[Awclist] [Fwd: RRFW Riverwire - Pearce Ferry Rapid Update]

[Thomas Robey]

RRFW Riverwire -- Pearce Ferry Rapid Update

October 12, 2007

 

The once tranquil waters of Lake Mead at the end of the Grand Canyon 
near Pearce Ferry, Arizona continue to change quickly, as the Colorado 
River is reclaiming 50 miles of territory that once was the flat 
reservoir of Lake Mead.

 

With the ninth year of drought continuing, Lake Mead has dropped 119 
feet, and as the river down cuts into lake sediment, it no longer 
follows its historic river bed. The "reborn" river now channels 
full-force into hillsides, crosses once-buried ridges and travels 
through rocky saddles far removed from the pre-lake river bed.

 

Approximately one mile north of Pearce Ferry, at river mile 280.8, the 
river now flows over a saddle between hills and then straight into a 
gravel hillside. At Devil's Cove, mile 292.4, the new river channel is a 
half mile from the historic river bottom and now flows through a saddle 
lined with very hard limestone outcroppings of rock on all sides of the 
river channel.

 

While the lake level is still high enough to cause no more than a riffle 
at Devil's Cove, a rapid has developed near Pearce Ferry, called Pearce 
Ferry Rapid.

 

A small riffle at the top of the rapid has formed two very small 
pour-overs along the shore, with a clear tongue in the middle of the 
riffle. Just below this riffle, the river passes a rock outcrop and 
makes a sharp ninety degree turn as the full force of the Colorado slams 
into a rocky hillside.

 

A large outcrop of cemented rocks sits in the middle right of the rapid, 
with a tongue going to the left of the outcrop into a strong reverse 
current, with an eddy on the left side of the reverse. A fast channel 
with a steep drop at low water has developed on the river right side of 
the outcrop.  See photos of the rapid online at our website here: 
http://www.rrfw.org/article.php?file=20071011.RRFW_Riverwire.Pearce_Ferry_Rapid_Update.

 

At water flows of 12,000 cfs and less, the run is now left of the 
outcrop heading right once passed it.

 

This rapid poses a threat to river travel, as a boat could wrap on the 
mid-stream outcrop. Night floating through this area is not recommended, 
and as this rapid may get more severe in the next 6 months as lake 
levels continue to drop, scouting on river left is an option.

 

The geologic term for this type of rapid is called a Nick Point. Here, 
harder bedrock material forms a waterfall which prevents further 
down-cutting upstream of the waterfall.

 

As of October 10, 2007, there are as many as eight nick points emerging 
in the 13 mile section of river between Pearce Ferry Rapid and the end 
of current in Lake Mead, presently in Gregg Bay near river mile 293.

 

The Pearce Ferry Rapid is cutting through consolidated gravels, and it 
is possible the river will be able to erode the gravels to avoid the 
creation of a more serious rapid. River runners should exercise caution 
in this reach as it continues to evolve while the river reclaims the 
receding reservoir.

 

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RIVERWIRE is a free service to the community of river lovers from River 
Runners for Wilderness. To join RIVERWIRE, send an e-mail address to 
riverwire at rrfw.org and we'll add it to the RRFW RIVERWIRE e-mail alerts 
list.

 

Support the RRFW Grand Canyon litigation seeking preservation of 
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Join RRFW's listserver to stay abreast of and participate in the latest 
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Check out RRFW's Rafting Grand Canyon Wiki for free information on 
Do-It-Yourself Grand Canyon rafting info 
http://www.rrfw.org/RaftingGrandCanyon/Main_Page.

 

RRFW is a non-profit project of Living Rivers.

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