MICROWAVE AND GROUND-BASED OBSERVATIONS OF SPRING FRESHET VARIABILITY IN A SUBARCTIC MINING DISTRICT

The spring freshet is the earliest spring flow in northern watersheds, and can be a significant influence on regional drainage of snow covered areas. Runoff often freezes on and around roads and culverts in developed areas, and can become a flood and pollution hazard in other areas. The timing and magnitude of the spring freshet is of particular interest to certain industries, such as mines, because a large influx of water can disturb or overtop settling ponds or waste storage areas, which has the potential to impact mining activities or cause downstream contamination. For this study, we compare passive microwave-derived estimates of the timing of melt onset and snow saturation in the Yukon River drainage, surface measured stream discharge on several tributaries, and logbooks describing ground conditions, maintained by the Anvil Range Mining Company, in Faro, Yukon. These records help to to assess the correlations among human and instrumented observations of this significant phenomenon. The mine ceased operating in 1995. Logbooks have been maintained since 1998 and are a helpful resource for determining whether and how the satellite records could be effective in an industrial and real time setting. We investigate the ability to predict the freshet timing or magnitude for future years, and the interannual variability over the period of overlapping records (1998-2006). 2005 data show good correlation, and a particularly significant freshet from the point of view of mine operations. SSM/I and AMSR-E sensors show melt – refreeze cycles occurring from approximately April 4 – May 8. Freshet initiation was observed on the ground starting April 26, with high flows, flume damage, and erosion extensive on May 17. The high flows were captured by aerial photos, ground observations, and hydrographs on the Rose Creek and Ross and Pelly Rivers, and were probably enhanced by a rain-on-snow melt at high elevations. Similar records at different magnitudes are available for the other years showing a range of possibilities. Understanding the variability of the freshet as well as its sensitivity to climate change will be critical in the future in areas with a mining heritage, such as much of the Yukon, Alaska, and Russia.