Iverson R.M.,U.S. Geological Survey |
Ouyang C.,CAS Chengdu Institute of Mountain Hazards and Environment
Reviews of Geophysics | Year: 2015
Earth-surface mass flows such as debris flows, rock avalanches, and dam-break floods can grow greatly in size and destructive potential by entraining bed material they encounter. Increasing use of depth-integrated mass and momentum conservation equations to model these erosive flows motivates a review of the underlying theory. Our review indicates that many existing models apply depth-integrated conservation principles incorrectly, leading to spurious inferences about the role of mass and momentum exchanges at flow-bed boundaries. Model discrepancies can berectified by analyzing conservation ofmass and momentum in a two-layer system consisting of a moving upper layer and static lower layer. Our analysis shows that erosion or deposition rates at the interface between layers must, in general, satisfy three jump conditions. These conditions impose constraints on valid erosion formulas, and they help determine the correct forms of depth-integrated conservation equations. Two of the three jump conditions are closely analogous to Rankine-Hugoniot conditions that describe the behavior of shocks in compressible gasses, and the third jump condition describes shear traction discontinuities that necessarily exist across eroding boundaries. Grain-fluid mixtures commonly behave as compressible materials as they undergo entrainment, because changes in bulk density occur as the mixtures mobilize and merge with an overriding flow. If no bulk density change occurs, then only the shear traction jump condition applies. Even for this special case, however, accurate formulation of depth-integrated momentum equations requires a clear distinction between boundary shear tractions that exist in the presence or absence of bed erosion. © 2014. American Geophysical Union. All Rights Reserved.
Fang Y.,CAS Chengdu Institute of Mountain Hazards and Environment |
Deng W.,CAS Chengdu Institute of Mountain Hazards and Environment
Energy | Year: 2011
Cascade hydropower exploitation (CHE) has become an inevitable trend of global hydropower development in the future, and also China's basic policy on hydropower exploitation. Most of works so far focus on the accumulated effects caused by CHE, but the systematic assessment of the security scale of CHE as well as section management according to different rivers and different sections of one same river is seriously lacking. This article selectively analyses the process, section management linkage, section control scale of CHE based on existing literatures review and cases experiment in Southwestern China. Remarked conclusions include: (1) The river health is the central issue for sustainable exploitation of the river and integrated management of the river basin, instream flow requirements in different sections of the river should be met first; it is the key scientific basis for CHE to determine the maximum scale and reference standard of hydropower exploitation in each river section according to the minimum ecological flow. (2) Three management issues of CHE should be emphasized: to integrate special cascade hydropower planning with river section planning, under integrated planning of river basin; to regulate the existing management system for CHE; to balance stakeholder's interest and benefit in exploitation decision-making. (3) The security scale of CHE on different rivers and different sections of one same river should be measured by three reference scales, i.e., the critical scale of CHE based on the minimum ecological flow, the critical scale of CHE based on per unit river fall and per unit flow, and by combinations of the three reference scales. © 2011 Elsevier Ltd.
Peng S.,CAS Chengdu Institute of Mountain Hazards and Environment |
Peng S.,University of Chinese Academy of Sciences |
Guo T.,Southwest University |
Liu G.,CAS Chengdu Institute of Mountain Hazards and Environment
Soil Biology and Biochemistry | Year: 2013
Soil aggregation is a crucial soil property that affects a wide range of physical and chemical processes in soil ecosystems. Arbuscular mycorrhizal (AM) association is recognised as an important promoter of soil aggregation through the action of individual roots, mycelia and an insoluble, glue-like and hydrophobic proteinaceous substance, which is (at least partly) of AM fungi origin, named glomalin-related soil protein. Considering the increasing application of commercial AM inoculants, we addressed how the soil aggregates respond to the hyphal functions of AM inoculation in the field with a resident AM community.To this end, we introduced a new system in which the hyphae were separated by mesh and regular rotation to break the ingrowing hyphae as a control and to demonstrate the causal link between the hyphae and soil aggregates under conditions simulating natural parameters. The results showed the following: (i) the hyphal length was positively correlated with the mean weight diameter (r = 0.384, P < 0.05), geometric mean diameter (r = 0.257, 0.05 < P < 0.10) and easily extractable glomalin (r = 0.296, P < 0.05); (ii) the colonisation rate of the roots in the cores was increased by constantly severing the extraradical mycelium and (iii) the colonisation rate of the control plant roots (approx. 10%) was significantly lower compared to those inoculated with AM fungi (ranging from 34% to 54%). It was concluded that the hyphal networks of AM inoculations can promote the formation and stability of soil aggregates under conditions that closely simulate those occurring in nature. © 2012 Elsevier Ltd.
Fang Y.,CAS Chengdu Institute of Mountain Hazards and Environment
Ambio | Year: 2013
The three-rivers headwater region (THRHR) of Qinghai province, China plays a key role as source of fresh water and ecosystem services for central and eastern China. Global warming and human activities in the THRHR have threatened the ecosystem since the 1980s. Therefore, the Chinese government has included managing of the THRHR in the national strategy since 2003. The State Integrated Test and Demonstration Region of the THRHR highlights the connection with social engineering (focus on improving people's livelihood and well-being) in managing nature reserves. Based on this program, this perspective attempts a holistic analysis of the strategic role of the THRHR, requirements for change, indices of change, and approaches to change. Long-term success of managing nature reserves requires effective combination of ecological conservation, economic development, and social progress. Thus, the philosophy of social engineering should be employed as a strategy to manage the THRHR. © 2013 Royal Swedish Academy of Sciences.
Liu E.,University of Sichuan |
He S.,CAS Chengdu Institute of Mountain Hazards and Environment
Engineering Geology | Year: 2012
A series of laboratory tests were performed to assess the effects of confining pressure on the mechanical properties and fatigue damage evolution of sandstone samples subjected to cyclic loading. Six levels of confining pressure (2.0, 10.0, 20.0, 30.0, 40.0 and 50.0. MPa) were applied during axial cyclic loading at a 1.0. Hz frequency using a MTS-815 Rock and Concrete Test System. Results from the cyclic dynamic loading tests indicated that the level of confining pressure had a significant influence on the cyclic dynamic deformation and fatigue damage evolution of the sandstone samples tested. With increasing confining pressure, the axial strain at failure increased, as did the residual volumetric strain at the initiation of dilatancy. The residual axial strains of sandstone samples obtained at a confining stress state can be described as three deformational stages, namely, the initial phase, uniform velocity phase and accelerated phase. Both the residual strain method and the axial secant modulus method proposed here could be used to describe the initial fatigue damage and degradation process of sandstone samples subjected to fatigue loading under a confining stress state; however, the latter also considers the influence of stress level on fatigue damage evolution when fatigue loads are applied. At a constant confining pressure, the shear fracture plane can form under static and cyclic dynamic loading conditions, and the higher the confining pressure, the wider the shear fracture planes become under cyclic dynamic loadings. © 2011 Elsevier B.V.
Jin X.,CAS Chengdu Institute of Mountain Hazards and Environment |
Xu C.-Y.,University of Oslo |
Zhang Q.,CAS Nanjing Institute of Geography and Limnology |
Singh V.P.,Texas A&M University
Journal of Hydrology | Year: 2010
Quantification of uncertainty of hydrological models has attracted much attention in hydrologic research in recent years. Many methods for quantification of uncertainty have been reported in the literature, of which GLUE and formal Bayesian method are the two most popular methods. There have been many discussions in the literature concerning differences between these two methods in theory (mathematics) and results, and this paper focuses on the computational efficiency and differences in their results, but not on philosophies and mathematical rigor that both methods rely on. By assessing parameter and modeling uncertainty of a simple conceptual water balance model (WASMOD) with the use of GLUE and formal Bayesian method, the paper evaluates differences in the results of the two methods and discusses the reasons for these differences. The main findings of the study are that: (1) the parameter posterior distributions generated by the Bayesian method are slightly less scattered than those by the GLUE method; (2) using a higher threshold value (>0.8) GLUE results in very similar estimates of parameter and model uncertainty as does the Bayesian method; and (3) GLUE is sensitive to the threshold value used to select behavioral parameter sets and lower threshold values resulting in a wider uncertainty interval of the posterior distribution of parameters, and a wider confidence interval of model uncertainty. More study is needed to generalize the findings of the present study. © 2010 Elsevier B.V.
Cui P.,CAS Chengdu Institute of Mountain Hazards and Environment |
Lin Y.-M.,China Agricultural University |
Chen C.,China Agricultural University
Ecological Engineering | Year: 2012
Geo-hazards induced by earthquakes have caused ecosystem degradation and vegetation destruction. Little, however, is known about the consequences of geo-hazards due to a lack of research data. We have undertaken a study in the Wenchuan earthquake-affected area of China in order to identify and characterize vegetation destruction and its consequent environmental impact. The Wenchuan earthquake on 12th May, 2008 induced numerous geo-hazards (including rock avalanches, landslides, landslide-dammed lakes and debris flows) that caused vegetation destruction up to 1249.5km 2, of which shrub comprised the largest proportional area with 338.559km 2. The vegetation coverage decreased by 4.76% in 9 severely damaged cities and counties and by 12.37% in the Subao river, Beichuan county. Rock avalanches and landslides were the most common destructive types, resulting in 98.73% of all types of geo-hazards, whereas debris flows and landslide-dammed lakes accounted for 1.27%. Vegetation destruction was distributed along both sides of rivers causing erosion, formation of debris flows and landslides. Hydrologic progress was changed and hydrological adjusting function diminished due to vegetation deterioration resulting in bare rock (infiltration reduced, runoff increased and flow concentration expedited) and deposit region (infiltration increased and runoff reduced) in catchment. Soil erosion was intensified causing increased sediment transportation of rivers, decreased storage capacities of reservoirs downstream, a significantly increased area that has suffered severe erosion and aggravated magnitude and damage capability of debris flows and landslides. Ecosystem function declined and vegetation restoration and reconstruction was difficult due to co-degradation of vegetation-soil system in the earthquake-affected areas. Finally, we summarized the challenges faced in the future for vegetation restoration and reconstruction. © 2012 Elsevier B.V.
Fang Y.-P.,CAS Chengdu Institute of Mountain Hazards and Environment
Journal of Mountain Science | Year: 2013
The interaction among different livelihood capitals is a key to generate a deeper understanding of the livelihood sustainability. In this paper, we use net income per capita (economic capital), meat and milk production per capita (physical capital), and areas of fenced pasture, livestock shelter, grassland rodent control and planted grassland (physical capital) as proxy indicators of livelihood promotion, livelihood provision, and livelihood protection respectively. By developing a correlation model between pastoralists' livelihood protection and improvement, we found that (1) there is a statistically significant correlation between the pastoralists' livelihood protection and promotion; (2) based on the maximum effect of pastoralists' livelihood promotion and provision, there is a benchmark in the effect of the intervention intensity of livelihood capital (grassland resource protection) on livelihood improvement; (3) on basis of two indicators, i.e. net income per capita and meat production per capita, the reasonable scales of fenced pasture, livestock shelter and planted grassland are less than 843, 860 and 46 thousand hectares (hm2) per year respectively. With the marginal effect of livelihood protection, moderately decreased areas of fenced pasture and planted grassland, and increased area of livestock shelter is a critical to ensure pastoralist's livelihood sustainability. © 2013 Science Press, Institute of Mountain Hazards and Environment, CAS and Springer-Verlag Berlin Heidelberg.
Fang Y.-F.,China Three Gorges University |
Ma W.-H.,China Three Gorges University |
Huang Y.-P.,China Three Gorges University |
Cheng G.-W.,CAS Chengdu Institute of Mountain Hazards and Environment
Chemistry - A European Journal | Year: 2013
The band structure of multicomponent semiconductor photocatalysts, as well as their reactivity distinction under different wavelengths of light, is still unclear. BiOBr, which is a typical multicomponent semiconductor, may have two possible valence-band structures, that is, two discrete valence bands constructed respectively from O 2p and Br 4p orbitals, or one valence band derived from the hybridization of these orbitals. In this work, aqueous photocatalytic hydroxylation is applied as the probe reaction to investigate the nature and reactions of photogenerated holes in BiOBr. Three organic compounds (microcystin-LR, aniline, and benzoic acid) with different oxidation potentials were selected as substrates. Isotope labeling (H2 18O as the solvent) was used to determine the source of the O atom in the hydroxyl group of the products, which distinguishes the contribution of different hydroxylation pathways. Furthermore, a spin-trapping ESR method was used to quantify the reactive oxygen species (.OH and .OOH) formed in the reaction system. The different isotope abundances of the hydroxyl O atom of the products formed, as well as the reverse trend of the .OH/.OOH ratio with the oxidative resistance of the substrate under UV and visible irradiation, reveal that BiOBr has two separate valence bands, which have different oxidation ability and respond to UV and visible light, respectively. This study shows that the band structure of semiconductor photocatalysts can be reliably analyzed with an isotope labeling method. Which isotope won? Hydroxylation in the BiOBr photocatalytic system with H2 18O solvent and 16O2 oxidant gives products with different isotope profiles under visible-light versus UV irradiation (see scheme). The isotope abundance is also affected by the oxidative resistance of the substrate. Together with the .OH/ .OOH ratio, the results show that BiOBr has two valence bands that have different oxidation abilities and responses to UV and visible light. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Jiang Y.-J.,CAS Chengdu Institute of Mountain Hazards and Environment |
Towhata I.,University of Tokyo
Rock Mechanics and Rock Engineering | Year: 2013
Shallow slope failure in mountainous regions is a common and emergent hazard in terms of its damage to important traffic routes and local communities. The impact of dry granular flows consisting of rock fragments and other particles resulting from shallow slope failures on retaining structures has yet to be systematically researched and is not covered by current design codes. As a preliminary study of the impact caused by dry granular flows, a series of dry granular impact experiments were carried out for one model of a retaining wall. It was indirectly verified that the total normal force exerted on a retaining wall consists of a drag force (F d), a gravitational and frictional force (F gf), and a passive earth force (F p), and that the calculation of F d can be based on the empirical formula defined in NF EN Eurocode 1990 (Eurocode structuraux. Base de calcul des structures, AFNOR La plaine Saint Denis, 2003). It was also indirectly verified that, for flow with Froude number from 6 to 11, the drag coefficient (C d) can be estimated using the previously proposed empirical parameters. © 2012 Springer-Verlag.