Re: Re: Yellow River: Facts on File

[Tim Bousquet <chicoexaminer@xxxxxxxxx>]

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
> skills" (Cressy).
> >
> > -- Two million lost their lives from drowning or
> starvation after the
> > flood of 1888. But too little rain can be worse
> than too much.
> > Serious draughts have been a regular occurence in
> the dry north,
> > particularly the provinces of Hopei, Honan,
> Shansi, Shensi, and
> > Shantung, where 100 out of the 216 greatest
> draughts have been
> > recorded
>
> --
>
> Michael Perelman
> Economics Department
> California State University
> Chico, CA 95929
>
> Tel. 530-898-5321
> E-Mail michael@xxxxxxxxxxxxxxxxx
>


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