Research Projects

Project at a Glance

Project Status: complete

Report Published 1987:

Title: Snow deposition, melt, runoff, and chemistry in a small alpine watershed, Emerald Lake Basin, Sequoia National Park 1987

Principal Investigator / Author(s): Dozier, Jeff

Contractor: Center for Remote Sensing and Environmental Optics

Contract Number: A3-106-32


Research Program Area: Ecosystem & Multimedia Effects

Topic Areas: Acid Deposition, Ecosystem Impacts


Abstract:

Investigation of the snow hydrology and chemistry of a small alpine watershed in the southern Sierra Nevada, California, was initiated in Fall 1984 as part of the California Air Resources Board's Integrated Watershed Study program to assess the current status and sensitivity of this alpine environment to damage from acid deposition. The objective of our study was to determine the role of snowmelt runoff in chemical processes in the watershed. The watershed was surveyed, control points were located, and an overflight was arranged so that a large scale topographic map and ortho-photo could be generated. A high resolution (5m) digital elevation model (DEM) was generated, and software developed to do rapid calculation of terrain parameters. Four sites were instrumented and meteorological parameters continuously monitored during the 1986 water year. These data were evaluated to determine the range of climatic variation in the watershed. The 1986 snow season was one of the largest on record, depositing 200% of the 50 year mean snowfall in the Emerald Lake region. Snowfall volume and chemistry were sampled on an event basis from snowboards, and at intervals from snow pits at several sites in the watershed. During spring, several detailed snow surveys were done to estimate the volume and distribution of snow in the watershed. Outflow stream stage has been monitored since mid-1983, and inflow stream stage since mid-1985. Stage-discharge rating functions were developed and discharge calculated for the outflow and the two major inflow streams. Energy transfer at the snow surface was calculated, and the relative magnitude of each transfer term evaluated. An energy balance snowmelt model was developed and tested. Calculated discharge volume from the outflow was nearly equal to the estimated maximum snow water equivalence in the watershed. Chemical loading to the watershed was calculated for the 1985 and 1986 water years. Snowfall during the 1986 snow season had uniformly low ionic concentrations, but the initial melt wave appeared to produce an acidic pulse that significantly lowered the ph and acid neutralizing capacity (ANC) of the basin surface waters. Spatial and temporal variations in the onset of melt over the watershed prolonged the time of elevated ionic concentrations, depressed pH and ANC. Energy transfer calculations showed net radiation as dominating the energy budget during melt, but indicated that sensible and latent heat exchange could be important in the colder months, January and February. Calculated sublimation and evaporation accounted for the loss of 20-25% of the snowfall which should also increase the ionic concentration of snowmelt. Calculated snowmelt, using monthly energy flux totals, corresponded closely with measured discharge. Preliminary testing of the snowmelt model indicates that it is an effective tool that could be coupled with calculations of meltwater ionic concentrations to better predict the duration and strength of acidic inputs during snowmelt.


 

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