Original ResearchWide river or narrow river: Future river training strategy for Lower Yellow River under global change
Introduction
The lower reach of the Yellow River, also referred to as the Lower Yellow River (LYR) has a length of 786 km measured from the Taohuayu Valley to the estuary of the Yellow River (Wang et al., 2005) (Fig. 1). The total elevation in this reach drops by 93.6 m, with an average slope of 0.12‰. Generally, based on its geomorphological features, the LYR is further divided into four sub-reaches along the river course (Chien & Wan, 1999). The first sub-reach, starting from Taohuayu Valley and ending at the Gaocun gauging station, is referred to as the highly wandering river with vast floodplains. The second sub-reach, located between the Gaocun gauging station and the Taochengpu, changes from highly wandering to meandering known as the transitional reach. The third sub-reach, from the Taochengpu to the Lijin gauging station, belongs to the category of a confined meandering river with a comparatively narrow plan configuration. The last sub-reach, from the Lijin gauging station to the Bohai Sea, is the estuarine area of the Yellow River.
Because of the serious soil erosion on the Loess Plateau, hyper-concentrated flows frequently occur in the middle and the lower reach of the Yellow River (Chien et al., 1987, Miao et al., 2011). Analysis of the hydrological records at the Sanmenxia (SMX) hydrological station shows that the annual average suspended sediment concentration (SSC) is as high as 35 kg/m3 over the last century, and an average of 1.6 billion t of silt and clay was delivered downstream annually (Wu et al., 2004); nearly 25% of the sediment load from upstream deposited in the LYR (van Maren et al., 2010, Wu et al., 2005). The continuous sedimentation in the LYR, which may lead to breaches of the levees, still imposes an immediate threat to the residents outside the Grand Levees that constrain the LYR to the narrow path shown in Fig. 1. Therefore, flood control by river training has long been one of the top priorities for both the local and central governments (Li, 2002, Ongley, 2000). Much effort has been devoted to training the river throughout the history of China.
A chronological review of the evolution in the river training strategies for the LYR shows that there are two completely different training strategies: wide-river training and narrow-river training (Li & Li, 2002). The fundamental idea of the wide-river training strategy is to keep vast floodplains between the main channel and the Grand Levees to retard floods and promote the deposition of over-loaded sediment. This strategy was put into practice two thousand years ago and can be traced back as early as to the Han Dynasty (206 BC–220 AD). In contrast, the aim of the narrow-river training strategy is to convey both floods and over-loaded sediment downstream through a comparatively narrow single river channel with the help from a variety of river training works to increase the sediment transport capacity. However, the narrow-river training strategy was applied only for a relatively short period because it had to face to the difficulties in maintaining the narrow channels and the increasing risk of frequent breaching of the levees (Chien, 1990). This situation of high risks finally led to gradual abandonment of narrow-river training, and later wide-river training was re-applied over the past two hundred years and is still currently applied.
The conflict between natural and societal functions of the LYR has long been one of the most intractable problems under the wide-river training strategy (Li et al., 2002, Niu et al., 2013, Wang and Zhang, 2013). Along both sides of the main channel of the LYR, the floodplains, which extend over an area about 4000 km2, are divided into hundreds of patches enclosed by levees constructed at low standards by local residents to protect their farmland and cottages. These low standard levees block the lateral exchange of water and sediment between floodplains and the main channel during inundation (Zhang et al., 2011), which gradually leads to “secondary suspended rivers”. Additionally, the low standard levees are not well-designed and constructed under the guidance of the principles of river engineering. The uncertainty with respect to safety of these structures is, therefore, a potential threat to the residents living on the floodplains when unexpected large floods occur (Li et al., 2002). As a result, there has been a controversy over many years as to whether these low standard hydraulic structures should be completely abandoned and the local residents relocated, or the local government should use their power to enforce the construction of permanent levees with sufficiently high standards to provide adequate protection for farmland and cottages.
Because of human activities and global climate change, there now seems to be an opportunity to resolve this dispute persisting for centuries. One of the most significant impacts on the LYR comes from the continuous damming in the Yellow River in the past fifty years (Chen et al., 2017, Hou and Wang, 2017, Zhou and Zhang, 2012), especially the construction of the Xiaolangdi (XLD) Reservoir which became fully functional in 1999. Up to 2014, XLD Reservoir accumulated to 32.5×108 m3 of sediment, indicating that nearly 80% of the total sediment load transported from the upstream catchment was trapped in the reservoir (Liu, 2016). At the same time, the hydrological features of the LYR have changed dramatically over the past decades (Huang et al., 2017, Liu et al., 2012, Liu et al., 2013, Miao et al., 2010, Si et al., 2017, Wang et al., 2006), showing a remarkable decrease of both runoff and sediment load (Shi et al., 2017). The varied runoff and sediment load under the operation of the XLD Reservoir have led the main channel to change from experiencing aggradation to experiencing degradation since 1999 (Fig. 2a) (Hu & Zhang, 2010). In turn, the cross-sectional bankfull discharge, an index that represents the conveyance capacity of main channels, has recently recovered to the levels of 1980s (Fig. 2b). Both the degradation and the increasing bank-full discharge in the LYR reduce the risk of overbank floods, and, thus, local residents believe that it is a luxury to maintain vast floodplains solely for flood detention and sediment deposition. Consequently, a growing opinion believes that narrow-river training should be re-examined, so that floodplains can be protected by permanent levees to promote local socio-economic development (Niu et al., 2013, Wang and Zhang, 2013, Zhang, 2004).
Therefore, several measures for narrow-river training have been proposed (An et al., 2013a, Hu, 2015, Niu et al., 2013, Zhang et al., 2011). The one that is preferred by the majority of the engineers is the one proposed by Zhang et al. (2011), in which a couple of longitudinal embankments along both sides of the main channel are to be built. Meanwhile, floodplains are separated into sub-floodplains by the lateral embankments. The purpose of the construction of longitudinal embankments is to increase flow velocity to obtain a high transport capacity of sediment load and at the same time, to prevent the lands inside the embankments from inundation when floods are below a certain return period. In addition, each of the sub-floodplains is equipped with two weirs on the longitudinal embankment to allow water to flow into/out of the sub-floodplains during floods larger than a certain return period. This arrangement is expected to help to alleviate the development of a “suspended river” (Fig. 3a).
However, whether it is possible to shift from wide-river training to narrow-river training has not been fully discussed under the new hydrological circumstances. The proposed measure to implement narrow-river training in the LYR requires detailed study concerning both long-term and short-term reactions to the changes in the river training strategy. Of particular importance, the long-term river erosion and deposition, and short-period flood events are two key problems that need detailed study. To realize narrow-river training in this study (Fig. 3b), the alignment of the embankments, which was refined by An et al. (2013a) on the basis of the proposal suggested by Zhang et al. (2011), was selected.
In this study, one-dimensional (1-D) and three-dimensional (3-D) numerical models are applied to tackle these issues and to assess the responses of the LYR to the two training measures. The aim of using a 1-D model was to study the long-term evolution of the LYR under different river training measures, while a 3-D model was used to simulate design floods with different return periods, focusing mainly on river morphology.
Section snippets
Hydrological scenarios
Due to the uncertainties with respect to the future runoff and sediment load in the LYR, two representative hydrological scenarios suggested by An et al. (2013b) were considered to investigate the future fluvial processes over the following 50 years with respect to different strategies in the LYR. Scenario One was determined by looping the observed hydrological series at the XLD hydrological station from 2000 to 2013 three times and adding the time series from 2001 to 2012 to form a
Numerical simulation
Numerical simulation is an effective means in studies of river training and flood management (Fang and Wang, 2000, Fang et al., 2008, Garcia et al., 2015, van Maren et al., 2010). In this section, the details of the 1-D and 3-D models used in this study are presented.
Results
In this part of the paper the results derived from the 1-D and 3-D modeling regarding erosion and deposition under the two training measures are presented.
Analysis of rationality about erosion and deposition
The fluvial processes in the LYR are closely related to incoming water and sediment load (Hu & Zhang, 2010). In general, the incoming sediment coefficient (ISC) defined as the ratio of sediment concentration to discharge (S/Q, kg s/m6) is regarded as an index of the sediment transport on a long-term scale (Cao, 2004, Xu, 1997). The relation between annual ISC and fluvial processes in the LYR is usually studied. Much effort has been devoted to finding the critical value of the ISC according to
Conclusions
The ever decreasing runoff and sediment load observed recently yield immediate influences on the fluvial processes of the LYR. Meanwhile, this change in runoff and sediment load makes it possible for the river training strategy to change, i.e. shifting from a wide-river training strategy to a narrow-river training strategy. However, the river training strategy in the LYR is of extreme importance to flood control, and thorough study is needed.
By means of 1-D modeling, for input scenario one, it
Acknowledgments
This research was sponsored by the Special Funds for Public-Good Research Project of Ministry of Water Resources in China (Grant No. 201401002), the Key Projects in the National Science & Technology Support Program during Thirteenth Five-Year Plan Period in China (Grant No. 2016YFC0402500), and National Natural Science Foundation of China (Grant Nos. 91547204 and 51379102). The authors gratefully acknowledge the valuable help from Prof. Chen Jian-Guo of the China Institute of Water Resources
References (73)
- et al.
Influences of retrogressive erosion of reservoir on sedimentation of its downstream river channel‐A case study on Sanmenxia Reservoir and the Lower Yellow River
International Journal of Sediment Research
(2017) - et al.
One-dimensional numerical simulation of non-uniform sediment transport under unsteady flows
International Journal of Sediment Research
(2008) - et al.
Generating inundation maps for a coastal lagoon: a case study in the Ria de Aveiro (Portugal)
Ocean Engineering
(2013) - et al.
Modelling extraordinary floods and sedimentological processes in a large channel-floodplain system of the Lower Paraná River (Argentina)
International Journal of Sediment Research
(2015) - et al.
Study on the assessment of the comprehensive benefits of the utilization of sediment resources in reservoir areas
International Journal of Sediment Research
(2017) - et al.
Copula-based identification of the non-stationarity of the relation between runoff and sediment load
International Journal of Sediment Research
(2017) - et al.
Changes in runoff and sediment load from major Chinese rivers to the Pacific Ocean over the period 1955–2010
International Journal of Sediment Research
(2013) - et al.
A preliminary estimate of human and natural contributions to the changes in water discharge and sediment load in the Yellow River
Global and Planetary Change
(2011) - et al.
Development and validation of a three-dimensional morphodynamic modelling system for non-cohesive sediments
Ocean Modelling
(2012) - et al.
Analyses of trends and causes for variations in runoff and sediment load of the Yellow River
International Journal of Sediment Research
(2017)
A semi-physical sediment yield model for estimation of suspended sediment in loess region
International Journal of Sediment Research
Flow resistance of gravel bed channels
International Journal of Sediment Research
Interannual and seasonal variation of the Huanghe (Yellow River) water discharge over the past 50 years: Connections to impacts from ENSO events and dams
Global and Planetary Change
Estimation of bankfull discharge in the Lower Yellow River using different approaches
Geomorphology
Suspended sediment transport on the continental shelf near Davenport, California
Marine Geology
Main measures for future management of the Lower Yellow River
Journal of Yellow River
SELFE: A semi-implicit Eulerian–Lagrangian finite-element model for cross-scale ocean circulation
Ocean Modelling
Seamless cross-scale modeling with SCHISM
Ocean Modelling
Evolution of the Yellow River delta, China: Impacts of channel avulsion and progradation
International Journal of Sediment Research
Coarse sediment and Lower Yellow River siltation
Journal of Hydro-environment Research
Research of the project on the channel renovation and floodplain training for the Lower Yellow River
Future variation of water-sediment and its design for the Lower Yellow River
Erosion rates of cohesive soils
Journal of the Hydraulics Division, ASCE
Relationship between variation of sediment carrying flows and readjustment of riverbed in the lower reaches of Yellow River
Journal of Hydraulic Engineering
On the formation mechanism of hump reach of the Lower Yellow River
Journal of Hydraulic Engineering
Fluvial processes in the Lower Yellow River after levee breaching at Tongwaxiang in 1855
International Journal of Sediment Research
Mechanics of sediment transport
Fluvial processes
Three-dimensional mathematical model of suspended sediment transport
Journal of Hydraulic Engineering
Formation and development of hump reach in Lower Yellow River
Journal of Sediment Research
Study of equilibrium sediment transport of Lower Yellow River
Journal of Sediment Research
Reservoir sedimentation
Changes in runoff and sediment load of the Yellow River and its downstream channel reconstruction
Water Resource and Hydropower Engineering
Modeling sediment transport in the lower Yellow River and dynamic equilibrium threshold value
Science in China Ser. E
Characteristics of the Lower Yellow River channel shrinkage and its discriminant parameters
Science China Technological Sciences
The research of mechanism of constructing riverbed and index of flow and sediment of floodwater in the Lower Yellow River
Scientia Sinica Technologica
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