Continuous in situ measurements of anchor ice formation, growth, and release

Abstract

Abstract. In northern rivers, turbulent water becomes supercooled (i.e. cooled to slightly below the freezing point) when exposed to freezing air temperatures. In supercooled turbulent water, frazil (small ice disks) crystals are generated in the water column, and anchor ice starts to form on the bed. Two anchor ice formation mechanisms have been reported in the literature: either by the accumulation of suspended frazil particles, which are adhesive (sticky) in nature, on the riverbed or by in situ growth of ice crystals on the bed material. Once anchor ice has formed on the bed, the accumulation typically continues to grow (due to either further frazil accumulation and/or crystal growth) until release occurs due to mechanical (shear force by the flow or buoyancy of the accumulation) or thermal (warming of the water column which weakens the ice-substrate bond) forcing or a combination of the two. There have been a number of detailed laboratory studies of anchor ice reported in the literature, but very few field measurements of anchor ice processes have been reported. These measurements have relied on either sampling anchor ice accumulations from the riverbed or qualitatively describing the observed formation and release. In this study, a custom-built imaging system (camera and lighting) was developed to capture high-resolution digital images of anchor ice formation and release on the riverbed. A total of six anchor ice events were successfully captured in the time-lapse images, and for the first time, the different initiation, growth, and release mechanisms were measured in the field. Four stages of the anchor ice cycle were identified: Stage 1: initiation by in situ crystal growth; Stage 2: transitional phase; Stage 3: linear growth; and Stage 4: release phase. Anchor ice initiation due to in situ growth was observed in three events, and in the remainder, the accumulation appeared to be initiated by frazil deposition. The Stage 1 growth rates ranged from 1.3 to 2.0 cm/h, and the Stage 2 and 3 growth rates varied from 0.3 to 0.9 cm/h. Anchor ice was observed releasing from the bed in three modes: lifting of the entire accumulation, shearing of layers of the accumulation, and rapid release of the entire accumulation.

Cryofouling avoidance in the Antarctic scallop Adamussium colbecki

“…In nature, unwanted ice accretion on surfaces can occur either by the accumulation of suspended adhesive frazil ice particles or by in situ initiation of ice growth (heterogeneous ice nucleation) on a surface 18,25 . To test the possibility of preferential ice nucleation, the scallops were subjected to ice nucleation measurements and an in-air frosting assay.…”

“…The formation of anchor ice (Fig. 1b), a form of cryofouling, has been proposed to occur either by the accumulation of suspended adhesive frazil ice particles, or by the in situ nucleation and growth of ice crystals on the host material 18,25 . Once formed, this underwater ice is stable as long as the temperature of the surrounding water remains at or below the freezing point, with additional growth favored by continued supercooling.…”

Prevention of Water Intake Blockage by Ice during Supercooling Events

“…Apparently, platelet ice forms when there is supercooling but few frazil crystals in suspension. Observations of platelet ice are relatively rare but have long been described in the literature (Schaefer 1950;Wigle 1970;Michel 1971;Osterkamp and Gosink 1983;Ghobrial and Loewen 2021;Kempema and Ettema 2016). Observations of water intakes blocked by platelet ice are strongly associated with large lakes, as discussed in the next section.…”

“…In lakes and reservoirs, supercooled water is transported throughout the entire mixed layer, which can extend to the bed in nearshore areas. Detailed observations of supercooling events in rivers and streams are available (Richard and Morse 2008;Kalke et al 2019;Ghobrial and Loewen 2021;. Detailed observations of supercooling events in lakes and reservoirs are not available, but reports of bottom ice conditions and intake blockage indicate that supercooling events do occur in these waterbodies (Kempema et al 2001;Daly and Kempema 2010;Daly and Ettema 2006).…”

Advances in Frazil Ice Evolution Mechanisms and Numerical Modelling in Rivers and Channels in Cold Regions

“…Dube [138] collected underwater photographs of anchor ice and information related to the water level, water temperature, and air temperature in the field to understand the development process by studying the crystal type and size, the growth mechanism, the pattern and orientation, and the porosity of anchor ice accumulations. Ghobrial [139] designed an imaging system to acquire digital images of anchor ice formation and release on the riverbed and observed different mechanisms of anchor ice initiation, growth, and release. Meanwhile, in the field observations and laboratory experimental studies mentioned above, researchers have focused on the relationship between frazil ice and anchor ice development, and the results indicate that the attachment and accumulation effects of frazil ice promote the formation and growth of anchor ice.…”