Re: Has the Merced ever dried up?

My favorite page from the Yosemite NPS website is the water flow at Happy Isles (here)

Looking at the average flow from 90+ years of data, and the current state of the river here in mid-July (less than 20 inches deep), I'm wondering if there is precedent for the river drying up completely?

I couldn't find anything on the river actually drying up but in 1986 the flow was down to about 100 cubic feet per second prior to the spring surge. This is still a lot of water but not much when compared to the years when the spring runoff is going at over 6000 cfs.

---

Old Dude

The Merced like many other southern High Sierra rivers and creeks that include as part of their drainage basins elevations above 11,000 feet, often have areas of permanent snow and or small glaciers. Our 7.5 minute USGS topographic maps of those higher elevations show a great many of those snow fields. Thus those snowfields may provide a source of minimum flows even after the driest periods like the drought of 1976/77. Although water tends to quickly drain off of the dominant Sierra granite geology, areas with considerable talus tend to seep out their water more slowly. In the Southern Sierra, the Kings River and San Joquin River often have the largest minimum late season fall flows even in droughty years because they have the most high elevation areas with permament snow areas.

And to the north of Yosemite where highest elevations tend to be quite a bit lower, there is often considerable volcanic geology that absorbs and releases water more slowly. Thus rivers like the Feather with its considerable volcanic areas always have significant late season flows.

In any case, there are a great many creeks and rivers in the Sierra that do dry up by mid fall every year and others that dry up only after droughty periods. In fact some of those rivers may be rather large during early summer. But if their basins do not source some of the above higher elevations or seeping geologies, they may dry up. ...David



Post Edited (07-14-07 23:22)

---

http://www.davidsenesac.com

i was there yesterday (7-15-07) and in Yosemite Valley, there were lots of people in rafts floating down the river.. i was swimming it myself. the waterfalls were almost at a dribble though. Upper Yosemite Falls wasn't much to brag about, the only fall that i saw that was still going pretty good was Nevada Falls (viewing it from Glacier Point).

Oh, I am so glad to hear that there were people rafting! I heard the water was very low and that that the raft rentals were closed, but I was hoping to at least take our own raft and find some water to float down in. So, do you think we would be ok to bring a raft for our trip beg. on 7/28? Thanks for your input!

family4yosemite wrote:

> Oh, I am so glad to hear that there were people rafting! I
> heard the water was very low and that that the raft rentals
> were closed, but I was hoping to at least take our own raft and
> find some water to float down in. So, do you think we would be
> ok to bring a raft for our trip beg. on 7/28? Thanks for your
> input!

You can also go lounge in your raft up at Tenaya Lake

there are areas where you'll probably have to get out of the raft and carry it (depending on how far you float, and where at), but i saw numerous people in rafts and inner tubes.. IMO, inner tubes are the way to go.

Thank you for your replies. Tenaya lake, yes, I hadn't even thought of it, that's a very good idea! Well, we are taking our rafts/tubes and will make the best out of whatever flow there is! We can't wait to jump in for a swim. BTW, what was the temp this week in the valley?

family4yosemite wrote:

> BTW, what was the temp this week in the valley?


It should be around 90.

The Merced River flow rate at Pohono has been as high as 25,000 cubic feet per second to as low as 10 cubic feet per second. No record of ever haveing been at 0 cfs.

---

Old Dude