查看更多>>摘要：Debris flow in or towards water bodies, and bed load transport in open channels manifest from the interaction of fluid with deformable granular media at varied spatiotemporal scales. The present study aims to formulate a robust two-dimensional coupled depth-averaged framework for simulation of submarine deformation of non-cohesive granular media and the corresponding effect on water and the otherwise. The unified framework consisting of conditional hyperbolic set of partial differential equations has been conceptualized as two con-current yet independent systems interacting through source/sink terms comprising of drag force, shear and water-surface gradient. The system is solved on a regular finite volume grid through a robust modification of the Harten-Lax-Van Leer (HLL) scheme. The interaction terms are embedded into the interfacial fluxes, where additional closure employs the effect of dry-wet zone transition and flow arrest for both modules. Various aspects of the proposed framework are validated against an array of test cases ranging from landslide induced tsunami to dambreak induced scour. The last representative scenario emphasizes the potential applicability of the model for real-time extension to field-scale problems. A few one-dimensional approximations are explored in the Appendix to calculate relative velocity between interstitial fluid and granular media for computation of drag force.
查看更多>>摘要：The headwater catchment of the Yellow River Basin (HCYRB) controls 35% of the streamflow of the Yellow River (YR) which faces increasing water shortages. To better understand streamflow variability in the region we require a better understanding of high and low flow characteristics. This study presents a new annual (Nov-Oct) streamflow reconstruction at the Tangnaihai station in the HCYRB for the last two millennia (159-2016 C.E.) using 12 tree-ring chronologies. The nested principal component regression model combined with the stepwise best subset selection method was proposed to improve the temporal length and model skill of reconstruction. The stepwise best subset selection method was presented to select the best principal components subset, instead of a confidence test, based on k-fold cross-validation error and Akaike's information criteria (AIC). The model assessment results verify that the proposed model exhibits strong reconstruction skills. Besides, the magnitude and duration of both high and low flow periods were analyzed. The results show that (1) the significant high-flow periods are the early 3rd century, circa 300 C.E., early 13th century, 16th century and circa 1900 C.E., while the low-flow periods are the late 5th century and late 15th century; (2) the durations and magnitudes of low-flow periods are longer and larger than high-flow periods and the severities of high-flow periods are greater than low-flow periods. The reconstruction also suggests that a warm climate is more likely accompanied by a highflow period and low-flow periods are more likely to occur in cold periods associated with the Asian Summer Monsoon and solar activity.
查看更多>>摘要：Baseflow is paramount to sustain the ecological integrity of river catchments. Identifying baseflow characteristics and influencing factors can facilitate the understanding of the water budget of catchments. In this study, a revised one parameter digital filter was used to separate baseflow from total daily streamflow in 18 mountainous catchments around the North China Plain (NCP). Nine baseflow signatures (BSs) including Baseflow Index (BFI), the five-distribution signature (with the representative percentiles Q(b1) Q(b33) Q(b50) Q(b66) Q(b99), respectively), and the three-dynamics signature (seasonality ratio, SR; concavity index, CI; and slope of the baseflow duration curve, S-BDC) were used to assess the baseflow hydrological behaviour (i.e., seasonality, stability, and sensitivity). Our findings showed (1) an apparent spatial pattern for most baseflow signatures (except for Q(b1)), but no particular temporal variation in the studied catchments, (2) that summer precipitation, evapotranspiration, soil texture, vegetation, and geomorphic factors (i.e., elevation and slope) were the main factors influencing the variation of baseflow, (3) that winter dominated baseflow was associated with the karst geological distribution, and (4) that Q(b50), Q(b66), Q(b99) and CI were good predictors to estimate the BFI (R-2 = 0.756). This study analysed the baseflow signature behaviour of mountainous catchments and provided insights into the hydrological processes related to baseflow.
Shamseldin, Asaad Y.Melville, Bruce W.Hendi, Ehsan
14页
查看更多>>摘要：The effects of inlet configurations in sediment retention ponds (SRPs) have been widely investigated by several researchers. However, when considering temperature differentials in the ponds where density and buoyancy change with temperature the challenges associated with the proper inlet design still exist. The buoyancy forces are generated due to the differences in temperature potentially changing the flow in the pond by forming density currents. This study evaluates the effects of different inlet width ratios (IWRs) on the flow pattern and residence time in a sediment retention pond when inflow is colder or hotter than the water in the pond. In this research, an innovative experimental setup was used to create the temperature differentials. The results in the present study show that when the inflow temperature is colder than the water temperature in the pond, increasing the inlet width to the full pond width can effectively increase the pond's performance. Likewise, when the inflow temperature is hotter than the water temperature in the pond decreasing the inlet width to 30% of the pond width can successfully improve the performance of the pond.
查看更多>>摘要：Land subsidence is a geological process mainly caused by groundwater overdraft. Numerical modeling of land subsidence is the main method used for its simulation and prediction. The elastic skeletal storage coefficient (S-ke), inelastic skeletal storage coefficient (S-kv), and the related specific values (S-ske and S-skv) are fundamental parameters to quantify land subsidence. In this paper, a novel approach integrating fast independent component analysis (Fast-ICA) with variable preconsolidation head decomposition method is proposed to disentangle S-ske and S-skv at various depth and over time from piezometric and extensometer records. The proposed method is applied to areas affected by severe land subsidence in the North China Plain (Tianzhu, Pinggezhuang and Cangzhou stations). The elastic and inelastic parameters of the aquifer systems are quantified at different depths. It is found that S-ske and S-skv decrease with depth. The finer the sediment grain size is, the smaller of the ratio S-ske/S-skv. Moreover, S-ke remains almost unchanged over time, while Sky decreases as compaction and land subsidence increase.
查看更多>>摘要：Permeability is one of the most important properties in subsurface flow problems, which measures the ability of rocks to transmit fluid. Normally, permeability is determined through experiments and numerical simulations, both of which are time-consuming. In this paper, we propose a new effective method based on convolutional neural networks with physical information (CNNphys ) to rapidly evaluate rock permeability from its three-dimensional (3D) image. In order to obtain sufficient reliable labeled data, rock image reconstruction is utilized to generate sufficient samples based on the Joshi-Quiblier-Adler method. Next, the corresponding permeability is calculated using the Lattice Boltzmann method. We compare the prediction performance of CNNphys and convolutional neural networks (CNNs). The results demonstrate that CNNphys achieves superior performance, especially in the case of a small dataset and an out-of-range problem. Moreover, the performance of both CNN and CNNphys is greatly improved combined with transfer learning in the case of an out-of-range problem. This opens novel pathways for rapidly predicting permeability in subsurface applications.
查看更多>>摘要：Wetland ecosystems have experienced dramatic challenges in the past few decades due to global climate change and human activities. Wetland maps are essential tools for conservation and management of terrestrial ecosystems. The objective of this study was to obtain an accurate wetland map using a parcel-level ensemble method based on Sentinel-1 SAR time series and segmentations generated from GF-6 MPS images. The Dongting Lake wetlands in China, which has a heterogeneous landscape, was deliberately chosen as a challenging case study. First, both VV and VH polarization backscatters (00 VV, 00 VH) were generated from time series Sentinel-1 SAR. Speckle noise inherent in SAR data can affect the performance on image segmentation by resulting in over segmentation or under-segmentation, and that will degrade the accuracies of wetland classification. Subsequently, optical data (Gaofen-6), which is effectively capable of delineating meaningful parcels, were applied to get the segmentations in this study. Finally, the ensemble method was utilized to extract the wetland information at parcel-level. The overall accuracy and Kappa coefficient of the object-based ensemble method are 90.58% and 0.88, which are 4.25% and 0.04 higher than that of the pixel-based method, respectively. Moreover, the object based ensemble method for classification in high heterogeneity areas is superior and can greatly improve the performance compared with single classifiers.
Wang, FenfangXiao, KaiSantos, Isaac R.Lu, Zeyang...
11页
查看更多>>摘要：Coastal wetlands regulate nutrient fluxes from the continents to the oceans. Salt marshes are rapidly encroaching into mudflat area in mangrove wetlands, shaping a mangrove-salt marsh ecotone, with unknown implications to coastal biogeochemical cycles. Here, we hypothesized that nitrogen and phosphorus cycling varied in mangrove and salt marsh, having significant implication on coastal waters. We investigated a tidal creek with a marked mangrove-salt marsh gradient in China using high-frequency time-series sampling of dissolved nutrients and observations of porewater exchange rate across the sediment-water interface over a spring-neap tidal cycle. The nitrogen transformation rates and microbiological activities were also investigated to explain the variability in nitrogen concentrations. The mangrove had net groundwater outflow rates of 3.6-4.3 mm d(-1) while the salt marsh had net infiltration of surface water with rates of 0.5-2.9 mm d(-1). Salt marsh had less capacity for ammonium (NH4-N) production (mineralization and dissimilatory nitrate reduction to ammonium DNRA) than mangrove. Denitrification dominated nitrogen removal reaching 97% and 83% in mangrove and salt marsh, respectively. Microbe distributions were consistent with nitrogen transformations with larger nirS and nrfA abundances for denitrification and DNRA in the mangrove than salt marsh. The mangrove had a net export of NH4-N but a net import of NOx-N (sum of nitrate and nitrite) and dissolved inorganic phosphorus (DIP) during the monitoring period. In contrast, the salt marsh had lower efflux of nutrient than influx leading to a net nutrient import during the monitoring period. Porewater released from the mangrove had a large DIN:DIP mole ratio (706 +/- 236) due to high NH4-N concentrations, while NH4-N in the salt marsh were lower than in the mangrove. Overall, this study revealed that mangrove-salt marsh ecotone will push the native mangrove wetlands from being a source towards a sink of NH4-N to coastal waters by decreasing porewater exchange, modifying the nutrients stoichiometry, and ultimately alleviating the potential of N-associated eutrophication in nearby coastal waters.
查看更多>>摘要：Grey water footprint (GWF) is an indicator that converts the pollution loads to the equivalent freshwater volume in water footprint (WF) assessment. The conventional application of GWF is to account the embedded water required for the assimilation of pollution loads discharged by production processes. However, this research highlights a deficiency in GWF accounting and proposes an integrated methodology to reinforce GWF to consider the regional environmental concerns in the WF of agricultural productions. This methodology has three main consecutive steps. First, the soil and water assessment tool (SWAT) is used for basin simulation. Second, the WFs of agricultural productions are assessed by the modeling outcomes and according to the conventional approach of GWF accounting. In the third step, an amendment is introduced in WF assessment for accounting the embedded freshwater required for environmental enhancement. This amendment develops multiple-pollutant GWF assessment and increases the WFs of agricultural productions in environmentally impaired basins. This approach is verified in Zrebar Lake basin where farmlands are the main non-point sources and the lake experiences eutrophication. Here, the average WFs of rain-fed and irrigated crops are increased 8.9% and 5.8%, respectively by the developed methodology. In addition, the average ratio of GWF to WF of crops grows from 1.3% to 7.6% and the water pollution level increases more than 5.3 times in basin for WF sustainability assessment. This enhancement in the quantification of GWF is mainly due to the fact that the majority of the GWF of crops in the study area is related to nitrogen pollution loads, while phosphorous reduction is more critical for eutrophication control. Thus, this approach enables the multiple-pollutant GWF to consider the impacts of both pollution loads and ecological impairment in the WF of products. This perspective can promote GWF as an environmental indicator and extend its application for decision-making.
查看更多>>摘要：Water problems have long been among the most urgent issues affecting China's lower Yellow River. In recent decades, the regime of the streamflow flowing into the lower Yellow River has been significantly altered by large reservoirs and dams. In this work, we investigate the "valve function" of Xiaolangdi Dam on the water discharge for multiple scales. Xiaolangdi Dam exhibits little impact on the total streamflow in the long run, although it dramatically changes the seasonal distribution. The ratio of average daily discharge during non-flood seasons to average daily discharge during flood seasons at Xiaolangdi station increased progressively from 39.8% during 1971-1989 to 93.2% during 1997-2016. Based on a linear relationship determined from historical data, the theoretical daily discharge at Huayuankou station in the absence of Xiaolangdi Dam was reconstructed. Through comparative analysis of the observed and reconstructed daily discharge series, we estimate that 78% of the potential flood events that could have happened during 1997-2007 were mitigated due to the construction and operation of Xiaolangdi Dam. Meanwhile, the peak discharge at Huayuankou station was also reduced from > 6000 m(3)/s to < 4500 m(3)/s. The redistribution of seasonal discharge by Xiaolangdi Dam not only is beneficial for meeting water demand but also effectively extirpates the river drying-up phenomenon.
NSTL
Elsevier