A review on the angle of repose of granular materials

Part I presents the statistical theory of turbulence, and Part 2 the coherent structures in open-channel flows and boundary layers. The book is intended for advanced students and researchers in hydraulic research, fluid mechanics, environmental sciences and related disciplines. References Index.

Turbulence in open-channel flows

Assessment of a groundwater quality monitoring network using vulnerability mapping and geostatistics: a case study from Heretaunga Plains, New Zealand.

In sparsely monitored basins, accurate mapping of the spatial variability of groundwater level requires the interpolation of scattered data. This paper presents a comparison of deterministic interpolation methods, i.e. inverse distance weight (IDW) and minimum curvature (MC), with stochastic methods, i.e. ordinary kriging (OK), universal kriging (UK) and kriging with Delaunay triangulation (DK). The study area is the Mires Basin of Mesara Valley in Crete (Greece). This sparsely sampled basin has limited groundwater resources which are vital for the island’s economy; spatial variations of the groundwater level are important for developing management and monitoring strategies. We evaluate the performance of the interpolation methods with respect to different statistical measures. The Spartan variogram family is applied for the first time to hydrological data and is shown to be optimal with respect to stochastic interpolation of this dataset. The three stochastic methods (OK, DK and UK) perform overall better than the deterministic counterparts (IDW and MC). DK, which is herein for the first time applied to hydrological data, yields the most accurate cross-validation estimate for the lowest value in the dataset. OK and UK lead to smooth isolevel contours, whilst DK and IDW generate more edges. The stochastic methods deliver estimates of prediction uncertainty which becomes highest near the southeastern border of the basin.

Comparison of stochastic and deterministic methods for mapping groundwater level spatial variability in sparsely monitored basins

A modified expression to predict the boundary shear distribution in compound channels is derived and is found to provide significant improved results. The practical method to predict the stage-discharge relationship uses the one-dimensional (1D) approach by taking due care of the momentum transfer. The proposed approach is tested for its validity using available experimental data. Error statistics including standard error and coefficient of determination ( R2 ) are applied to ascertain the effectiveness of the model. The method also gives satisfactory results when applied to two sets of natural river data.

Stage-Discharge Prediction for Straight and Smooth Compound Channels with Wide Floodplains

The primary network of groundwater level observation wells aims at realizing a regional groundwater management policy. It may give a regional picture of groundwater level with emphasis on the natural situation. Observation data from the primary network can be used to estimate the actual state of groundwater system. Since the cost of the installation and maintenance of a groundwater monitoring network is extremely high, the assessment of effectiveness of the network becomes very necessary. Groundwater level monitoring networks are the examples of discontinuous sampling on variables presenting spatial continuity and highly skewed frequency distributions. Anywhere in the aquifer, ordinary kriging provides estimates of the variable sampled and a standard error of the estimate. In this article, the average Kriging standard deviation was used as a criterion for the determination of network density,and the GIS-based approach was analysized. A case study of groundwater level network simulation in the Chaiwopu Basin, Xinjiang Uygur Autonomous Region, China, was presented. In the case study, the initial phreatic water observation wells were 18, a comparison of the three variogram parameters of the three defferent variogram models shows that the Gaussian model is the best. Finally, a network with 55 wells was constructed.

Design of groundwater level monitoring network with ordinary kriging

The failure of conventional methods for discharge prediction in compound channels results from their ignorance of the loss in conveyance arising from the complicated flow interaction between the main channel and its associated floodplains. In this paper, a new method is presented for assessing the stage-discharge relationship and the discharge distribution in compound channels by considering both the momentum transfer between the upper and lower main channel flows and that between the upper main channel and its adjoining floodplain flows. A calibration using data from the laboratory channels and three natural rivers demonstrates that the presented method can give predictions that agree better with the experimental and field data. The computed results also show that the method not only is well capable of predicting the discharge distributions of the floodplain and the whole main channel, but also of predicting the discharge distribution in the lower main channel. In addition, the momentum transfer ...

Stage-Discharge Prediction in Compound Channels

A conception of exposure degree is used in this article to account for the hiding and exposure mechanism of nonuniform sediment transport. The force arms of particles on the bed slope are assumed to be a function of the exposure degree, which is stochastically related to the size and gradation of bed materials. Based on this conception, the formula for the angle of repose of nonuniform sediment is developed. The angle of repose of nonuniform sediment is experimentally investigated in rotation drum at the rolling motion of sediment particles. The nonuniform sediment is gotten from the mixture of two kinds of uniform sediment with different weight ratios and two experimental plans that one for changing the weight ratio of two kinds of uniform sediment from 1:9 to 9:1 and the other changing the uniform sediment size and weight ratio are used. The effect of the rotation speed and the filling degree on the angle of repose is investigated, too. Finally, the formula has been tested against a wide range of laboratory data, the prediction by the newly proposed formulas is very good.

Study on The Angle of Repose of Nonuniform Sediment

A series of experiments was carried out in a large symmetric compound channel composed of a rough main channel and rough floodplains to investigate the resistance characteristics of inbank and overbank flows. The effective Manning, Darcy–Weisbach, Chezy coefficients and the relative Nikuradse roughness height were analyzed. Many different representative methods for predicting the composite roughness were systematically summarized. Besides the measured data, a vast number of laboratory data and field data for compound channels were collected and used to check the validity of these methods for different subsection divisions including the vertical, horizontal, diagonal and bisectional divisions. The computation showed that these methods resulted in big errors in assessing the composite roughness in compound channels, and the reasons were analyzed in detail. The error magnitude is related to the subsection divisions.

Flow resistance and its prediction methods in compound channels

The depth-averaged equation of flow in a rectangular compound channel with secondary flows is established by analyzing the forces acting on the elemental water body and using Newton’s second law The analytical solution to the transverse variation of depth-averaged velocity is presented that includes the effects of lateral momentum transfer and secondary flow in addition to bed friction Different forms of boundary conditions at the internal wall between the rectangular main channel and the adjoining floodplain are presented A comparison with the published experimental data demonstrates that the present model is capable of predicting the distributions of depth-averaged velocity and boundary shear stress The results also indicate that the secondary flow and boundary conditions have influences on them Finally, the key parameters in the model, such as the Darcy–Weisbach coefficient, the momentum transfer coefficient, and the secondary flow coefficient are also discussed and analyzed

Xingnian Liu

Papers

Design of groundwater level monitoring network with ordinary kriging

Stage-Discharge Prediction in Compound Channels

Study on The Angle of Repose of Nonuniform Sediment

Flow resistance and its prediction methods in compound channels

Modeling Depth-Averaged Velocity and Boundary Shear Stress in Rectangular Compound Channels with Secondary Flows