MILITARY HYDROLOGY Research & Development Branch DESTRUCTION AND PROTECTION OF DAMS AND LEVEES Dr. Engr. Professor OTTO KIRSCHNNER, Paris From Schweizerische Bauzeitung 14 March 1949 Translation by H. E. Schwarz, Washington District Corps of EngineersDESTRUCION AND PROTECTION OF DAMS AND LEVEES During World War II three of Germany's dams located on the MOHNE, SORPE and EDER Rivers were attacked on the same night, This operation was carried out by the Royal Air force during the night of 16 and 17 May, 1943 as a low-level surprise attack from a height of approximately 18 m, using special heavy rotating bombs (Roll Bombs).1 Figures 1 and 2 show the location of these works. The flood wave released by their destruction caused widespread devastation. To obtain a basis for the preparation of plans for precluding or reducing damages from such occurrences in the future, these flood waves were later carefully studied. It is believed that the results of these investigations are of sufficient general interest to be published. I. Description of the Dams and the Damages A. The MOHNE Dam. This dam was built in the period 1908-1913, from a design by E. LINK, mainly for the purpose of providing domestic and industrial water supply in RUHR area. The drainage area above the dam is 430 km2, the average annual inflow is 240x106 m3, the reservoir capacity is 134xl06 m3, and the surface area is 10.2 km2. This gravity dam with an arched axis is 650 m long at the crest and 40 m high. (Maximum water level 32 m). The top width is 6.25 m and the base width 34 m (Figure 3). The attack by the Royal Air Force was carried out during the period when the reservoir was completely full. On 17 May 1943 at 12:49 a.m., a bomb exploding close to the face of the dam approximately 10 m below the water surface breached the upper part of the dam. A gap 76 m wide at the top and 22 m deep developed in the center of the dam. Within the next 12 hours 116x106 m3 of water escaped through this breach. On the 16 of May 1943 the storage in the reservoir was 132.2x106 m3. It was later determined that the initial rate of flow through the gap was 8,800 m3/sec. In the narrow MOHNE Valley this caused a surge 10 m high which caused great destruction. This surge was considerably higher than the highest flood of record, the flood of 1890. Approximately 1200 lives were lost. All buildings situated on low ground between the dam and HAGEN (approximately, 65 km downstream) were either swept away or damaged. All bridges for 50 km downstream were destroyed. Eye witnesses report that the water piled up as high as 2 m on the bridges before they collapsed. The power stations, No. I located at the foot of the dam (4,800 kw output, four generating units), and No. II (300 kw, two generating units) located at the re-regulation pool at GUNNE, just disappeared. At the confluence of the RUHR and the RHINE Rivers (148.5 km from the MOHNE Valley dam) the stage rose about 4 m when the crest of the flood wave, 25.5 hours after the catastrophe, passed there. This meant that the discharge of the RHINE River increased by 1100 m3/sec. The effects of the rupture of the MOHNE dam were very serious because on one hand this dam was the main source for the water supply of the densely populated RUHR area, and on the other hand its rupture flooded most other water supply plants in the RUHR all the way to ESSEN, and put them out of commission. A large number of towns like HAMME, HAGEN, BOCHUM, and DORTMUND were without water. Also, the pump storage plant at HERDECKE on the RUHR, 60 km below the MOHNE dam, which with its 132,000 kw output is one of the most important power stations of the RHEINISCH-WESTFALISCHEN Electric Power Company (RWE), could not operate for 14 days because its power house was under 2 m of water.B. The SORPE Dam, Here we deal with a dam constructed in the period from 1922-1933 as an earth fill structure with a watertight concrete core wall also designed and built under the direction of E. LINK (Figure 3). The height of this dam above the valley floor is 60 m, the maximum water depth is 57 m, and crest is 700 m long. The upstream and downstream slopes at they center of the dam are 1 on 2.25 and 1 on 2.50, respectively. To make it difficult for water to penetrate the dam the upstream part is constructed of impervious material covered by a protective layer. The downstream part is constructed of pervious material to allow that that water which seeps through the impervious part and the core wall to drain as fast as possible. The storage capacity of the SORPE reservoir is 81x106 m3. When com-pletely full a lake of 3.8 km2 is created. The annual flow of water from the catchment area into the reservoir is 31x106 m3. The air attack on the SORPE dam was carried out at the same hour as the one on the MOHNE dam, apparently with the intent to cause them to fail simultaneously. This earth dam however did not fail, although the crest of the dam received two direct hits which created craters 12 m deep. The attacks on the SORPE dam were later repeated several times, including a concentrated attack on 16 October 1944. In all these attacks 11 hits were scored on this earth dam without causing a collapse or leakage. After the first attack, however, the water level in the reservoir was lowered a few meters as a precautionary measure. The fact that the gravity masonry dam on the MOHNE was ripped open while the earth dam across the SORPE withstood the attack is of decisive importance. The effect on the RUHR area would have been of catastrophic proportions if the SORPE valley reservoir also would have run out during those early morning hours of the 17 of May 1943, and the two flood waves would have combined and superimposed themselves on each other. C. The EDER Dam. This -dam is located at WALDECK in the vicinity of KASSEL and was, after the successful action against the MOHNE dam, the target of the same Royal Air Force outfit. These two dams are only 80 km airline distance apart. The EDER dam is Germany’s second largest dam (second only to the BLEILOCK dam on the upper SAALE in THURINGEN), and was constructed in the years 1908-1913 as a rubble masonry gravity structure. This dam stores 202x106 m3 water, and when completely full creates the impressive and beautiful EDER Lake which covers an area of 11.7 km2. The average annual inflow into the reservoir is 500x106 m3. The EDER Lake augments low flows, helps control floods on the FULDA