New instrument cluster design and installation

Existing Infrastructure

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The proposed Hydrologic Observatory will address research infrastructure needs in the Sierra Nevada and the hydrologic basins draining from it, including the Sacramento-San Joaquin rivers that drain into the ocean through San Francisco Bay, the rivers draining eastward into the basin and range, and the groundwater basins in and downgradient from the mountain range

The Sierra N//evada, as defined by the Sierra Nevada Ecosystem Project (SNEP) is about 650 km long and 120 km wide, for an area of 80,000 km2. There are 24 main sub-catchments that make up the Sierra Nevada, each of which drains from a few hundred to about 5,000 km2 above the mountain front. Of the 20 main rivers draining the Sierra Nevada, 14 lie on the west side and 6 on the east. The greater San Joaquin (mountains & valley together) is on the order of 35,000 km2, or 50,000 km2 including the Tulare Lake basin. Much of the range is public land, and land cover includes significant forests, but also meadow, chaparral scrub, woodland, savanna, canyon land, alpine habitat, bare rock, water, and agriculture.

At its foundation, the Sierra Nevada is an enormous deposit of granitic rock whose exposed slopes are readily visible at the crest. The gradual west slope rising from the expansive Central Valley is dissected by deep, west-trending river canyons. At the eastern edge of the uplift, the high peaks dominate the uppermost elevations, forming rolling highlands in the north, with elevations mostly less than 2,700 m, and expansive, highly dissected mountains in the broad southern alpine zones, where Mount Whitney rises to 4,421 m. The range ends abruptly at the eastern escarpment, dropping with a shallow gradient in the north, but in the south plunging more than 3,000 m from the crest to the floor of the Owens Valley.In the northern Sierra the older rocks are overlain by younger volcanic rocks of the southern Cascades.

This juxtaposition of highly permeable and moderately porous Cascade volcanics with granites of low permeability and porosity makes the Sierra an excellent laboratory for testing geologic controls on groundwater flow, storage and the role of groundwater in surface water. Characterizing “geo-hydrologic landscapes” to better understand stream baseflow processes in mountainous regions like the Cascades is of primary importance. Drainage density and the frequency of alpine lakes in the Sierra are significantly greater in the granite regions as compared to the volcanics, probably reflecting the differing near-surface permeabilities. While this phenomenon is well known to hikers in the region, it has not been quantitatively studied. Granites and volcanics can be found as mixed assemblages in the Tahoe area of the Sierra, while monotypes of granite aquifers dominate in the southern Sierra. Volcanics dominate in the northern Sierra, but their properties vary significantly with their age.

Contact: Roger Bales, rbales@ucmerced.edu | Bob Rice, rrice@ucmerced.edu | Sierra Nevada Research Institute | CUASHI