For our ENVS 330 Normative Research Project, my lab group (which includes Phe, Katie-Lauren, and Hannah) have chosen to concentrate on the Bonneville Dam as a hybrid object.
More specifically, we want to measure how the function of the dam has changed over time. Our project focuses on the impending doom of the 9.0 earthquake due to hit to Pacific Northwest in the future. The last earthquake to impact the region was well before Euro-American settlement, and therefore the infrastructure and population of the Pacific Northwest is ill-prepared for the violent shaking of the subduction zone off the coast of Oregon and Washington. The Bonneville dam was built at a time without the knowledge of the seismic activity of the region. The dam was also built on a historic landslide, which poses another series of risks for when the earthquake happens. Without a case study to look at in the Pacific Northwest, our group researched the impacts of dams in other countries shaken by earthquakes to hypothesize how the Bonneville dam will brave the next quake. By researching how these dams were affected by earthquakes and landslides, we can draw comparisons to Bonneville and hopefully gain a more clear understanding of how the Bonneville dam will survive.
Aratozawa Dam, Japan (June 14, 2008)
Landslide into reservoir (from Kayen et al., 2008)
On June 14, 2008, the Aratozawa Dam survived the Iwate-Miyagi-Nairiku, Japan Earthquake (6.9 magnitude) with on slight damage. The earthquake caused a landslide that caused a seiche that overtopped the spillway, but not the dam. The Aratozawa dam is a earth and rockfill embankment completed in 1991 and placed in service in 1998. Located on the Nihasama River, the dam impounds a 14,139 million meters cubed reservoir, which controls flood, generates hydroelectric power, and irrigates farmland. It is important to note that the Bonneville dam is a concrete gravity, run-of-the-river dam used primarily for hydroelectric generation and built in 1934. The Aratozawa Dam is relevant, however, because of the landslide it suffered. Three and a half kilometers of an access road to the dam were obliterated by the landslide (Kayen et. al., 2008). So, although the dam may be intact with little need for repair, the landslide not only causes a threat to the dam, but to the area surrounding the dam. A landslide could limit transportation to the dam and cause a public safety transportation risk. This context also serves as a reminder of the need to assess the effects on reservoirs (USSD Committee on Earthquakes).
Bajina Basta Dam, Serbia
This next context is not about any specific earthquake, but about a dam that is a case of persistent neotectonic movements. Neotectonic movements are, “all kinds of tectonic movements active in the earth’s crust in recent geologic times and is inclusive of seismic and aseismic movements along distinct faults and movements of larger tectonic units,” (USSD Committee on Earthquakes). After the Bajina Basta Dam was completed in 1966 on the Drina River, authorities have observed that the dam has moved as a whole towards the left bank. I specifically bring this case up rather than another because this dam was knowingly built on a seismically active zone and is also a concrete gravity dam. While the dam has not been impacted by an earthquake, the subduction zone beneath it has compromised the dam’s structural integrity and safety. The dam was designed to withstand normal neotectonic influence, which is supposedly less risk than seismic movements, but even then , a large vertical crack formed through the whole thickness os a hollow gravity block. Since then the area has been reinforced and the dam is under constant monitoring. To compare this to Bonneville, the same type of dam located on a area of high risk seismic activity, the dam movements need to be monitored and reinforced in order to reduce cracking and failure. Needless to say, the Bonneville dam needs a touch-up in the biggest way.
Sefid-rud Dam, Iran (June 20, 1990)
Built in 1962, the concrete buttress dam, the Sefid-rud Dam (also know as the Manjil Dam), dams the Sefid-Rud in northern Iran. This dam experienced a M7.6 earthquake on June 20, 1990. Located near the epicenter, the dam was severely shaken, so much so that cracks penetrated the wall causing leakage. Even with this severe damage, the dam was repaired and had no general failure. One of the primary purposes of the dam is power. This dam is relevant because like the Bonneville, its primary function is to generate electricity. It also puts the effects of earthquakes on dams into perspective. Although the Sefid-rud Dam suffered through a M7.6 earthquake right next to the epicenter, it did not fail. Comparing this case to the Bonneville dam, it seems as if dams are generally very hardy, and they generally don’t seem to have irreversible damage cause by earthquakes (Ghaemmaghami et al., 2008)
References
Ghaemmaghami, A. R. and Ghaemian, M. (2008), Experimental seismic investigation of Sefid-rud concrete buttress dam model on shaking table. Earthquake Engng. Struct. Dyn., 37: 809–823. doi:10.1002/eqe.791
Kayen, Robert; Cox, Brady; Johansson, Jorgen; Steele, Clint; Somerville, Paul; Kongai, Kazuo; Zhao, Yu and Tanaka, Hajime (2008), “Geoengineering and Seismological Aspects of the Iwate Miyagi-Nairiku, Japan Earthquake of June 14, 2008,” GEER Report 2008.2 v.1 http://www.geerassociation.org/GEER_Post%20EQ%20Reports/Japan_2008/Cover_Japa n2008.html
USSD Committee on Earthquakes. Observed Performance of Dams During Earthquakes. Report no. 2014932950. Vol. 3. Denver, CO: United States Society of Dams, 2014.