Observed Runoff model allows the inclusion of an observed time series for runoff and uses a digital filter to separate the quick flow and slow flow components.
Scale
Observed Runoff is applied to a functional unit (FU).
The model is applicable to daily time-step data.
Principal developer
Cooperative Research Centre for Catchment Hydrology. The original slow flow filter was developed by Boughton (1993) and published as Method 2 in Grayson et al. (1996, p78).
Scientific provenance
Chapman (Chapman, 1999) tested a number of base flow separation methods, with one, two and three parameters, and found that the formulation used here was the most satisfactory, while noting that fitting the parameters was subjective . (Note that the term "base flow" is often used synonymously for "slow flow". When calculated using the method below Source uses the term "slow flow" because the method does not explicitly separate sub-surface flow components considered to contribute the base flow.)
Version
Source v3.2.7
Dependencies
None.
Availability & conditions
Observed Runoff is automatically installed with Source.
Structure & processes
Flow from functional units is required to be in two parts, quick flow and slow flow. When a time series of inputs is a source of runoff a method is required to separate this flow into these two components. The Observed Runoff filter Equation 2 identifies the base flow component of flow and when subtracted from the total flow gives the quick flow.
Equation 2 |
|---|
subject to
where:
qb(i) is filtered slow flow response for the ith sampling instant
q(i) is original stream flow for the ith sampling instant
k is the filter parameter given by the recession constant (several methods for computation given in Nathan and McMahon, 1990)
C is parameter that enables the shape of the separation to be altered
It is applied as a single pass through the data.
Modifying the C and k parameters may be particularly useful when additional data are available on actual flow path separation eg tracer studies. See Chapman and Maxwell (1996). |
The equation may be used to fit a curve to the observed data by adjusting parameter C.
Table. Model parameters
| Parameter | Description | Default | Min | Max |
|---|---|---|---|---|
| k | Filter parameter given by the recession constant | 0.95 | 0 | 1 |
| C | Shape parameter | 0.15 | 0 | 1 |
The quick flow and slow flow should not be regarded as true amounts of surface (quick) and subsurface (slow) flow from the catchment. Only when additional information, such as from tracer studies, is available can physical interpretations be placed on the filtered responses (Grayson et al. 1996). |
Input data
The model requires daily flow data.
The time series needs to be continuous (free of gaps) . |
Rainfall data may be obtained from rain gauges or rainfall surfaces but will need to be converted to a time series record that is spatially representative of the whole sub-catchment. Note that the time that rainfall data are collected may be important. Very often rainfall data are collected in the morning, the usual time is 9 am, and may be more representative of the previous day’s rainfall. |
Parameters or settings
Values of k and C are provided for 13 Australian streams in Chapman (1999).
Output data
The model outputs quick flow and slow flow in the same units as the input data.
References
Boughton, W. C. (1993) A hydrograph-based model for estimating the water yield of ungauged catchments. Hydrology and Water Resources Symposium: Towards the 21st Century: Newcastle: June 30 - July 2 1993: Preprints of Papers. p317-324
Chapman, T. and Maxwell, A. 1996, Baseflow separation - comparison of numerical methods with tracer experiments 23rd Hydrology and Water Symposium: Water and the Environment. Preprints of Papers. 21-24 May 1996, Hobart, Tasmania, v.1, pp.539-545
Chapman, T. 1999, A comparison of algorithms for streamflow recession and baseflow separation. Hydrological Processes 13(5): 701-714.
Grayson, RB, Argent, RM, Nathan, RJ, McMahon, TA & Mein, RG, 1996, Hydrological recipes: estimation techniques in Australian hydrology, Cooperative Research Centre for Catchment Hydrology, Clayton, pp. 77-79.
Nathan, RJ & McMahan, TA 1990, ‘Evaluation of automated techniques for baseflow and recession analysis’, Water Resources Research, vol. 26, no. 7, pp. 1465-1473