青藏高原山区河流广义河相关系与多频率沿程河相关系

Generalized hydraulic geometry and multi-frequency downstream hydraulic geometry of mountain rivers originated from the Qinghai-Tibet Plateau

山区河流地貌由流域来水来沙和地质地貌等下垫面背景因素决定,基岩限制性河段与冲积河段相间分布,这些河流是否存在稳定的河相关系,是山区河流地貌演变研究亟待回答的重要问题。本研究以发源于青藏高原的六大水系共129个水文测验断面的实测流量和实测大断面数据为主要数据源,以青藏高原六大水系的沿程河相关系为研究对象,探讨了同一河段与同一流域不同河段平滩流量下的沿程河相关系,分析了不同频率流量下沿程河相关系系数和指数的相关关系及协同变化规律,提出了多频率沿程河相关系概念,并在时间和空间两个维度上分析了多频率沿程河相关系的意义。青藏高原山区河流平滩流量下同一河段与同一流域不同河段均存在较强的沿程河相关系,本文把山区河流上、下游间断冲积河段之间所具有的沿程河相关系,称为山区河流的广义河相关系,河宽-沿程与水深-沿程河相关系强度总体上大于流速-沿程河相关系强度;不同频率流量下沿程河相关系系数和指数间存在较好的对数-线性关系,并将其定义为多频率沿程河相关系;同一河段的多频率沿程河相关系强度一般大于同一流域不同河段的多频率沿程河相关系强度。多频率沿程河相关系将沿程河相关系的空间多维属性在时间维度上进行延伸,刻画了断面几何参数与流量在时、空两个维度上的相关关系。研究结果丰富和发展了河相关系理论,可为河相关系从平原河流走向山区河流及河流地貌在河网水系的分布规律等研究提供依据。

Landforms of mountain rivers are determined by flowing water and sediment,and underlying sur⁃face conditions including local geology,geomorphology,soil,vegetation et al.The alternatively distributed bed rock constrained reaches and alluvial reaches of mountain rivers contributes to less consistent variation in hydraulic parameters and flow discharges downstream.Whether there is stabilized hydraulic geometry is an important question that need to be answered in the study of geomorphic evolution of mountain rivers.In-situ measured hydrological and morphological data of 129 cross sections of six river systems originated from the Qinghai Tibet Plateau(QTP)were used to fit DHG relations under bankfull condition.Relations between downstream hydraulic geometry(DHG)coefficients and exponents under different discharge frequen⁃cies were analyzed.Two conditions were considered:cross sections along the same river reach and cross sections located in different reaches but in the same river basin.Multi-frequency downstream hydraulic ge⁃ometry(MFDHG)was proposed and the significance of it was revealed in terms of spatial and temporal di⁃mensions.Mountain rivers originated from the QTP exhibit strong DHG relations.Generalized hydraulic geom⁃etry of mountain rivers refers to DHG of alluvial reaches disconnectedly located for mountain rivers.Strength of width-DHG and depth-DHG are generally larger than velocity-DHG.Log-linear relations that found for DHG coefficients and exponents under different discharge frequencies is defined as MFDHG.MFD⁃HG of a river reach is generally stronger than that of a river basin.MFDHG extends multi spatial dimen⁃sions of DHG in time dimensions.Results of this study enrich the hydraulic geometry theory and provide basis for the study of spatial distributions of river morphology upon river systems.