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 <[EMAIL PROTECTED]>
> 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 [EMAIL PROTECTED]
> >
>
>
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--
Michael Perelman
Economics Department
California State University
Chico, CA 95929
Tel. 530-898-5321
E-Mail [EMAIL PROTECTED]
