Abstract. The existence of glacial lakes in the southeastern Tibetan Plateau
(SETP) is a potential hazard to downstream regions, as the outburst of such
lakes has the potential to result in disastrous glacial lake outburst floods
(GLOFs). In the present study, we conducted a comprehensive investigation of
Bienong Co, a moraine-dammed glacial lake in the SETP. First, the lake basin
morphology was determined, and the lake volume was estimated, showing that
the maximum lake depth is ∼181 m and the lake volume is
∼102.3×106 m3. These scenarios included
the possibility of GLOFs being triggered by ice avalanches (Scenarios A1–3)
from the mother glacier or by landslides from the lateral moraines
(Scenarios B1–3 and C1–3). Avalanche volumes of the nine trigger scenarios
were obtained from the Rapid Mass Movement Simulation (RAMMS) modeling results. Next, the Basic Simulation Environment for Computation of Environmental Flow and Natural Hazard Simulation (BASEMENT) model was
used to simulate the generation and propagation of the avalanche-induced
displacement waves in the lake. With the model, the overtopping flows and
erosion on the moraine dam and the subsequent downstream floods were also
simulated. The results indicate that the ice avalanche scenario may cause
the largest mass volume entering the lake, resulting in a displacement wave
up to 25.2 m in amplitude (Scenario A3) near the moraine dam. Landslide
scenarios with smaller volumes entering the lake result in smaller
displacement waves. Scenarios A1, A2, and A3 result in released water
volumes from the lake of 24.1×106, 25.3×106, and 26.4×106 m3, respectively.
Corresponding peak discharges at the moraine dam are 4996, 7817, and 13 078 m3 s−1, respectively. These high discharges cause
erosion of the moraine dam, resulting in breach widths of 295, 339, and
368 m, respectively, with the generally similar breach depth of
approximately 19 m. In landslide scenarios, only overtopping flows generated
by Scenarios B3 and C3 cause erosion on the moraine dam, with breach depths
of 6.5 and 7.9 m and breach widths of 153 and 169 m, respectively.
According to our simulations, GLOFs generated by Scenarios A1–3 all flow
through 18 settlements downstream in 20 h, threatening more than half of
them. Both Scenarios B3 and C3 produce GLOFs that flow through the first
eight settlements downstream in 20 h and have a relatively small impact on
them. Comparisons of the area, depth, and volume of glacial lakes for which
the bathymetry data are available show that Bienong Co is the deepest known
glacial lake with the same surface area on the Tibetan Plateau. This study
could provide a new insight into moraine-dammed glacial lakes in the SETP
and be a valuable reference for GLOF disaster prevention for the local
government.