"Without dams, many watercourse would have dried up this year"

Prof. Dr. Dirk Carstensen, President of the German Dam Committee

In an exclusive interview with "Industriearmaturen & Dichtungstechnik", Prof Dr Dirk Carstensen talks about the enormous importance of dams. The President of the German Dam Committee explains why these impressive structures are useful helpers during periods of drought and flooding. He also discusses the interaction between industrial valves and dams.

How many dams are there in Germany?

Dirk Carstensen: According to the definition, we have 371 large reservoirs in Germany. These are dams whose barrier structures are higher than 15 metres from the lowest point of the foundation base to the top of the structure and/or whose total storage capacity of the reservoir is greater than 1 million m3. These figures can also be viewed via the World Register of Dams, which is published by the International Commission on Large Dams (ICOLD), whereby it should be noted that internationally, large dams are considered to have a total storage capacity of 3 million m3. In relation to the total area of Germany, it can be stated that we have one dam per 1,000 km2 . Of the above-mentioned number of large reservoirs in Germany, 231 are used for multiple purposes, i.e. they are used for flood protection, hydropower generation, irrigation, fishing, as supply water for artificial and natural shipping routes, tourism, raw and drinking water production, the provision of industrial and/or cooling water and the increasingly important low water elevation of rivers and streams during dry periods.

The Schwarzenbach dam in the northern Black Forest has been in operation since 1926.

What is the function of dams in times of extreme climate change?

Dirk Carstensen: As I have just mentioned, flood protection, water supply and the raising of low water levels in rivers and streams during dry periods are essential purposes for the construction and operation of dams. When we talk about the change in hydrological conditions in our country as a result of climate change, extreme weather conditions with heavy rainfall and flooding in our rivers as well as drought and aridity are just as much an issue as falling groundwater levels or falling water levels in standing water bodies. Without dams, many a watercourse would have dried up this year. Looking back to 2021, however, it can also be seen that most of the dams in the federal states of North Rhine-Westphalia and Rhineland-Palatinate that were most affected by the floods were generally built as multi-purpose facilities. For historical reasons, they primarily serve to supply raw water. Realistically, it can be realised in retrospect that in 2021, every single one of these plants operated by the various operators in the flood region made a significant contribution to mitigating the consequences of the floods while continuing to fulfil their supply tasks. The impact of this natural disaster would otherwise have been many times greater.

Is the drinking water supply secure in the long term or do we need more dams?

Dirk Carstensen: Germany can generally be categorised internationally as a water-rich country. Despite a declining water use index since the early 1990s, which is a parameter for assessing the impact on water withdrawals in comparison to renewable water resources - currently at around 11 per cent and therefore well below the critical value of 20 per cent - more than 15 billion tonnes of water have been lost in Germany since this time. This loss, which represents a deficit in the comparison of precipitation and inflows to evaporation and outflows for a given level of consumption, is only partially recognised in the country's surface waters. It mainly manifests itself in the sometimes extreme drop in groundwater levels groundwater levels, which, however, generally remain hidden from the population. At present, it would not be correct to speak of global water stress in Germany.
However, it must always be emphasised that there are regional and seasonal differences in the various parts of the country as a result of unevenly distributed precipitation. These regional differences in water availability can be compensated for by dams and connected distribution systems, if available. One of the multiple purposes of a dam is to supply raw water, currently benefits around 10 per cent of Germany's population by providing around 570 million m3 of water from our reservoirs. From a prognostic point of view, there is an enormously high degree of certainty that greater demand will arise as a result of future requirements and cutbacks, partly due to climate change and population growth in our country. In this respect, it is already becoming clear in some parts of Germany that more dams will be needed.

This year, the historic valves at the Pirk dam in the Vogtland district of Saxony were replaced with new ring piston valves.

On the one hand, floods are occurring more and more frequently, while on the other hand there are increasingly long periods of drought. What impact does this have on dams?

Dirk Carstensen: I need to expand a little on this question and emphasise in advance that you are certainly referring to flooding in the discharge areas of our watercourses. In my opinion, dams are generally valued and accepted by society. Despite this fact, however, from time to time, often triggered by extreme hydrological events, they are repeatedly the subject of discussion and are then presented in a very differentiated way. As a rule, only individual facts are emphasised in these discussions, competing uses are particularly highlighted, but the primary purposes of the dams, which represent the actual value for nature and society, are hardly mentioned or not mentioned at all. It is understandable that a dam equipped with a large flood protection or flood retention area does not necessarily offer lucrative conditions for tourism, leisure and recreation, the utilisation of hydropower or the provision of industrial water. If we want to effectively operate flood protection as a purpose of a dam in today's world - and I am alluding to climate change here - we have to keep a certain amount of space in the reservoir free for this purpose due to the sometimes very short warning times. However, the picture described above, including all the associated organic and chemical processes in and on the river bed, also occurs after a long period of low precipitation. However, if we did not have the dam, the watercourse system would possibly have collapsed completely at the same time as a result of the drought and the raw water supply would not be guaranteed, to emphasise just two facts.

Where are industrial valves used in a dam?

Dirk Carstensen: The use of industrial valves in and on dams is so varied that it is difficult to draw a clear line here. Wherever something needs to be shut off or the flow needs to be regulated, we need appropriate valves. From operating equipment for raw water extraction to the bottom outlet or from control valves for hydropower generation to valves for flow control in water distribution, we need valves, gate valves or butterfly valves everywhere.

What properties must a valve for a dam have?

Dirk Carstensen: Valves on dams are exposed to enormous pressures and pressure fluctuations. These result on the one hand from the water level in the dams and the corresponding reservoir height and on the other hand from the purposes and operation of the dam. The opening and closing of valves on hydropower plants in particular present special challenges. Of course, the issue of cavitation is also a particular challenge for every valve manufacturer. In line with the required flow rate, these valves are usually of a corresponding size, but from the point of view of the civil engineer or operator of a dam, they should actually be quite slim and small in terms of construction, maintenance or replacement. All the parameters mentioned determine the choice of material, the wall thickness of the housing and/or the design of the flange areas in addition to the respective and special actuator options of the various valves. Of course, the respective flange insulation or galvanic isolation also play an important role in such a system.

"The effects of flooding would have been many times greater without dams," says Prof. Dr. Dirk Carstensen.

Is it worth simply maintaining valves in dams or will major modernisation measures be necessary in the future?

Dirk Carstensen: To put it bluntly, you don't change an annular piston valve in a dam's bottom outlet pipe every ten years. Of course, the dam operators maintain their control equipment, opening and closing it according to specified maintenance intervals. However, it goes without saying that valves on dams are also subject to a certain amount of ageing with regard to the materials used and corresponding wear in line with the operating times of the individual components and equipment. Consider, for example, suspended solids that are transported with the water and result in material wear or the effects of cavitation. Taking into account the constant further development of gates, valves or flaps, there are a number of reasons, in addition to the hydraulic properties of newer components, safety issues with regard to the function of the valve or the age of the components, which can lead to modernisation when weighing up various influencing factors. On average, our dams are around 70 years old, so here and there they need to be renovated or modernised.

Are the valves in dams digitally controlled or monitored?

Dirk Carstensen: Of course! Valves of this type and size are digitally controlled and also monitored. Of course, you have to consider the age of individual valves and the sometimes limited possibilities. However, the trend is moving in this direction everywhere. It is particularly important to mention here that for safety reasons, based on the n-1 criterion used in hydraulic engineering, certain elements are duplicated and the actuator options are generally designed redundantly.

ABOUT THE PERSON

PROF. DR. DIRK CARSTENSEN
Completed his doctorate and habilitation at the Technical University of Dresden. In addition to his work on river and transport hydraulic engineering as well as flood and coastal protection, after his appointment to Nuremberg Institute of Technology in 2012, his research work focussed on constructive hydraulic engineering for spillways, complex structures and the continuity of water structures. He heads the Institute for Hydraulic Engineering and Water Management at the Nuremberg Institute of Technology, which was founded under his leadership, is the author and editor of a wide range of specialist literature and is in his second term as President of the German Dam Committee (DTK).