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Northwest A&F University (2017)

Runoff-sediment Coupling Mechanism of Different Geomorphic Unit in the Loess Hilly-gully Region


Titre : Runoff-sediment Coupling Mechanism of Different Geomorphic Unit in the Loess Hilly-gully Region

Auteur : 王玲玲;

Grade : Doctoral Dissertation 2017

Université : Northwest A&F University

Résumé partiel
The scale problem exists in the whole process of soil erosion,and the scale of soil erosion is considerably important in soil erosion process simulation.Diversity stratum,various erosion type and nonlinear energy consumption process are the unique erosion environment in the hilly and gully region of the Loess Plateau.So,in the ―slope-gully-watershed‖ system,the effect on soil erosion,sediment transport and deposition mechanism is not completely clear,geomorphic units of different spatial scales water and sediment collocation differences is not clear.Therefore,to study the runoff-sediment coupling mechanism of different geomorphic unit in different spatial scales is urgently-needed.Based on this,in this paper,the methods of field location monitoring,indoor simulated rainfall experiment,hydrological analysis and mathematical analysis are used to carry out this research.In terms of field prototype observation,a typical small watershed(Peijiamaogou watershed)in the Loess hilly-gully region was taken as an prototype observation area and makes use of the observation facilities therein including four gauging stations,namely the first branch of Qiaogou,the second branch of Qiaogou,the Qiaogou and the Peijiamao,and five large-scaled field runoff plots,namely the top-hillyslope,the down-hillyslope,the hillyslope,the gullyslope and the entire slope which located in different topographical units.Observation data including rainfall,runoff and sediment during 1986-2008 of the four gauging stations and five large-scale field runoff plots were collected.Based on these observation data,the characteristics of sediment transport and flow-sediment relationship of different spatial and temporal scales in the system of ―slope-gully-watershed‖ system were systematically analyzed.And the difference of flow-sediment relationship of different spatial and temporal scales was expounded.In terms of indoor rainfall simulation,Qiaogou was taken as the prototype of laboratory-simulation experiment.According to the level scale(1:60)and vertical scale(1:50),the generalized small watershed model was built with bilayer-ditch network.Based on the rainfall simulation experiment,the process of the runoff and sediment yield and the runoff-sediment relationship comprehensively in different topographical units such as slope,channel and watershed was analyzed.Furthermore,the flow-sediment coupling mechanism was analyzed from hydrodynamic and geomorphic evolution.So,to research on further understanding the process of soil erosion in hilly area of the Loess Plateau and its mechanism has the important scientific significance and application value for ecological environment management of Loess plateau.The main conclusions are as follows :(1)At different spatio-temporal scales,there are different characteristics of erosion and sediment transportation in the different geomorphic units.At the annual scale,for the entire slope,the distribution of soil erosion modulus in the different micro-geomorphology unit of the entire slope showed : the top-hilly slope < the down-hilly slope < hilly slope < gully slope < entire slope.The ratio of erosion modulus of different geomorphic units is 1 : 1.2 : 1.7 : 2.4:2.9,which illustrate that all sediment produced by erosion was transported by runoff in the different geomorphic units of the whole slope.For the ―slope-gully-watershed" system,the sediment transport modulus of slope was greater than each watershed’s and sediment transport modulus trended to be decrease with the watershed scale increasing.For the single rainfall event,the crest value of sediment transport modulus may occur in someone of the geomorphic unit of the whole basin,so the distribution patterns of erosion and sediment yield were nonunique.(2)There were different dynamic factors of soil erosion and sediment transport in different topographical units of different spatial scales.At the slope scale,sediment yield was mainly related to depth of runoff.The relationship could be well described by runoff shear stress and there are obvious linear correlation between runoff shear stress and sediment transport rate.At the watershed scale,sediment yield was related not only to runoff depth but also to peak flood flow.Sediment delivery rate was a power function of the runoff erosion power at the watershed scale,the decisive factor of the power function fitting relationship reached 0.80 above.(3)For the ―slope-gully-watershed" system,sediment transport capacity are significantly different in the different topographical units of different spatial scales.With the increasing in spatial scale,the sediment transport capacity decreased dramatically.

Mots clés : runoff-sediment relationship; spatial scale effect; different geomorphologic units; hydrodynamic characteristics; Geomorphic evolution characteristic;

Présentation (CNKI)

Page publiée le 16 janvier 2018