Cress Help - Ice forces - A21.5

Ice dams

Ice dams (see [a]):

Ice dams are piles (blockages) of ice in a river. Ice dams can form near piers, bends and constrictions in a river. The consequences of damming by ice are: considerable rises in water level (in the order of 4 metre); erosion hollows behind the ice dam and resulting from the creation of sand ridges; and a thickening of the ice cover (the actual dam). The thickness of the dam can increase to ca. 5 metre and extend to the bed of the river. In addition, the initiation and growth of van ice dams is also determined by the Froude number Fr (see [e] and [f]):

in which:

• g = acceleration of gravity [m/s2]
• h = water depth [m]
• v = flow velocity [m/s]

• Fr < 0.07: Ice accumulates at the upstream end of the ice cover, growing in the horizontal plane.
• 0.07 < Fr < 0.09: the ice cover has the tendency to become thicker, growing in the vertical direction.
• Fr > 0.09: Approaching ice is carried under the surface ice and attaches itself the closest place at which the shear stress against the ice cover is below a critical value. When the accumulated ice has constricted the cross section the velocity increases and the ice will be carried further.

Ice dams form much less frequently in Dutch rivers than they previously did because of:

• river control measures
• warming of the water by the discharge of cooling water.

 

References
[a] ing. C.J.A. Zijlmans, IJsbezetting -bestrijding op de grote rivieren in Nederland, Literatuurstudie, Rijkswaterstaat, Dir. benedenrivieren, afd. AXB, org. IJsopruiming, sektie onderzoek, nov. 1980.
[b] Stormvloedkering Nieuwe Waterweg, document ontwerp, deel 1, RWS Directie sluizen en stuwen, 31 juli 1989, BMK.
[c] ir A.W. de Haas, april 1986, Ice afvoerproblematiek voor de grote rivieren en de Rijndelta, bijzondere onderwerpen, RWS dir. Benedenrivieren, Organisatie IJsopruiming Sectie Onderzoek.
[d] ir T. Stoutjesdijk e.a. Grondmechanica Delft, oktober 1991, Taludbekledingen van gezette steen, bijzondere belastingen, co-320030/3.
[e] H.R. Kivisild, Proceedings 8th IAHR-congres 1959, Montreal-Canada-Volume III, "Ice problems in hydraulic structures.
[f] ir F. Gerritsen, Proceedings POAC-conference "The first international conference on port and ocean engineering under Arctic conditions", Vol. I Norway 1971, Ice problems in Dutch rivers and estuaries, blz. 582 e.v.
[g] Korzhavin, K. N., Action of ice on engineering structures, Novosibirsk, Akad. Nauk. USSR 1962.Vertaling: TL 260 van CRREL Hanover, New Hampshire, 1971
[h] Russische ontwerpregels uit 1986.
[i] Carstens T. editor, Working group on ice forces on structures, A State-of-the-art report, special report 80-26, june 1980.