Averaging Period being modeled in BATHTUB. If FLUX is applied to data from a full year, the Averaging Period would = 1.0. If FLUX is applied to data from May-September, the Averaging Period would = 0.42.

Note that the Flow values entered in BATHTUB are mean flow rates (not total volumes) over the Averaging Period. If the Averaging Period = 1, the total flow volume *hm3) would equal the mean flow rate (hm3/yr). If the Averaging Period = 0.5 years and the mean flow rate is 100 hm3/yr, the total flow volume over the averaging period would = 50 hm3.

The average FLOW RATES generated by FLUX consider only days with non-missing daily flow values. Missing flow records should be estimated independently before using FLUX to calculate average flows and loads.

FLUX estimates average flows and loads in the DOWNSTREAM direction only. If the stream has significant reverse (negative) flows (this happens in Florida sometimes!), reverse flows and fluxes should be calculated separately (by setting the FLOW SIGN factor in FLUX to -1). In BATHTUB, a separate tributary (TYPE CODE=4) should be specified to account for reverse flows.

Tributary flows and concentrations can also be estimated by the user independently of the FLUX program or computed from user-specified land use & export coefficients .