EFFECTS OF THE 2022 DEATH VALLEY FLOODS ON GOWER GULCH AND MOSAIC CANYON: MEH

Gower Gulch and Mosaic Canyon are narrow slots that illustrate the power of flash floods in exceptionally arid Death Valley National Park. Unprecedented rainfall on 5 August 2022 and again on 13 September 2022 generated extensive flash floods that brought large debris flows across roads, damaging and ultimately closing all roads in the Park. On August 5, in just a few hours the Furnace Creek gauge recorded 43 mm of rain, 75% of the annual average, making it the rainiest day in recorded history at Furnace Creek. Photos of buried cars in a parking lot at the mouth of Furnace Creek Wash (FCW) went viral. We expected major geomorphic changes in Gower and Mosaic, and found almost nothing.

Major floods damaged facilities at Furnace Creek in several times in the 1930s, and so in 1940-41 a berm was constructed across FCW to divert floodwaters down Gower Gulch, which is carved in soft siltstone. However, since construction of the berm, only a small proportion of water in noteworthy FCW floods in 1954, 1968, 1976, 1984, 1985, 1987, and 2004 went down Gower Gulch as planned. In the 80 years since the diversion the new slot at the head of Gower Gulch has been eroded from zero to a depth of 12.5 m by these diverted floods, and consequent deepening, widening, and upstream migration of the FCW knickpoint have also been extensive. Lower Mosaic Canyon, 30 km to the northwest, is a slot carved in marble. Since 2009 nearly 2 meters of gravel have filled in the slot and buried the beautiful marble by unremarkable rainfall events.

We did a qualitative study of Gower Gulch and Mosaic Canyon three weeks after the August "1000-year" flood event and again after the September floods, expecting major changes. We found almost nothing. The flooding that did such damage at the mouth of FCW did bupkis at the Gower diversion. In Mosaic Canyon, the gravel filling the marble slot is ~30 cm lower at the mysterious ladder, but several cm higher a few tens of meters upstream. When, how, and why debris flows do their work remain mysterious.