Modeling groundwater as a control on river ice thickness
The Tanana River flows through interior Alaska, a region characterized by discontinuous permafrost. Studies link degrading permafrost to increased winter river discharge due to increasing groundwater input. In winter, interior Alaskan rivers are exclusively fed by groundwater, which serves as an external source of heat. In fact, some portions of rivers fed by groundwater maintain thin ice throughout the winter, or remain altogether ice-free, despite very cold air temperatures. These ice conditions represent a significant danger to winter travelers who use rivers for wintertime travel, particularly in this largely roadless area.
We developed a model to explore how fluctuations in groundwater discharge control ice thickness on the Tanana River. The model allows us to examine how local changes in groundwater characteristics affect ice dynamics by addressing two questions: 1) What are the dominant factors controlling seasonal ice dynamics on the Tanana River? 2) What are the rates of change in ice thickness resulting from observed and projected changes in these factors?
Ice melt is amplified by increased water column temperatures, flow velocities, air temperature, and snowfall. Abrupt changes in snowfall were illustrated to contribute to decreased ice thickness and more hazardous conditions for winter travelers. The model examines the physical mechanisms that underlie dangerous ice conditions in winter and early spring, and suggests that GW flow parameters need to be better characterized to model mid-winter ice degradation in sub-arctic environments.
A warming climate in regions with discontinuous permafrost is expected to increase groundwater input into rivers, decrease the temperature gradient between the atmosphere and the ice/water interface, and increase snow depths. Future research should characterize winter groundwater discharge in more detail to better understand how changes in groundwater flow lead to decreased ice thickness and thus more hazardous conditions for winter travelers. The model illustrates that we still need additional information before we fully understand the physical mechanisms to corroborate reports from Alaskans that ice conditions have become more dangerous in the spring, and to determine if permafrost degradation is contributing to the degradation of river ice in a warming climate.
Jones, C.E., K. Kielland, & L.D. Hinzman. 2015. Modeling groundwater upwelling as a control on river ice thickness. Hydrology Research. 46.4: 566-577. [Download]
Jones, C.E., K. Kielland, L.D. Hinzman. 2013. Modeling groundwater upwelling as a control on river ice thickness. Proceedings of the 19th International Northern Research Basins Symposium and Workshop. Southcentral AK. August 11–17, 2013. [Download]
Permafrost degradation and subsequent changes in groundwater affect ice thickness