Dynamic variability of at-a-station hydraulic-geometry for mountain rivers in the southeast Qinghai-Tibet Plateau: The cases of Yalong River and upper Jinsha River

To be able to precisely estimate discharges in un-gaged streams and reconstruct hydrological features in river systems, the temporal and spatial variations of at-a-station hydraulic geometry (AHG) and their impacting factors need to be detected. To this end, the Yalong River and Upper Jinsha River, which located in southeast Qinghai-Tibet Plateau, are selected as case study. This investigation explores quantitative data on the magnitude of spatial and temporal variations in AHGs over a period of 10 years for 38 mountain reaches with drainage areas ranging from 0.53 x 10(3) to 259.18 x 10(3) km(2). Effects of ice regime and drainage area on AHG were discussed and the stability of AHG was analyzed. 42.1% of the reaches have flow velocity exponents that are greater than the river width and flow depth exponents combined. No significant spatial variation tendency is observed for AHG exponents while significant temporal variations are reported. Larger fluctuations are found for AHG exponents in annual variations compared with those in inter-annual variations. Ice regimes significantly contribute to the seasonal changes of AHGs. The relative differences of AHG coefficients (a, c, k) and exponents (b, f, m) with and without ice vary between -49.4 to 80.8% and - 70.1% to 22.6%, respectively. Compared with no ice regime, the reaches with border ice and slush ice run have smaller exponents m and Froude Number and larger coefficients c and exponents f. Besides, coefficients a and exponents m increase while coefficients k and exponents b decrease with the increase of drainage area. However, coefficients c and exponents f exhibit no tendency with drainage area changes. AHG stabilities increase with the increased stream order and drainage area. Results of this study can enrich the AHG database for mountain rivers and provide a preliminary understanding of ice effects on AHG variations.