ABSTRACT

The method of releasing submerged compressed air to create a vertical circulation has been applied to prevent freezing in the 10 km long Holandsfjord in northern Norway. A hydroelectric power plant discharges large amounts of fresh water to the inner part of the fjord. The fresh water supply in winter initiates severe ice conditions. In order to establish a permanent protection against freezing, a bubble curtain arrangement has been designed and is now in operation.

INTRODUCTION

It is a well-known technical principle that the release of submerged compressed air will create a vertical circulation of the water masses. This principle has been implemented in several marinas to prevent freezing. When the same principle is transferred to the freezing of brackish water in a fjord, the scales and dimensions increase significantly, making great demands on accurate knowledge of the prevailing environmental conditions and the necessary technical solutions to meet these conditions. The Holandsfjord (figure 1) is 10 km long and located in Nordland County in northern Norway. A hydroelectric power plant discharges large amounts of fresh water to the inner part of the fjord, also during winter. The fresh water supply in winter causes severe ice conditions and prevents ordinary ship traffic in the fjord. In order to establish a permanent protection against freezing, the effect of a bubble curtain arrangement has been evaluated. The bubble curtain system should fulfil two criteria:

  1. The speed of the bubble-induced surface current should be at least equal to the natural brackish surface flow.

  2. The thickness of the bubble-induced surface current should be at least equal to the thickness of the brackish surface flow. (figure 1 shown in paper)Figure 1.

The Holandsfjord and the surrounding fjord system. The planned location of the bubble curtain system is marked (Courtesy of C-MAP Norway).

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