Uncertainty in the estimation of mean annual flood due to rating-curve indefinition

Authors
Citation
Rt. Clarke, Uncertainty in the estimation of mean annual flood due to rating-curve indefinition, J HYDROL, 222(1-4), 1999, pp. 185-190
Citations number
5
Categorie Soggetti
Environment/Ecology,"Civil Engineering
Journal title
JOURNAL OF HYDROLOGY
ISSN journal
00221694 → ACNP
Volume
222
Issue
1-4
Year of publication
1999
Pages
185 - 190
Database
ISI
SICI code
0022-1694(19990913)222:1-4<185:UITEOM>2.0.ZU;2-2
Abstract
When rating-curves of the form Q = gamma(h + alpha)(beta) are fitted by lea st-squares, goodness of fit as measured by the coefficient of determination r(2) is Often close to 1, suggesting that estimated discharges have high p recision. This can be illusory if (a) no account is taken of the uncertaint y in estimate of the parameter alpha, and/or (b) the stage h at which disch arge is to be estimated is such that log(e)(h + alpha) lies far from the me an value of this variable calculated using the data points (h,Q) that defin e the rating-curve. Furthermore, since the annual maximum discharges in any M year period of record are all estimated from the fitted rating-curve, th ey will be correlated, even if the annual maximum stages in the M years are statistically independent. The usual maximum likelihood procedures for fit ting extreme-value distributions do not take account of this correlation. E xpressions are given for the conditional (on the values of the M annual max imum stages) and unconditional variances of the mean annual flood (Q) over bar which take account of rating-curve uncertainties. (C) 1999 Published by Elsevier Science B.V. All rights reserved.