Study Area

This research was performed in the upper basin of the Aconcagua river located in V region of Valparaíso in central Chile. Basin localization is delimited by 32° - 33° south latitude parallels and 71°30' - 70° west longitude meridians.

When we talk about an upper basin, we generally refer to a basin located above 1.500 msnm (about 5.000 ft); were variables such as wind, solid or liquid precipitation, temperature, incident solar radiation, etc, play a very important role in snowpack parametrization/characterization. Hence, we have chosen a mountainous sub basin as our study basin: Estero Navarro (Navarro's Creek) 

Figure: General basin localization. In red Aconcagua river basin and in blue Navarro sub basin

Navarro's sub basin is located in the upper basin of the Aconcagua river, so is characterized by a cold mountainous weather. Its average elevation reaches 3.879 masl (12.730 fasl). According to WMS 7.1 simulations, this sub basin covers an approximate area of 60,9 square kilometers (23,5 square  miles). Furthermore, it is estimated that 55% of its slopes are north-facing.

Figure: Navarro basin elevation (in meters above mean sea level, masl)

 

As you could realize, Navarro basin is located in an elevated area of Chile's Central Andes. Navarro's highest peaks are Cerro Leon Blanco 5.158 masl, Cerro Puntón amarillo 4.159 masl, and Portezuelo de Navarro 4.140 masl.

 

Figure: Navarro Basin Chart

 

Snowpack water equivalent

One of the most common properties of snowpacks needed by snow hydrologists is snowpack water equivalent. The water equivalent of a snowpack represents the liquid water that would be released upon complete melting of the snowpack.Water equivalent is measured directly or computed from measurements of depth and density of the snowpack as:

 

 

Given measurements of snowpack depth of 0.22 m and snowpack density of 256 kg m−3, the snowpack water equivalent would be:

 

   

Snowpack water equivalent includes any liquid water that may be stored in the snowpack along with the ice crystals at the time of measurement. Snowpack water equivalent is treated as a primary input to the discussion

of snow hydrology.

 

SWE can be indirectly determined trough snow density and depth. On field measurements do not measure SWE by itself, we measure snow depth and density (weight at the end) with a very rustic (?) and simple system.
   

Figure: Snow depth measurement. Farellones, Chile. ( 33.36S, 70,31W)

 

We first measure snow depth with a regular ruler, and then at a certain given snow depth we introduce a wedge. Carefully you slide a cutter at the top of the wedge and you will have a piece of snow inside this wedge (imagine it as a piece of pizza).

    

Figure: 'Wedge' inside the snowpack. Farellones, Chile

 

Figure: Snow perfectly cut and fit into the 'wedge' . Farellones, Chile.

 

Since the 'wedge' mass is known, weighting it you will have snow mass. Wedge volume it is also known (250cc or 1000cc), thus you can determine snow density at that given depth. Then with the snowdepth you can estimate Snow Water Equivalent.

Principles of snow hydrology

Snow hydrology is a specialized field of hydrology that is of particular importance for high latitudes and mountainous terrain. In many parts of the world, river and groundwater supplies for domestic, irrigation, industrial, and ecosystem needs are generated from snowmelt, and an in-depth understanding of snow hydrology is of clear importance. Study of the impacts of global warming has also stimulated interest in snow hydrology because increased air temperatures are projected to have major impacts on the snow hydrology of cold regions.
 
Snow Hydrology describes the factors that control the accumulation, melting, and runoff of water from seasonal snowpacks over the surface of the earth. This research field addresses not only the basic principles governing snow in the hydrologic cycle, but also the latest applications of remote sensing, and principles applicable to modeling streamflow from snowmelt across large, mixed land use river basins.

 

Figure: Estero Monos de Agua Basin. Central Andes, Chile

Although history suggests that technical understanding of snow hydrology was a relatively recent phenomenon, some evidence exists that the role of snow was understood by some very early in our study of the physical world. References to the philosophy of the ancient Greek, Anaxagoras (500–428 BCE), indicate a rather surprising early understanding of the relationships between river flows and freezing and thawing of water, for example (Franks 1898): “The Nile comes from the snow in Ethiopia which melts in summer and freezes in winter” (Aet. Plac. iv 1;385); “And the Nile increases in summer because waters flow down into it from snows at the north” (Hipp. Phil. 8; Dox. 561). 


Much later, literature from the writings of naturalist/geologist AntonioVallisnieri (1661–1730) in Italy showed specific recognition of the role of snow in hydrology. He correctly theorized that rivers arising from springs in the Italian Alps came from rain and snowmelt seeping into underground channels.

In the United States during World War II, the US Army Corps of Engineers and the USWeather Bureau initiated the Cooperative Snow Investigations in 1944 (US ArmyCorps of Engineers, 1956). The snow investigations were organized to address specific snow hydrology problems that were being encountered by both agencies. In order to meet snow hydrology objectives of both agencies, it was deemed necessary to establish fundamental research in the physics of snow. An extensive laboratory program across the western United States was established and observations were gathered starting in 1945. Analysis of these data formed the basis for developing the basic relationships and methods of application derived to develop solutions to the key snow hydrology problems (US Army Corps of Engineers, 1956).

Figure: Instrumentation at the Central Sierra Snow Laboratory in Soda Springs, CA. United States