A PRELIMINARY GEOMORPHOLOGICAL ANALYSIS OF WATER STORAGE CAPACITY: THE PROVIDENCE WATERSHED, CALIFORNIA

The Critical Zone of Earth, as defined by NSF in 2007, is series of systems that extend from the top of the canopy to the bottom of the aquifer. The soil system has been used as the primary connection between the various systems. Knowledge of water storage capacity is essential for predicting water availability in the critical zone. Soil depth is one of the most important parameters used to study water storage capacity. Unfortunately, it is challenging to obtain an accurate representation of the degree of spatial variability of soil depth in a watershed. To obtain this data requires extensive and expensive surveys, which can be compounded in forested regions. We make the assumption that soil depth is a function of surface and subsurface geomorphological processes.

The Providence Watershed, which is a Critical Zone Center (CZO) is located in the Southern Sierra Nevada of California. The Providence Watershed is ~ 2.8 km2. The general trend of the watershed is northeast and ranges in elevation from 1,700 m to 2,100 m. The dominant vegetation cover is coniferous.

In this area, we compiled indices from LIDAR imagery and compared these to hand-auguring profiles collected along Ground Penetrating Radar (GPR) transects. Auguring profiles exist at a spacing of 123 m. The depths of these profiles varied from 0.5 to 7.0 m. We correlated the auguring data with nine indices. None of the correlations, which ranged from -0.50 to 0.21 (Pearson product-moment), were strong. The most significant finding of this study strengthens the important role that GPR can provide to capture the spatial heterogeneity present. GPR lines complimentary to geomorphological mapping can be used as an approach to obtain more accurate results in soil depth and bedrock topography mapping. The appropriate scale of work, however, depends on the understanding of the scale of processes controlling soil formation and erosion.

This work is part of the collaborative effort of the Southern Sierra Critical Zone Observatory.