This post covers two issues:
1.) Can daily data be used for a 1-hour time step simulation in ResSim?
2.) What is the difference in using period average and instantaneous in the alternative editor?
To answer the first question, it is important to understand how ResSim will handle simulation time step and input data.
When instantaneous is selected as the flow computation method, the stair step pattern goes away.
Due to this difference in how the data is interpolated, the inflow values vary slightly at each time step. Below is a table of a small portion of the inflow time series.
From this table, we can see that the inflow is 400 cfs at midnight on January 14 and 800 cfs at midnight on January 15. So, we would expect to see inflow values between 400 cfs and 800 cfs throughout January 15 when using an hourly time step. The table below show the differences in the values when using period average and instantaneous.
Note that the average of the instantaneous values gives the period average value. In other words, the average of 566.7 cfs (10:00 instantaneous value) and 583.3 cfs (11:00 instantaneous value) is 575.0 cfs (11:00 period average value).
1.) Can daily data be used for a 1-hour time step simulation in ResSim?
2.) What is the difference in using period average and instantaneous in the alternative editor?
To answer the first question, it is important to understand how ResSim will handle simulation time step and input data.
- If the computation time step is less than the original interval of the input time series data (in other words, using an hourly time step with daily data), then the input data will be interpolated at the new desired interval.
- If the computation time step is an interval greater than the original interval of the input time series data, the computation time step will become the interval at which data input is read. So, a six hour simulation time step using hourly inflow data will read the inflow data every 6 hours.
The figure below shows the inflow data given at one time each day.
The model, however, is run on an hourly time step.
This model simulated with no errors. In the figure above, notice that "Period Average" is selected. With this option selected, the inflow data is constant over the entire time step giving a stair step presentation of the data. The inflow data is the dark line. It becomes coincident with the release (green line) on 14Jan2015.
When instantaneous is selected as the flow computation method, the stair step pattern goes away.
Due to this difference in how the data is interpolated, the inflow values vary slightly at each time step. Below is a table of a small portion of the inflow time series.
From this table, we can see that the inflow is 400 cfs at midnight on January 14 and 800 cfs at midnight on January 15. So, we would expect to see inflow values between 400 cfs and 800 cfs throughout January 15 when using an hourly time step. The table below show the differences in the values when using period average and instantaneous.
Note that the average of the instantaneous values gives the period average value. In other words, the average of 566.7 cfs (10:00 instantaneous value) and 583.3 cfs (11:00 instantaneous value) is 575.0 cfs (11:00 period average value).
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