Hydrograph separation-related functions

Functions related to hydrograph separation

mfobs.sep.ih_method(Qseries, block_length=5, tp=0.9, interp_semilog=True, freq='D', limit=100)

Baseflow separation using the Institute of Hydrology method, as documented in Institute of Hydrology (1980) and Wahl and Wahl (1988).

Parameters:

Qseriespandas Series

Pandas time series (with datetime index) containing measured streamflow values.

block_lengthint

N parameter in IH method. Streamflow is partitioned into N-day intervals; a minimum flow is recorded for each interval.

tpfloat

f parameter in IH method. For each three N-day minima, if f * the central value is less than the adjacent two values, the central value is considered a turning point. Baseflow is interpolated between the turning points.

interp_semilogboolean

If False, linear interpolation is used to compute baseflow between turning points (as documented in the IH method). If True, the base-10 logs of the turning points are interpolated, and the interpolated values are transformed back to linear space (producing a curved hydrograph). Semi-logarithmic interpolation as documented in Wahl and Wahl (1988), is used in the Base-Flow Index (BFI) fortran program. This method reassigns zero values to -2 in log space (0.01) for the interpolation.

freqstr or DateOffset, default ‘D’

Any pandas frequency alias Regular time interval that forms the basis for base-flow separation. Input data are resampled to this frequency, and block lengths represent the number of time increments of the frequency. By default, days (‘D’), which is what all previous BFI methods are based on. Note that this is therefore an experimental option; it is up to the user t o verify any results produced by other frequencies.

limitint

Maximum number of timesteps allowed during linear interploation between baseflow ordinances. Must be greater than zero.

Returns:

Qpandas DataFrame

DataFrame containing the following columns: minima : N-day minima ordinate : selected turning points n : block number for each N-day minima QB : computed baseflow Q : discharge values

Notes

Whereas this program only selects turning points following the methodology above, the BFI fortran program adds artificial turning points at the start and end of each calendar year. Therefore results for datasets consisting of multiple years will differ from those produced by the BFI program.

References

Institute of Hydrology, 1980b, Low flow studies report no. 3–Research report: Wallingford, Oxon, United Kingdom, Institute of Hydrology Report no. 3, p. 12-19

Wahl, K.L and Wahl, T.L., 1988. Effects of regional ground-water level declines on streamflow in the Oklahoma Panhandle. In Proceedings of the Symposium on Water-Use Data for Water Resources Management, American Water Resources Association.