CASE 5: EXTREME WAVE ANALYSIS DATA
(contributed by IAHR Maritime Hydraulics-Working Group on Extreme Wave
Analysis, p.hawkes@hrwallingford.co.uk )
General Description
The statistical analysis of extreme wave data is an important tool in the
determination of the design wave height for many coastal and offshore
structures. The methodology for the statistical analysis of these extreme data
is quite diversified depending on the preference of the analysts and there
seems to be no consensus as to the most reliable method of extremal data
analysis.
Four sets of extreme wave data are presented in the following. The first set
(Haltenbanken.txt) consists of three-hourly sea-state records collected during
a nine year period with a wave buoy at Haltenbanken off the Norwegian coast.
The second (Kodiak.txt) comprises a 20-year period of storm peak wave
heights, obtained via a numerical hindcast of historical storms. The last two
data sets (samples.txt and samples_above6point5.txt) consist of synthesized
samples of wave heights, coming from a known statistical distribution. Both
uncensored (complete) data and censored data are used, each with 500
samples.
Extreme Data Sets
A short description of the four data sets is presented below:
(1) Haltenbanken.txt : contains nine years of continuous three-hourly
measured Hs and Tp data from Haltenbanken (Fig. 1), on the Norwegian
coast. Wave data were collected at three-hourly intervals from March 1980
until October 1987 (1st location: 65o05’N, 7o34E and 280m local water depth)
and from November 1987 until March 1988 (2 nd location: 65o11’N, 7o15E and
290m local water depth). Missing or poor wave data have been supplemented
by hindcast data enabling the composition of a continuous series of threehourly data for a nine year period, starting on January, 1, 1980 and ending on
December 31, 1988. The hindcast data were obtained with the WINCH model
at six-hourly intervals after which they were interpolated to obtain three-hourly
data.
(2) Kodiak.txt: contains twenty years of all peak storm wave heights with a
significant wave height (Hs) exceeding 6m from Kodiak, Alaska (Fig. 2). The
Kodiak data consist of hindcast results, obtained through the Wave
Information Study (WIS) performed at CERC. Data have been retrieved from
deep water grid point 17, located at 57o50’N, 148o70W. In total 78 storms
have been hindcast to generate a data set covering twenty years, from
January 1, 1956 till December 31, 1975.
Figure 1. Geographic location of the Haltenbanken measurements.
Figure 2. Geographic location of the Kodiak grid point.
(3) samples.txt: contains 500 uncensored (threshold zero) synthesized
samples of wave heights (m) from a known statistical distribution. The number
of data per sample is 100, which corresponds to the record duration of twenty
years with the mean rate of λ=5 extreme events per year on the average. The
parent distribution was selected as the Weibull distribution with a shape
parameter k=1.4: F(x)=1-exp{-[(x-4.922738)/2.190484]1.4} with 4.922738 ≤ x ≤
∞ and samples were produced using Monte Carlo simulation.
(4) samples_above6point5.txt: contains 500 censored synthesized samples
of wave heights (m) from a known statistical distribution. Only those data that
exceeded the threshold of 6.5m were retained. The number of data in the
censored samples varies form sample to sample. The mean sample size is
N =53.25 with the standard deviation of σ(N)=5.31. The parent distribution
was selected as the Weibull distribution with a shape parameter k=1.4:
F(x)=1-exp{-[(x-4.922738)/2.190484]1.4} with 4.922738 ≤ x ≤ ∞ and samples
were produced using Monte Carlo simulation.
Download data
The file (Haltnenbanken.txt) consists of five columns: the first one contains the
RDS, the second contains the year, month, day, hour and minutes of the
measurement, the third the storm index (0. , 1. , 2. , 3.) for ordinary data, local
maxima, monthly maxima and yearly maxima respectively, the fourth the
significant wave height measurements in meters and the fifth the spectral
peak period of the measurements in seconds. The maximum wave height in
this data set is 12.51m.
The file (Kodiak.txt) consists of three columns: the first one contains the date
of the storm peak, the second the maximum significant wave height (>6m)
and the third the period. The maximum wave height in this data set is 11.70m.
The file (samples.txt) consists of 500 uncensored samples indexed by RUN#1
- RUN#500. For each sample the number of simulated data and the threshold
used are mentioned. Each sample contains ten columns of data.
The file (samples_above6point5.txt) consists of 500 censored samples
indexed by RUN#1 - RUN#500. For each sample the number of simulated
data and the threshold used are mentioned. Each sample contains ten
columns of data, but the data in each RUN are limited compared to those in
file samples.txt, due to the censoring used.
Haltenbanken.txt
Kodiak.txt
samples.txt
samples_above6point5.txt
References
Van Vledder, G., Goda, Y., Hawkes, P. Mansard, E., Martin, J. M., Mathiesen,
M., Peltier, E., Thompson, E., 1993. Case Studies of Extreme Wave
Analysis: A Comparative Analysis, Proceedings of the Second International
Symposium OCEAN WAVE MEASUREMENT AND ANALYSIS, Sponsored
by the Waterways, Port, Coastal and Ocean Div.IASCE , 1993, New Orleans,
Louisiana, pp 978-992.
Goda, Y., Hawkes, P. Mansard, E., Martin, J. M., Mathiesen, M., Peltier,
E., Thompson, E., Van Vledder, G., 1993. Intercomparison of Extremal
Wave Analysis. Methods using Numerically Simulated Data, Proceedings
of the Second International Symposium OCEAN WAVE MEASUREMENT
AND ANALYSIS, Sponsored by the Waterways, Port, Coastal and Ocean
Div.IASCE , 1993, New Orleans, Louisiana, pp 963-977.