Baseflow Seperation

Implements the Lyne and Hollick filter for baseflow seperation. This function utilizes the approach in Ladson et al. (2013).

Usage

bf_sep_lh(discharge, a = 0.98, n = 3, reflect = 30)

Arguments

discharge

numeric vector of daily discharge values

a

alpha, numeric values between [0-1].

n

number of passes for the filter. Must be a numeric value, defaults to 3.

reflect

the number of values to reflect at the start and end of discharge to reduce "warm-up" and "cool-down" issues with the recursive filter. Must be less than or equal to the length of discharge. For long discharge records this value does not matter much, for short records the reflection should approach the length of discharge. The default is 30 as implemented in Ladson et al. (2013).

Value

vector of numeric values representing estimated baseflow.

Details

This function implements the Lyne-Hollick filter (Lyne and Hollick, 1979) using the approach detailed in Ladson et al. (2013). The filter is:

$$Y_{k} = \alpha \times Y_{k-1} + \frac{1+\alpha}{2} \times (Q_k - Q_{k-1}),$$

where \(Y_k\) is the filtered quick response at the \(k^{th}\) sample. \(Q_k\) if the original streamflow and \(\alpha\) is the filter parameter between [0-1].

Ladson et al. (2013) suggest a standardized approach for applying the filter by: (1) reflecting streamflow at the start and end of the series to address warm-up and cool-down; (2) specify the initial value of each pass as the measured flow; and (3) using three passes for the filter (forward, backward, forward); Ladson et al. (2013) also provide additional suggestions for handling missing values and appropriate alpha parameter values that are not covered here.

Note

This function an updated and modified version of the baseflows() function in the hydrostats package by Nick Bond. The hydrostats version returns additional summary measures and utilizes different starting values. Outputs between the two packages will slightly vary.

References

Lyne, V., & Hollick, M. (1979, September). Stochastic time-variable rainfall-runoff modelling. In Institute of Engineers Australia National Conference (Vol. 79, No. 10, pp. 89-93). Barton, Australia: Institute of Engineers Australia.

Ladson, A. R., Brown, R., Neal, B., & Nathan, R. (2013). A standard approach to baseflow separation using the Lyne and Hollick filter. Australian Journal of Water Resources, 17(1), 25-34, doi:10.7158/W12-028.2013.17.1 .

Author

Nick Bond n.bond@latrobe.edu.au modified by Michael Schramm

Examples

bf <- bf_sep_lh(lavaca$Flow, a = 0.975)
head(bf)