OLD DATA GIVES KNOWLEDGE FOR FLOOD CONTROL
Smart, G.M.1
1
NIWA
Aims
Catastrophic losses are escalating worldwide (Fig. 1 shows the past 45 years) and the most
significant component is flooding (SwissRe, 2015). Fig. 2 shows the history of serious floods from
the Yellow River, China, since year 0.
This presentation considers historic flood disasters and flood control techniques worldwide. It
aims to draw conclusions relevant to the present day.
Figure 1. Insured catastrophe losses, 1970-2014, in USD billion at 2014 prices, SwissRe (2015).
Figure 2. Major breaches of Yellow River levees over the past 2000 years, after Wang et al (2015).
Method
As return intervals for large flood disasters are typically longer than societal memory of flooding
consequences and as morphological change in rivers takes place relatively slowly, the long-term
effects of river training and control practices may not be apparent in the lifetime of the planners,
designers or organisations responsible for the original schemes. Consequently, information from
past disasters is often not incorporated in planning current and future flood mitigation strategies.
This presentation analyses past flood history and draws conclusions relevant to the present day.
Results
Figures 1 and 2 demonstrate a trend of increasing flood disasters over the past 100 and 1000
years respectively. The history of river control on the Yellow River (Fig. 2) is described here as
an example. Starting in 69 AD, following serious floods in the Yellow River, Wang Jing (30-85 AD)
engineered a wide river bed to allow for sediment deposition and flood diversion. For the
following 800 years the Yellow River aggraded slowly but had relatively few serious flood
outbreaks. The main river then became unstable and “control” was by way of diversions. In 1289
AD the main channel diverted to a new mouth 400km to the south. From 1565-1592 Pan Jixun,
the minister of construction, applied a theory that narrowing the river would enhance the velocity
and carry sediment to the sea. He built primary and secondary levees to confine the Yellow River
to a single thread. Annual levee maintenance was carried out from the 1660s. There were many
flood breakouts and severe disasters but “the river was deliberately tied in an unfavourable
course at an ever-increasing price”, elevated some 10 m above the surrounding plains (Chen et
al, 2012). In an 1855 flood the river returned to a northern mouth. To halt the Japanese army, in
1938, Chiang Kai-shek ordered breaching of the Yellow River levees towards the south causing
hundreds of thousands of deaths and millions of homeless. The ongoing flooding disaster fuelled
discontent and boosted recruitment for the Communist movement. In 1947 the river was returned
to its previous channel. From 1950, Wang Huayun (Director of the Yellow River Commission) reapplied the wide river theory and the river has not breached its banks since then. However,
soaring water abstraction has reduced the mean annual discharge of the lower river by 75%. In
1972 the lower river ran dry for the first time in recorded history. Rapid aggradation (100mm/year)
is now occurring during normal flows and the river bed is again some 10 m above the plain. While
other influences such as hinterland sediment supply, economic conditions, warfare and water
abstraction are important factors, from the Yellow River’s turbulent history we can conclude that,
in the long term, a wide river fairway has resulted in a more stable river with fewer breaches.
Other examples of historic flooding lessons are described in the presentation.
References
SwissRe. (2015) Natural catastrophes and man-made disasters in 2014. Sigma Technical report 2/2015.
Wang, Z., Lee, J. Melching, S. (2015). River Dynamics and Integrated River Management. Tsinghua Press,
Beijing.
Chen, Y., Syvitiski, J.,Gao, S.,Overeem, I., Kettner, A. (2012). Socio-economic Impacts on Flooding: A 4000Year History of the Yellow River, China. Ambio 41(7): 682–698.