9526875 Williams The primary objective of this study is to develop a definitive set of observations of spatial and temporal heterogeneity of: 1) surface structure of a snowpack during melt, 2) internal flow paths, and 3) delivery of water at the snowpack base. From these data we will the define the spatial statistics of meltwater flow through snow. Modeling and additional field efforts will build on this empirical data base to extend our understanding of meltwater pathways through snow to the small basin scale (8ha). We concentrate in this proposal on observations which will characterize and quantify the detailed processes which determine infiltration and runoff. This more detailed knowledge of the physics of snow hydrology will make possible more reliable modeling and prediction of snowmelt runoff. We propose to quantify the spatial and temporal variation of meltwater flow through snow using an extensive array of 116 snow lysimeters that will determine i) the characteristic correlation lengths of snowmelt runoff: ii) the spatial variance of meltwater flow; and iii) effective hydraulic conductivity of the snowpack. Aerial photographs using near-IR wavelengths will be used to provide a specific methods for inferring the onset and degree of heterogeneous infiltration from remote sensing observations, and to more accurately predict the discharge hydrograph of a ripening snowpack, again from remote sensing measurements. The evolution of internal flowpaths will be constructed from non-destructive temperature and comductance probes and from destructive measurements of snowpack stratigraphy and dye tracers. The information on snow physical characteristics will be used to parameterize an existing meltwater infiltration model coupled with the development of a second model that explicitly includes the dynamics of preferential flowpaths. Plot and modeling efforts will be then be scaled to the 8 ha Martinelli basin to evaluate the importance of spatial and temporal variations of meltwater infiltration at the catchment scale.
