Effects of frequent debris flows on barrier lake formation, sedimentation and vegetation disturbance, Palongzangbo River, Tibetan Plateau

• Published in: Catena (Giessen) 2023-01, Vol.220, p.106697, Article 106697
• Main Authors: Meng, Zhe, Lyu, Liqun, Xu, Mengzhen, Yu, Guoan, Ma, Chao, Wang, Zhaoyin, Stoffel, Markus
• Format: Article
• Language: English
• Subjects: Barrier lake; Debris flow; Dendrogeomorphology; Sedimentation; Stepped river; Tree growth disturbance
• ISSN: 0341-8162; 1872-6887
• DOI: 10.1016/j.catena.2022.106697

•Debris flows near the dam and barrier lake complicated river sedimentation rate.•Vegetation growth disturbance was consistent well with river sedimentation rate.•Trees recovery time lagged behind debris flow event 1–3 years in glacial valley. In incised mountain valleys, debris flows often cause damage to vegetation, especially when debris flows form fans or block receiving rivers. In such contexts, riparian trees may be partially buried in aggrading fans or temporary lakes. The Guxiang gully is the largest debris flow system along the Palongzangbo River on the Tibetan Plateau and at least 13 debris flows (volume > 104 m3) have occurred since 1953. Four of these debris flows (in 1953, 1965, 1975 and 2005) dammed the river forming a barrier lake which is now more than 25 km in length. The repeated damming by debris flows has increased the dam height and thereby affected the sedimentation rates in the barrier lake. The frequent debris flow activity has prevented vegetation recovery on the fan, while sedimentation in the barrier lake has allowed vegetation to colonize the deltas. This study investigated the effects of frequent debris flow damming on sedimentation rates as well as on revegetation and tree disturbance along the river. We documented the landscape evolution and measured the sedimentation thickness and grain size of deposited material at different locations of the barrier lake using cores. We also collected and analyzed growth-ring records from disturbed trees on the fan and the deltas of the barrier lake. We found that frequent debris flows had created a stepped river morphology and greatly increased sedimentation rates in the lake, affecting vegetation on the fan and behind the dam.