Flood Defense and Water/Sediment Management—With Particular Reference to The Yellow River - River Dynamics and Integrated River Management - page 339

from the existing levees of the lower Yellow River, which were more than 6 km apart, and to build new
levees near the tips of the dikes, 800 m apart (Freeman, 1922). Freeman's suggestion rekindled the
century's debate on whether the levees should be close or far apart as they were at the time. Engles
conducted physical model experiments, authorized by the Chinese National Economic Council in
1931-1934. The test results indicated that with the levees set far apart, a somewhat better scour was
produced in the main channel than when the levees were close to the main channel edges (Engels, 1932).
Franzius conducted another physical model experiment and obtained different results. Yen (1999)
indicated that Franzius' experiments were conducted without tail gate regulation and the results are not
reliable as those of Engels.
6.1.4 RiverTrainingTheories
Many river harnessing theories have been advocated. including:
(1) Naturalization theory proposed by Tian Fen (Han dynasty 2000 years ago)
It is the river's nature to move and people cannot harness it. The only way to reduce flooding losses is
to evacuate the area at risk and freely allow river flooding over the land. A levee breach occurred and the
river flowed over the north China plain for 23 years during Tian-Fen time, which caused disasters to the
people but also created fertile land.
(2) Leveeless river valley theory
In this theory the river should flow over low ground without levees. It will shift to a new low land if
the old one is silted up.
(3) Artificial migration theory
If the old channel is silted up, people may guide the river to a new channel. People may also utilize the
river to resist an invading enemy army, which was practiced in 1112 and 1938.
(4) Flood diversion with branch channels
Flood diversion channels are necessary to reduce flood damages.
(5) Flood diversion basins
Build flood diversion basins to retain flood water in order to protect people in the lower reaches.
(6) Narrowing channel and enhancing sediment carrying capacity
Narrow the channel with levees and spur dikes, cut branch channels, and confine the flood in one
channel to enhance the flow velocity and the sediment carrying capacity of the flow, to prevent sediment
deposition and scour the channel bed (Pan Jixun).
(7) Upper reaches storing, lower reaches discharging and two sides retaining.
The theory which has guided the flood control practices in the past 50 years are: Reducing flood
discharge with reservoirs in the upper reaches, enhancing discharge capacity of the lower reaches
channel by enhancing and reinforcing the levees; and retaining rare flood water with detention basins on
the two sides of the river.
6.2 Flood Defense Strategies
Many of the previously described theories were applied and people have developed many more flood
control methods in the recent century. In the past 50 years, within which 10 major floods of discharge
over 10,000 m 3 /s occurred, the river has been controlled within the Grand Levees and no great disasters
have occurred. The nation has spent $1 billion for flood control and saved $500 billion in flood loss
(Chen, 1999). The main flood control practices are described in the following subsections.
6.2.1 WideRiverValley
The Yellow River flows from mountainous areas into the North China plain near Zhengzhou. A sharp