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Flash Flood
Published in Saeid Eslamian, Faezeh Eslamian, Flood Handbook, 2022
Even small glaciers on tributary streams of the Indus in the Karakoram have generated GLOFs with disastrous effects. A severe glacial lake outburst flood occurred on July 27, 2000, at Kande from a tributary of the Hushe River (a tributary of the Shyok). The outflow originated from the Kande glacier and villagers referred to a supraglacial lake on the glacier before the flood occurred. A previous flood had occurred from the same source on July 25, 1997, but was much less severe than the one in 2000. Kande village was virtually destroyed, with 124 houses and a primary school destroyed (Figure 1.8a). Flood boulders cover the entire surface and there is no remaining evidence of houses, cultivation terraces, or trees. Villagers heard a roar in the hills about ten minutes before the arrival of the flood (as in the first example from Ethiopia) and fled to higher ground; there were no casualties.
Reservoir operation of Mangdechhu project and safety of the structure
Published in Jean-Pierre Tournier, Tony Bennett, Johanne Bibeau, Sustainable and Safe Dams Around the World, 2019
B. Joshi, N. Kumar, K. Deshmukh, R. Baboota, M. Mishra
The project envisages construction of a 56 m high concrete gravity dam across Mangdechhu above river bed. The gross capacity of reservoir at Full Reservoir Level (FRL) at EL 1747 m and Minimum Drawdown Level (MDDL) at EL 1730.5 m is 2.13 million cubic meters (MCM) and 0.96 million cubic meters (MCM) respectively. The live storage is 1.17 MCM. Length of the reservoir at FRL is around 800 m. The dam has been provided with an orifice spillway with 4 gates (10 m wide x 16 m high). The crest of the spillway is at EL 1702.2 m. The spillway is designed to pass a flood of 8500 m3/sec with one gate inoperative and to pass check flood of 10,615 m3/sec comprising of Probable Maximum Flood (PMF) of 6900 m3/s and Glacial Lake Outburst Flood (GLOF) of 3715 m3/s with all gates operative. A ski-jump bucket with 35 m radius, 35° lip angle and invert at EL 1692.1 m is provided for energy dissipation. The power intake is located just upstream of spillway on the left bank with invert level at EL 1720 m and comprises twin intake tunnels leading to a single power tunnel. The design discharge for the power intake is 135.7 m3/s. Two Dufour type desilting chambers of size 14.0 m (W) x 17.7 m (H) are provided to remove 90% of 0.2 mm and above size sediment particles. The sediment laden water is removed through silt flushing tunnels. General layout plan of dam, longitudinal section of spillway and upstream elevation of spillway are shown in Figures 2, 3 and 4 respectively.
Impulse waves in reservoirs
Published in Willi H. Hager, Anton J. Schleiss, Robert M. Boes, Michael Pfister, Hydraulic Engineering of Dams, 2020
Willi H. Hager, Anton J. Schleiss, Robert M. Boes, Michael Pfister
Carey (2008) provides an eyewitness report from a Glacial Lake Outburst Flood event in Peru: ‘On December 13, 1941, the blinding force of nature unleashed its power, making the mountains shake; the avalanche came, killing and swallowing, destroying and demolishing everything in its path. It cut short the lives of thousands of innocent people who just happened to live or be located in this picturesque and beautiful land. [The flood] converted the city and its precious lands into a heaping pile of inert material’. This event, leading to the destruction of large parts of the city of Huaraz and nearly 5000 fatalities, was triggered by a glacier break off into Lake Palcacocha. The ice masses generated an impulse wave with a height up to 15 m (Carey, 2010) overtopping and eroding the top of the lake’s moraine dam thereby presumably creating an incision for a gradually advancing dam breach. The water flooded downstream Lake Jiracocha and made its moraine dam fail as well. An estimated 8 × 106 m3 of water and debris eventually impacted the city of Huaraz, 23 km downstream of Lake Palcacocha (Carey, 2008). In 2003, a landslide into Lake Palcacocha generated waves of 8 m height. The released flood affected the drinking-water infrastructure in the valley downstream and cut off the citizens of Huaraz from water supply for more than a week (Klimeš et al., 2016). Further events triggered by impulse wave impact on natural dams include outburst floods e.g. at Lake Dig Tsho, Nepal, in 1985 (Vuichard and Zimmermann, 1987), and at Nostetuko Lake in 1983 (Blown and Church, 1985; Clague and Evans, 2000) as well as Queen Bess Lake in 1997 (Clague and Evans, 2000), both Canada.
Mitigating cavitation on high head orifice spillways
Published in ISH Journal of Hydraulic Engineering, 2021
R.R. Bhate, M.R. Bhajantri, V.V. Bhosekar
The studies were conducted for orifice spillway on 101.5 m high and 213.7 m long concrete gravity diversion dam. Seven orifice openings of size 6.1 m wide x 12.6 m high with crest level at El. 990 m. have been provided to pass a design flood (PMF) of 11,811 m3/s along with Glacial Lake Outburst Flood (GLOF) of 1,170 m3/s. The discharge intensity for design discharge is 300 m3/s/m. The velocity is about 30 m/s on the spillway surface. The FRL has been fixed at El. 1045 m. Radial gates have been provided at the downstream face of breastwall for controlling the outflow discharge. The equation of the downstream profile is X2 = 195 y. Figure 1 shows cross-section of the spillway. Experiments were conducted on a 1:40 scale 2D sectional model in a flume for assessing the pressure profiles. The accepted equations for similitude, based on Froudian criteria were used to express mathematical relationship between the dimensions and hydraulic parameters of the model and the prototype. Photo 1 shows the view of the model.
Earth observation and sustainable development goals
Published in Geomatics, Natural Hazards and Risk, 2020
Raj (2010) has used satellite remote sensing data for a hazard assessment of glacial lakes in the Zanskar basin, Jammu and Kashmir, India. Using multi-temporal satellite data, Bhatt et al. (2017) performed an assessment of one of the worst floods in the past 60 years in the state of Jammu and Kashmir in North India, which occurred in the first week of September 2014. The flood disaster footprints were extracted by using Indian Remote Sensing (IRS) satellite RISAT-1 and Canadian satellite Radarsat-2. The spatial and temporal dynamics of flood inundation and an evaluation of impacts were undertaken. Aggarwal et al. (2016) used multispectral satellite images of Landsat and IRS satellites and have mapped glacial lake outburst flood (GLOF) and evaluated risk assessment in the Teesta river basin in the Sikkim state of India. They have utilized normalized difference snow index and slope map of the area for risk evaluation from the GLOF in 140 lakes in Sikkim area.
Increase in hazard from successive landslide-dammed lakes along the Jinsha River, Southwest China
Published in Geomatics, Natural Hazards and Risk, 2020
Hai-mei Liao, Xing-guo Yang, Hai-bo Li, Bin-Rui Gan, Jia-wen Zhou
Figure 6 shows the relationship between the outburst peak discharge at the dam site and the landslide volume. The calculated peak discharge for natural breaching of the first dam is 13,293 m3/s and the second dam with an artificial spillway is 31,988 m3/s, which are 32.9% and 3.2% greater than the measured values, respectively. This deviation might be accepted in the emergency stage. Like the dam height, there is also a notable difference in the peak discharge between the conditions of the first and second episodes. For example, the outburst discharge of the dam with a 3.5 and 6.5 million m3 volume is 2151 and 3146 m3/s under the condition of the first episode, and it is up to 20307 and 36901 m3/s for the second episode, indicating an increase of 844% and 1073, respectively. Such a difference also increases with the landslide dam volume. Consequently, a landslide with the same volume can probably form a much higher dam and larger outburst flood in the second episode valley condition than that in the first episode. For example, the minimum height and potential outburst discharge of the dam with 23.5 million m3 volume are approximately 43 m and 10000 m3/s in the first episode, while only 3 million m3 (13%) volume is possibly needed to get the same dimensions in dam height and outburst flood for the second episode condition.