Re: Re: Re: Re: Yellow River: Facts on File

[Tim Bousquet <chicoexaminer@xxxxxxxxx>]

Yes, but doesn't the high-silt content of the river
date back several thousand years at least? Isn't it
pretty much the prehistoric, natural state of the
river?

--- Michael Perelman <michael@xxxxxxxxxxxxxxxxx>
wrote:
> Reforestation can actually reduce the size of
> deserts over time.
>
> On Wed, Jun 27, 2001 at 02:37:47PM -0700, Tim
> Bousquet wrote:
> > How do you "take care of" the Gobi Desert?
> >
> > tim
> > --- Michael Perelman <michael@xxxxxxxxxxxxxxxxx>
> > wrote:
> > > You can't tame rivers, but you can take care of
> the
> > > land on the hillsides
> > > to reduce siltation.
> > >
> > > Ricardo Duchesne wrote:
> > >
> > > > I have come to the conclusion that China's
> > > hydraulic lock-in and
> > > > long term patter of development cannot be
> fully
> > > grasped without a
> > > > clear appreciation of the ecological dynamic
> of
> > > the Yellow River.
> > > > This, the most unsubordinate, intractable,
> > > turbulent river of the
> > > > world, has long driven a hard bargain. In
> exchange
> > > for its heavily
> > > > sedimented water,  the fruit that nourished
> the
> > > Shang, the Zhou,
> > > > the Chhin, the Han, the Sui, and the Tang
> > > civilizations (to 907AD),
> > > > it killed more people than any other river in
> the
> > > world.
> > > >
> > > > Here are some facts on file:
> > > >
> > > > -- The Hwang Ho, with a lenth of 2,900 miles,
> is
> > > China's second
> > > > largest river, and the 10th longest  in the
> world.
> > > >
> > > > --Carrying up to 40 percent sediment by weight
> (in
> > > some stretches
> > > > as much as 60 percent), it is the most
> silt-laden
> > > river of the world.
> > > > Sediment over 10 percent by weight is very
> rare
> > > among the large
> > > > rivers of the world; even 2 to 3 percent is
> high
> > > (Cressy, 1955).
> > > > Much of the silt is loess, a fine wind-blown
> soil
> > > which the river
> > > > picks up in its upper course as it flows
> through
> > > the "yellow earth"
> > > > region. "Much of this silt is then dropped in
> its
> > > more sluggish lower
> > > > reaches, building up the height of the river
> bed,
> > > and making its
> > > > course unstable" (Blunden and Elvin, 17)
> > > >
> > > > --While the Yangzi River discharges a greater
> > > volume of water, the
> > > > Hwang Ho is much more unstable in its flow; at
> low
> > > water, the flow
> > > > may drop to 5000 cubic feet per second; in
> flood
> > > it can reach
> > > > 1,000,000 (Cressy). But the most challenging
> > > engineering aspect
> > > > is control of the exceptionally high sediment.
> As
> > > the river passes
> > > > through the loess lands and erodes the loess,
> it
> > > becomes a river of
> > > > yellow mud which is then deposited across the
> > > North China Plain.
> > > >
> > > > -- To deal with this shifting, sediment-loaded
> > > river, dykes were built,
> > > > to keep the water stable, but as a result of
> dike
> > > building, the
> > > > surplus sediment which nature would have
> otherwise
> > >  spread far
> > > > and wide has been confined between artificial
> > > barriers. Thus the
> > > > bed of the river has been continually raised
> > > requiring dikes to be
> > > > built higher and higher. This dyking has gone
> on
> > > indefinetely.
> > > > Millions now live below the level of the diked
> > > floor water. Areas
> > > > miles from the river have elevations many feet
> > > below the bottom of
> > > > the river.
> > > >
> > > > --But this river refuses to be tamed. Not only
> has
> > > the river's levees
> > > > been breached thousands of times, its lower
> course
> > > has changed
> > > > 26 times in China's history. A highly
> devastating
> > > change of course
> > > > occurred in 1194 AD  when flood water rushed
> onto
> > > the Huai River
> > > > basin taking over this river's drainage system
> for
> > > the next 700 years
> > > > (Leung, 1996). Siltation at the mouth of the
> River
> > > has extended the
> > > > length of the river by about 35 miles betweern
> > > 1975 and 1991.
> > > >
> > > > -- By the 1950s the northwest province of
> Shensi
> > > had 13 modern
> > > > canal systems, with a total length of 600
> miles.
> > > Currently the
> > > > Chinese are constructing a massive new dam
> called
> > > Multipurpose
> > > > Dam Project with 10 intake towers, nine flood
> and
> > > sediment
> > > > tunnels, six power tunnels and an underground
> > > powerhouse.
> > > >
> > > > --The floods of Hwang Ho are the most
> destructive,
> > > since they
> > > > persist for long periods and spread over the
> > > countryside in every
> > > > direction (unlike the Mississipi where the
> flooded
> > > areas are usually
> > > > a ribbon between the river and its bluff).
> When
> > > the flood ends, a
> > > > veneer of sand and mud covers everything
> except
> > > for the few tree
> > > > tops which had remained above water. While the
> > > Egyptians referred
> > > > to the annual flooding of the Nile as the
> "Gift of
> > > the Nile", the
> > > > Chinese have nicknamed their unruly Hwang Ho
> > > "China's Sorrow".
> > > >
> > > > --When the river's current  slows, and the
> river
> > > loses its carrying
> > > > power, excessive sedimentation takes place
> within
> > > a few days. The
> > > > bed of the river is thus raised. When the next
> > > flood arrives, dikes
> > > > are overtopped before there is a chance for
> the
> > > increased
> > > > movement of the water to excavate previous
> > > accumulations.
> > > >
> > > > -- No amount of dyking can entirely eliminate
> the
> > > wide variations in
> > > > its flow, which to an extent seen nowhere else
> in
> > > the world it is
> > > > also a flow of mud. Each year 1,890, 000, 000
> > > metric tons of silt
> > > > are brought to the head of the delta plain.
> "The
> > > control of the
> > > > Hwang Ho is surely one of the most baffling
> > > hydrologic problems on
> > > > earth; were the river in the United States it
> > > would tax all the
> > > > country's financial resources and engineering
>
=== message truncated ===


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