Hydrologic Implications for Seasonally Draining Lakes in the Central Oregon Cascades

Alex Simpson , Eric Levenson, Leif Karlstrom, Sarah Cooley

The hydrogeology of volcanic terrain exhibits characteristics that reflect both a legacy of volcanic construction and transient evolution of bedrock hydraulic conductivity on million year timescales. Here, we study a drainage basin in the Central Oregon High Cascades in which Holocene lava flows dammed streams, creating seasonal lakes that fill with the spring snowmelt, and drain completely over the summer. The filling and draining of these lakes depends both on the volume of snowmelt and the permeability of their porous lava dams, providing a natural experiment for disentangling multiscale hydraulic properties from climate. We measure the drainage of two seasonal lakes in the watershed of permanent Clear Lake (the highest elevation permanent source of the McKenzie River) with in situ sensors and satellite remote sensing, and compare this with the larger scale summer recession of the McKenzie river at the outlet of Clear Lake. Clear Lake recession is modeled with 2 parallel linear reservoirs, which are linked to aquifer properties and imply watershed scale transmissivity that varies with spatial scale of the aquifer. We also find, using remote sensing-derived timeseries, that all three systems, but particularly the draining lakes, have responded to declining snowpack since 1990. These results suggest that seasonal variations in surface water storage encode the structure of volcanic aquifers generally, and can be used to infer groundwater dynamics in the Cascade Range.