Developing a hydrologic foundation for environmental flow management: Context-specific applications

The Ecological Limits of Hydrologic Alteration (ELOHA) framework is built upon a 'hydrologic foundation' of baseline and developed hydrographs for stream and river segments throughout a region.  These flow series are subsequently used to identify statistical departures in the ecologically-relevant components of the two flow regimes.  Building a hydrologic foundation for environmental flow management necessarily relies on region-specific combinations of streamflow gauge analysis and hydrologic modeling.  At ungauged locations and for time periods not represented in the period of record, statistical techniques can be used to estimate flow metrics, or hydrologic simulation models of rainfall-runoff and other watershed processes can be developed to generate flow time series.  Although the basic data required to develop the hydrologic foundation at daily to monthly resolution are now available for much of the globe, prediction accuracy remains a significant concern, especially in sparsely gauged regions.  We discuss techniques and challenges associated with developing hydrologic foundations for applying ELOHA given the widely varying availability of gauge data and existing models.  Example applications that combine gauge data and modeling with the aim of balancing prediction accuracy with the complexity of the modeling exercise are presented to illustrate how strategies can be tailored to region-specific constraints.