The geomorphic process and sedimentary characteristics of the “11·3” Baige Dammed Lake outburst flood event in the upper reaches of the Jinsha River from Benzilan to Shihku

doi:10.13745/j.esf.sf.2020.9.19

Abstract

Abstract:

Reconstruction of paleo-dammed lake outburst floods is one of the hotspots in current Earth science research. Collecting enough reference cases of modern outburst floods is the basis for this research. The outburst flood on November 13, 2008, referred to as the “11·3” Baige Dammed Lake outburst flood, is a once-in-1000-year event when the outburst flood discharged from the Baige Dammed Lake, blocking the mainstream of the Jinsha River. As the flood event occurred during the dry season, the flood peak was solely from the outburst flood; therefore, this rare case provides a great reference for evaluating the impact of dammed lake outburst flood on the basin landform and sedimentary system. In this flood event, the upper reaches of the Jinsha River from Benzilan to Shihku, the focus area of this study, was most devastated. Based on detailed field investigation and preliminary hydrodynamic estimation, we found that the geomorphic process of the outburst flood was mainly manifested in bank slope collapse and sediment accumulation, with no significant bedrock erosion observed in the flooded area. The outburst flood sediments are mainly composed of well sorted, horizontally laminated sand. Due to relatively low slope gradient of the Jinsha River, the bed shear stresses exerted by the outburst flood, ranging from 27 to 142 N/m ², were relatively weak and could not suspend and transport gravels larger than 5 cm, nor could it produce obvious abrasion and impact marks. Some collapsed banks show gravels falling from the bank slope into the outburst flood sediments; even turbidity sequences appear. These phenomena provide new geomorphologic evidence for further understanding the complex geomorphological process and sedimentary characteristics of dammed lake outburst floods.

Key words: outburst flood, geomorphic process, sedimentary characteristics, Baige Dammed Lake, Jinsha River

CLC Number:

SU Huai, SHI Zhengtao, DONG Ming, YE Liaoyuan, YE Lei. The geomorphic process and sedimentary characteristics of the “11·3” Baige Dammed Lake outburst flood event in the upper reaches of the Jinsha River from Benzilan to Shihku[J]. Earth Science Frontiers, 2021, 28(2): 202-210.

Figures/Tables 17

Fig.1 Overview of the study region

Fig.2 The floodmark of the “11·3” outburst flood from the Baige Dammed Lake on the Jinsha River

Fig.3 Photo showing varnish grew only on the exposed gravel surface

Table 1 Estimated shear stresses and flow rates of the outburst flood in each survey reach

段落	τ_b/ (N·m^-2)	Q_估算/ (10³ m³·s^-1)	Q_实测/ (10³ m³·s^-1)
布丁村大桥	142	15.8	—
奔子栏	120	15.7	15.7
托顶	110	12.7	—
其宗	71	10.4	—
巨甸	44	9.78	—
士林	35	7.70	—
石鼓	27	7.37	7.17

Fig.4 Bank slope erosion caused by the “11·3” Baige Dammed Lake outburst flood event

Fig.5 Collapsed building remains, unable to be transported by floods, at the Benzilan hydrometric station

Fig.6 Varnish surface still keeping the original direction on the floodplain after washed by the outburst flood

Fig.7 The Benzilan hydrometric station scoured after the outburst flood

Fig.8 Wooden piles inclined along the outburst flood on the foodplain

Fig.9 Damaged plastic greenhouse from the outburst flood

Fig.10 The outburst flood sediments overlaying the farmland

Fig.11 Leaky subsidence micro-landforms on the outburst flood sediments overlaying the farmland

Fig.12 Grain size distribution of the outburst flood sediments at Benzilan

Fig.13 Horizontally laminated beds of the outburst flood sediments

Fig.14 Bouma-like sequence in the outburst flood sediments

Fig.15 Gravels falling into the outburst flood sediments

Fig.16 Paleo-flood sediments in the upper reaches of The Jinsha River from Benzilan to Shihku

References 18

[1]	LI N, WANG R, LIU Y B, et al. Robust river boundaries extraction of dammed lakes in mountain areas after Wenchuan Earthquake from high resolution SAR images combining local connectivity and ACM[J]. ISPRS Journal of Photogrammetry and Remote Sensing, 2014,94:91-101. DOI URL
[2]	CARRIVICK J L, JONES R, KEEVIL G. Experimental insights on geomorphological processes within dam break outburstfloods[J]. Journal of Hydrology, 2011,408(1/2):153-163. DOI URL
[3]	WU Q L, ZHAO Z J, LIU L, et al. Outburst flood at 1920 BCE supports historicity of China’s great flood and the Xia dynasty[J]. Science, 2016,353(6299):579-582. DOI URL
[4]	LIU W M, CARLING P A, HU K H, et al. Outburst floods in China: a review[J]. Earth-Science Reviews, 2019,197. DOI: 10.1016/j.earscirev.2019.102895. DOI
[5]	董广辉, 张帆宇, 刘峰文, 等. 喇家遗址史前灾害与黄河大洪水无关[J]. 中国科学D辑: 地球科学, 2018,48(4):467-475.
[6]	LI L, CHEN J, HEDDING D W, et al. Uranium isotopic constraints on the nature of the prehistoric flood at the Lajia site, China[J]. Geology, 2020,48(1):15-18. DOI URL
[7]	陈祖煜, 陈生水, 王琳, 等. 金沙江上游“11·3”白格堰塞湖溃决洪水反演分析[J]. 中国科学: 技术科学, 2020,50(6):763-774.
[8]	余志球, 邓建辉, 高云建, 等. 金沙江白格滑坡及堰塞湖洪水灾害分析[J]. 防灾减灾工程学报, 2020,40(2):286-292.
[9]	蔡耀军, 栾约生, 杨启贵, 等. 金沙江白格堰塞体结构形态与溃决特征研究[J]. 人民长江, 2019,50(3):15-22.
[10]	GOLDSMITH Y, STEINM, ENZEL Y. From dust to varnish: geochemical constraints on rock varnish formation in the Negev Desert, Israel[J]. Geochimica et Cosmochimica Acta, 2014,126:97-111. DOI URL
[11]	POTTER R M, ROSSMAN G R. Desert varnish: the importance of clay minerals[J]. Science, 1977,196(4297):1446-1448. DOI URL
[12]	LAMB M P, FONSTAD M A. Rapid formation of a modern bedrock canyon by a single floodevent[J]. Nature Geoscience, 2010,3(7):477-481. DOI URL
[13]	O’CONNOR J E, BAKER V R. Magnitudes and implications of peak discharges from glacial Lake Missoula[J]. 1992,104(3):267-279.
[14]	崔之久, 张梅, 崔鹏, 等. 初论堰塞湖溃坝沉积相特征[J]. 山地学报, 2015,33(2):129-140.
[15]	CARLING P A, FAN X M. Particle comminution defines megaflood and superflood energetics[J]. Earth-Science Reviews, 2020,204. DOI: 10.1016/j.earscirev.2020.103087. DOI
[16]	BAKER V R. The Channeled scabland: a retrospective[J]. Annual Review of Earth and Planetary Sciences, 2009,37:393-411. DOI URL
[17]	康志成, 李焯芬, 马蔼乃, 等. 中国泥石流研究[M]. 北京: 科学出版社, 2004.
[18]	吴庆龙. 金沙江、雅鲁藏布江发现史前巨大洪水事件[J]. 南京师大学报(自然科学版), 2019,42(3):163-164.