Earthquakes and Proposed Largest Storage Demands

Nepal is intending to build in future high dam projects that will be having very big storage reservoirs to regulate river flow. Large areas of lands would be devastated with great loss of life and property if any such storage dams collapsed during

May 22, 2015, 5:45 p.m. Published in Magazine Issue: Vol: 08 No. -22 May 22- 2015 (Jestha 08, 2072)

It is correctly said that earthquakes do not kill people but it is the structures that we build are the cause of earthquake related calamities. Big storage reservoirs pose the greatest threat.

Storage Reservoir

Nepal is intending to build in future high dam projects that will be having very big storage reservoirs  to regulate river flow. Large areas of lands would be devastated with  great loss of life and property if any such storage dams collapsed during the earthquakes or due to any other reasons. Unfortunately our country is not seen paying  proper attention to this matter.  Decisions are being taken turning  a blind eye to  dam safety aspect.

 Earthquake Risk

We are planning to implement 195 meters high  concrete faced rock-fill  type West Seti dam. The West Seti dam site is very close to the Lesser Himalayas/MBT  fault which has the maximum earthquake potential.    There is  too great  a risk to build one of the  world’s  highest  concrete faced rock-fill  dam (CFRD)  in  the very dangerous earthquake zone at the foothills of the Himalayas.  Some years back  a report from the Water and Energy Commission was sent  to caution the Ministry of Water Resources that it would be risky to build the proposed  West Seti dam (CFRD).  Very recently the Committee on Seismic Aspect of the International Commission on Large Dams (ICOLD) has also published in the journal International Water Power and Dam Construction  dated September, 2009 that the CFRD dams are  vulnerable to strong ground shaking due to large in-plane forces  during earthquakes.  

Sichuan Earthquake

The earthquake that struck Sichuan on the 12th of May 2008, in the district of Chengdu of Southern China resulted in tens of thousands of casualties, the destruction of many towns, and damages to public works.  The 158 meters high Zipingpu (CFRD) dam was on the verge of collapse.  We can arrive at a conclusion based on the performance of the Zipingpu dam that it would be too risky to opt to select concrete faced rock-fill (CFRD)  type dam for the West Seti project   instead of  central earthen  core rock-fill dam  which  has long since been regarded as the safest type dam for the region where weak geology is the dominant factor.

 Fujinuma Dam

Very recently on 11 March 2011the Fujinuma dam of Japan failed after the Tohoku earthquake.  The dam  was built across the Ebna river.

Double Curvature Arch Dam

It is said our country is studying to implement 260 meters high double curvature arch dam across the Budhigandaki river.  This project is going to have a very large storage reservoir. Unfortunately even France had in the past bad experience of implementing this type of dam.

The double curvature Malpasset Arch Dam was built for irrigation and the storage of drinking water. It was located in a narrow gorge of the Reyran river valley, in the Department of Var,  approximately 12 km upstream of Frejus on the French Riviera. The  double curvature arch dam  had  a 65 m maximum height, with a crest length of 223 m. The maximum reservoir capacity was meant to be 55 106 m3 however the dam failed explosively at night in December 1959 - more precisely at 21:14 on 2nd December. The filling of the reservoir had first been very slow, but the last 4 m had been filled in 3 days, because of exceptionally heavy rain in the preceding days. To cope with the flood, the bottom outlet gate had been opened at 18:00 to control the rising reservoir.

The flood wave ran along the Reyran valley to Frejus. A total of 433 casualties were reported.

Little of the dam arch remained, and a deep trough was cut through the rock foundations on the left bank. 1.5 km downstream, a 800 m portion of the Esterel freeway and a bridge were destroyed. Huge blocks were carried out and deposited downstream. Trace marks of the flood wave show that the flood rose to a level as high as 20 m above the original bed level.

Investigations after the accident showed that key factors in the failure of the dam were the pore water pressure in the rock, and the nature of the rock. Under the increasing pressure of rising water, the arch separated from its foundation and rotated as a whole about its upper right end. The whole left side of the dam collapsed, followed by the middle part, and then the right supports.

Banqiao Dam Failure

The Banqiao dam built in China failed in 1975 accompanied with enormous loss of life and property. The cause of dam disaster was exceptionally high flood.

Reservoir Triggered Earthquake

During the filling of the Vajont dam reservoir of Italy in 1962 a grade five Mercalli scale  earthquake was triggered although the main cause of that dam disaster was landslide.  There are a considerable number of experts who regard that the recent Sichuan earthquake was triggered by reservoirs.

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