Yu-Jia Chiu

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Papers by Yu-Jia Chiu

Decision Support System for Water Resources Management - Optimization of Groundwater Resources Management

EAGE Workshop on Dead Sea Sinkholes – Causes, Effects and Solutions, 2012

The greater competing demand for water requires an efficient use of water resources. Therefore, a... more The greater competing demand for water requires an efficient use of water resources. Therefore, an optimum management is necessary in order to deal with the constraining factors. In African countries, irrigated agriculture is the largest user of surface water resources. Nevertheless, recent assessments in small-scale surface irrigation schemes resulted in poor performance indicators: Water use efficiency indicators of existing schemes are below 50 percent, owing to inadequate management modes. The paper sheds the light on the potential development of a decision-support system based knowledge with the Mapping System and Services for Canal Operation Techniques approach, merged with the MIKEHydro Basin model as a versatile and flexible framework conceived for a large variety of applications in small-scale irrigation. The model aims to improve water service, increase irrigation efficiency, comply with socioeconomic objectives at country level. In order to address the prevailing heterogeneity of small-scale irrigation scheme, numerous variables are adjusted in the model, in terms of cropping patterns, climate data, and irrigation time. The evaluation of established water balance under different scenarios showed that tackling supply-driven scheduling and distributive issues significantly increases efficiency. Nevertheless, water allocation according to socioeconomic objectives of food security and market security implies trading off the efficiency objectives.

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Hydrodynamic Characteristics of Flow in a Strongly Curved Channel with Gravel Beds

Water

This study experimentally and numerically investigated the hydrodynamic characteristics of a 180°... more This study experimentally and numerically investigated the hydrodynamic characteristics of a 180° curved open channel over rough bed under the condition of constant downstream water depth. Three different sizes of bed particles (the small, middle and big cases based upon the grain size diameter D50) were selected for flume tests. Three-dimensional instantaneous velocities obtained by the acoustic Doppler velocimeter (ADV) were used to analyze hydrodynamic characteristics. Additionally, the Renormalization-Group (RNG) turbulence model was employed for numerical simulations. Experimental results show that rough bed strengthens turbulence and increases turbulent kinetic energy along curved channels. The power spectra of the longitudinal velocity fluctuation satisfy the classic Kolmogorov −5/3 law in the inertial subrange, and the existence of rough bed shortens the inertial subrange and causes the flow reach the viscous dissipation range in advance. The contributions of sweeps and ejec...

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Estimation of Soil Redistribution Rates Using 137Cs Fallout Radionuclide

Propagation and Separation of Downslope Gravity Currents over Rigid and Emergent Vegetation Patches in Linearly Stratified Environments

Journal of Marine Science and Engineering

Large eddy simulation (combined with the mixture model) and laboratory experiment were used to in... more Large eddy simulation (combined with the mixture model) and laboratory experiment were used to investigate the impact of emergent and rigid vegetation on the dynamics of downslope gravity currents in stratified environments. The reliability of the numerical model was assessed with the corresponding laboratory measurements. The results show that the vegetation cylinders lead to severe lateral non-uniformity of the current front, causing more evident lobe and cleft structures. In stratified environments, the smaller driving force leads to less propagating velocity until the current separates from the slope. The transition point (from acceleration to deceleration phases) of current velocity appears earlier as the vegetation becomes denser. The peak value of the bulk entrainment coefficient Ebuik is inversely proportional to the vegetation density, while the final converged value of Ebuik is proportional to the vegetation density. Vegetation patches make the degree of fluctuation of the...

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Budget of landslide-induced sediment for the watersheds in Taiwan–– a case study in pre-and post-typhoon morakot periods

Quantification of gully erosion in Baishi watershed of Shihmen Reservoir

[[abstract]]蝕溝係土壤沖蝕作用初期在坡面上切割所形成之深溝，且為坡面土壤強烈沖蝕作用之表徵與地形夷平過程之濫觴。蝕溝形成後即會因下切、橫向與溯源沖蝕而擴張，造成大量的地表沖刷。本研究... more [[abstract]]蝕溝係土壤沖蝕作用初期在坡面上切割所形成之深溝，且為坡面土壤強烈沖蝕作用之表徵與地形夷平過程之濫觴。蝕溝形成後即會因下切、橫向與溯源沖蝕而擴張，造成大量的地表沖刷。本研究使用全站儀，進行石門水庫集水區內白石溪流域內四條蝕溝變化地形測量，並結合航空攝影圖估算研究區域內的蝕溝數量及其規模，再分析白石溪流域蝕溝沖蝕產砂的總量。蝕溝測量的結果顯示蝕溝產砂狀態依照其發育程度的不同，可分為產砂型蝕溝以及穩定型蝕溝，產砂型蝕溝發育期較為年輕，其平均單位面積產砂量為0.2758m^3/m^2；穩定型蝕溝發展成熟，產砂量較少，平均單位面積產砂量為0.0108m^3/m^2。由航照圖判釋集水區共120條蝕溝，其中，面型蝕溝41條與線型蝕溝79條。因此，2006年7月至12月，集水區蝕溝產砂總量推估為27,744m^3。假設產砂量與研究期間內累積降雨量為一線性正比例關係，則集水區內蝕溝沖蝕產砂量為每年176,280噸，相較於崩塌地產砂量每年1,023,480噸，以及土壤沖蝕量每年30,960噸，蝕溝產砂量佔集水區總產砂比14%，為一不可忽略之產砂來源。[[abstract]]Gully is a landform with narrow channel cutting by runoff on hillslope. Gully landform indicates rapid soil erosion and initiation of denudation process on hillsope. After gullies are formed, a large quantity of sediment is produced by the incision, lateral erosion and head-cutting. This study aims to estimate the sediment yield due to gully erosion in the Baishi watershed of Shihmen Reservoir. We measured the morphology change of gullies by using Pulse Laser Total Stations, and interpreted the gullies from aerial photographs. Then, sediment yield from gully erosion was estimated in the watershed.The results show that gullies can be categorized into two types, active gully and stable gully, based on its sediment yield. Active gully, which is in the initial stage of gully evolution, has an average sediment yield of 0.2758 m^3/m^2. In contrast, stable gully, which is highly-developed, has with a smaller sediment yield of 0.0108 m^3/m^2 relatively. There are 120 gullies interpreted from aerial photographs, which 41 are polygon shapes and 79 are line shapes. The total sediment yield from gully erosion in the Baishi Watershed is 27,744 m^3 during July to December in 2006. The annual sediment yield from gully erosion is 176,280 t yr^(-1) based on the assumption of linear ratio of sediment yield with accumulated rainfall. The gully erosion contributes 14% of annual sediment in the　watershed, comparing with the landslide erosion of 1,023,480 t yr^-1 and soil erosion of 30,960 t yr^(-1). Gully erosion is a significant source of sediment yield in the watershed

TXT-tool 3.886-1.2: Simulation for the Debris Flow and Sediment Transport in a Large-Scale Watershed

We highlight a methodology of simulation of large-scale watershed mass transport, including lands... more We highlight a methodology of simulation of large-scale watershed mass transport, including landslide, debris flow, and sediment transport. A case study of Tsengwen reservoir watershed under the extreme rainfall triggered by typhoon Morakot is demonstrated. This approach starts with volume-area relation with landslide inventory method to predict temporal and regional landslide volume production and distribution. Then, debris flow model, Debris-2D, is applied to simulate the mass transport from hillslope to fluvial channel. Finally, a sediment transport model, NETSTARS, is used for hydraulic and sediment routing in river and reservoir. Near the water intake at the reservoir dam, the simulated sediment concentration is in good agreement with the measured one. The proposed approach gives good prediction and should help the management of reservoir operation and disaster prevention.

A Simple Route in Fabricating Carbon-Modified Titania Films with Glucose and Their Visible-Light-Responsive Photocatalytic Activity

Catalysts, 2018

Carbon-modified titania (C-TiO 2) films were easily prepared by using an impregnation process wit... more Carbon-modified titania (C-TiO 2) films were easily prepared by using an impregnation process with a glucose-containing TiO 2 sol. Through controlling calcination conditions, the as-obtained C-TiO 2 products exhibited highly photocatalytic activity for the degradation of gaseous NO x under visible light and ultraviolet illumination. The effects of carbon content and calcination temperature on the photocatalytic performances and their photochemical and physical properties were investigated. Carbonaceous species on the TiO 2 surface enhanced the visible-light absorption of TiO 2 films; however, an excessive amount of carbon on the TiO 2 surface reduced its photocatalytic ability due to the serious coverage effect on active sites. The results show that a suitable glucose addition is about 50-100% of the weight of TiO 2 content and the optimized calcination temperature is 300 • C, which leads to better photocatalytic activity under ultraviolet and visible-light irradiations. Accordingly, the simple-prepared C-TiO 2 films functioned as visible-light-responsive catalysts, allowing for a feasible producing route for real applications.

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Modeling Sediment Yields and Stream Stability Due to Sediment-Related Disaster in Shihmen Reservoir Watershed in Taiwan

Water, 2019

Accurate and reliable estimates of sediment yields from a watershed and identification of unstabl... more Accurate and reliable estimates of sediment yields from a watershed and identification of unstable stream reaches due to sediment-related disaster are crucial for watershed management, disaster prevention, and hazard mitigation purposes. In this study, we added hydrodynamic and sediment transport modules in a recently developed model to estimate sediment yields and identify the unstable stream reaches in a large-scale watershed (> 100km2). The calibrated and verified models can well reproduce the flow discharge and sediment discharge at the study site, the Shihmen Reservoir Watershed in Taiwan, during several typhoon events. For the scenario applications, the results revealed that the contribution (> 96%) of landslides on sediment supply is much more significant than compared to soil erosion (< 4%). The sediment contribution from the upstream of the hydrological station-Yufeng is approximately 36–55% of the total sediment supply for the rainfall events of 25, 50, 100, and 2...

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Dynamic Modeling of Sediment Budget in Shihmen Reservoir Watershed in Taiwan

Water, 2018

Qualifying sediment dynamic in a reservoir watershed is essential for water resource management. ... more Qualifying sediment dynamic in a reservoir watershed is essential for water resource management. This study proposed an integrated model of Grid-based Sediment Production and Transport Model (GSPTM) at watershed scale to evaluate the dynamic of sediment production and transport in the Shihmen Reservoir watershed in Taiwan. The GSPTM integrates several models, revealing landslide susceptibility and processes of rainfall–runoff, sediment production from landslide and soil erosion, debris flow and mass movement, and sediment transport. For modeling rainfall–runoff process, the tanks model gives surface runoff volume and soil water index as a hydrological parameter for a logistic regression-based landslide susceptibility model. Then, applying landslide model with a scaling relation of volume and area predicts landslide occurrence. The Universal Soil Loss Equation is then used for calculating soil erosion volume. Finally, incorporating runoff-routing algorithm and the Hunt’s model achiev...

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A New Technique for Batch Production of Tubular Anodic Aluminum Oxide Films for Filtering Applications

Applied Sciences, 2018

With larger surface areas and nanochannels for mass delivery and gas diffusion, three-dimensional... more With larger surface areas and nanochannels for mass delivery and gas diffusion, three-dimensional tubular anodic aluminum oxide (AAO) films have practical advantages over two-dimensional AAO films for medical and energy applications. In this research, we have developed a process for batch production of tubular AAO films using a 6061 Al tube. The tubular AAO films have open nano-channels on both sides, with average pore dimensions of about 60 nm and pore densities of about 10 8 to 10 9 pore/cm 2. It was found that the porous AAO material with nano-channel structure exhibited dialysis behavior, allowing for liquid/gas exudation through diffusion between the inner and outer surfaces of the tubular AAO films. Ar gas bearing test and aeration test were conducted to find the pressure bearing capacity of tubular AAO films. It was demonstrated that the AAO film with a thickness of 100 µm can resist an argon pressure up to 8 atm; however, 30 µm AAO film can only withstand 3 atm of Ar gas. The tubular AAO films with exudation characteristics have the potential for applications in advanced technologies, such as liquid or gas filters, drug delivery, and energy applications.

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Reconstructing more than 40 years soil re-distribution in two Taiwanese watersheds

Taiwan is a little smaller than the Netherlands, an island surrounded by the sea and has a popula... more Taiwan is a little smaller than the Netherlands, an island surrounded by the sea and has a population of circa 23 million. Add a central range of steep mountains and it is clear that the pressure on living space and natural resources is enormous. This is exemplified by the fact that Taiwan has become one of the countries facing water shortages in the next decades. Taiwan has around 40 large reservoirs that hold around 4200 million cubic meter of all water. A recent study shows that each year, around 400 million cubic meter of silt accumulates in Taiwan's reservoirs, yet only around 10% of sediment is removed. Reservoir management aims to counter the sedimentation problem at the source namely the erosion and transport of soil material.. However, effective measures require reliable data on patterns and rates of erosion in the hinterland. For example, the effects of tropical cyclones on erosion rates of forested slope land soils are not well established. Therefore, the authors present a novel method to reconstruct more than 40 years of soil erosion and deposition within the two largest reservoir catchments in Taiwan. The method combines the 137 Cs isotope technique, widely used to calculate soil redistribution rates, with a detailed representation of the watersheds in a GIS. More than 160 soil profile samples were collected in undisturbed and disturbed locations across the watersheds. Sampling was based on a priori stratification of the watersheds into landscape units. Inside each unit 137 Cs activity levels in multiple soil profiles were analysed and published conversion techniques were applied to compute soil redistribution rates for each site. Statistical methods were then applied to obtain the relations between redistribution rates and landscape units. These relations were then distributed using a GIS representation of the landscape units in each watershed. The result is a series of maps that show 40 years soil erosion across the studied watersheds as well as estimates of uncertainties. It was found that soil erosion may well account for up to a quarter of total sedimentation and forested areas account for the majority of the sediment found today in the reservoir. The absolute highest erosion rates are measured in farmland. The authors believe that the method has great potential for soil erosion mitigation programs and should become a part of standard watershed investigation procedures.

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Combination of landslide volumes estimation and debris flow simulation in the Xinkai village, southern Taiwan

Many debris flows in the tropical and mountainous areas, including Taiwan, are triggered by heavy... more Many debris flows in the tropical and mountainous areas, including Taiwan, are triggered by heavy rainfall with failed materials from large landslides and usually induced severe natural hazards. To assess debris flow hazards, numerical simulation for affecting zone is widely adopted in Taiwan. As for the simulation, the estimation of triggering volume of debris flow is a critical component. Previous studies have estimated these volumes by field surveys or equilibrium concentration concept, which estimates the volume of debris flow by using accumulated rainfall. However, as shown in many studies in recent years, the volume of failed materials triggered by landslide could be more accurately estimated by empirical relationships relating the volume of individual landslides to its area. In this study, we propose a new novel methodology comprising this scaling relationship for landslide volume estimation and Debris2D, which is a numerical model and developed by Liu and Huang (2006, Comput...

Estimation of soil erosion rates in a subtropical mountain watershed using 137Cs radionuclide

Natural Hazards, 2011

The formulation of watershed management strategies to protect water resources threatened by soil ... more The formulation of watershed management strategies to protect water resources threatened by soil erosion and sedimentation requires a thorough understanding of sediment sources and factors that drive soil movement in the watershed. This paper describes a study of medium-term water-driven soil erosion rates in a mountainous watershed of the Shihmen Reservoir in Taiwan. A total of 60 sampling sites were selected along a hillslope. At each sampling site, the inventory 137 Cs activity was determined and then calculated with the diffusion and migration model to derive soil erosion rates. The rates are one to two orders of magnitude lower than estimates using the Universal Soil Loss Equation, a soil erosion model often used in Taiwan. Results of multiple regression analysis indicate that the spatial variability of soil erosion rates is associated with the relative position of a sampling site to the nearest ridge and soil bulk densities (r 2 = 0.33, p \ 0.01). Finally, the patterns of soil redistribution rates on the hillslope follow the 137 Cs hillslope model as soil erosion increases in the downslope direction. No deposition site is found at footslope because soil deposition is swept away by regular flooding along the stream channel. This study is an important first step in using 137 Cs as a tracer of soil redistribution in mountainous watersheds of Taiwan.

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Quantifying rainfall controls on catchment-scale landslide erosion in Taiwan

Earth Surface Processes and Landforms, 2012

Landslide erosion is a dominant hillslope process and the main source of stream sediment in tropi... more Landslide erosion is a dominant hillslope process and the main source of stream sediment in tropical, tectonically active mountain belts. In this study, we quantified landslide erosion triggered by 24 rainfall events from 2001 to 2009 in three mountainous watersheds in Taiwan and investigated relationships between landslide erosion and rainfall variables. The results show positive power-law relations between landslide erosion and rainfall intensity and cumulative rainfall, with scaling exponents ranging from 2Á94 to 5Á03. Additionally, landslide erosion caused by Typhoon Morakot is of comparable magnitude to landslide erosion caused by the Chi-Chi Earthquake (M W = 7Á6) or 22-24 years of basin-averaged erosion. Comparison of the three watersheds indicates that deeper landslides that mobilize soil and bedrock are triggered by long-duration rainfall, whereas shallow landslides are triggered by short-duration rainfall. These results suggest that rainfall intensity and watershed characteristics are important controls on rainfall-triggered landslide erosion and that severe typhoons, like high-magnitude earthquakes, can generate high rates of landslide erosion in Taiwan.

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Calibrating landscape process modelling with Caesium-137 data and typhoon rainfall records

Calibration of landscape evolution models (LEMs) needs long term input data on climate and soil r... more Calibration of landscape evolution models (LEMs) needs long term input data on climate and soil redistribution. Rainfall data over the last decades can often be estimated from field stations and interpolation. A decadal estimate of soil redistribution can be derived from analysing the spatial variation of the Caesium-137 inventory in the soil. The objective of this case study is to calibrate LEM LAPSUS for a small watershed in Taiwan, using historical rainfall records and Caesium-137 derived soil redistribution estimates. In general, the point location soil redistribution estimates from the Caesium-137 activity can be modelled with LAPSUS within a certain margin of error. However, the LAPSUS soil redistribution maps can differ considerably from the point-interpolation derived maps. This is mainly due to the process based LAPSUS methodology, where the DEM and water flow routing are the main driving factors.

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Landscape Dynamics: Calibrating landscape process modelling with Caesium-137 data, separating water driven erosion from landslides

Variation of atmospheric Be-7 in relation to PM concentrations

Applied Radiation and Isotopes, 2013

The 7 Be and PM concentrations in air were monitored simultaneously during 1998-2011. Both PM and... more The 7 Be and PM concentrations in air were monitored simultaneously during 1998-2011. Both PM and 7 Be concentrations increased as a result of the northeasterly monsoon. Both the lowest PM and 7 Be concentrations were observed in July and August. The 7 Be concentrations in surface air can be predicted from the PM concentrations.

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Deposition of beryllium-7 in Hsinchu, Taiwan

Applied Radiation and Isotopes, 2012

In the present study, factors that influence the distribution and variation of (7)Be in Hsinchu, ... more In the present study, factors that influence the distribution and variation of (7)Be in Hsinchu, Taiwan were elucidated. The (7)Be activity including the deposition flux and air concentration was continuously monitored and recorded throughout a 15-year period (1996-2010). To explain the observed variability in the (7)Be activity over time, air concentration and deposition flux of (7)Be were correlated to rainfall and solar activity. The monthly average deposition flux and air concentration of (7)Be were inversely related to solar activity with the 11-year cycle and were not strongly correlated to rainfall. The highest seasonal deposition flux of (7)Be occurred in March, which is commonly referred to as the spring maximum, due to air-mass mixing processes in the troposphere. The air concentration of (7)Be was seasonally variable and was significantly affected by monsoons. The lowest deposition flux and air concentration of (7)Be were observed in July and August due to the occurrence of southwest monsoons from low latitudes, which carry air masses with low concentrations of (7)Be. The deposition flux was enhanced by precipitation, which increased the deposition velocity, transferring more (7)Be from the troposphere to the ground. The fraction of dry to total deposition varied seasonally and was equal to 9.86%, on average.

GIS-based Decision Support System for Management of Landslide Hazard after Typhoon Event

… 2010, held 2-7 May, 2010 …, 2010

The paper presents a GIS-based decision support system (DSS) for landslide hazard emergency respo... more

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