Evaluation of drainage networks under moving storms utilizing the equivalent stationary storms

This paper investigates the effect of rainstorm movement on the peak discharge response (PDR) of drainage networks by comparing it with the corresponding equivalent stationary and uniform rainfall. A synthetic circular watershed is introduced to avoid biases from interaction between catchment geometry and storm orientation. The drainage network of the watershed is simulated by the Gibbsian model to examine the effect of network configuration on the peak response depending on the storm kinematics. This study utilizes two types of the equivalent stationary storm (ESS): the average rainfall intensity over the entire catchment (ESSAV) and the point stationary rainfall intensity (ESSQ) to evaluate the effect of moving rainstorms in terms of the PDR. The results show that there exists an interval in which the same rainfall duration produces higher peak responses for moving storms compared with ESSQ. The augmentation of the peak response by moving rainstorm is dependent on the relative rainstorm speed, size, and direction as well as drainage network configuration of the catchment; especially, the results show that a less efficient network tends to mitigate the effect of rainstorm movement on peak response. In contrast, a more efficient network is more sensitive to storm kinematics and the peak response increases compared with ESS. Therefore, the results in this study imply a potential improvement in urban drainage networks in terms of efficiency as well as safety to moving rainstorms. Also, this study suggests the range of variation in peak flows due to storm kinematics compared with the ESS, which can be a reference to the current design practices.     

Variational elastic solution for axially loaded piles in multilayered soil

Most analytical or semi‐analytical solutions of the problem of load‐settlement response of axially loaded piles are based on the assumption of zero radial displacement. These solutions also are only applicable to piles embedded in either a homogeneous or a Gibson soil deposit. In reality, soil deposits consist of multiple soil layers with different properties, and displacements in the radial direction within the soil deposit are not zero when the pile is loaded axially. In this paper, we present a load‐settlement analysis applicable to a pile with circular cross section installed in multilayered elastic soil that accounts for both vertical and radial soil displacements. The analysis follows from the solution of the differential equations governing the displacements of the pile–soil system obtained using variational principles. The input parameters needed for the analysis are the pile geometry and the elastic constants of the soil and pile. We compare the results from the present analysis with those of an analytical solution that considers only vertical soil displacements. The analysis presented in this paper also provides useful insights into the displacement and strain fields around axially loaded piles. Copyright © 2011 John Wiley & Sons, Ltd.     

Engineering Characteristics of the Lightweight Air-Mixed Soil (LWS) Containing Silty Marine Sediment

This study was conducted to find out the characteristics of the lightweight air-mixed soil (LWS) used for a road embankment. Compressive strength, permeability, and capillary height of the LWS were studied, and to support these studies, its inside structure was analyzed in detail. Various size air pores exist in the LWS, and their distribution with a location is almost constant. Numerous tiny cracks formed by different grain sizes between in-situ soil (silty marine sediment) and solidificator exist inside the air pores so that the LWS can be affected by water. Peak strength of the LWS is found to be less dependent on the water, but the behavior of strength-strain was affected by water. Permeability is a little bit higher than clay's permeability. Capillary rise is rapid in the beginning of the test, and then slows down. The capillary rise can increase the density of the LWS, and thus requires special attention during design and maintenance of the structures, which were constructed with the LWS.     

Numerical analysis of passive pile groups in offshore soft deposits

The performance of pile foundations in offshore soft deposits is frequently dominated by passive loading from approach embankments for reclaimed land in Korea. This is mainly because of a Korean offshore soil profile, involving an over 30 m normally consolidated soil, with a strength that varies linearly with depth. This paper presents the results of an investigation on short- and long-term passive loading on the piles using two dimensional elastoplastic-consolidation coupled FEM analyses with large strain mode. This numerical scheme is essentially based on an updated Lagrangian formulation, which is favorably validated in cases of both centrifuge tests and field measurements. Although a parametric study is limited by some of the application, it is shown that passive pile loading is primarily affected by soil profile, pile head boundary condition, magnitude of embankment load, and average degree of consolidation. Simultaneously, time-dependent effect of shear transfer at the pile head is explicitly identified and a useful starting point in design is recommended for passive pile loading in construction (short-term) and consolidation (long-term) phases.     

Validating infrared-based rainfall retrieval algorithms with 1-minute spatially dense raingage measurements over Korean peninsula

Summary ?This study compares and contrasts six infrared-based satellite rain estimation techniques and their validation during a 2-month period from June 20–August 20, 1998 over the Korean peninsula. Two probability matching techniques (PMM1, PMM2), a look-up table technique (LUT), a convective-stratiform technique (CST), the Negri-Adler-Wetzel technique (NAWT), and the Arkin technique (ARKT) are applied to hourly infrared GMS imagery. Retrieved rainrates are compared against one-minute reporting raingage observations from the dense Automated Weather Station (AWS) network of Korea. The high spatial resolution and fine temporal resolution of the AWS measurements provide a unique and effective means to validate rain estimates derived from instantaneous space measurements, which is a main scientific focus of this study. Validation results indicate that all techniques exhibit better performance for more evenly spread rain events while exhibiting lesser performance for weak and sporadic rains for which validation sampling becomes more of a problem. Validation statistics show that climatologically-local techniques such as the PMM and LUT algorithms perform better than techniques developed in climatologically different regimes, indicating the well-known dependence of rain physics on the immediate environment. Nevertheless, the validation results suggest how the rain determination parameters including attributed rain and threshold brightness temperature could be optimized locally before application. As others have found, the most difficult problem with satellite infrared techniques is in the detection and quantification of heavy rainfall events arising from uncertainties in discriminating non-precipitating anvil clouds from convective clouds. However, for the set of algorithms under examination here, given the sharp resolution of the validation measurements, it is evident that the CST algorithm exhibits superior performance in differentiating between non-precipitating anvil and heavy rain. Received January 4, 2002; revised March 11, 2002     

Numerical simulations for effects of anisotropy and heterogeneity on well responses to slug tests

Because of their simplicity, assumptions of isotropy and homogeneity are often applied to slug test analyses, determining hydraulic conductivity of heterogeneous and anisotropic formations, in spite of their inherent unfitness. In this study, it was examined how anisotropy and heterogeneity of the formation affect well recovery curves and therefore estimates of hydraulic conductivity in slug tests. Using a finite element method (FEM) slug test model, several hypothetical slug tests in anisotropic and heterogeneous formations with known hydraulic parameters and actual formations of unknown parameters were analyzed. Error factors as a result of the assumptions of isotropy and homogeneity were quantified through sensitivity analyses of well recovery curves. Results of slug tests analyzed in this study indicate that: (1) the well recovery curves in slug tests do not show unique shape or signs reflecting the anisotropy and heterogeneity of the tested formation; (2) the assumption of isotropy does not deviate estimates of hydraulic conductivity significantly when the radial hydraulic conductivity is larger than the vertical one in the formation; (3) the assumption of homogeneity in a layered heterogeneous system has a high potential for errors in hydraulic conductivity estimation, however it can be avoided by placing the screened section apart from the adjacent layers; (4) a low permeability well skin skews the hydraulic conductivity of the original formation, depending on the size and hydraulic conductivity of the skin.     

Rainfall estimation using raingages and radar — A Bayesian approach: 1. Derivation of estimators

Procedures for estimating rainfall from radar and raingage observations are constructed in a Bayesian framework. Given that the number of raingage measurements is typically very small, mean and variance of gage rainfall are treated as uncertain parameters. Under the assumption that log gage rainfall and log radar rainfall are jointly multivariate normal, the estimation problem is equivalent to lognormal co-kriging with uncertain mean and variance of the gage rainfall field.The posterior distribution is obtained under the assumption that the prior for the mean and inverse of the variance of log gage rainfall is normal-gamma 2. Estimate and estimation variance do not have closed-form expressions, but can be easily evaluated by numerically integrating two single integrals. To reduce computational burden associated with evaluating sufficient statistics for the likelihood function, an approximate form of parameter updating is given. Also, as a further approximation, the parameters are updated using raingage measurements only, yielding closed-form expressions for estimate and estimation variance in the Gaussian domain.     

Estimating fractional green vegetation cover of Mongolian grasslands using digital camera images and MODIS satellite vegetation indices

ABSTRACT

Fractional green vegetation cover (FVC) is a useful indicator for monitoring grassland status. Satellite imagery with coarse spatial but high temporal resolutions has been preferred to monitor seasonal and inter-annual FVC dynamics in wide geographic area such as Mongolian steppe. However, the coarse spatial resolution can cause a certain uncertainty in the satellite-based FVC estimation, which calls attention to develop a robust statistical test for the relationship between field FVC and satellite-derived vegetation indices. In the arid and semi-arid Mongolian steppe, nadir pointing digital camera images (DCI) were collected and used to produce a FVC dataset to support the evaluation of satellite-based FVC retrievals. An optimal DCI processing method was determined with respect to three color spaces (RGB, HIS, L*a*b*) and six green pixel classification algorithms, from which a country-wide dataset of DCI-FVC was produced and used for evaluating the accuracy of satellite-based FVC estimates from MODIS vegetation indices. We applied three empirical and three semi-empirical MODIS-FVC retrieval models. DCI data were collected from 96 sites across the Mongolian steppe from 2012 to 2014. The histogram algorithm using the hue (H) value of the HIS color space was the optimal DCI method (r² = 0.94, percent root-mean-square-error (RMSE) = 7.1%). For MODIS-FVC retrievals, semi-empirical Baret model was the best-performing model with the highest r² (0.69) and the lowest RMSE (49.7%), while the lowest MB (+1.1%) was found for the regression model with normalized difference vegetation index (NDVI). The high RMSE (>50% or so) is an issue requiring further enhancement of satellite-based FVC retrievals accounting for key plant and soil parameters relevant to the Mongolian steppe and for scale mismatch between sampling and MODIS data.     

Wave-like wind fluctuations observed in the stable surface layer over a plant canopy

Observations of wind velocity and temperature fluctuations were made in the nocturnal surface inversion layer over a paddy field. A remarkable wave-like motion of about 8 min period was seen in horizontal wind speed and standard deviation of vertical wind velocity. In addition, fluctuations of horizontal wind speed and anticlockwise rotation of wind direction with a period of about 30 min were found by power spectral analysis. The phenomena persisted for more than 2 hours. Similar phenomena were also observed at a coastal site at a distance of about 10 km from the paddy field.