Abstract: At-site flood frequency analysis is used to estimate
flood quantiles when at-site record length is reasonably long. In
Australia, FLIKE software has been introduced for at-site flood
frequency analysis. The advantage of FLIKE is that, for a given
application, the user can compare a number of most commonly
adopted probability distributions and parameter estimation methods
relatively quickly using a windows interface. The new version of
FLIKE has been incorporated with the multiple Grubbs and Beck test
which can identify multiple numbers of potentially influential low
flows. This paper presents a case study considering six catchments in
eastern Australia which compares two outlier identification tests
(original Grubbs and Beck test and multiple Grubbs and Beck test)
and two commonly applied probability distributions (Generalized
Extreme Value (GEV) and Log Pearson type 3 (LP3)) using FLIKE
software. It has been found that the multiple Grubbs and Beck test
when used with LP3 distribution provides more accurate flood
quantile estimates than when LP3 distribution is used with the
original Grubbs and Beck test. Between these two methods, the
differences in flood quantile estimates have been found to be up to
61% for the six study catchments. It has also been found that GEV
distribution (with L moments) and LP3 distribution with the multiple
Grubbs and Beck test provide quite similar results in most of the
cases; however, a difference up to 38% has been noted for flood
quantiles for annual exceedance probability (AEP) of 1 in 100 for one
catchment. This finding needs to be confirmed with a greater number
of stations across other Australian states.
Abstract: Climate change will affect the hydrological cycle in
many different ways such as increase in evaporation and rainfalls.
There have been growing interests among researchers to identify the
nature of trends in historical rainfall data in many different parts of
the world. This paper examines the trends in annual maximum
rainfall data from 30 stations in New South Wales, Australia by using
two non-parametric tests, Mann-Kendall (MK) and Spearman’s Rho
(SR). Rainfall data were analyzed for fifteen different durations
ranging from 6 min to 3 days. It is found that the sub-hourly
durations (6, 12, 18, 24, 30 and 48 minutes) show statistically
significant positive (upward) trends whereas longer duration (subdaily
and daily) events generally show a statistically significant
negative (downward) trend. It is also found that the MK test and SR
test provide notably different results for some rainfall event durations
considered in this study. Since shorter duration sub-hourly rainfall
events show positive trends at many stations, the design rainfall data
based on stationary frequency analysis for these durations need to be
adjusted to account for the impact of climate change. These shorter
durations are more relevant to many urban development projects
based on smaller catchments having a much shorter response time.