Taking layer J-II of Upper Jurassic of Kumkol South oilfield in South Turgay Basin, Kazakstan as an example, the article studied the architecture characteristics and heterogeneity of delta sandstones, and determined the influence of sandstone architecture on waterflooding sweep characteristics using fine characterization of sandstones, comprehensive interpretation of waterflooded layers, statistical analysis of production and injection profiles, reservoir numerical simulation methods. The result shows that the delta sandstones have a complex architecture of mosaic structure with mudstone baffles and mud-interbeds, and the sandstone architecture controls the sweeping characteristics of waterflood: due to impermeable or low permeable boundaries between single sand bodies, and lateral and vertical blocking of underwater distributaries bay mudstone, sands in delta have very complicated architecture, and the injected water flows priorly into underwater distributaries channel sand and estuary bar sand with better physical properties, making these two types of sands suffer stronger warterflooding, and have higher recovery degree and better waterflooding sweep effect in plane. Inside single sand bodies, on the one hand, underwater distributaries channel sand and estuary bar sand have high vertical producing degree and good waterflooding sweep effect because mud interbeds in the sands have vertical blocking and shunt effect on injected water; on the other hand, these two types of sands have inhomogeneous waterflood sweeping because of large permeability difference and high development of dominant water channels. In contrast, made up of thin homogeneous fine sand with poor physical properties, lateral sheet sand often has even water-flooding and poor waterflooding sweep effect.
Abstract Bed form‐driven hyporheic exchange is vital to biogeochemical processes occurring within aquatic sediment. The integrated effects of hyporheic processes in a bed form ultimately impact watershed‐scale water quality. However, much of what is understood regarding bed hyporheic exchange is based on idealized two‐dimensional bed forms despite the prevalence of potentially complex three‐dimensional (3‐D) bed forms in sandy riverbeds. We thus examined the impact of bed form three‐dimensionality on hyporheic exchange. Bed form three‐dimensionality was represented by two groups of geometric parameters: (1) crest planform curvature and (2) transverse and longitudinal wavelength and amplitude. A wide variety of synthetic bed forms was generated based on the geometric parameters. Then, surface flow over and hyporheic flow through each bed form was calculated using a 3‐D multiphysics computational fluid dynamics model implemented across a range of Reynolds Number. We found that hyporheic exchange is sensitive to both types of parameters that determine the bed form three‐dimensionality. Hyporheic exchange is dominated however by the three‐dimensionality caused by out‐of‐phase superimposed sinusoidal surfaces. The results of the complex flow models were synthesized into simple equations for predicting hyporheic flux and bulk residence time based on bed form longitudinal and transverse wavelengths, bed form height, and Reynolds Number.
Abstract This study assesses a large‐scale hydrologic modeling framework ( WRF ‐Hydro‐ RAPID ) in terms of its high‐resolution simulation of evapotranspiration ( ET ) and streamflow over Texas (drainage area: 464,135 km 2 ). The reference observations used include eight‐day ET data from MODIS and FLUXNET , and daily river discharge data from 271 U.S. Geological Survey gauges located across a climate gradient. A recursive digital filter is applied to decompose the river discharge into surface runoff and base flow for comparison with the model counterparts. While the routing component of the model is pre‐calibrated, the land component is uncalibrated. Results show the model performance for ET and runoff is aridity‐dependent. ET is better predicted in a wet year than in a dry year. Streamflow is better predicted in wet regions with the highest efficiency ~0.7. In comparison, streamflow is most poorly predicted in dry regions with a large positive bias. Modeled ET bias is more strongly correlated with the base flow bias than surface runoff bias. These results complement previous evaluations by incorporating more spatial details. They also help identify potential processes for future model improvements. Indeed, improving the dry region streamflow simulation would require synergistic enhancements of ET , soil moisture and groundwater parameterizations in the current model configuration. Our assessments are important preliminary steps towards accurate large‐scale hydrologic forecasts.
Abstract The slope effect on flow erosivity and soil erosion still remains a controversial issue. This theoretical framework explained and quantified the direct slope effect by coupling the modified Green‐Ampt equation accounting for slope effect on infiltration, 1‐D kinematic wave overland flow routing model, and WEPP soil erosion model. The flow velocity, runoff rate, shear stress, interrill, and rill erosion were calculated on 0°–60° isotropic slopes with equal horizontal projective length. The results show that, for short‐duration rainfall events, the flow erosivity and erosion amounts exhibit a bell‐shaped trend which first increase with slope gradient, and then decrease after a critical slope angle. The critical slope angles increase significantly or even vanish with increasing rainfall duration but are nearly independent of the slope projective length. The soil critical shear stress, rainfall intensity, and temporal patterns have great influences on the slope effect trend, while the other soil erosion parameters, soil type, hydraulic conductivity, and antecedent soil moisture have minor impacts. Neglecting the slope effect on infiltration would generate smaller erosion and reduce critical slope angles. The relative slope effect on soil erosion in physically based model WEPP was compared to those in the empirical models USLE and RUSLE. The trends of relative slope effect were found quite different, but the difference may diminish with increasing rainfall duration. Finally, relatively smaller critical slope angles could be obtained with the equal slope length and the range of variation provides a possible explanation for the different critical slope angles reported in previous studies.
Sediment tracers moving as bed load can exhibit anomalous dispersion behavior deviating from Fickian diffusion. The presence of heavy-tailed resting time distributions and thin-tailed step length distributions motivate adoption of fractional-derivative models (FDMs) to describe sediment dispersion, but these models require many parameters that are difficult to quantify. Here we propose a considerably simplified FDM for anomalous transport of uniformly sized grains along straight channels, the subordinated advection equation (SAE), which is based on the concept of time subordination. Unlike previous FDM models with time index γ between 0 and 1, our SAE model adopts a value of γ between 1 and 2. This γ describes random velocities deviating significantly from the mean velocity and models both long resting periods and relatively fast displacements. We show that the model quantifies the dynamics of four bed load transport experiments recorded in the literature. In addition to γ, SAE model parameters—velocity and capacity coefficient—are related to the mean and variance of particle velocities, respectively. Successful application of the SAE model also implies a universal probability density for the heavy-tailed waiting time distribution (with finite mean) and a relatively lighter tailed step length distribution for uniform bed load transport from local to regional scales.
In this paper, linear-quadratic optimal control problems of state delay systems under full and partial information are investigated. Under the full information case, bothe discrete and distributed delays are taken into account in our model. We obtain the optimal control by Hamiltonian system which consists of distributed delayed SDE and distributed anticipated BSDE. And a feedback representation of optimal control is derived by the value function method. We also consider the partial observed problem with state delay, the optimal control is given by backward separation method and optimal filtering with delay. Closed-form optimal solution under partial information is obtained in some particular case.
Abstract The sediment regime in the middle Yangtze River has been significantly changed from quasi‐equilibrium to nonequilibrium since the impoundment of the Three Georges Reservoir (TGR). To understand the effects of the TGR on vertical distribution of suspended sediment concentration (SSC) and estimation accuracy of mean concentration, vertical sediment concentration and flow velocity data at the Shashi and Jianli hydrological stations in the reach before and after the impoundment were collected. Comparisons and analysis of vertical profiles of SSC before and after the TGR impoundment show that after the impoundment of the TGR, due to the coarsening of sediment particle size, the reduction in sediment load, and the significant decrease in sediment saturation, the vertical distribution of SSC in the downstream reaches became more uneven under medium and low water flows, which was reflected in the vertical gradient and the fluctuation degree of SSC significantly increased. In addition, the depth‐average sediment concentrations were calculated by the selected‐point method and the mean values calculated by the “multi‐point method” were regarded as the “true mean” to evaluate the accuracy of the mean value calculated by the “few‐point method.” It was found that the relative errors for the selected‐point method were mainly positive before impoundment but mainly negative after impoundment. Additionally, the correction factors of one‐point, two‐point, and three‐point methods and the position of the near‐bed substituted point for the five‐point method were given to reduce the error when the point measurements were used to calculate the depth‐average sediment concentration in the downstream reaches.
Abstract This study analyses the changes in sediment transport regimes in the middle Yellow River basin (MYRB) using sediment rating parameters. Daily streamflow and suspended sediment concentration data were collected at 35 hydrological stations from the 1950s to 2016, which can be divided into three periods based on the type and intensity of human activities: the base stage before 1970, the restraining stage from 1971 to 1989, and the restoration stage after 2002. Data within each period were fitted by log‐linear sediment rating curves and the sediment rating parameters were utilized to analyse the spatial and temporal variations in sediment transport regimes. The results show that sediment rating parameters are indicative of sediment transport regimes. In the base stage and the restraining stage, the hydrological stations can be categorized into four groups based on their locations on the rating parameter plot. The stations with small drainage basins were characterized by the highest sediment transport regime, followed by those located in the coarse‐particle zone, the loess zone, and the mountainous/forest zone. In the restoration stage, the difference in sediment transport regimes between different geomorphic zones became less distinguishable than in previous stages. During the transition from the base stage to the restraining stage, sediment rating parameters showed no significant changes in sediment transport regimes in all four geomorphic groups. During the transition from the restraining stage to the restoration stage, significant changes were observed in the coarse‐particle zone and the mountain/forest zone, indicating that the revegetation programme and large reservoirs imposed a stronger influence on sediment transport regimes in these two zones than in the rest of the MYRB. This study provides theoretical support for evaluating sediment transport regimes with sediment rating parameters.
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