LowFlows: Low Flows

In UKFE: UK Flood Estimation

Low Flows

Description

A function to estimate lower flow quantiles in ungauged catchments.

Usage

LowFlows(
  CDs = NULL,
  AREA = NULL,
  SAAR = NULL,
  BFIHOST = NULL,
  Exclude = NULL,
  FARLRange = NULL,
  N = 10
)

Arguments

CDs	Catchment descriptors derived from the GetCDs or CDsXML function.
AREA	Catchment area (km2) - for when CDs is not applied
SAAR	Average annual rainfall (mm) - for when CDs is not applied
BFIHOST	An estimate of baseflow index - for when CDs is not applied
Exclude	A site reference. This is to exclude sites that you do not want used in the estimate. For example, if you're seeing how the function performs on a gauged site, you may want to exclude it from the analysis.
FARLRange	A vector of length 2. For example c(0.9,1). This determines a FARL range for the catchments you wish to be included in the analysis. Primarily this is to exclude sites which have significant reservoir or lake influence when the site of interest does not. If it is NULL (default) all NRFA sites are included.
N	Number of donor gauges to use for the assessment. The default is 10.

Details

This function provides estimates of the mean flow, Q95, Q70, Q50, Q10, and Q5. The function works by calculating scaled flows for the catchment of interest from the catchments in the NRFA data set. The scaled flow is calculated as Qsi = Qdi * (Area_s / Area_di) * (SAAR_s / SAAR_di), where the subscripts s and d denote the subject site and the donor site, respectively. A Euclidean distance measure is then used to find the most similar sites using catchment area, SAAR, and BFIHOST. The distance measure is weighted by how correlated each variable is to the scaling factor: Scale_f = Q_d / (Area_d * SAAR_d), and the variables are normalised by the standard deviation (log variables are used). A weighted average of the scaled flow is taken from the most similar N sites, and the weighting is based on the reciprocal of the similarity. The function was subjected to a leave one out cross validation (LOOCV). The results across the estimated flows show no systematic biases and the errors show no correlation with the descriptors used in the estimation process. The factorial standard error (FSE) was calculated from the LOOCV process for each of the six estimated flows and these are used to calculate 90 percent confidence intervals for the estimates. The FSEs are 1.25, 1.74, 1.44, 1.34, 1.29, and 1.27, for the mean flow, Q95, Q70, Q50, Q10, Q5, respectively.

Value

A list. The first element of which is a data.frame with three columns. The first is the flow estimates, the second and third are the 90

Author(s)

Anthony Hammond

Examples

# Get some catchment descriptors, then estimate the flows
## Not run: 
CDs_27083 <- GetCDs(27083)
LowFlows(CDs_27083)

## End(Not run)
# Now estimate again but remove gauge 27083 from the analysis
## Not run: 
LowFlows(CDs_27083, Exclude = 27083)

## End(Not run)

UKFE documentation built on Sept. 24, 2026, 1:06 a.m.