Regional patterns in hydrologic response, a new three-component metric for hydrograph analysis and implications for ecohydrology, Northwest Volcanic Aquifer Study Area, USA
Jennifer A. Curtis, Erick R. Burns, Roy Sando
2020
Journal of Hydrology: Regional Studies
Keywords: NVASA hydrograph separation hydrologic response baseflow interflow groundwater-dependent ecosystem volcanic aquifer A B S T R A C T Study Region: Oregon, California, Idaho, Nevada and Utah Study Focus: Spatial patterns of hydrologic response were examined for the Northwest Volcanic Aquifer Study Area (NVASA). The utility of established hydrograph-separation methods for assessing hydrologic response in permeable volcanic terranes was assessed and a new three-component metric for
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... aph analysis was developed. The new metric, which partitions streamflow into subcomponents defined by the timescales of hydrologic response (e.g. fastrunoff, intermediate-interflow and slow-baseflow), was used to gain a fundamental understanding of the regional hydrology, investigate sub-regional differences, influencing factors, and ecohydrological implications. New Hydrological Insights: The combined effects of NVASA's physiography, climate and geology create a strongly coupled surface-groundwater system that produces copious baseflow and limited quantities of runoff and interflow. Patterns of hydrologic response are influenced by the type and rate of precipitation and permeability of the underlying geology. Under variable precipitation conditions the hydrologic response of volcanic terranes with similar permeability and subsurface-storage capacity can be significantly different. From a water management and ecohydrology perspective, understanding regional patterns of hydrologic response and sub-regional differences is fundamental. Minimum-flow methods provide the most conservative estimate of baseflow and may be the most robust for filtering out snowmelt bias in baseflow estimates. Baseflow contributes ∼75% of the perennial streamflow across the NVASA and represents a critical component of the regional water supply that also provides critical cold-water habitat. T hydrologic response across the NVASA. Although, the mean annual precipitation from 1980 to 2015 (61.1 cm/yr) was close to the long-term mean (60.5 cm/yr), precipitation anomalies (Fig. 2) for a western region of the United States that includes the NVASA, indicate an increase in the magnitude, frequency, and duration of precipitation extremes since 1980 (Vose et al., 2014) . Snowmelt discharge is an important process for generating surface and subsurface flow in the mountainous regions of the NVASA. A recent assessment of western snowpack (Mote et al., 2018) found that 90% of long-term snow monitoring sites showed declines in snowpack and 33% of these sites had declines with significant trends. A regional hydrograph analysis under historic climates for the NVASA will provide an understanding of how changes in precipitation under historic climates influence hydrologic response. A stream hydrograph represents the net balance of water discharged from a surface-water basin. There are numerous automated methods for hydrograph-separation that partition streamflow into two or more subcomponents, which can be assigned to surface (e.g. fast flow) or subsurface (slow flow) sources of water. Although heuristic, these methods provide consistent results that are particularly useful for gaining an understanding of the regional hydrology particularly when hydrologic data are spatially and temporally sparse. J.A. Curtis, et al.
doi:10.1016/j.ejrh.2020.100698
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