Figure 1. Map of drainages above Beatty s property.

Transcription

1 July 13, 2011, corrected Observations of post-monument Fire flows at, Miller Canyon, Coronado National Forest, July 11 th, 2011 Ann Youberg, AZGS Tom Beatty reported 1.05 of rain at his house on July 10 th, followed by significant and damaging flows through his property. The ALERT rain gauge that had been installed on the Reef, east of Carr Peak and just above the Beatty s, recorded 1.64 of rainfall between 13:31:40 and 14:35:40 on July 10 th. A quick assessment of the raw ALERT data indicates that during the highest intensity rainfall 0.72 fell in 10 minutes. The Sue Cannon Rule of Thumb is that 0.25 in 10 minutes is sufficient for post-fire debris-flow initiation. At the request of the Coronado National Forest Ann Youberg, AZGS, visited the Beatty s on July 11 th to assess what kind of flows (floods or debris flows) had impacted the Beatty s property. She was accompanied by Rebeca Franco, Coronado BAER PIO. A.Youberg had previously visited the Beatty s on July 8 th, prior to significant flows. The following are a few comments and photos showing conditions from a visit to the Beatty s on July 8 th, and again after the flows on July 11 th. Yellow arrows indicate the same object between photos, trees or rocks. Blue arrows indicate direction of stream flow. There are several drainages above the Beatty s property. Miller Creek crosses the south end of the property (Figure 1). The next drainage north is informally called Marshall Canyon and a smaller drainage north of that has just been informally named Beatty s Gulch (Figure 1). Miller Canyon had a small debris flow. At first it appeared that the flow in Miller was a flood flow, but then we found a debris-flow snout just upstream of the confluence between Miller and Marshall. Marshall Canyon, on the other hand, definitely produced debris flows. Based on the amount of material there were likely several pulses. Clasts from Marshall Canyon ranged from cobbles to very large boulders. The thickness of the Marshall Canyon debris fan at the channel of Miller Creek is approximately seven feet. There is now a very large debris fan where the apple orchard used to be. Material from the Marshall Canyon debris flows extends down Miller Canyon to approximately the Miller Canyon Trailhead. Beatty s Gulch produced flood flows. The largest material from this drainage was large cobbles to small boulders, but most of the material was composed of sand and gravel. This is the drainage that filled the frog pond. Figure 1. Map of drainages above Beatty s property. The upper watersheds still have plenty of material available for transport. The risk of post-fire floods and debris flows continues. These now-disturbed channels that cross the Beatty s property will shift with subsequent flows. Channels will episodically fill and scour as pulses of sediment move through the system.

2 View from footbridge over Miller Creek near campsites, July 8th. View of the same Miller Creek riparian area, July 11th, from river left. This material came from Marshall Canyon.

3 , July 11th. View upfan of Marshall Canyon debris fan from confluence w/miller Creek New channel of Miller Creek Photos above and below are of Miller Creek riparian area below Marshall Canyon.

4 Miller Creek at the FS boundary, July 8th and 11th. View upstream, July 8th and 11th. View downstream, July 8th and 11th.

5 Marshall Canyon, July 8th and 11th. View upstream of Marshall Canyon, July 8th and 11th. View of Marshall Canyon debris fan, July 11th.

6 View of Marshall Canyon debris fan looking downstream at the confluence of Marshall (left arrow) and Miller Creek (right arrow), July 11 th. Looking upstream in Miller Creek, July 11 th. Small debris flow snout just above confluence with Marshall Canyon. View downstream of Beatty s Gulch, July 8th. View downstream of Beatty s Gulch, July 11th.

7 View of Beatty s pond, July 8 th. View of Beatty s pond, July 11 th. View looking up Marshall Canyon, July 8 th. View looking up Marshall Canyon, July 11 th. Note freshly scoured channels in upper watershed. For more information contact: Ann Youberg Research Geologist Arizona Geological Survey 416 W Congress, Suite 100 Tucson, Arizona ann.youberg@azgs.az.gov (direct) (fax)