La Jencia Flash Flood!

Moving at about 5 miles per hour (as judged by floating tumbleweed), the front of the flood (visible here with lots of foamy flotsam) made a roaring sound easily audible at the ranch house.  The brunt of the thunderstorm had passed more than half an hour previous.  Based on cross sections of this reach, the flood was only about 30cm deep, and represented a flow of approximately 50 CFS.  This amount of water may be "bankfull": the bank-side sedges were underwater, the willow got their feet wet, and no major channel geomorphic changes occurred. 

Advancing front of flash flood.

 The next day.

 Flooding along old channel where side canyon empties in.  This channel was abandoned in 2009 when the creek cut through a meander bend.

Bankfull Flood on the Haw River, North Carolina

There is abundant evidence of a bankfull flood event on the Haw River, upstream of Bynum, North Carolina.

Let's see what the USGS Gauge at Bynum says.

 A gauge height over 11 feet counts as a flood...and it is more than 7 feet above current flow.  Note that this is a very wide river, so the actual volume was much more than 7 times...according to the USGS calculation, the flow was near 20,000 CFS, over 30 times the current flow of 600 CFS.

How does the compare to previous floods?

This January flood appears to be a bankfull event that was surpassed in 2008 (the first year of record for Bynum), 2009, and 2010, (but not in 2011 or 2012).  Many of these large floods happen in the early spring, perhaps when the heavy rains fall on an already-saturated watershed.

This is what happened the week of January 13th.  On top of the previous week's rain, there was significant rain on Monday the 14th and Wednesday the 16th.  The storm continued into Thursday, bringing more than an inch of thunderstorm rain (and snow) on top of the saturated landscape.  The Haw river flow peaked soon thereafter, in the early morning hours of January 18th.

USGS concludes 2006 was 1,000-year flood near Tucson

Floods are described in terms of their recurrence interval. A 10-year flood has a 1 in 10 chance of occuring each year. Many engineers and flood planners work with 100-year floods, since this is approximately the length of accurate and reliable observations in the West. However, much larger events can, and do, occur.

After studying the aftermath of the floods that wiped out Sabino Canyon in Tucson in 2006, the USGS has concluded that the event was virtually unprecedented. By dating geological deposits, they estimated that the floods that swept down most of the West-facing canyons in the Santa Catalina Mountains were probably on the order of a 1,000 year flood.

However, with climate change and associated land cover changes on the mountains, that interval may no longer hold. Pearthree, section chief of AZGS Environmental Geology, warns, “increasing fire frequency on the steep slopes of the Santa Catalina Mountains due to invasive species like bufflegrass may result in greater runoff, and possibly increased debris flow frequency, in the coming decades.”

Details, including an map.

Other recent flash floods.

Santa Fe River Stream Team 2009

We had a great turnout of volunteers to help us plant native willow and cottonwood in the Santa Fe River. This planting continued a 10-year Wild Earth Guardian project to restore continuously linked habitat from the Santa Fe River's confluence with the Rio Grande 50 miles up to its headwaters in the Santa Fe National Forest.

From Santa Fe River Stream Team 2009

The SNOW:

From Santa Fe River Stream Team 2009

The FLOOD:

From Santa Fe River Stream Team 2009

Looking upstream BEFORE:

From Santa Fe River Stream Team 2009

Looking upstream AFTER:

From Santa Fe River Stream Team 2009

On to the NEXT Stream Team:

From Santa Fe River Stream Team 2009