Simulated Results

Fig. 12 shows simulated longitudinal distributions of (A) - (C) flow velocity and (D) water temperature at y = 290m. In Fig. 12B, a wind driven current of u = -0.05m/s and v = -0,01m/s was given at the surface. It is noted that the cold water from the inlet (glacier terminus) is dispersed by sediment-laden underflow, and that the strong return flow toward the inlet occurs in the middle layer. These flows are not intensified by increasing inflow from 3 to 10 m3/s (Fig. 12A and C), but by the wind-driven current at the surface toward the inlet (Fig. 12B). Fig. 12A indicates that, in a glacial lake, the coupling of outflow at an outlet and subaqueous inflow at the glacier terminus tends to strengthen the inner lake currents, especially on the basin slope probably underlain by dead-ice mass [29]. The inflow - outflow system could thus play the role on the lake deepening by ice-melt, since the relatively large heat transport occurs on the slope. The water temperature distribution (Fig. 12D) calculated in the velocity field of Fig. 12B exhibits the stratification of 5°C at the surface to 2°C at the bottom except 1.0 - 1.5°C at near the inlet, which is similar in pattern to the observation (Fig. 4A). However, the setup toward the glacier terminus by the valley wind is not simulated, since the free oscillation of water surface is not taken into account in the model (i.e., rigid lid model). Hence, the uplift of the thermocline (Fig. 5 and Fig. 6) is not also simulated. The unsteady calculation by the free surface model is needed for more realistic simulation of water temperature.

Fig. 13 shows simulated, longitudinal distributions of suspended sediment concentration in volume fraction for the five particle sizes of 0.977 to 250^m at y = 290m, where the velocity field is given in Fig. 12B. Most of the 250^m particles concentrate or deposit at or around the deepest point, where the volume fraction is more than 0.6. On the whole, the suspended particles are mostly converged in the layer of more than 90m in depth. Considering the total volume fraction of particles in the vertical water column at the deepest point, suspended particles at depths of more than 90m become coarser toward the lake bottom with increasing sediment concentration. This tendency is reasonable to the observation at site MD of Fig. 1 (Fig. 5 in [19]). The sediment-laden underflow from the inlet appears to selectively carry silt and clay particles (less than 62.5^m). Of the particles, the clay particles of 0.977^m and 3.91 ^m behave similarly, showing the dispersal larger than for the coarser particles.

Figure 12. Simulated results of (A)-(C) flow speed and (D) water temperature. The meltwater inflow, Qin, and flow speed, V^, of wind-driven current at the surface were given constant (or zero) at (A) 3m3/s and 0m/s, (B) 10m3/s and 0.051m/s, and (C) 3m3/s and 0m/s, respectively.
Figure 13. Simulated results of suspended sediment concentration in volume fraction in the velocity field of Fig. 12B. The unit volume fraction for 250^m particles means complete deposition of suspended sediment.

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