List Balances

Menu: List Water & Mass Balances

Choices on Sub Menu:

Overall - all segments combined
Segment - each segment (detailed)
Summary - each segment (summary)

Results Depend Upon Mass Balance Option set on the Model Selections input screen:

0 - Use observed outflow concentrations to compute outflow loading terms
1 - Use estimated outflow concentrations to compute outflow loading terms (default)

If Option 0 is specified and the observed concentration is missing, the estimated concentration is used.

For Water Balances, the TOTAL OUTFLOW is the total discharge out of the segment network.

GAUGED OUTFLOW is sum of directly-specified outflow streams (TYPE= 4 Tributaries).

ADVECTIVE OUTFLOW is difference between TOTAL and GAUGED outflows, calculated from water balance.

If all outflow streams are specified in theTributary Group, ADVECTIVE OUTFLOW represents the net water-balance error.

In the Summary table (List Balances Summary), the retention column = sedimentation - internal load.

Interpreting Mass-Balance Tables

The FLOWS and LOADS listed in the water-balance and mass-balance tables are mean RATES (not TOTALS).

To calculate TOTALS, the listed RATES must be multiplied by the length of the AVERAGING PERIOD .

For example, if the AVERAGING PERIOD is .5 years (April-September), and the listed FLOW rate is 20 hm3/yr, the total FLOW volume
between April and September would be .5 years x 20 hm3/yr = 10 hm3 (not 20 hm3 !!)

Similarly, if the listed LOADING rate is 400 kg/yr, the total LOAD between April and September would be .5 years x 400 kg/yr = 200 kg (not 400 g !!).

RATES and TOTALS are equal only if the AVERAGING PERIOD = 1 yr.

Checking Drainage Areas

If specified drainage areas are complete and correct, the sum of the external tributary drainage areas and the reservoir surface area (sum of segment areas) should equal the sum of the specified drainage areas for all reservoir outlets.

The List Balances Overall procedure checks the drainage area accounting. Net error in drainage area specification (as well as the net error in the water balance) is specified in the 'ADVECTIVE OUTFLOW' term listed at the at the bottom of the water balance table.