2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 5
Presentation Time: 2:50 PM


MOHAMMED, Ibrahim N., Civil and Environmental Engineering, Utah State University, Utah Water Research Laboratory, Logan, UT 84322-4110 and TARBOTON, David G., Civil and Environmental Engineering, Utah State University, 4110 Old Main Hill, Utah State University, Logan, UT 84322, nourein@cc.usu.edu

The Great Salt Lake (GSL) level fluctuates due to the balance between inflows and outflows. These fluctuations are of interest whether they are high (flooding hazards) or low (economic impacts). Previous work examined the probability distribution of historic bi-weekly lake volumes (1847-1992) and found multiple modes. These have been interpreted as potentially due to separate attractors in the nonlinear dynamics of the system. The topographic area-volume relationship in the GSL plays a role in the system dynamics because area is a control on the evaporation outflux, the only outflow from the system. The increase in lake area with increasing lake volume has a stabilizing effect on the volume and level of the GSL. Where for a given change in volume the lake area goes through a large change, the outflux evaporation will go through a correspondingly large change, tending to stabilize the volume at that point. On the other hand if for a given change in volume the lake area only changes by a small amount the outflux evaporation will only change by a small amount resulting in a small stabilizing effect. These considerations suggest that modes of lake levels should coincide with peaks in the area-volume derivative. This paper compares peaks in the area − volume derivative with modes in the lake volume distribution to examine which modes may be attributable to this effect. This is part of a project exploring a better quantification of the full set of interactions between basin hydrology and lake inputs and outputs. We found that one of the peaks in the GSL volume distribution matched a peak in the area-volume derivative (another peak was close). However the largest mode in the volume distribution did not correspond to a peak in derivative of the area-volume relationship suggesting that stability at this level may be due to some other cause such as perhaps the balance between average climate inputs and outputs. The results of this study improve understanding of the sensitivity of the GSL level to the interplay between topography and fluctuations in precipitation and climate and thereby contribute to knowledge on the interactions between hydrologic processes and long-term large-scale climatic fluctuations.