Upstream morphological effects of a sequential check dam adjustment process

Sediment flushing and the morphological responses to the procedure of check dam removal are still unclear. Following laboratory experiments that revealed three stages (deepening, widening, and volume release) of check dam adjustment, a check dam built in 2007 at Landao Creek in central Taiwan was adjusted in 2015 by removing central bars and cutting 2.5 m from the middle two piers (stage 1 + 2), with the purpose of regulating sediment transfer and keeping the thalweg at the center of the channel, while also preventing hill slope toe erosion. In 2019, four central piers were removed (stage 3) to increase the volume of sediment released. Annual surveys were conducted after the initial adjustment in 2015 through to 2020 using unmanned aerial vehicles (UAVs). The check dam adjustments revealed that the channel had narrowed and stabilized as indicated by regenerating riparian vegetation. Additionally, distinct terraces had formed on the hill slope toes of the creek channel in proximity to the check dam. The meander upstream weakened following the dam adjustments. This study combining laboratory experiments with actual field observation contributed immensely to check dam decommissioning. Additionally, this study illustrated how an adjustable check dam may aid regulation of sediment transport and thereby sediment balance. It can be adjusted accordingly based on the prevailing channel condition.     

Application of differential evolutionary optimization methodology for parameter structure identification in groundwater modeling

Parameter structure identification is formulated in terms of solving an inverse problem, which allows for a determination of an appropriate level of parameter structure complexity, and the identification of its pattern and the associated parameter values. With the increasing complexity of parameter structure identification in groundwater modeling, demand for robust, fast, and accurate optimizers is on the rise among researchers from groundwater hydrology fields. A novel global optimizer, differential evolution (DE), has been proposed to solve the parameter-structure-identification problem. The Voronoi tessellation is adopted for the automatic parameterization. The stepwise regression method and the error covariance matrix are used to determine the optimal structure complexity. Numerical experiments with a continuous hydraulic conductivity distribution are conducted to demonstrate the proposed methodology. The results indicate that the DE can identify the global optimum effectively and efficiently. A sensitivity analysis of the control parameters and mutation schemes implemented in the DE is employed to examine their influence on the objective function. The comparison between DE and genetic algorithm shows the advantage of DE in terms of robustness and efficiency. The proposed methodology is also applied to a real groundwater system, Pingtung Plain in Taiwan, and the properties of aquifers are successfully identified.     

Probability-based damage assessment for reinforced concrete bridge columns considering the corrosive and seismic hazards in Taiwan

In this paper, we consider the time at which earthquake events occur when analyzing seismic structural damage to a deteriorating RC bridge within a specified period. Because the uncertainty exists in the occurrence time of earthquake events, Monte Carlo simulation is applied. The proposed procedure for evaluating the exceedance probability, which corresponds to a specified limit state, is then applied to a case study of RC bridges in Taiwan to demonstrate its applicability. This study selects three typical RC bridges located in the Taipei Basin, Taiwan, to analyze exceedance probabilities of specified damage states during various specified periods and then discusses the cumulative damage effect on the exceedance probabilities of specified damage states. Additionally, for the chloride-induced deteriorating bridges at various distances to the sea in Suao, Taiwan, the effects of the deterioration and seismic structural damage on the exceedance probabilities of specified damage states are demonstrated and discussed. The proposed assessment procedure can help engineers understand whether the deterioration would accelerate the declining seismic performance of bridges and shorten their serviceability-related and safety-related service lives, as well as provide reference for repairing RC bridges and retrofitting their seismic performance.     

Thermal processing and crystallization of amorphous Mg‐Ca silicates

The structural evolution of sol–gel‐produced amorphous Mg_(x)Ca_(1–x)SiO₃ silicates is investigated. Mid‐IR Fourier transform infrared spectroscopy and synchrotron X‐ray diffraction are used to confirm the amorphous nature of the as‐prepared silicates, while subsequent in situ synchrotron X‐ray powder diffraction measurements are used to study the evolution of crystalline mineral phases as a function of annealing temperature. Multiple silicate phases, including diopside, enstatite, forsterite, and SiO₂, are identified, while Rietveld (i.e., structure) refinement of the diffraction data is used to quantify phase change relationships. Investigated as possible analogs for the refractory dust grain materials likely to have been present in the early solar nebula, the likely relevance of these investigations to the observed silicate compositions of chondritic meteorites and cometary bodies and the processing of their precursor materials is discussed.     

Hybrid-optimization algorithm for the management of a conjunctive-use project and well field design

Hi-Desert Water District (HDWD), the primary water-management agency in the Warren Groundwater Basin, California, plans to construct a waste water treatment plant to reduce future septic-tank effluent from reaching the groundwater system. The treated waste water will be reclaimed by recharging the groundwater basin via recharge ponds as part of a larger conjunctive-use strategy. HDWD wishes to identify the least-cost conjunctive-use strategies for managing imported surface water, reclaimed water, and local groundwater. As formulated, the mixed-integer nonlinear programming (MINLP) groundwater-management problem seeks to minimize water-delivery costs subject to constraints including potential locations of the new pumping wells, California State regulations, groundwater-level constraints, water-supply demand, available imported water, and pump/recharge capacities. In this study, a hybrid-optimization algorithm, which couples a genetic algorithm and successive-linear programming, is developed to solve the MINLP problem. The algorithm was tested by comparing results to the enumerative solution for a simplified version of the HDWD groundwater-management problem. The results indicate that the hybrid-optimization algorithm can identify the global optimum. The hybrid-optimization algorithm is then applied to solve a complex groundwater-management problem. Sensitivity analyses were also performed to assess the impact of varying the new recharge pond orientation, varying the mixing ratio of reclaimed water and pumped water, and varying the amount of imported water available. The developed conjunctive management model can provide HDWD water managers with information that will improve their ability to manage their surface water, reclaimed water, and groundwater resources.     

Analysis of space–time patterns of rainfall events during 1996–2008 in Yilan County (Taiwan)

Stochastic Environmental Research and Risk Assessment - Understanding local precipitation patterns is essential to water resource management and flood mitigation. Precipitation patterns can vary in...     

Spatial and Temporal Changes of Groundwater Level Induced by Thrust Faulting

Changes of groundwater level, ranging from a fall of 11.10 m to a rise of 7.42 m, induced by thrust faulting during the 1999 M_w 7.6, Chi-Chi earthquake have been recorded in 276 monitoring wells in Taiwan. Most coseismic falls appeared near the seismogenic fault as well as other active faults, while coseismic rises prevailed away from the fault. Coseismic groundwater level rises and falls correlated fairly well with hypocentral distance in the vicinity of the thrust fault. We found a major difference of coseismic changes in wells of different depths at most multiple-well stations. The recovery process of coseismic groundwater level changes is associated with the confining condition of the aquifer. Cross-formational flow is likely to play an important role in groundwater level changes after the earthquake. In the hanging wall of the thrust fault, an abnormal decline of groundwater level was observed immediately before the earthquake. The underlying mechanism of the unique preseismic change warrants further investigation.     

Comparison of TRMM and water district rain rates over New Mexico

This paper compares monthly and seasonal rain rates derived from the Version 5 (V5) and Version 6 (V6) TRMM Precipitation Radar (TPR, TSDIS reference 2A25), TRMM Microwave Imager (TMI, 2A12), TRMM Combined Instrument (TCI, 2B31), TRMM calibrated IR rain estimates (3B42) and TRMM merged gauge and satellite analysis (3B43) algorithms over New Mexico (NM) with rain gauge analyses provided by the New Mexico water districts (WD). The average rain rates over the NM region for 1998–2002 are 0.91mmd?1 for WD and 0.75, 1.38, 1.49, 1.27, and 1.07mmd?1 for V5 3B43, 3B42, TMI, PR and TCA; and 0.74, 1.38, 0.87 and 0.97 mm d?1 for V6 3B43, TMI, TPR and TCA, respectively. Comparison of V5 3B43 with WD rain rates and the daily TRMM mission index (TPR and TMI) suggests that the low bias of V5 3B43 for the wet months (summer to early fall) may be due to the non-inclusion of some rain events in the operational gauge analyses that are used in the production of V5 3B43. Correlation analyses show that the WD rain rates vary in phase, with higher correlation between neighboring WDs. High temporal correlations (>0.8) exist between WD and the combined algorithms (3B42, 3B43 and TCA for both V5 and V6) while satellite instrument algorithms (PR, TMI and TCI) are correlated best among themselves at the monthly scale. Paired t-tests of the monthly time series show that V5 3B42 and TMI are statistically different from the WD rain rates while no significant difference exists between WD and the other products. The agreements between the TRMM satellite and WD gauge estimates are best for the spring and fall and worst for winter and summer. The reduction in V6 TMI (?7.4%) and TPR (?31%) rain rates (compared to V5) results in better agreement between WD estimates and TMI in winter and TPR during summer.     

Space Telescope Astrometry from CCD images

The astrometric application of the Wide Field Camera and the Planetary Camera is reviewed. It is shown that the digital image centering algorithms can yield a positional accuracy of 0.1 milli-arcsecond. Deconvolution of CCD's sensitivity, non-flatness of the filters, and crinkling of the CCD surface may limit the positional accuracy to 1 milli-arcsecond.Presented at the Symposium Star Catalogues, Positional Astronomy and Celestial Mechanics, held in honor of Paul Herget at the U.S. Naval Observatory, Washington, November 30, 1978.