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Hydrology Menu

Activate the hydrology menu. The following options are available:

Hydrograph
Analyze partial duration series


Hydrograph

The hydrograph option is applicable to Xtremes Time Series. It is a special construction of a scatterplot employed in flood frequency analysis. Local thresholds are introduced to detect a clustering and to select floods and droughts. Notice that the hydrograph is not explained in Statistical Analysis (yet see Demo 11.1). To reduce the huge number of, e.g., daily measurements y[i] of discharges or water levels at time i, certain upward and downward peaks are selected. The approach to this question is guided by the method of building clusters by runs.
First, we deal with the selection of upward peaks. Three parameters must be selected, namely

The default parameters are c = 0.25 and r(0) = r(1) = 1. Increase these parameters to reduce the amount of information inherent in the hydrograph. Details:

Likewise, downward peaks are selected for the same parameters out of downward clusters with respect to thresholds u[i] = (1+c)y[i]. Finally, the upward and downward peaks are combined and plotted.

Analyze partial duration series

Flood peaks, given as an Xtremes Time Series, are dealt with under the assumption that the frequencies of occurrence and the magnitudes only exhibit a seasonal dependency. The option Analyze partial duration series is applicable if the modeling by an inhomogeneous Poisson process with independent marks is adequate.
Therefore, it can be necessary to decluster the data (also see Demo 11.3) in a first step. For that purpose use the option
Save Cluster Maxima to get independent cluster maxima over a certain threshold. Visualize the resulting time series in a Scatterplot. Executing Analyze partial duration series one enters a dialog box where several parameters must be specified:

Pressing OK one gets a scatterplot of the data (modulo 365), a plot of weekly frequencies, the T-year values u(T) (read the pages 265-267 in Statistical Analysis) plotted against T, and an active data set called pardur.dat. For each day where parameters were evaluated, the shape and scale parameters of the estimated generalized Pareto distributions are stored in pardur.dat (the values are put equal zero, otherwise). Visualize the parameters by means of scatterplots!

© 2005
Xtremes Group · updated Jun 21, 2005