Maotian Li

The sharp decrease in suspended sediment supply from China's rivers to the sea : anthropogenic and natural causes

Abstract Based on data from river gauging stations, the multi-year variations in suspended sediment flux (SSF) from Chinas nine major rivers to the sea were examined. The decadal SSF decreased by 70.2%: from 1.81 Gt/year for 1954–1963 to 0.54 Gt/year for 1996–2005. The decrease in SSF was more dramatic in the arid northern region than in the wet southern region; from north to south, the SSF decreased by 84% in the Yellow River, 42% in the Yangtze River, and 22% in the Pearl River. Dam construction was the principal cause for the decrease in SSF. At present, approximately 2 Gt/year of sediment is trapped in the reservoirs within the nine river basins. Reduced precipitation and increased water extraction and sand mining have also played a role in the decrease in SSF. Although water and sediment conservation programmes have not counteracted the influence of deforestation, they have enhanced the decrease in SSF in recent years. It is concluded that human activity has become a governing factor on riverine sediment delivery to the sea in China.

Impacts of human activity on the late-Holocene development of the subaqueous Yangtze delta, China, as shown by magnetic properties and sediment accumulation rates

Development of the Yangtze delta during the late Holocene, and its relationship to human activities in the drainage basin, was analyzed using data from 16 cores collected from distributaries to the prodelta. We used AMS 14C dating and digital elevation model (DEM) data from marine charts from 1864 through 2005 to determine ages and estimate sediment accumulation rates. The results demonstrate that the latest major subaqueous delta front formed within the past c. 0.8 cal. ka and features remarkably high accumulation rates (1—4 cm/yr) in comparison with those of previous delta fronts. We also examined the temporal distribution of grain size and magnetic susceptibility in all 16 cores. Results show soil-derived superparamagnetic (SP) minerals generally occur, and even dominate, in the recent (c. 1.7 cal. ka) Yangtze delta fine-grained sediment, as shown by high values of frequency-dependent magnetic susceptibility (both χFD and χFD%). Rock-derived magnetite dominates generally in the river channel and delta front sand bodies as a result of hydrodynamic sorting, but is also enriched in both fine and coarse-grained sediment formed more recently (c. 0.8 cal. ka), as evidenced by rising values of mass specific magnetic susceptibility (χLF). SP grains were deposited as early as the late Neolithic, possibly indicating local deforestation associated with the use of fire at that time. We suggest major deforestation in the drainage basin started c. 1.7 cal. ka BP, and intensified after c. 0.8 cal. ka BP when both χLF and χFD show the highest values. We therefore conclude that upland deforestation and cultivation as a result of the migration of human populations from northern China since c. 1.7 cal. ka BP resulted in increased sediment discharge of the Yangtze and played an important role in recent delta construction.

The drivers of risk to water security in Shanghai

Big cities are often said to have big water problems, and Shanghai is no exception. In this paper, we examine and compare the influence of the major factors that give rise to the risk of water insecurity in Shanghai. There is an extensive and diverse literature on these issues, dealt with in isolation, and here, we provide a synthesis of the literature, together with our own assessments and calculations, to assess what are the risks to Shanghai’s water supply and what is our degree of confidence in this assessment. We describe the systems that supply water to the city, and past and future changes in the systems, including changes in the glaciers that supply some water to the river, changes in climate, changes in land use, the construction of dams, and water diversions. We show how, at the same time as Shanghai is increasing its dependence on the Yangtze river, water diversions and sea level rise are increasing the risk that this water will be too saline to consume at certain times of the year. This analysis suggests that most of the major drivers of the risk to water security in Shanghai are within the power of environmental managers to control.

Morphodynamic processes of the Elbe River estuary, Germany: the Coriolis effect, tidal asymmetry and human dredging

The Digital Elevation Model (DEM) based on the historical sea-charts and on-site hydrological records were used to examine the morphological change of the Elbe River estuary. The results show that siltation predominated in the tidal flat in the northern estuary, with a net siltation rate of 1.8 cm·a−1 during 1927–2006. In contrast, a continuous erosion prevailed in the main river channel, south of the estuary, with a net erosion rate of 2.5 cm·a−1 in the same time. In addition, a seaward shift of the estuarine island has happened with the old island coalescing to the northern tidal flat and new one emerging through siltation process. The tidal asymmetry via ebbing flow (maximum at 140 cm·s−1, and average at 76 cm·s−1) prevailed in the tidal flat, meaning continuous aggradation northwestward, while flooding flow (maximum at 100 cm ·s−1, and average at 67 cm·s−1) dominated in the main river channel with deepening thaweg at south, showing a landward sedimentation via the tidal pumping processes. This dextral extension of the estuarine morphology is due to the Coriolis force, leading to the inconsistent directions of in-out flows, which enables to facilitate the estuarine siltation. Human dredging prevailing in the estuary has dramatically altered the nature of the silted river channel to erosional since the last century. This is characterized by a net erosion rate of 3.2 cm·a−1 derived from the DEMs mapping, but only partially accounting for the dredging amount of 1994–2006, when the total dredging volume was 67 × 106 m3, equal to 5.9 cm·a−1.

Constructing Water Shortages on a Huge River: The Case of Shanghai

Abstract Shanghai is located on the world’s third largest river (by volume).Yet it faces therisk of shortages of drinking water. Many decisions and environmental charac-teristics have contributed to this threat. First, Shanghai has become dependent onwater brought into the municipality by rivers. Second, it has become increasinglyreliant on water from the Changjiang (Yangzi River), principally in order tocontrol the levels of pollution in the water that enters its treatment plants. Third,for reasons associated with inter-provincial administrative arrangements, thecity’s water intakes are located within the municipality, within the estuary zoneand subject to tidal intrusions of salt water. Fourth, at high tide and when theChangjiang’s discharge is low, salt intrudes far into the estuary, beyond thecurrent water intakes. If sea levels rise, these intrusions will become more pro-nounced. Fifth, large-scale central government infrastructure projects (such asdams and the South-North Transfer) are altering the hydrological characteristicsof the river. Such projects raise the probability of salt water intrusions into thewater intake zone. The Shanghai and central governments have thus made a seriesof decisions that, taken together, have led the municipality to rely on a source ofdrinking water that is increasingly unreliable and subject to the risk of shortagesdue to salt water intrusions. Why these decisions have been made – independently– is an important problem for those who would understand the provision of waterfor cities and the practical efficacy of Chinese governance systems.KEY WORDS

Innovative Engineering Solutions and Best Practices to Mitigate Coastal Risk

Engineering solutions are widely used for the mitigation of flood and erosion risks and have new challenges because of the expected effects induced by climate change in particular sea level rise and increase of storminess. This chapter describes both active methods of mitigation based on the reduction of the incident wave energy, such as the use of wave energy converters, floating breakwaters and artificial reefs, and passive methods, consisting of increase in overtopping resistance of dikes, improvement of resilience of breakwaters against failures, and the use of beach nourishment as well as tailored dredging operations.Existing coastal management and defense approaches are not well suited to meet the challenges of climate change and related uncertanities. Professionals in this field need a more dynamic, systematic and multidisciplinary approach. Written by an international group of experts, Coastal Risk Management in a Changing Climate provides innovative, multidisciplinary best practices for mitigating the effects of climate change on coastal structures. Based on the Theseus program, the book includes eight study sites across Europe, with specific attention to the most vulnerable coastal environments such as deltas, estuaries and wetlands, where many large cities and industrial areas are located. * Integrated risk assessment tools for considering the effects of climate change and related uncertainties* Presents latest insights on coastal engineering defenses* Provides integrated guidelines for setting up optimal mitigation measures* Provides directly applicable tools for the design of mitigation measures* Highlights socio-economic perspectives in coastal mitigation

Chapter 3 – Innovative Engineering Solutions and Best Practices to Mitigate Coastal Risk

Engineering solutions are widely used for the mitigation of flood and erosion risks and have new challenges because of the expected effects induced by climate change in particular sea level rise and increase of storminess. This chapter describes both active methods of mitigation based on the reduction of the incident wave energy, such as the use of wave energy converters, floating breakwaters and artificial reefs, and passive methods, consisting of increase in overtopping resistance of dikes, improvement of resilience of breakwaters against failures, and the use of beach nourishment as well as tailored dredging operations.Existing coastal management and defense approaches are not well suited to meet the challenges of climate change and related uncertanities. Professionals in this field need a more dynamic, systematic and multidisciplinary approach. Written by an international group of experts, Coastal Risk Management in a Changing Climate provides innovative, multidisciplinary best practices for mitigating the effects of climate change on coastal structures. Based on the Theseus program, the book includes eight study sites across Europe, with specific attention to the most vulnerable coastal environments such as deltas, estuaries and wetlands, where many large cities and industrial areas are located. * Integrated risk assessment tools for considering the effects of climate change and related uncertainties* Presents latest insights on coastal engineering defenses* Provides integrated guidelines for setting up optimal mitigation measures* Provides directly applicable tools for the design of mitigation measures* Highlights socio-economic perspectives in coastal mitigation

Erratum to: Estimating urban water demand under conditions of rapid growth: the case of Shanghai

• On page 4 the first line in the first paragraph should read as follows: of 4.10 9 10 m a. These are located in remote and rural. • On page 4 the second line in the second paragraph should read as follows: supplied 3.12 9 10 m a in 2013, and which are mostly. • On page 4 the numbers on the y axes of both Fig. 1a, b should be reduced by a factor of 10. • On page 4 lines 11 to 16 in the third paragraph should read as follows: period 1978–2013 increased from 0.97 9 10 m a to 3.10 9 10 m a; of this, the water for residential and public open space increased from 0.36 9 10 m a to 1.97 9 10 m a, a fivefold increase and therefore a rate obviously greater than that of industrial water (0.62–1.15 9 10 m a over the same period) (Fig. 1a). • On page 4 lines 20 and 21 in the third paragraph should read as follows: water pumping grew from 1.17 9 10 m a in 1978 to 4.10 9 10 m a in 2013 (Fig. 1b). • On page 6 the numbers on the y axis of Fig. 5 should be reduced by a factor of 10. The online version of the original article can be found under doi:10.1007/s10113-016-1100-6.