Pumping rate estimation
The forcing transformation function pumpingRate_SAestimation allows the downscaling of infrequent (>daily) groundwater pumping data to daily, weekly or monthly rates. This extension to HydroSight was funded by the Department of Environment, Land, Water and Planning.
The downscaling is required when pumping is metered, say, only annually and when there are unmetered periods. The downscaling is undertaken by simulating the pump as being either on or off for each user-set downscaling time step. When the period is metered then the number of days pumping is used to estimate the mean daily pumping rate. The median of all metered periods is then applied to non-metered periods. This approach requires no assumption of the behaviour of groundwater users or their response to climatic conditions.
Importantly, in assessing if a time-series of pump state produces a TFN model in agreement with the observed head, the number of combinations of pump state over, say, a decade far exceeds the largest number possible on a 64 bit machine. The implications are that the calibration cannot assess all combinations and that if an identical model is re-calibrated an alternate optima may be identified, which may have a slightly different time series of pump state and model parameters. To manage this challenge the approach is analogous to simulated annealing (SA); note SA comes from annealing in metallurgy, a technique involving heating and controlled cooling of a material to increase the size of its crystals and reduce their defects. The approach does however increase the calibration time by approximately one order of magnitude. Trials are being undertaken to identify adequate calibration setting and preliminary results indicate approximately 8 SP-UCI complexes give reasonable results.
The different metering scenarios are defined from the TFN input forcing data file. Any pumping period that was infrequently metered is defined by -999 values in the forcing data file followed by the total extraction volume over the preceding period of -999s. A period with no metering is defined by a period of -999 values ending with a zero pumping rate.
Also, it is important that there are >=1 period is metered so that the calibration can constrain the draw-down parameters (eg T and S).
The diagram below summarises the calibration algorithm for downscaling the pumping.
