Effects of hydrology and river characteristics on riverine wetland morphology variation in the middle reaches of the Yarlung Zangbo–Brahmaputra river based on remote sensing

Abstract

River and floodplains are process-response systems that geomorphic states are typically results of hydrologic drivers and geologic setting. Large sand-bed braided rivers geomorphology shows more sensitive dynamic evolution and significant space–time difference. However, few investigations have been focused on it. Here we show that river characteristics including expansion–contraction and elevation heterogeneity of the river cross sections affect erosion and deposition partially and cause spatially differential variation of morphology in the Yanni Wetland, in the middle of Yarlung Zangbo–Brahmaputra River (YBR), and interannual hydrology process is main responsible for temporal river morphology variation as the different impact of each HIs on river morphology. We found the river morphology varied significantly with main channel shifting and branches removing over the past 35 years. Within HIs, bankfull flow (Qbf) is the channel forming discharge equal to 5.6 year flood approximately. The sub-bankfull flow (Qsf), and main channel full flow (Qmf) are channel maintaining discharge. Affected by the broad width, main channel straighten was a result of years of large floods over Qbf. Small and moderate floods within the Qsf and Qbf are also important as the morphology adjustments were mainly observed in sub-channels. And effective discharges with the Nash approach (Q1/2) are more suitable in braided river compared with Wolman-Miller approach (Qef). Our research highlighted complexity response of landform and hydrology to river morphological variations in sand-bed braided riverine wetland. It provides reference basis for studying the ecological importance of flood dispatches and complements the scarcity of research data on morphological evolution in Tibet. And a new method for assessing the HIs with remote sensing was established that is convenient with high accuracy and suitable for wide-valley river with multiple channels. We anticipate our method to be a new view to analyze ecological hydrology, and promote better managing river ecosystems.