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The Dams Raid > Air Attacks on Reservoirs and Dams > Air Staff Report

Effects British attacks on German dams in World War 2

March 28, 1943


1. The principal dams situated in the Catchment Area of the River Ruhr are:

Name of

Year of
1909 - 1913
1929 - 1933

1909 - 1911
1902 - 1904
1901 - 1905
Water Volume
Millions m3


Masonry Wall
Earth with
Concrete Core
Masonry Wall
Masonry Wall
Masonry Wall
Height of


Total capacity 254 million m3

2. There are said to be a further seven small dams with a total storage volume of about 12 million m3, all situated in this Catchment Area, bringing the total capacity up to 266 million m3.

3. It will be noted that the Möhne reservoir holds 50% of the total reservoir capacity in the Ruhr Catchment Area and the Möhne and Sorpe together holds over 75% of the total.

4. All evidence on the subject points to the fact that the primary function of these dams is to provide the Ruhr district with both industrial and domestic water supplies. Towards the end or the last century the large increase in pumping stations in the growing industrial district of the Ruhr valley created a seasonal shortage of water which became an increasing handicap and threatened not only to bring the power plants to a standstill during dry periods, but also rendered an adequate supply of drinking water doubtful. (In this situation, it should be noted that the waters of the other rivers in the Ruhr industrial area, the Wupper, Emscher and Lippe, are not suitable for drinking purposes). In consequence, a large programme was evolved for the erection of barrages to conserve the natural water supplies. This programme, however, has consistently lagged behind requirements and it is known that before the war an additional storage capacity amounting to 180 million cubic metres had been planned.

The effects of the destruction of the Möhne Dam can be considered conveniently under the following headings:

(i)Direct destruction by the escaping waters.
(ii)Denial of water supply to industry and reduction in electric power output.
(iii)Dislocation of rail and water transport in the Ruhr.
(iv)Reduction in domestic water supplies.
(v)Effect on morale.

Direct Destruction

5. Considerable local flooding would be caused immediately by the breach of the Möhne Dam. The amount of damage which would be done is difficult to assess accurately but would be appreciable. Before any damming schemes were in operation the mean average flow in the River Ruhr at Mülheim was 82.5 cubic metres per second and the mean maximum rate of flow was 153.5 cubic meters per second. It is known that flooding was experienced before the dam control was instituted in the low lying districts of the River Ruhr (where the fall is only 6 feet per mile) which include the towns of Herdecke, Wetter, Witten, Hattingen, Linden, Steele, Kupferdreh, Werden, Kettwig, Mülheim and Duisburg.

6. Assuming that the breach effected in the Möhne Dam would lead to the total emptying of the reservoir in 10 hours, the average rate of flow during this period would be 3,720 cubic metres per second, while the maximum rate would be much higher. The capacity of this reservoir alone is, therefore, great enough to cause a disaster of the first magnitude even in the lower reaches of the Ruhr. Flooding might also extend into the equally low lying and more densely populated areas between the Ruhr and the Duisburg-Dortmund-Ems Canal.

Effect on industry

7. There should be a substantial loss of electrical capacity in the district due to the destruction of the thirteen hydro-electric plants situated between the feet of the dams and the mouth of the river at Mülheim. The total capacity of these is about 250,000 HP of which the plant at Herdecke supplies 194,000. Even if the plants were not totally destroyed their utility would be largely limited by variations in the flow of water which would follow the loss of control by the reservoir.

8. In addition the output of the great thermo-electrical generating stations, which utilise large quantities of water for cooling purposes, might be seriously impaired at least during the summer months.

9. The restriction of water supplies to the heavy industries of the Ruhr would have a most serious effect on activities in the foundries, coal mines, coke ovens, blast furnaces and chemical plants which require enormous quantities of water for their operation.

10. Thus, inadequate supplies of water would have a two-fold effect on industrial activity. Firstly, the direct effect of lack of water for the operation of processes and, secondly the reduction in power supplies due to lack of water required for generating purposes.

Coal mines require 1 cubic metre of water per ton of coal mined.
Coke ovens require 2 cubic metres of water per ton of coke produced.
Blast furnaces require 2 cubic metres of water per ton of pig-iron produced.
Factories are even larger consumers in proportion to output.

Effect on Transportation

11. The lower reaches of the river Ruhr appear to be navigable at least as far upstream as Herdecke and the loss of water control would undoubtedly hinder bulk traffic for the heavy industries on the river.

12. The Ruhr railway network crosses and re-crosses the river at many points and runs parallel to it for almost the whole of its length from the dam to the Rhine, indicating that the slope of the valley sides is steep. The confinement to this narrow valley of the flood waters released by the breach of the dam we might, therefore, do considerable damage to the railway and its bridges throughout the full length of the river.

Domestic Water Supplies

13. As already stated above, the other Ruhr rivers, the Wupper, the Emscher and Lippe are not suitable for drinking purposes and hence the supply of water to the whole of the Ruhr industrial region extending as far as Hamm and Ahlen to the North East depends to a great extent on the Möhne reservoir.

14. In view of the need to conserve water for fire-fighting and essential household consumption, it is probable that any measures for economy in water consumption which would have to be introduced would, of necessity, fall mainly on industry.

Effect on morale

15. The general morale in the Ruhr area must have been considerably affected by the series of bombing raids which have been carried out in recent months culminating in the two devastating attacks on Essen. The destruction of the dam with all its consequences, would undoubtedly have further and serious repercussions on morale.

16. The increased danger to which the population would be exposed in the absence of water for fire-fighting purposes could be exploited by Political Warfare methods as an excellent opportunity for spreading panic amongst the population. This might result in the authorities, as a counter, making a lavish expenditure in water storage for fire-fighting purposes, thus further depleting the supplies available for industrial purposes.

The Sorpe Dam

17. The Sorpe Dam has about half the capacity of the Möhne Dam (72 million cubic metres or 72 million metric tons of water). Its construction is such that greater difficulty would be experienced in destroying it by the means at present under consideration. It is by no means impossible, however and the tactical problems are not greater than those involved in an attack on the Möhne Dam. The destruction of the Sorpe Dam which together with the Möhne would account for 75% of the water supplies available to the Ruhr, would if effected at the same time as the destruction of the Möhne Dam, produce a paralysing effect upon the industrial activity of the Ruhr and would result in a still further lowering of morale.

The Eder Dam

18. The Eder Dam was constructed primarily as a means of regulating the flow of the River Eder which is the principal tributary of the River Weser. Prior to its construction the Weser was a most unruly river which overflowed its banks regularly during the winter and inundated wide stretches of country

19. The dam, which has a capacity of over 202 million cubic metres, prevents this by storage of the surplus winter rainfall which is gradually fed away during the summer. Indirectly, this dam is responsible for some of the feed water in the Mittelland Canal. It is also provided with electricity generating stations and a pumped storage station for power load equalisation. These are all, however, to be regarded as subsidiary functions.

20. Although the results of the destruction of this dam would be spectacular, economic effects would be problematical. No important industrial area would be deprived of water supply; the loss of electric power would be of secondary importance, and the effects on navigation on the Weser and on the Mittelland Canal would probably not be of long duration. From the economic standpoint, therefore, this dam cannot be considered as a first-class objective.


21. (i) The Möhne reservoir is a factor of the first importance in the water supply of the Ruhr and its destruction would have serious effects on industrial activity and would greatly affect morale, particularly in the light of our recent bombing of the Ruhr and Essen.

(ii) The simultaneous destruction of the Sorpe Dam would result in a critical situation in the Ruhr industries and would add greatly to the moral effect caused by the destruction of the Möhne

(iii) The destruction of the Eder Dam would have spectacular results and the moral effects would be important if the operation was carried out in conjunction with the two Ruhr dams mentioned above. The economic effects, however, are unlikely to be substantial.

The Air Staff report pointed to the Möhne reservoir as a factor of the first importance in the water supply of the Ruhr. Its destruction would have serious effects on industrial activity and would greatly affect morale, particularly in the light of the recent bombing of the Ruhr and Essen.

The construction of the Sorpe dam was such that greater difficulty would be experienced in destroying it with Upkeep bombs, but that it would be by no means impossible. Simultaneous destruction of the Sorpe dam would result in a critical situation in the Ruhr industries and would add greatly to the moral effect caused by the destruction of the Möhne dam.

The destruction of the Eder dam would have spectacular results and the moral effects would be important if the operation was carried out in conjunction with the Möhne and Sorpe dams. However, the economic effects would be unlikely to be substantial.

The Ministry of Economic Warfare corrected, in a separate report, the over-stated expectations that were attributed to the Scientific Advisers in the RAF Air Staff report.

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