‫ە‬Messages from Departments and Centers of NILIM

Promoting river projects that ensure
safety and security
YAMAMOTO Akira, Head
Director of the River Department(Key words)  Climate change, flood control, risk assessment, adaptation measures
1. Change surrounding river administration
Extremely sharp changes of direction are facing
flood control projects intended to ensure the safety andsecurity of the people of Japan. One is abnormal
weather occurring frequently throughout Japan andelsewhere around the world in recent years. Weather
phenomena, which can be described as the source offlood disasters, are frequently taking abnormal form,resulting in expressions we use to describe them often
including “the highest (or lowest) ever observed”.
The severe impact on the world’s grain markets ofthe serious damage to grain production in Australia inrecent years inflicted by its severe droughts andunprecedented giant floods is still fresh in ourmemories. It is impossible to state positively that thecauses of these abnormal weather phenomena is
climate change. But we can conclude that some occur
when climate changes, and that we must now begin
considering how to respond to these changes.
The second change in the environment surrounding
flood control projects is the arrival of the era when ourpriority has abruptly shifted to management. Generally,
regarding the provision of public capital, in thebeginning, Japan responded to a shortage of neededfacilities by providing (constructing) more, increasing
the quantity of facilities being managed, a process
resulting in a shift of emphasis from provision tomanagement. It has long been pointed out that an era
dominated by facility management would eventually
arrive, but spurred by financial restrictions, thisprocess is abruptly accelerating. This is not a simple
shift of emphasis from provision to management; wemust not only manage existing facilities without errors,
but must shift to appropriate management byadvancing our methods in order to maximize ourutilization of our facilities, requiring proposals fortechnical support measures for appropriate andefficient management.   In the midst of this recent change of both theclimate and facility needs, a major challenge facing
flood control projects which must be resolved is todecide the best measures to adapt to climate change.
Another major challenge is the efficiency of rivermanagement. This report introduce some of theresearch which the River Department has undertaken
in response to these two challenges.

2. Measures to adapt to climate changeHalf of Japan’s population and about three-quartersof its assets are concentrated on alluvial plainsaccounting for only about 10% of its national land.
And the three large metropolitan regions, which serve
as Japan’s administrative and economic centers, arelocated beside three large bays (Tokyo Bay, Ise Bay,and Osaka Bay) on low “zero-meter” zones facing thesea. Japan’s national land is also susceptible to floods,
debris flows, and storm surge disasters at a location
exposed to the threat of typhoons passing or crossing
its land, and on the eastern end of the monsoon regionof Asia, a zone of heavy rainfall unmatched by anyother part of the world. In an effort to overcome such national land
conditions, Japan has worked strenuously to
implement flood control measures by, for example,
constructing uninterrupted lines of levees and building
dams and other flood regulation structures, achieving a
big improvement in the level of safety from floods.
But the state of provision of flood control structures
remains at a low level, at only about 60% of thepresent target levels. Already vulnerable to natural
disasters in this way, finding ways to respond to thisrise in external forces occurring in response to climatechange is a major challenge facing future national landmanagement. Studies to develop measures to adapt to climatechange are now guided by the following
considerations.
(1) Evaluation of risk accompanying climate change.
The effects on society and the economy of flood
disasters occurring under the impact of climate change
are evaluated as disaster risk. Evaluating flood risk isimportant in the sense that it not only shows present
vulnerabilities, but also permits the clarification ofeffectiveness of introducing adaptation measures. (2) Proposed measures to minimize inundation
damage We study comprehensive measures combining
facility provision—the excavation of river courses toincrease rivers’ flow capacity and the construction ofretention facilities to supplement present inadequacyof flood control planning—with “drainage basinmeasures” (for example, setting flood control safety‫ە‬Messages from Departments and Centers of NILIM

levels according to land use, doubled levees, and otherinundation prevention measures). 
And to minimize the harm to residents, we conduct
basic studies of non-structural measures outside riverareas, the improvement of evacuation guidancesystems or land use guidance, among them. 
At the same time, we study the increase in rainfall
plus ways to increase the precision of climate models.
Recent analysis has obtained the results of calculatingthe relationship: increasing torrential rain ĺ
increasing flood flow rates ĺ increasing river
improvement works, but even if the torrential rainincreases only 10% over present levels, the flow rate
will rise 20%, and the quantity of works necessary tohandle this increase in the flow rate, will rise 80%.
Unable to define the extent of hypothesized climatechange, we have to study adaptation measures
resigned to the fact that they must be extremelyextensive. 

3. Performing more efficient maintenance  Ensuring the safety and security of the peoples’
lives is an important policy target, and in order to deal
with river damage such as the breaching of levees etc.,
we must continuously implement appropriate rivermanagement adapted to changes in the state of rivers
such as runoff etc. and to changes in rivermanagement facilities which have been constructed.
But there are limits to maintenance which rivermanagers can perform with their limited budgets,
manpower, and systems, so performing effective andefficient maintenance is an urgent challenge. A predominant feature of river management is thatlevees, which are the major facilities managed, areextremely long linear structures which, when breachedat even one point, result in the loss of the flood control
functions of the entire patrol section. A characteristicof the soil used to build levees is, that as result of thefrequent reconstruction and repair of the levees in thepast, its quality is inconsistent, and it is also difficult
to fully clarify the erosion resistance capability of thevegetation on the surface of the levees. Under thesecircumstances, the NILIM is currently undertaking thefollowing research. ࣭Research to improve inspection and maintenancetechnologies to maintain the safety of levees
This is intended to propose the minimum necessarylevel of management by clarifying the quantitative
relationship of deterioration of its functions such aschange of the looseness of levees or of erosion
resistance according to the level of levee vegetation
maintenance.
࣭Improving maintenance technologies
This will allow managers to perform maintenancemore efficiently and at less cost and will advancetechnologies used to analyze photographic and video
data concerning levees by using the most advanced
technologies such as IT technologies andnon-destructive inspection technologies, and toevaluate these technologies. ࣭This will systematize data and analysis results related
to patrols and inspections, maintenance and repair, andevaluation of rivers, to build a database of, and toevaluate the results, thereby contributing toappropriate maintenance in the future. 
4. Aiming at river management which can ensure
safety and security It is essential that Japan, which is vulnerable toflood disasters, look back at its history to clearly
evaluate risk posed by the impact of climate change
and to propose appropriate and effective responses inorder to recover from the many natural disasters whichhave been caused by violent wind and rain etc. and toprevent future disasters. And at the same time, Japan
also has the duty of sharing its advanced technologies
with countries around the world. At any rate, we havelittle time left to implement measures to adapt to theimpacts of climate change, so we are determined toquickly undertake research needed to do so. 