Search Results (2)

Anchor ice dams and water–ice flows are widespread on the mountain rivers of Southeastern Kazakhstan. Due to the mild winter climate, continuous ice cover is not formed on these rivers. During severe cold spells, anchor and shore ice accumulate in various river sections and causes water levels to rise by 1.5–2 m compared to winter low flows. In the event of a rapid warming, the ice breaks apart, forming water flows mixed with ice debris similar to mudflows. These flows move at high speeds and can cause significant destruction and loss of life. Our research aims to study the characteristics and formation conditions of these flows. Statistical methods were applied to analyze the data, revealing that thermal conditions greatly influence the formation of anchor ice. During these periods, minimum air temperatures drop below −20 °C, and the rate of cooling can reach 10 °C per day. An empirical formula for water level rise based on cumulative daily air temperatures was derived. The ice dam growth rate reaches 61 cm/day. Rapid ice breakage occurs during sharp warming periods. Sometimes this causes destructive water–ice flows similar to mudflows. The volume of the water–ice flow can exceed 10,000 m³, the path length can reach 8 km, the maximum speed exceeds 10 m/s, the flow depth can reach 5 m, and the discharge can be as high as 300 m³/s. The Random Forest algorithm identified characteristic meteorological conditions for water–ice flow formation. The most important meteorological parameters for the formation of water–ice flows are the 5-day sum of daily air temperature during the cooling period and the daily gradient of air temperature during the warming period. Full article

The upgrade of Akkats power station in Sweden included a new, separate waterway for the addition of a 75 MW generating unit. The vertical intake of its headrace was formed by means of lake tapping. A physical model was used to help understand the blasting process involving fragmented rock, water, air, and gas. Upon commissioning of the unit, swirling flows occurred unexpectedly at the intake, which gave rise to negative consequences including limitations in power output. Echo-sounding showed that the blasted piercing resulted in an irregular intake. A hydraulic model, as part of the design process, was built to examine potential countermeasures for vortex suppression. The final solution was a segmented barrier between the intake and the dam. It effectively suppressed the intake flow circulations; only minor intermittent vortices were left. The fabricated steel segments were anchored into the bedrock, stretching to 1.0 m below the lowest legal reservoir level. The local intake headloss was also reduced. The implemented solution was tested under full turbine loading and the result was satisfactory. Even during winter seasons with ice cover above the wall, the power station ran normally. The case study is expected to provide guidance for solving similar problems with vortex formation. Full article