The Great Salt Lake Basin serves as a model for much of the western U.S. in that the hydrologic system is driven by snowmelt in the mountains that supplies water to the relatively arid valleys. The region is dominated by nonlinear interactions between snow deposition and loss in the mountains, streamflow, and groundwater recharge at high and mid-elevations, and evaporation from the desert floor. Few hydrologic models are able to represent the complexity of western mountain systems, making an observatory in this region critical for advancing these models.

The Great Salt Lake Basin terminates in a closed basin lake. Thus, it is uniquely suited to be a hydrologic observatory because it presents the opportunity to close the water, solute, and sediment balances in a way that is rarely possible in a watershed of a size sufficient for the study of atmospheric interactions. The steep topographic, climatic, and land-use gradients in the Great Salt Lake Basin provide a compactness that is unparalleled in the U.S., and that is more proximal to logistical support than any other comparable location in the U.S. For example, a 30 km transect can span from regional base-level to alpine catchment while remaining within 50 km of major research universities, an international airport, and major government agencies.

Overall the Great Salt Lake Basin is a unique location ideally suited, both physically and in terms of infrastructure, to addressing fundamental hydrologic science questions in western mountain basin systems in an open community-driven hydrologic observatory. The Great Salt Lake Basin Hydrologic Observatory represents a significant advance in scale relative to scales over which hydrologic processes have previously been comprehensively measured. Furthermore, the scales over which atmospheric processes operate in the western U.S. require consideration of an area of this size. The Great Salt Lake acts as a collector and integrator of hydrologic signals from the surrounding basin providing the opportunity to investigate fundamental hydrologic processes at scales that have been previously unexplored. Analysis of the geologic record in accumulated lake sediments offers the ability to determine historic trends in lake inflow, volume and water quality.

The Great Salt Lake Basin is tractable as a Hydrologic Observatory not only because it is closed, but also because the extremes in topography, climate, geology, ecology, and land use are captured in much smaller representative areas, allowing the overall system to be represented by a nested sampling design. In addition, due to the interest in water development of the early settlers, the basin has a rich hydrologic measurement infrastructure (precipitation, snowpack, streamflow, groundwater). Furthermore paleohydrologic research in the closed basin lakes (Bear Lake and Great Salt Lake) extends our knowledge of hydrologic processes well beyond the historical record.

The GSLB hydrologic observatory design team is fully committed to the principle of openness that is at the foundation of CUAHSI. The input of the national hydrologic community is not only requested, but is essential for optimal development of this (and any other) hydrologic observatory.