查看更多>>摘要：Japan recently introduced a feed-in tariff for small-scale hydropower plants, promoting the development of run of-river hydropower plants in small-sized basins; however, appropriate implementation requires gauging station streamflow data at substantial costs and time (i.e., more than several years). Thus, in this study, we generated streamflow maps for small-sized basins (~10 km(2)) throughout Japan using artificial neural networks (ANNs). Modeled output streamflow characteristics relied upon the input variables obtained from 176 basin characteristics and consisted of mean annual streamflow (Q(MEAN)), daily streamflow indices in a flow duration curve (Q(D)), and a water volume index for run-of-river hydropower energy production (W-D95). We preliminarily investigated the impacts of selecting the input variables obtained from 176 basin characteristics on performances of the ANNs, which indicated that the ANNs showed high robustness for disinformative input variables and multicollinearity between input variables. Although Q(MEAN), high Q(D), and W-D95 performed well, low Q(D) were inadequate, possibly due to snowmelt contributions and small catchment sizes obstructing the detection of geological impacts. To accurately estimate the streamflow characteristics throughout Japan, we emphasize the importance of developing robust methods for correcting wind-induced precipitation undercatch and a spatial interpolation for precipitation in high-montane areas. Nevertheless, the ANNs for Japan proposed herein significantly outperformed a previous study exhibiting excellent global-scale ability. A map expressing run-of-river hydropower potential in small-sized basins was generated and closely corresponded to the spatial distribution and electrical output of existing hydropower plants. Furthermore, we demonstrated that the hydropower potential map reproduces the hydropower developments corresponding to the history of the electric power systems in Japan, which reflects its high reliability. Therefore, the hydropower potential map can greatly aid the exploration of optimal sites for hydropower developments.
查看更多>>摘要：Vulnerability analysis is crucial to assess natural hazard risk. Methods for vulnerability assessment include indices as well as vulnerability curves. Vulnerability curves make use of empirical data to show the relationship between the process intensity and the resulting degree of loss on each affected building whereas vulnerability indices are based on a number of indicators representing building characteristics and their surroundings. In the present paper, damage data from two relatively recent torrential events in the European Alps are used to compare results using a vulnerability curve (Beta model) and a physical vulnerability index (PVI). Following the appli-cation of both methods, their strengths and weaknesses are outlined. Vulnerability curves constitute a valuable quantitative method for the assessment of physical vulnerability but, in the present study, they tend to over-estimate damages. On the other hand, vulnerability indices better support the understanding of local-scale damage patterns but they require detailed data and further research on weighting and indicator selection. The study leads to the conclusion that both methods complement each other providing better insights into the physical vulnerability of buildings exposed to torrential hazards. Furthermore, uncertainties associated with the two approaches are related to the required data. Therefore, a sensitivity analysis is carried out showing that process intensity is a key variable for the assessment of vulnerability, whereas, differences in the calculation of the degree of loss based on different building values are less important. Finally, the paper gives clear recom-mendations for improved event and damage documentation and provides an outlook on future needs in vulnerability assessment, including constant updating of both methods based on recent events.
查看更多>>摘要：Identifying the influence of seasonal source water on tree growth is essential to understand the effect of climate change on forest dynamics. However, due to the lack of available long-term monitoring studies, little is known on how long moisture originating from winter precipitation influences tree growth in the following growing season. Herein, we developed a tree-ring latewood oxygen isotope (delta O-18(LW)) chronology from the Karakoram (1955-2013) in northern Pakistan. We investigated whether winter climate signals are incorporated in the delta O-18(LW) and how long winter precipitation through soil moisture contributed to tree growth during the growing season. Significant correlations were found between delta O-18(LW) with both, winter to spring (January-May) temperature (r = 0.43, p < 0.05) and summer (July-August) precipitation (Local: r =-0.38, p < 0.05; Moisture source region: r =-0.44, p < 0.05). As shown by the cross-spectrum and commonality analysis, the climate signals in the delta O-18(LW) are frequency-dependent. Winter temperature signals stored in the delta O-18(LW) variations dominate at low frequencies more than 7 years (59% variance explained), while the summer precipitation signals dominate variations with higher frequencies shorter than 7 years (47% variance explained). Further analysis using reanalysis data shows that the growing season soil moisture at root depth (10-40 cm) is more strongly related to winter precipitation than to summer rainfall. Winter precipitation formed as ground snow provides root-zone soil moisture and tree growth via snowmelt during the growing season. Our study highlights that winter precipitation is the dominant water source contributing to Karakoram tree growth until the late growing season. Given the possibility of a decrease in winter precipitation under climate change in the Karakoram region, local forest is potentially threatened by the declining water supply during the growing season.
查看更多>>摘要：Covering the soil surface with mulch is a cropland management practice that can provide several benefits to the soil environment, especially in rainfed systems. Soil mulching tends to enhance plant growth by reducing soil evaporation and potentially increasing transpiration, but its effectiveness vary widely across rainfall regimes and mulching materials. Here we investigate this variability using a process-based modeling framework coupling the dynamics of soil and mulching moisture and of crop growth. Supported by field observations under different mulching materials, we study the effectiveness of soil mulching in increasing transpiration and growth under different rainfall regimes and mulching layer thickness. The analysis suggests that in most rainfall scenarios soil mulching can increase plant transpiration by up to 100% and reduce soil evaporation by up to 40%. However, there exist rainfall conditions (low frequency and high intensity) under which soil mulching may cause lower transpiration. We also show that soil mulching is particularly beneficial during a dry spell, a phenomenon that is projected to occur more frequently in many climatic zones. In the event of a dry spell during the growing season, soil mulching helps maintain moist conditions for longer, hence limiting the negative effects on plant transpiration and growth. The analysis helps better understand the role of soil mulching on transpiration and crop growth and provides important information for improving soil mulching depending on mulching material and the site-specific rainfall regime.
查看更多>>摘要：Reservoir ecological operation creates artificial hydrological and hydrodynamic conditions to meet the demand of fish during key life periods, which provides eco-environmental protection to alleviate the negative impact of hydropower development on ecosystems. However, based on practical ecological operation experience, the flow experiments were rough in terms of plan design, most of which were implemented over short time frames, and circumstances where downstream flow conditions existed were inconsistent with fish requirements during periods affected by different local reservoir operation conditions. This finding suggests that current ecological operations leave considerable space for strategy refinement. This study proposed a methodology for designing refined operation strategies incorporating more ecological demands into reservoir operation releases to create and improve suitable ecological conditions for the spawning of representative fish species. A joint water quantity operation model of cascade reservoirs and an under dam-river hydrodynamic model coupling the operation conditions of hydroelectric generators was built. The proposed methodology was applied to the Three Gorges Dam (TGD) and Gezhouba (GZB) Dam cascade reservoirs in China. The simulation results indicated that (1) in most cases, the target of continuous flow increase on an hourly scale could be simply accomplished via hourly joint water quantity operation of TGD-GZB cascade reservoirs. (2) Maintenance of the average Dajiang and Erjiang generator output during the spawning period of Chinese sturgeon at a high outflow of 15000 m3/s could more effectively expand the integrated suitable space of Chinese sturgeon. We aimed to provide suggestions and references suitable for cascade reservoirs in China and worldwide to develop and optimize ecological operation conditions in more refined and diverse ways.
查看更多>>摘要：A marginal gas injection method was previously proposed based on two-dimensional (2-D) homogeneous porous media, and the feasibility of isolating the oil shale pyrolysis zone from the surrounding hydrological environment had been demonstrated. The gas-water flow characteristics and dynamics during gas injection in 2-D porous media with a high-permeability zone (HPZ) were studied further based on the presence of a HPZ after fracturing oil shale reservoirs. A series of experiments were performed when the gas-injection point was located outside, at the boundary, or inside the HPZ (Case1-3). The HPZ enriched the injected gas, and in Cases 2 and 3, the gas inside the HPZ permeated to the low-permeability zone (LPZ) on both sides, forming two wing tributaries. However, in Case 1, water flowed into the HPZ in the opposite direction. In Cases 2 and 3, the direction of the local pressure gradient on both sides of the HPZ was completely opposite, indicating that the distribution of the pressure field was the direct cause of the gas-water flow characteristics. Therefore, the water-stopping effect of gas injection is primarily reflected in the HPZ. Additionally, the effect was best when the gas-injection point was set at the boundary or inside of the HPZ. These results were verified using reservoir-scale simulations and tests, in which the water yield decreased to ~ 100 kg/d. Subsequently, we recommended the sites of gas-injection wells for water stopping. All results are expected to provide strategies and theories for dealing with the adverse hydrological environment in large-scale oil shale in situ exploitation.
Vadibeler, DevakunjariStockinger, Michael P.Wassenaar, Leonard I.Stumpp, Christine...
9页
查看更多>>摘要：The hydrogen and oxygen stable isotopes of water ((SH)-H-2 and (SO)-O-18) are powerful tracers for studying subsurface water flow processes, but the extraction of porewater from unsaturated soil is complex and laborious. The direct liquid-vapor equilibration method (DLVE) for isotope analysis overcomes this challenge by analyzing headspace vapor in isotopic equilibrium with the porewater under closed system conditions. However, the effect of the equilibration time, soil texture, and porewater saturation on isotopic results is not fully understood yet. We tested three differently textured, disaggregated soils (sandy, silty loam and clay) to assess how the equilibration time is impacted by (i) porewater saturation (100%, 80%, 60%, and 40%), and (ii) soil surface area. For all tests, the water loss through diffusion was negligible (< 0.3%). The experiments showed that for disaggregated sandy soil, 24 h was a sufficient isotopic equilibration time regardless of water saturation level. Similarly, 24 h was sufficient for kaolinite samples with 100% saturation exhibiting little isotopic variance even after 168 h of equilibration. For saturated silty loam with 2% organic carbon content, 96 h was the optimal equilibration time, whereas saturated silty loam with 4% organic carbon content did not reach isotopic equilibrium by 168 h. The optimal equilibration time increased depending on whether soil samples were disaggregated or kept in a core cutter. Inconclusive results for silty soils with organic carbon revealed the need to further investigate the possible in-fluence of organic carbon on the DLVE method.
查看更多>>摘要：Advance forecast of water inrush can help ensure operational safety in underground engineering. In this study, a coupled thermal-hydraulic-mechanical (THM) model is developed to simulate the process of water inrush from collapse columns in coal mines with complex geological environments. Specifically, nonlinear fluid flow and heat transfer in porous media associated with the erosion and damage of collapse columns are considered. This numerical model is validated against water-inrush field data from two coal mines with regard to flow rate. Fluid pressure and temperature profiles over time are also investigated. There is a water pressure accumulation phenomenon in hidden collapse columns. Temperature is found to change more significantly than velocity in the early stages of water inrush. In addition, the spatial variation of temperature can be divided into three zones during the process of water inrush. According to the rules governing the spatio-temporal variation of temperature, a novel method utilizing a real-time monitoring temperature-dependent risk index (TRI) and a water inrush induced increasing temperature zone (WIT) is proposed to determine whether and where water inrushes will occur. This study demonstrates how this novel method can predict water inrush and overcome the main limitations in previous studies where temperature was used as a predictor. This method has the potential to be applied in practice to better understand the risks related to coal mine management and water inrush and thus improves mine safety.
查看更多>>摘要：Excessive anthropogenic nutrient input has resulted in eutrophication and algal blooms which have severely impacted the function and sustainability of aquatic ecosystems, underscoring the need to implement nutrient management strategies. It was assumed that the increasing rainfall during flood season would affect the stoichiometric ratio of total nitrogen (TN): total phosphorus (TP), driving the nutrient limitation of algal growth. In order to test this concept and explore corresponding nutrient management strategies, nutrient addition bioassays were carried out in Xiangxi Bay, one of the largest tributaries of the Three Gorges Reservoir (TGR), China. Results indicated that nutrient limitation on algal growth fluctuated from nitrogen (N) to phosphorus (P) limitation. N limitation dominated in the early flood season. However, the reduction of dissolved P, accompanied with an increase of TN: TP caused by an increase in extreme rainfall events intensified P limitation throughout the bay. Then P limitation was alleviated due to the reduction of rainfall and the process of impoundment after the flood season. The variation of TN: TP caused by the increasing of rainfall and flooding could be the main driving factor of the nutrient limitation shift in aquatic ecosystems mainly affected by external nutrient inputs. Nutrient dilution and enrichment bioassays showed that TN and TP concentration thresholds should be targeted at below 0.55 mg/L and 0.057 ~ 0.064 mg/L respectively, to limit the growth of algae and maintain chlorophyll a below 30 mu g/L. Dual nutrient (N & P) reductions were required for long-term bloom mitigation in the entire basin. This study provided a scientific basis for a nutrient management strategy to combat eutrophication and reduce algal bloom potentials in the tributaries of the TGR. We recommend that long-term determinations of nutrient limitation and nutrient threshold will be needed to control algal growth, considering future anticipated changes in land use, population density and the impacts of climate change.
查看更多>>摘要：In recent decades, water levels in many closed inland lakes over north-western China experienced severe declines, among which the Daihai Lake in Inner Mongolia, China was particularly significant. Remotely sensed investigations indicated that the Daihai Lake had shrunk approximately 64% in an area with the dramatic decline of water level approximately 9 m from the 1980 s to 2010 s, which has caused serious concern on the sustainable development of the surrounding region. Consequently, several previous studies have concentrated on the possible causes of lake shrinkage. However, predicting climate variability and anthropogenic activities' relative contributions to lake water decline is challenging due to the lack of direct water consumption upstream and watershed-scale natural runoff observations. In this paper, a hydrological modeling approach was presented to quantitatively evaluate and separate the relative contributions of climate variations and intensifying anthropogenic activities. The simulation accuracy was evaluated through comparisons with observed data and cross validation with previous studies. Based on a baseline period, the natural streamflow draining into the lake was reconstructed using the model. The results revealed that the water loss of the Daihai Lake was caused predominately by human activities rather than climate variability. Specifically, for wet conditions, the climate factors posed a negative effect on the water level decline of the lake and delayed the shrinking process of the lake area. The anthropogenic factors took a dominant role (roughly 58%) of lake shrinkage at the annual average scale for normal and dry conditions, while the climate factors accounted for approximately 42%. Hence, the rational policy for water resource management, ecological restoration, and dam and reservoir constructions/ operations should be the essential precautions for sustainable development of the Daihai Lake and its surroundings. Additionally, the hydrological modeling approach adopted in this investigation serves as a useful example of the quantitative assessment of climate variations and human activities, especially for the ungauged catchments.
NSTL
Elsevier