the general situation of Saroma Lagoon during this time. As a whole, inflow of ice floes into the lagoon was limited be. cause freezing in the lagoon was accelerated by cold waves while the force generated by the ice floes was not significant.
4-2 Status of ice floe control
Fig. 5 shows typical status of ice floe control when ice floes are flowing into the lagoon. It was confirmed that 6 spans of fan- shaped ice booms operated together to trap in- coming ice floes.
4-3 Observation results
Of the observation items, the results and characteristics as- sociated with the tension of the main wires are described be- low.
(1) Conditions of current
The maximum flow velocity (at middle layer) in the direc- tion of inflow of ice floes was l.30m/sec at 14:45 on March 20, while that in the direction of outflow of ice floes was 0.68m/sec at l9:30 on February 18. Throughout the observa- tion period, the peak inflow velocity was approximately 1.0 m/sec and the peak outflow velocity was approximately 0.5 m/sec (both are average values over 10min). Flow velocities measured in the middle and lower layers showed no signifi- cant differences and bad almost the same tendencies. Al- though flow velocities correlate with the rate of change in the tide level, the flow velocity during inflow tends to be greater than that of the flow velocity during outflow, even when the absolute value of the rate of change in the tide lev- el remains the same.
(2) Wind direction and velocity
N- E wind directions are predominant, although wind velocities are not very significant. However, wind velocities which exceed 10m/sec are predominant in SE- B directions.
(3) Tension of the main wires
The changes over time in the tension and flow velocity (at middle layer) are shown again in Fig.6. As the forces of ice floes were relatively small, the peak- time tension was slight-ly less than 10tf. Although times of peak occurrence for tension and flow velocity during inflow closely correspond, the relation between the intensity of tension and flow veloci- ty is scattered.
Time and dates when 5 greatest tension values occurred and respective flow velocities are shown in Table 6. It should be noted that the maximum tension obtained in the research conducted in 1994 was 17.8tf.
