Classification of Oklahoma streams using the hydroecological integrity assessment process

Maintenance of the natural flow regime has been linked to the ecological integrity of streams, but the flow regime is not often described at the regional scale.  We used least-altered flow periods from 88 stream gages in and near Oklahoma to classify flow regimes using the Hydroecological Integrity Assessment Process (HIP).  Principal components analysis was first used to reduce 160 hydrologic indices to 27 that were non-redundant and information-rich.  The selected indices describe the five major components of flow regime with 8 indices in magnitude, 4 in frequency, 9 in duration, 3 in timing, and 3 in rate of change.  Streams were then classified into four groups using cluster analysis.  Groups had some geographical patterns but most groups occurred in multiple ecoregions.  The four groups of stream types could be generally described as: 1) perennial run-off streams, 2) perennial flashy streams, 3) stable groundwater streams, and 4) intermittent streams.    This classification of Oklahoma streams by grouping similar flow regimes will aid in the conservation, restoration, and management of aquatic ecosystems.  This hydroecological classification of streams is being validated with fish assemblage data from 32 sites by correlating index values selected for each stream type with degree of impairment.