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The Pennsylvania (USA) Instream Flow Advisory Committee completed a hydrologic classification of all rivers within the State of Pennsylvania according to the U.S. Geological Survey's Hydroecological Integrity Assessment Process (HIP).  To define river types, first, 205 hydrologic metrics were derived from mean daily discharge data for 136 relatively unimpaired stream gauges.  Next, a principal components analysis (PCA) eliminated redundancy, thereby reducing the number of metrics from 205 to 151.  Three different clustering procedures were then tested for their ability to group Pennsylvania's streams according to flow regime and to identify the ecologically relevant flow metrics that best characterize them.  Ultimately, five river types were defined based on a subset of 11 metrics that describe streamflow magnitude, variability of high flows, and flood frequency (Apse et al. 2008).  This approach was similarly used to define river types in New Jersey, Missouri, Texas, and Massachusetts (Kennen et al. 2007, 2009; Cade 2008).

In Washington, USA, researchers have completed a statewide hydrologic classification based on 99 metrics describing ecologically relevant characteristics of the natural flow regime (Reidy Liermann et al, 2012).  Metrics were calculated from continuous time series (>15 years of record) of mean daily discharge data for 52 stream gauges, and classification was undertaken using a fuzzy partitional method - Bayesian mixture modeling.  This analysis has identified distinctive flow regime types that differ in their seasonal patterns of discharge, variation in low flow and flood magnitude and frequency, and other aspects of flow predictability and variability.  Factors related to catchment (watershed) topology, surficial geology, and climate were found to be strong discriminators of flow regime, and this information is being used in statistical models to predict flow regime type and flow metrics for streams and rivers across the state.  The spatial context provided by the hydrologic classification improves understanding of the interaction between hydrology and ecology in rivers of the Pacific Northwest United States, and provides a benchmark against which flow-ecology relationships can be assessed.


In Australia, two different steps were used to classify river types. The first step involved empirically derived streamflow discharge data from 830 gauges located throughout Australia. A total of 120 hydrologic metrics were calculated for each gauge and a Bayesian clustering technique was used to group gauges according to similarity in flow regime. The second step used data derived from Geographic Information Systems (GIS) to model streamflow for 1.2 million stream segments to derive a classification flow.  A specialized River Analysis Package was used to prepare data and metrics used in the classification. The Australian hydrologic classification contains 12 distinct classes of river types.(Pusey et al, 2009; Kennard et al, 2010).