Hello Gerrit!

30 Aug 16 17:49, you wrote to me:

 KvE>>  There is a difference, we do not have that type of hurricanes and
 KvE>> we know how to keep our feet dry most of the time.

 GK> You name it: "most of the time". Is drowning once every 50 years
 GK> tolerable?

 Getting your feet wet is not drowning, but you have to define a context.
 If the same disaster strikes in the same place every 50 years, it is
 not acceptable.

 But the Netherlands is not one basin with one dike around it. It is also
 basins within basins. You can get your feet wet, because of a lot of rain,
 an overflowing river or storm damage to dikes.

 You can make a fair prediction on expected sea levels, where a number of
 factors add together. You have high tide, high high tide due to the sun and
 the moon cooperating and extra tide due to storms pushing the Nothsea into
 the straits of Dover/Calais. To that you can add expected rise of the
 sealevel due to melting of the Icecaps.

 You can build heavy dikes and use dunes to protect agains that menace.
 The problem is you also have to make structures, to prevent the high
 sea levels going upstream of the rivers. Afterall The Netherlands is the
 estuary of the Rhine and the Meuse and the smaller Schelde. For these rivers
 there is also the increased affluent of rainwater from the hinterland.

 But you also have the inland dikes dating back from the middle ages build from
 whatever material swamps provide. When it is hot and dry, the dikes can
 forms cracks due to shrinking of the building materials. When the water
 rises to high, they become weak due to the material being soacked with water.

 We have had floods due to war actions by the alied forces on the island of
 Walcheren and the Wieringermeer-polder. The last major floods due to
 bad wether combined with the hightides was in 1953.

 KvE>>  It would help if you restored the flood planes in the higher
 KvE>> regions of
 KvE>>  the Rhine. But the people in Koeln are asking for the same, so that
 KvE>> will
 KvE>>  be covered.

 GK> This is not only a matter of the Rhine, this mistake has been done with
 GK> almost every major river. However, the rivers are not the main threat imo,
 GK> the sea is.

 The rivers are unpredictable, storms at sea maybe, but the rising due to
 melting of the icecaps is a slow process.

 The places that are at risk because of rising of the sea are the coral
 island, that rise barely above the sea and the large estuaries of the
 big rivers in Asia that are maginally above sealevel with no artificial
 defences.

 The lowest spot in Sleswig-Holstein is somewhere around 10 meters below
 sealevel. An extension to Rotterdam is built in the Alexander-polder,
 if I remember well it is 17 meters below sealevel. I do not expect that
 your feet will get wet in those places anytime soon.

 Working on your defences against the sea is a continuous effort, not a
 one time investment.

Kees

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