Bad News For Holland

Have you ever heard the expression: “Lighten Up.” ?
Of course nobody wishes any ill will for the Netherlands; and a goo dmany of us believe they are in no immediate danger of any inundation; other than from natural variability causes.

This story about Holland/The Netherlands disappearing in a hundred years comes from a man who apparently does not understand the basic principals of deltas, sedimentary processes or even elementary geology. Yet he is partially correct, for completely the wrong reasons. The only reason why Holland is likely to get flooded is that through more than a thousand years of engineering, the Delta has been constrained by dikes and thus controlled waterways.
Holland is sinking for a number of reasons. One is that Holland is on the opposite side of the post-glacial see-saw rebound (Scandinavia is coming up, Northern Germany&Holland is going down). Secondly, a major structural (low)/tectonic element, the Rhine Graben runs right through Holland. Hence major run-off (rivers) find the low spot and so, the Rhine ,Schelde and Maas, find their way to the Ocean through Holland.
As it is with deltas, rivers bring sediment and build land by dumping that sediment where the flow rates are reduced. This is a very dynamic process, where rivers and sea are in a constant battle for dominance. Deltas are areas where the rivers win and land is being added. With every spring flood new sediment is dumped on the flood plains, while sand and gravel is moved out to the shore line where beaches and dunes are formed in high energy processes (waves and winds). Sediments settle and compact over time, which is the third reason why Holland “sinks”. Sediments added by the rivers keep filling the low areas. All these processes have been going on for millions of years, and have little to do with climate variability (although climates play a minor role). Without building dikes, the delta would be an area constant under natural flood threats (river induced with occasional oceanic storm surges) because deltas are basically near sea level by virtue of they way they are formed. They tend to build out into the sea, not up to many tens or hundreds of meters. They remain flat and low and are located in low lying, generally sinking parts of the Earth’s Crust. Due to the constant sediment load brought by rivers, they remain at/near sea-level and build up to the highest possible flood level, so in general slightly above mean sea level. Every spring flood adds a few milli-meters and this keeps the delta as a land building phenomenon. Holland as a country has elected to control the spring floods with river dikes. This has significant advantages don’t get me wrong, but over a prolonged period of many hundreds of years, this will make the low lying areas sinking without the benefit of annual addition of thin layers of mud that could keep the land in balance with the sea. So… warnings about Holland eventually losing the battle need to be taken very seriously. Building bigger dams alone is not enough; where mother nature can not add sediment naturally, over time, geo-engineering has to step up and build up low floodplains. New developments are generally build on/with added sand, several meter thick, so some progress is being made. Funny enough is that might Holland eventually flood and conform the “2107 picture”, all manmade dikes are gone and the natural delta processes will be in full swing, thus completely contradict and counter the prediction. As long as the rivers bring sediment, the deltas always win. It is more predictable than who will win the World Cup.
On a side note: Bangladesh is a similar very successful delta, with the largest sediment supply in the world running off the Himalayas. As long as the rivers are not constrained, that delta will always be there, near sea level, prone to flooding, mainly by river run-off (not rising sea level), and growing. It still remains a very good idea when living in a delta to learn how to swim and have a boat.

George E. Smith says:
July 13, 2010 at 8:57 am
Have you ever heard the expression: “Lighten Up.” ?
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Judging from a number of comments, the notion of Holland flooding was treated as a joke. Some comments were demeaning, ignorant and unintelligent. I have a good sense of humour including the self-depricating version, but some comments were not even remotely funny. That has nothing to do with “lightening-up”.
The Dutch take sea level rises quite seriously and it doesn’t have to be 7 metres, one or two will be a headache.

David,
if you are interested in isostatic rebound I am sure you will be able to do your own research, as you should, and don’t take my word for it. The estimates of positive (and negative) rebound run from about 0.5 to 1 cm/year. Maybe you can find some references as high as 2 cm/year. The estimates are based on dividing obvious uplifts and relative sinks from marker beds by the time/age difference of those marker beds. Then taking post glacial sea level rise into account. Wether the number is 0.5 or 2 cm/year does not really matter too much. The point is that it is the sediment supply that allows deltas to develop. Matching sea level rise to subsidence is missing the key element. But yes, Holland is sinking, and not by peat removal (which is not sinking, but human induced surface mining). But you are right, not every point is sinking and not at an equal rate. Brabant and Limburg are more under the influence of structural control. The Peel still shows active faulting due to tectonic activity in the Rhine graben. The rivers are where the subsidence leads them. The beauty of deltas is that they are in a dynamic balance with seal level. if sea level drops, the rivers bypass their previously formed delta and start forming a new lobe. rivers switch course and new sediment fills in an area under compaction. If sea level rises, the flood level rises, as you noted, and thus the accommodation space for new sediment deposition increases. As long as the sediment supply is sufficient, deltas build out and up (with and up to sea level, not much higher). Holland’s problem is not the sediment supply, but the fact that the rivers are diked-in and can no longer freely distribute their annual sediment load evenly, thus subsidence due to the formerly stated reasons takes over. The Bangladesh/Brahmaputra delta has been building for millions of years and has effectively kept up and thrived during one of the fastest sea level rises in geological history. It also has been flagged as an area that will drown (Gore’s movie). If there is any area that will never drown due to sea level rise, it is Bangladesh; as long as the Himalayas are there and the rivers are allowed their seasonal flooding. Get to know your deltas, how they are formed and what keeps them there. good luck.