Evaluation of suspended sediment sources in the Yeongsan River
영산강 부유토사의 기원지 평가

DC Field Value Language
dc.description학위논문 (박사)-- 서울대학교 대학원 : 사회교육과 지리 전공, 2016. 2. 김종욱.-
dc.description.abstractLarge direct human impacts on the Yeongsan River resulting from the construction of two large weirs on the main stream and dredging of almost all sections of the main river have occurred since late 2009. Subsequent to these human impacts, some problems related to the sediment budget, such as channel changes, have occurred. To establish appropriate policies for control of sediment-associated problems, it is necessary to identify the physical and geochemical characteristics of the reservoir sediments in particulate form in the Yeongsan River. Furthermore, from a management perspective, determining sediment provenance is an essential prerequisite for handling excessive sediment problems in the source-transport-sink system. Hence, the objectives of this study were: i) to identify the physical and geochemical characteristics of the reservoir suspended sediments, ii) to evaluate promptly and quantitatively the relative contributions of slope-floor and channel-bank materials to reservoir sediment, using Cs-137 as a tracer, and iii) to apportion sediment sources of the reservoir sediment by applying composite fingerprinting procedures combined with a multivariate mixing model.
Time-integrated suspended sediment samplers were installed in July 2012 at the Seungchon weir (YS-S1), the Juksan weir (YS-S3), and a point halfway between the two weirs, located at the Yeongsanpo waterfront park (YS-S2). Reservoir sediment samples from three samplers were obtained at monthly intervals until October 2014. Strikingly high rates of reservoir sedimentation were recorded in summer, with increased precipitation and discharge. Medium to coarse silt-sized particles dominated the suspended sediment load, however, the proportion of the coarser fraction increased at high flows. Concentrations of the major and trace elements of the collected sediments were analyzed and compared with the chemical composition of the underlying rocks. It was noticeable that easily mobilized elements, such as Ca, Mg, K, and Na, were considerably depleted in the suspended sediments relative to the bedrock of the river basin, indicating weak to moderate degrees of weathering. Trace elements including Ba, Co, Cr, Cu, La, Li, Mo, Nb, Ni, Pb, Rb, Sc, Sn, Sr, Ta, V, W, Y, Zn, and Zr were detected, with an abundance of several elements (e.g. Cu, W, Mo, Ba, Zn, Li, Cr, Rb, Ni, Co, and Pb) that are more likely to be affected by anthropogenic input.
For the second objective of this study, potential sources of the suspended sediment were sampled using a soil scraper on the forest floor and channel bank. Source fingerprinting was conducted using Cs-137, which exhibits distinguishable characteristics between surface and subsurface (bank) materials. Probability distribution functions fit to the detected values of Cs-137 at the forest floor and channel bank were derived. The relative contributions of forest floor and bank materials to suspended sediments in the Yeongsan River were calculated using Monte Carlo simulation and a simple mixing model. The results indicated that the dominant source of suspended sediment was bank materials. Conveyance losses of delivered forest floor materials would be expected to occur due to various forms of impediment (e.g., hill-foot zones, alluvial fans, and agricultural dams) that act as barriers to sediment movement. Embankments largely prevent slope materials from flowing into the channel and consequently influence sediment connectivity. Dredging a riverbed and constructing river-crossing facilities can affect the channel in many ways
dc.description.abstracthowever, it remains unclear from this study as to how and to what extent human impact has influenced channel erosion, due to the absence of pre-interference data.
To reduce the uncertainty and limitations of the Cs-137 methodology, a composite fingerprinting analysis, using fallout radionuclides, geochemical elemental concentrations, and the magnetic properties of each source material coupled with a multivariate mixing model, was conducted. Cropland topsoils, forest topsoils, and channel bank materials were selected as end-members. By applying the Kruskal–Wallis H-test and stepwise discriminant function analysis (DFA), final fingerprints were composed of different characteristics of the properties including excess Pb-210, Zr, V, Pb, and Co. According to the mixing model result, channel bank materials were the dominant source of reservoir sediment during the entire monitoring period. In winter, there was a slight increase in the contribution from forest topsoils, which can be influenced by freeze–thaw actions. An examination as to whether or not incorporation of particle size and organic matter content correction factors into the mixing model was appropriate showed that there is no consistent significant correlation between element concentration and specific surface area (SSA) or organic matter content (LOI). Careful application of tracer-specific correction factors combined with uncertainty analysis is needed to better estimate source apportionment.
dc.description.tableofcontents1. Introduction 1
1.1. Background 1
1.2. Research trends 4
1.3. The objectives of this study 7

2. Study area and Methods 10
2.1. Study area 10
2.2. Method 16
2.2.1. Field monitoring and suspended sediment sampling 16
2.2.2. Laboratory analysis 18
2.2.3. Hydrological data acquisition 22

3. The physical and geochemical properties of suspended sediments in the Yeongsan River 24
3.1. Temporal variation in physical characteristics 24
3.2. Geochemical characteristics of suspended sediments 32
3.2.1. Major elements 32
3.2.2. Trace elements 37
3.3. Discussion and summary 40
3.3.1. Weir construction effects on fluvial system 40
3.3.2. Seasonal changes of the geochemical properties 44
3.3.3. Correlation between geochemical elements and affecting factors 51
3.3.4. Summary 57

4. Evaluation of suspended sediment sources in the Yeongsan River using Cs-137 after major human impacts 59
4.1. Temporal variation in discharge and reservoir sedimentation 59
4.2. 137Cs measurement and construction of a probability density function 62
4.2.1. 137Cs activities in potential source materials and suspended sediments 63
4.2.2. Comparison of 137Cs distribution in forest floor with 137Cs in the channel bank 64
4.2.3. Probability distribution of 137Cs of the source materials 66
4.3. Contributions of forest floor and channel bank to suspended sediments 68
4.3.1. Simple mixing model and Monte Carlo simulation 68
4.3.2. Relative contributions to suspended sediments 69
4.4. Discussion and summary 71
4.4.1. Hillslope–channel connectivity 71
4.4.2. Channel changes resulting from human interference 76
4.4.3. Uncertainty and limitations of the methodology for using 137Cs 78
4.4.4. Summary 79

5. Suspended sediment source tracing of the Juksan weir in the Yeongsan River using composite fingerprints 81
5.1. Research scope 81
5.2. Data analysis 84
5.2.1. End-member selection 84
5.2.2. Sediment source discrimination 86
5.2.3. Sediment source apportionment 89
5.3. Results and discussion 91
5.3.1. Discriminating sediment source groups 91
5.3.2. Contributions of potential source materials to reservoir sediments 92
5.3.3. Seasonal variations in the contribution of source materials to reservoir sediment 95
5.3.4. Uncertainties and limitations associated with the mixing model 96

6. Conclusions 102

References 106

국문초록 129
dc.format.extent4421690 bytes-
dc.publisher서울대학교 대학원-
dc.subjectSuspended sediment-
dc.subjectSediment source fingerprinting-
dc.subjectMixing model-
dc.subjectHuman impacts-
dc.subjectYeongsan River-
dc.titleEvaluation of suspended sediment sources in the Yeongsan River-
dc.title.alternative영산강 부유토사의 기원지 평가-
dc.citation.pagesix, 132-
dc.contributor.affiliation사범대학 사회교육과(지리전공)-
Appears in Collections:
College of Education (사범대학)Dept. of Social Studies Education (사회교육과)Geography (지리전공)Theses (Ph.D. / Sc.D._지리전공)
Files in This Item:
  • mendeley

Items in S-Space are protected by copyright, with all rights reserved, unless otherwise indicated.