The Exponential Pattern And The Power Function Pattern For The HCFs' Spatial Adjustments In The LYR

Yellow River has the largest sediment concentration among the rivers all over the world.It's known for its secondary suspended channel.HCFs?hyper concentration floods?with a great portion of fine particles are to blame for the sedimentation in the main river channel of the LYR?Lower Yellow River?.Being very peculiar in sand gradations and boundary conditions,these HCFs and their spatial adjustments along the way exert a profound impact on the broad basins of the LYR,while the study of which is still a weak link.This paper mainly discusses the spatial adjustments of the HCFs in the LYR,both in the sediment exchange and the energy dissipation.First,the attenuation phenomena of sediment concentration of HCFs are analyzed.Based on the field data of 41 typical hyper concentrated floods during 1960-1999,exponential pattern and power function pattern are adopted to simulate the spatial adjustments of the HCFs,the key fitting coefficients of which being b1 and b2 respectively.To compare the two fitting patterns quantitatively,we tested several prevailing sediment capacity expressions on the LYR,using the daily data in 40 years.Then,the superior expressions are applied in the calculation of the sediment capacity S* and the expotianal coefficient b2=?^?/qfor the HCFs in the LYR.Thus,the inherent connection of the two patterns are revealed,and the fitting validities are judged by the statistical parameter F and coefficient of determination.Also,the ways that possible factors,like the overbank process,the percentage finer and the matching patterns of flow and sediments,may influence coefficient b,which indicates the characteristics of the floods' special adjustments,is fu rth er elab o rated in th is p ap er.The research illustrates the sediment exchange and energy dissipation function of the braided reaches.We found that,the overbank process quickens the spatial adjustments of floods and therefore shortens the length needed for the quasi-equilibrium state to be achieved.The sediment expression by Zhang Hongwu,which boasts a higher relativity between the calculated sediment capacity and the measured concentration,suffers from a systematic deviation.Relatively,the expression by Fei and the amended EngelundHansen expression seem to be more suitable for the hyper consentration in the LYRs.For the connection and comparison between the two patterns,the exponential coeffient b1 decreases along the way rather than stay still,which makes the flood adjustments in the lower reaches fit better into the power function pattern as a whole.But this doesn't mean that the exponential pattern is invalid.For shorter channel lengths with the sediment capacity and the exponential coeffient in a smaller span,the exponential pattern actually works better than the power function pattern.