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A hydrogeochemical model for stream chemistry, Cascade range, Washington, U.S.A.
Author(s) -
Dethier David P.
Publication year - 1988
Publication title -
earth surface processes and landforms
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.294
H-Index - 127
eISSN - 1096-9837
pISSN - 0197-9337
DOI - 10.1002/esp.3290130405
Subject(s) - weathering , snowmelt , geology , groundwater , colluvium , hydrology (agriculture) , soil water , aquifer , bedrock , subsurface flow , saprolite , geomorphology , soil science , snow , geotechnical engineering
A simple mixing model demonstrates that chemical variations in Cascade surface waters reflect flow from three general zones: alpine areas, forested colluvial slopes, and seasonally saturated areas. The chemistry of weathering solutions in alpine portions of the Williamson Creek catchment (North Cascade Range) results from alteration of plagioclase, hornblende, and biotite to kaolinitic material and vermiculite. Surface and shallow groundwater in forested portions of the catchment reflect these reactions, dissolution of small quantities of carbonate, and biologic activity. Both at‐a‐point and downstream chemical variations are explained quantitatively by the volume of water that originates in each of the hydrogeochemical source areas. Water from the forested colluvial slopes is most significant on an annual basis. However, summer low‐flow is a mixture of colluvial waters and dilute solutions from the alpine zone, whereas 10 to 30 per cent of peak flow in snowmelt and rainstorms is produced from seasonally saturated areas. Poor concentration/discharge ( C/Q ) correlations, typical of Cascade rivers, result from mixing of significant C/Q relations for water leaving each source area. Model predictions could be substantially improved by better data for the effects of temperature, water‐contact time, and biologic cycling on the chemistry of soil water from forested zones.