Proposal Report
onFlood Hazard Mapping Projectin
Taihu Basin

Prepared by Lin Hejuan
Taihu Basin Authority of Ministry of Water Resources
China

Flood Hazard Mapping Training Course
Nov. 25, 2008

1. Background of the proposal
1.1 Training situation
In the Asia areas, especially East and Southeast Asia, there are many floods everyyear, and much human life and property are lost by flood, and it is predicted that
population in urban area will rapidly increase in the near future. In order to reduce thedamage caused by flood, in addition to the structural countermeasures, non-structuralcountermeasures have also been more and more paid attention. Flood hazard map as
an important non- structural measures was already very mature in Japan and waswidely applied in the nationwide.
In order to provide professional knowledge and techniques of Japan to thedeveloping countries, JICA have been implementing the training course “FloodHazard Mapping” since 2004. I participated in this year's training course fortunately.
Through this training, I understood the present situation of flood hazard mapping inJapan and learned how to make flood hazard map. This will be helpful to my work. I
think Japan's flood management idea is very advanced. It is worth while to learn thedisaster prevention activities by our country.
1.2 Present situation of flood hazard mapping in China
In China, the first flood risk map had drawn in 1976, it is very simple. From
1997, China was practices of drawing flood risk mapping. Such as zhejiang province,
the risk map is concerned the probability in 5, 10, 20, 50 and 100 years. In2004，
Chinese government chose some area inthe prefecture of seven river basinagencies
respectively
tomakeexperiments of flood risk mapping. Taipu
River was chose to make experiments offlood risk mapping in Taihu Basin. Thistask was finished in 2007. Because oflacking of some basic data, such as detail
Distribution of inundation depth
DEM, distribution of property and so on, of Taipu River(flood of once in50 years)
flood risk map is not yet in use.

Distribution of flooding velocityof Taipu River(flood of once in50 years)
1

Distribution of flood reaching timeof Taipu River(flood of once in50 years)

1.3 Significance of flood hazard mapping in China
China typically suffers from the flood damage. Affected by the climate andtopography,torrential rains and floods occur frequently in China and about 40% of thepopulation, 35% of the agricultural lands and 70% of the gross product of the industry
and agriculture exist on the alluvial plains that are vulnerable to water inundation.
With economic growth, urbanization and the subsequent concentration of populationand property, the direct economic loss per unit area has increased rapidly. Therefore,
the flood damage relief is an important and urgent task in China.
China has taken many structural and non-structural mitigation measures.
Structural measures have so far had a remarkable effect. But no matter how highengineering standards, it is not realistic to rely on the flood projects completely toreduce flood damage. As an important non-structural measures, flood hazard mapping
will play an effective mitigation role in China. First, flood hazard map can serve forthe flood control and flood fighting decision-making. Secondly, flood hazard map candirect the land use plan and construction of safety facilities in the target area. Thirdly,
flood hazard map can help the residents evacuating in emergency.
1.4 Problems of flood hazard mapping in China
The most important things in flood hazard mapping are whether we can collectdetailed datum and develop advanced hydrological and hydraulic numerical models,and also the experience is indispensable. The main problems we may probably
encounter in the process of producing flood hazard maps as below:(1) Lack of laws support. Flood Control Law of People’s Republic of China
came into force as of January, 1998, but no such provision about flood risk and hazard
maps. So it’s not an obligation for local governments to produce flood hazard maps, if
local governments are lack of enthusiasm or fund, they may not impel this work.
(2) The evacuations are difficult to be established. Some important embankmentsof lower major rivers protect wide lands and many residents, and the flood level isseveral meters higher than the inland ground level. Residents live sporadically in thisarea and the transportation is not convenient, the farthest evacuation routine may
exceed 10 km, so the evacuation time will be very long. If the levees are broken inthese protective areas,, large areas and thousands of residents will be inundated, how
to estimate the inundation area and establish the evacuation plan is a difficult
problem.
(3) Low flood control standard. Because flood control standard of many levees
can only prevent the flood which occurs once in 10 years. So 10-year, 20-year,50-year, 100-year flood, and maximum flood inundation areas should be drawn out inthe maps with different colors so that the risk of different flood magnitude can bedisplayed. The work load is very heavy.
(4) Lack of detail information and experience. Although China Institute ofHydraulic and Hydropower Research is pursuing in the flood risk study, they havetaking several pilot study about flood risk, yet this study has not been demonstrated byactual floods. And production of flood hazard maps just starts, now there is no flood
hazard map is perfect. In addition, the information possessed by different departments2are not sharing. So collecting data is often difficult.
(5) The technology is very difficult. China has a vast territory with large
differences in the natural climate, and flood characteristics and socio-economic arealso very different. The flood hazard mapping involves the aspects of nature, economy,society and so on, the technology difficulty is very big. Especially in the plain river
networks of Taihu Basin, the flooding and waterlogging are often concurrent.
1.5 Plan of flood hazard mapping in China
In 2005, the guideline for draw flood risk mapping was issued by the Office ofState Flood Control and Drought Relief Headquarters of China. Based on theexperiments of flood risk mapping, the guideline is being revised at present and intend
to place the flood hazard mapping on the national construction plan. Because China is
too big and restricted by fund, Chinese government will plan to make flood risk maps
in batches by stages in whole country.
2. Outline of the Taihu Basin
2.1 Natural condition and socio-economic situation
Taihu Basin is selected as target area to apply a flood hazard map. It situated in
the Yangtze Delta and across Jiangsu and Zhejiang provinces and Shanghai
Municipality. In the basin, land is flat and rivers are densely distributed. The water
surface of basin accounts for 15% of the total area. The climate there belongs tosubtropics monsoon climate and is mild, with distinctive seasons and plentiful rainfall.
The mean annual rainfall is about 1177mm. The rainfall from June to August accounts
for 40% of annual rainfall. The flood season is concentrated in June to July.
Taihu Basin is one of the most active economic areas in China. Numerous large,
middle and small-sized cities arescattered like stars in this densely
populated basin, such as Shanghai,Suzhou, Wuxi, Changzhou, Zhenjiang,Hangzhou, Jiaxing and Huzhou, with anurbanization rate of 74.3%. By the endof 2006, the area of Taihu Basin isabout 36,900 km2, with a population of
44.66 million, and gross domestic
product (GDP) of 2106 billion RMB,
accounts for 0.4%, 2.9% and 10.7% of
Taihu Basin Map
the national total.
2.2 Disaster characteristics
The flood in Taihu Basin caused mainly by “plum rains” and typhoon. The
former has a long duration, is widely distributed and easy to cause basin-wide floodand water logging disaster, such as 1954, 1991 and 1999 flood. The latter has a shortduration but higher intensity and is easy to cause serious regional flood and water3

logging disaster, such as Rananim typhoon in 2004, Matsa typhoon in 2005, Saomai
typhoon in 2006.
Due to Taihu Basin is an alluvial plain and above 80% of total basin area is plain
and water surface, once Taihu encounters continuous monsoon rain or sudden storm,
water levels in Rivers and Lakes will rise rapidly. Under the simultaneous attack offlood and waterlogging, a prosperious and rich land, will become a flooded area,causing a severe damage.

1991 flood

1999 flood

2.3 Structural countermeasures to mitigate flood
Taihu flood control project including eleven key components has been
completely implemented after 1991 catastrophic flood. A flood control components
system has been substantially formed, with functions such as regulating storage of
Taihu Lake, flood discharged northward to Yangtze River, eastward to Huangpu Riverand southward to Hangzhou Bay. At present, we are positively implementing theOpinions on the Recent Flood Control Construction in Taihu Basin for furtherperfecting layout of flood control components and water resources dispatch capability.
3. Schedule of implementation
In view of the significance of flood hazard mapping, I think it is very necessary
to impel the relevant works in Taihu Basin. According to the practical situation, it canbe implemented step by step.
Afetr I go back to China, I plan to make a lecture about flood hazard mapping formy colleagues and report to my Bureau Director what I learned in Japan and suggestthat we should do the work of flood hazard mapping as soon as possible, of course,
also depends on fund. At the same time, I will put the funding application for theflood hazard mapping into the annual contingency fund application plan for flood
prevention so as to strives for financial support by the central government.
Concrete implementation items of the schedule as below:
3.1 Collecting data
Collecting past floods information and flood control projects information of thedistrict of Jiaxing, Huzhou and so on within Taihu Basin.(have funds);
Collecting base map with 1:10000(depend on funds);
Collecting social and economic data of basin, including population, GDP,4

property and their distribution(depend on funds);
Collecting historical hydrological data in Taihu Basin(have funds);
Update land use information(depend on funds);
Collecting flood dispatching plan of key flood control components within basin(have funds).
Above tasks will be finished at the end of 2009 year based on the supporting byfunds.
3.2 Flood risk analysis
The hydrological model and one dimension hydraulic model of river network
have been developed in Taihu Basin. In order to calculate and simulate the flood
evolution after levees break oroverflowing, we will commission
Hohai University to develop 2D
hydraulic model of Taihu Basinwhen I return to Shanghai and plan
to finish in June of 2009.
Through hydrological andhydraulicmodel,
anticipatedinundation areas of different
magnitude floods can be calculated,
including extent of inundation, water
depth, flow velocity, arrival timing
etc. This tasks will be finished byGeneralization chart of river network for modelling
Mr. JinKe after he come back toChina.
3.3 MappingThis task is depend on the situation of data collecting and funding. If theconditions are ripe, it should be able to be completed before the end of 2010 year.
4. Estimated budget
No.
12345

item
data collecting
model developing
flood risk analysis
mapping
dissemination
sumcost(thousand Yuan)
3000
1100
1300
1600
500
7500

5. Expected effectiveness5.1 Expected benefit and progress for residents
Residents easily know how to get flood information and where, when, how to5

evacuate, evacuation time will be shorten effectively.
Residents’ self-help and mutual-support ability will be improved.
Residents’ awareness of flood disaster prevention will be greatly increased.
5.2 Expected benefit and progress for administrators
Government’s public assistant ability will be improved.
Flood hazard map can serve administrators for the flood control and floodfighting decision-making and the managing level of disaster will be improved.
Flood hazard map can direct land use plan and construction of safety facilities.
Flood prevention lord of river basin agency and local governments will bereduced greatly.

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