Applications of data assimilation techniques have been widely used to improve upon the predictability of hydrologic modeling. Among various data assimilation techniques, sequential Monte Carlo (SMC) filters, known as "particle filters" provide the capability to handle non-linear and non-Gaussian state-space models. This paper proposes a dual state-parameter updating scheme (DUS) based on SMC methods to estimate both state and parameter variables of a hydrologic model. We introduce a kernel smoothing method for the robust estimation of uncertain model parameters in the DUS. The applicability of the dual updating scheme is illustrated using the implementation of the storage function model on a middle-sized Japanese catchment. We also compare performance results of DUS combined with various SMC methods, such as SIR, ASIR and RPF.
This paper presents the extension of the previous work on the development of short-term flood forecast model using rainfall downscaled from the global NWP outputs. The proposed downscale method has considered physically based corrections to the NWP outputs for optimization of parameters used for calibration phases using artificial neural network (ANN). Downscaled rainfall was then used as inputs to the modified super tank model for runoff forecast. Model uncertainties were quantified against forecast lead-times in order to integrate forecast results into the existing alarm levels for early flood warning. Results showed that flood forecasts based on the downscaled rainfall by ANN outperformed those using multiple linear regression methods. Though it showed larger uncertainties along with the forecast lead-times, the model can provide reliable forecasts up to 18-hour ahead. It has demonstrated an added value in flood forecasting and warning practices for river basins in Central Vietnam.
Tonle Sap Lake (TSL) plays an important role not only as a source of water resources, but also as a part of the Mekong River (MR) ecosystem. Therefore, assessment of current situation and possible future change of water budget in TSL is needed for water resources management and conservation of ecosystem of this region. In this study, we propose the methodology for simulating water budget of the TSL which can incorporate the interaction between the lake and surrounding hydrological system by coupling the River Lake Water Exchange (RLWE) model and the Yamanashi distributed Hydrological Model (YHyM). The performance of coupled model was verified by comparing simulated and observed daily water volume of TSL. Then the impact of precipitation change on TSL hydrological system was analyzed as a trial application using the coupled model. The results indicate a decrease of maximum water volume of TSL under future scenario which is mainly due to the reduction of water flow into the TSL from MR.
This present study is proposed to overcome the lack of distributed data, usually occurs in developing country, in order to simulate fully distributed flood runoff response to land cover change in urbanized catchment. A method to produce spatial distributed hourly rainfall is developed. Linear interpolation approach is used to estimate hourly rainfall by considering hourly rainfall deviation from daily average. Infiltration in urban area is accommodated by applying spatial distributed urban density. The urban density is detected using the land cover and district area data. This parameter is further adjusted to get the value of infiltration coefficient in urban area which determines the loss of water in urban area. The model, a combination of 2D runoff model with NCF tank model, is applied to the upper part of Ciliwung River basin in Indonesia. By using spatial distributed parameters, model performance has improved. It is also shown that land cover changes due to urbanization, in response, have intensified flood runoff discharge.
This paper highlights the application of Water and Energy Transfer Processes (WEP) Model to two highly urbanized watersheds within Tokyo, Japan; Nomikawa and Meguro watershed. Major model improvements include refinement of time-resolution input rainfall data from 1 hr. to 10 min. intervals, and addition of subroutine to accommodate weir/side-weir effects and rainfall input. 2007 heavy rainfall data from Tokyo AMESH were used in Nomikawa watershed simulation. 2008 heavy rainfall data from Tokyo Metropolitan Construction Bureau were also used to simulate runoffs for Meguro watershed. The improved model was validated using comparative analysis of previous and new model using simulated river discharges and actual gauge measurements. Results show the new model simulates rapid runoffs well.
Land use and land cover (LULC) have been continuously changing, through human activities, leading to variations in hydrological cycle. In this study, we applied SWAT model to investigate potential impacts of LULC on water budget of the Chi river basin in Thailand. Five plausible scenarios of land use change were evaluated, including an conversion of forested area, expansion of farmland, switching of rice paddy fields to energy crops and two scenarios involving conversion of farmland to rice and sugarcane plantation. The results indicated that different land use scenarios contributed to various effects in annual and seasonal water yield and evapotranspiration (ET). Conversion of forested area and farmland showed slightly small changes on water flows and ET. Substitution of paddy fields by sugarcane plantation showed clearly reduced water flows and increased ET by almost 5.0% in dry season. Particularly, in case of expansion of rice paddy fields to farmland, small changes occur on annual flow and ET but more significant effect occur on seasonal flows. The results showed decrease in ET by nearly 12.0%, leading to increase of water yield by up to 5.1% during dry season. Finally, conversion of farmland to sugarcane plantation for biofuel production showed significant effect on seasonal ET, mainly decreasing in dry season by 4.5 % but small changes were detected on water yields.
This paper verifies satellite-based rainfall data GSMaP_MVK+ with gauge observed rainfall over the Nepal Himalayas. Assessment of the accuracy is done at two levels, firstly for the whole country and secondly for physiographic regions. Verification of daily rainfall at a country level shows that the GSMaP_MVK+ captures the spatial distribution of rainfall well but underestimates with a correlation coefficient 0.79, bias -2.6 and RMSE 4.8 mm day-1 and percentage error of -55%. Verification with physiographic regions show that the GSMaP_MVK+ performs well in flatter terrain with a correlation coefficient of higher than 0.8 and prediction accuracy of 70%; however, performance deteriorates with increase in altitude. In the Mid and High Mountain areas the correlation coefficient is 0.4 with prediction of 40% or less. The results indicate the need for improvement of GSMaP_MVK+ estimates by considering orography in the algorithm or bias adjustment before application in the Himalayas.
Near real time rainfall information is necessary for early warning of rainfall triggered hazard such as floods and landslides. Remote sensing based rainfall estimation has been considered to be used to fulfill that purpose. This research is addressed to use geostationary based rainfall estimation by using Multi Transport Satellite (MTSAT) data which is blended with Tropical Rainfall Measuring Mission (TRMM) 2A12 datasets in order to provide near real time rainfall information, especially for hazard study purposes over Java Island, Indonesia. Comparison to TRMM Multi Precipitation Analysis (TMPA) datasets is performed. Spatial and temporal validation of those rainfall estimations is conducted by validating them with available rain gauge data during a rainy season in December 2007. Temporal validation result shows that TMPA demonstrated better statistical performance than MTSAT blended. However for the spatial correlation, MTSAT blended shows relatively better performance than TMPA.
This paper describes a multi-velocity TOPMODEL approach applied to the Amazon basin. Comparison with the original TOPMODEL approach evaluates this new approach in terms of hydrograph simulation, physical meaning of the parameters and sub-surface flow generation. The new meteorological data and the improvements in estimates of area and distances may be responsible for higher efficiencies of both model approaches. Hydrograph simulation indicates, since the parameters are constrained according to literature review, that the multi-velocity approach performs quite better and the sub-surface flow parcel in the total flow is consistent with tracer studies carried out in the basin. There are evidences that higher values of saturated hydraulic transmissivity in the original model approach are a model response to compensate the spatial invariant velocity parameterization and/or the grid resolution. The multi-velocity model approach seems to be a suitable alternative, since it represents in a better way the sub-surface flow and whence saturated areas in Amazon basin.
Many studies have been carried out in order to produce measures capable of ensuring the sustainable use of the water resources. A better management of water resources systems can be achieved if the long term information of hydrologic variables is available, which is not always the case. Stochastic simulation of such hydrologic variables is an attractive alternative to extend the length of observed records. This paper applies an Artificial Neural Network (ANN) model for simulating daily groundwater levels for the city of Matsuyama, Japan. The stochastic generated series must keep not only the statistical properties but also the seasonal oscillations of the observed series. Ten years of observed daily data were used for calibrating the model parameters. The results show that the model preserves the major statistical properties.
Calibration and uncertainty analysis is necessary to perform the best estimation and uncertainty identification of hydrological models. This paper uses the Soil and Water Assessment Tool-Calibration and Uncertainly Procedures (SWAT-CUP) model to analyze the uncertainty of SWAT model in a Japanese river catchment. The GLUE and SUFI-2 techniques used in this analysis show quite good results with high value of R2 as 0.98 and 0.95 for monthly simulation. Daily simulation results during calibration and validation are also good with R2 as 0.86 and 0.80. For uncertainty results, the 95% prediction uncertainty (95PPU) brackets very well with the observation. The p-factors of uncertainty analysis for the calibration and validation periods are 92% and 94%. The calibration result by using GLUE shows better than that by using SUFI-2. However, the processing time of the GLUE approach is longer than SUFI-2 approach when they were run in the SWAT-CUP. The uncertainty analysis indicates that the parameters of effective hydraulic conductivity in main channel alluvium (CH_K2) and base-flow alpha factor for bank storage (ALPHA_BNK) play important roles for calibration and validation of SWAT model.
This study estimated the contribution of seasonal glacier and snow cover variation on runoff generation in the Tagliamento River catchment in Italy. The normalized difference snow index (NDSI) and band combination method were employed to estimate the glacier and snow melting over different seasons in two catchments and link with the tank model to simulate the river discharge. Approximately 51 percent of the catchment area is covered with glacier and snow during the winter, which dramatically reduces to about 5 percent during summer. Markedly, 50-75 percent of the river discharge from April to June is generated by the glacier and snow melting. With reference to the climate change, it is noted that the snowpack in this region is often close to its melting point (e.g., -0.9°C in February), which may respond rapidly even to minor changes in temperature (62 km2/°C) resulting possible early season runoff. The dependency of the model parameters on different climatic and geographical settings was also discussed.
The distributed biosphere hydrological model (WEB-DHM) was physically improved in snow physics, by incorporating the 3-layer energy balance based snow module of the Simplified Simple Biosphere 3 (SSiB3) model and albedo module of the Biosphere Atmosphere Transfer Scheme (BATS). The new version of WEB-DHM is referred to as WEB-DHM-S. In this study, the WEB-DHM-S is evaluated at Valdai site (Russia) from 1966 to 1983, to check its performance in simulating the interannual variability of snow cover. Results show that the WEB-DHM-S is capable of reproducing the point-scale interannual variations of snow water equivalent, soil and snow surface temperature well. In addition, the good performance of WEB-DHM-S was further confirmed in simulating soil moisture (top 1 m) and evapotranspiration.
In this paper are investigated the net radiation (Rn) and the potential glacier melt discharge trends in a glacier in the tropical Andes, for the assessment of climate change impacts on the water resources availability in remote regions. It is assessed the applicability of remote sensing techniques, through the performance evaluation of the Surface and Energy Balance algorithm (SEBAL). For the calibration it is used ground data observed on the ablation surface of the Zongo glacier in Bolivia. The potential climate change impacts quantified are on the glacier melt discharge. The inferences are calibrated in the period 2004-2007. Results show that the SEBAL performance is adequate from an engineering perspective (Root Mean Square Error for albedo estimations are 0.15, in average). Climate change impacts for the period 1986-2005 are an increase of 42% in the Rn, and the loss in the glacier ablation area of 37% (both in reference to 1986). The melt from the studied glacier in the period 2004-2007 is estimated to produce a maximum potential energy of 3.1 [MW h] in average per day (dry season), which in the practice can be used to quantify the potential impacts of the climate change in partially glacierized catchments.
Future river flow changes in the Tone River basin, Japan, were investigated using a fine resolution distributed hydrologic model and the MRI-AM20km projection output, which is simulated under the A1B climate change scenario. Multiple dam reservoir operations and current water usage information were also considered for realistic river flow simulations. The future water usage and reservoir operation was assumed to be the same as under current conditions. Analysis results show that the river flow change downstream of the basin seems to be insignificant compared to the area upstream of the basin; however, more frequent water shortage days are expected in the future, especially at the Tone-Ozeki station. Revised dam reservoir operation rules should be prepared unless the current water demand changes properly in the future.
Several countries utilize the sedimentary soft rock for nuclear waste disposal because it has a potential to use as a host rock. Therefore, the analytical researches on the unsaturated flow of this type of rocks have been increased to assure the safety of the disposal. In this study, the applicability of three models; Brooks-Corey/Burdine (BC), Campbell (CB) and van Genuchten (VG) that have been used commonly for soil was studied, by applying these to one dimensional flow induced by evaporation in six disk shaped soft rock samples. The best parameters in each model were inversely estimated by adopting genetic algorithm (GA). It was clearly found that the best parameters in BC and CB models can be easily estimated and the measured evaporation change could be well analyzed. However, the parameters in VG model could not be estimated easily. It was found that BC and CB models are more robust than the VG model for the analysis of unsaturated flow in soft rock.
This study proposes a theoretical model to predict soil wetting pattern and water balance in a negative pressure difference irrigation (NPDI) system and describes laboratory experimental results from which this model was derived. The experiments were conducted by using a porous pipe, a water reservoir and a soil column filled with Kawanishi sand. The temporal variations in volumetric water content profile, supplied water, soil water storage and evaporation were calculated by the proposed model. The calculated results were in good agreement with the experimental results. The margin of error of the water balance was in the range of 3 to 7 %. It is concluded that the proposed model is valid for an optimal design of the NPDI system.
Negative pressure difference irrigation (NPDI) is considered to be an attractive mode of irrigation because water use efficiency in this case is higher than that in conventional irrigation methods such as basin irrigation, furrow irrigation and sprinkler irrigation. In order to investigate the water balance in a NPDI system, experiments involving the use of a soil column, porous pipe and water reservoir were carried out in a temperature and humidity controlled room. The evaporation (Meva), supplied water (Msup), soil water storage (Msoil), wetted soil surface area and configuration of the wetted soil around the porous pipe were determined for three different negative pressures. Empirical equations were proposed for the calculation of Meva and Msoil. The proposed simple model could well reproduce the temporal variations in Meva and Msoil. With a decrease in the negative pressure, the water use efficiency increased and was in the range of 0.92 to 0.97.
Ensemble rainfall short-term prediction with flood simulation in urban river basin is presented. Considering the small scale of storm event, the radar echo extrapolation by translation model was used for predicting rainfall from X-band polarimetric radar. A new attempt of the ensemble prediction system by using initial condition perturbed by singular vector was introduced to find perturbations of advection vector, which linearly grow most rapidly. The methodology was demonstrated throughout case studies in Kofu urban river basin, Japan, with convective and stratiform precipitation system cases. SV found two leading perturbations over three hour prediction, giving five ensemble members. The members were subsequently considered as uncertain input of distributed hydrological model for developing ensemble flood prediction. Verified with observed data, this approach could serve as a reliable and effective system for operational flood disaster prevention in urban area.
The Kirindi Oya irrigation scheme is considered water scarce since its inauguration in 1986. At present, it is faced with the grave problem of its farmers leaving paddy cultivation especially in the RB sub system. The present governance of the irrigation system was evaluated using inequality in irrigation water supplies as an indicator of farmer dissatisfaction. Gini Coefficient proved strong for our cause, of the three inequality measures used. Monitoring inequality in the irrigation system provides approaches to better future governance. The Lorenz curves provided a wide insight into the inequality conditions as well. The introduced methodology will facilitate irrigation management in the whole Asia.
A quasi-2D model of hydrodynamics and sediment transport has been developed in this study. An eddy viscosity model with a function of artificial viscosity has been applied to the Boussinesq-type equations to produce wave decay as well as sediment transport due to breaking. Numerical results are then compared with laboratory experimental data in order to verify the applicability of the numerical model. The results demonstrate that the proposed eddy viscosity model can be used to simulate wave propagation in the surf zone as well as suspended concentration distribution. Erosion before the breaking point can be predicted fairly well. However, the bar crest and erosion in the surf zone can not be predicted accurately.
In this study, we perform a theoretical study on channel inception in the case of steep slopes. The conceptual model for the channelization process under steep slope is formulated by considering uniform steady shallow water flowing in a typically smooth straight ending with upward concave steep slope gradually changing to a very mild slope. The flow on the steep slope is assumed to be supercritical whereas the flow on mild slope is assumed to be subcritical in the Froude sense. In the formulation process, we used two-dimensional depth-averaged shallow water equations. A linear stability analysis is used to study the problem. The problem is an eigenvalue boundary problem, solved using the spectral collocation method with the Chebyshev polynomials. Finally, we found a relation between growth rate of perturbation and characteristic wave number for the case of steep slopes. The dominant wave length is found to be 20 to 29 times the Froude critical depth.
The glacial lake outburst due to moraine dam failure has been investigated through numerical model and flume experiments. A numerical model has been developed to compute the characteristics of the glacial lake outburst due to moraine dam failure by seepage flow and overtopping. Numerical analyses of seepage and moraine dam failure have been also performed. To compute the pore water pressure in the dam and slope stability of the dam, a seepage flow model and a slope stability model are incorporated into a numerical model of flow and dam surface erosion. The simulated results of the outburst discharge, seepage profile, failure surface and dam surface erosion are compared with the experimental results.
In this study, the conventional water-phase (one-phase) as well as water-air two-phase seepage flow numerical simulation models has been developed individually for seepage calculation inside the body of landslide dam. Janbu’s simplified method as well as extended Spencer method has been used in slope stability analysis. Simulation results obtained by two-phase seepage flow model and extended Spencer method are comparatively in good agreement with the experimentally observed results than that of conventional seepage flow model and Janbu’s simplified method. The two-phase seepage flow phenomenon in the dam analysis has been verified by performing one dimensional numerical and experimental analysis.
Alluvial rivers at low land as in Bangladesh are highly dynamic in nature; where huge landloss due to severe bank erosion at high flood as well as repeated interruptions of navigation system due to rapid sedimentation at low flow are very common. Groynes, revetments etc. are typically used to overcome these problems, but the goals are not achieved as expected. This study investigates the optimum design of a groyne for its effective functioning. A 2D model, RIC-Nays is utilized in this study upon confirmation. The channel and flow parameters are based on conformity to a typical river of Bangladesh. Four orientations and three configurations of groynes are considered here. The performance of groynes is evaluated through three key indices erosion in channel bed (thalweg), deposition in groyne field, and scour near groyne-tip. Computations reveal that a modified groyne functions better over the straight ones through protection of channel bank from erosion and maintenance of navigation channel as well.
In this paper, the applicability of bandal-like structures as an alternative method for traditional river training structures like groins is investigated. This structure is usually used in Indian Sub-Continents for riverbank protection and improvement of navigation conditions in alluvial rivers. The mechanism behind the utilization of this type of structure which affects the flow patterns and sediment transport process was studied through experimental measurements and numerical simulations. During the calculations, the water flow is computed by solving the Reynolds-averaged Navier-Stokes equations in 3D domain. The k model is used for the turbulence closure and the numerical simulation is conducted on the unstructured meshes with the finite volume method. The main characteristics of the sediment erosion/deposition process around the bandal-like structures are clarified. The promising use of bandal-like structures is demonstrated through the comparisons with conventional structures as impermeable groins.
The failure of natural dam may occur with a variety of failure modes which includes overtopping, seepage or piping, sudden sliding etc. Natural dams may fail due to seepage or piping because they have not undergone systematic compaction and they may have high porosities. In-depth knowledge of the mechanism of the dam failures by seepage or piping and measured data are still lacking. Extensive laboratory experiments are carried out to study enlargement of the pipe due to internal erosion and resulting outflow hydrographs by varying size of initial pipe, lake water level, lake water volume, slope and location of the pipe. This paper highlights limitations of simplified models used to predict outflow hydrograph due to piping failure of the dam based on experimental results and provides data set for the validation of numerical model. Experimental results show that the initial size, slope and location of pipes have significant effects on magnitude and occurrence time of peak discharge.
Sedimentation is a big problem in the sense of sustainability of surface water resource, especially in North Africa under the Mediterranean climate system. The counter measure to that problem is simply dredging but it has not been carried out in North African countries due to the financial reason. In this study, the present condition of sedimentation on the reservoir in Tunisia is reported and the practical countermeasure to that problem is suggested with regard to the possibility of using sediment as soil amelioration for alkaline saline soil which is very serious in North Africa.First, the bathymetric survey was carried out in order to grasp the development of sedimentation. And then, the water quality parameters were observed for the discussion of mass transfer in the water body. Finally, humic substances which can play a role of soil amelioration for saline alkaline soil are confirmed in the sediment sample.
This paper evaluates the performance of the sediment bypass tunnel that diverts the suspended sediment from Lake Miwa to downstream reaches below Miwa dam. In such a complex processes during bypassing, it is difficult to predict the sediment bypassed efficiency numerically. Therefore, the digital image techniques were developed and implemented to measure the flow pattern and suspended sediment concentration SSC for the first time in Miwa dam. Where, field measurements were conducted during flood seasons in June and July 2010. Surface flow velocity and SSC were analyzed to clarify the performance before and after the commencement bypassing operation mode. The measured sediment bypassed efficiency assists the decision making on optimization of bypassing performance and validates numerical prediction. The facility proved its effectiveness in mitigating reservoir sedimentation in Miwa dam and turbidity of river water contributing towards restoration of downstream environment.
In this study, analysis of inundation flow considering overflow from a river channel due to heavy rainfall is carried out for establishment of countermeasures against flood disasters. The numerical simulations and the laboratory experiments are conducted for estimation of these phenomena. Especially, a numerical model for simulation of inundation flow considering overflow from a river channel is proposed and evaluated. The numerical model proposed in this study includes 2D horizontal model and 3D RANS (Reynolds Averaged Navier-Stokes) model. Two models are coupled by simultaneous grid method and all hydraulic quantities are connected in overlapped position of meshes. And, the standard k-e model for turbulence closure and the VOF (Volume of Fluid) method for free-surface modeling are also included in the numerical model. The proposed 2D-3D numerical coupling model is applied to a domain with a river channel and a floodplain, and the laboratory experiments are also conducted to compare with the numerical results. The numerical results have good agreements with those of experiments for the variations of the inundation flow into a floodplain considering overflow from a river channel and the effects of water level rise by river structures. It is judged that the proposed model can be helpful to establish countermeasures against inundation disasters.
Open-channel confluence flows are common in natural river systems as well as in environmental and hydraulic engineering, such as in river engineering. Often, these flows are three-dimensional and complex,while numerical studies fully describing confluence flow are still few. This paper presents the results of investigation of confluence flow using a three-dimensional numerical model with the linear and nonlinear k-ε models. To treat the dynamic boundary condition at the free surface, non-hydrostatic pressure is included in the present model. The model is validated using the experimental data available. Adequacy of the present model with two turbulence models above is indicated based on the result analysis. The nonlinear model is indicated as the more advantageous one than the linear one.
Linear stability analysis of a turbulent flow in a wide rectangular open channel partially covered with vegetation is performed using a shallow-water approach. The vegetated and non-vegetated zones are configured so that violent transverse mixing occurs at the vicinity of the interface between the two zones. In the base state there is no transverse velocity, although there is an abrupt variation in the streamwise velocity near the interface between the non-vegetated and the vegetated zones. The perturbations were analysed in order to find their maximum growth rate. Results show that depending on the assumed wavenumber, the maximum growth rate of perturbations is positive, what means that the perturbations may grow as time progresses.
A non-linear k-epsilon model coupled with a vegetation model has been applied to three turbulent flows in partially vegetated open channels to scrutinize its performance. Three test cases include flow in a straight rectangular channel with vegetation belts along both sides of the channel and flows in a compound channel with different emergent vegetation zones over a floodplain, where experimental data have been obtained by the authors. Comparison with the experimental results demonstrates that the non-linear k-epsilon model can reasonably captures secondary flows of the second kind and a row of large vortices along the interface between main channel and vegetated zones, which the standard k-epsilon model fails to produce. The calculated results are found to show fairly good agreement with the measurements in terms of mean streamwise velocity, secondary currents of the second kind and Reynolds shear stresses components.
This paper deals with a numerical model to simulate flow through a box culvert, which represents flow during flash floods under highways in Oman. We firstly show the typical flow patterns with the transition from free surface flows to pressurized flows and overflows over a culvert, based on hydraulic experiments. Then, a numerical model applicable to the full/partial full pressurized flows is tested to simulate the typical flow patterns under the conditions of experiments.It is pointed out that although the numerical model used here can simulate the simple flow patterns to some extents, the model should be improved further to get better results.
This study reports the experimental results of velocity measurements in an embayment with two entrances. The typical flow patterns were revealed in the embayment with two entrances. The flow patterns in the embayment were extremely changed by narrowing the entrance width. The flow mechanism is divided into two groups according to the interaction at the interface between main channel and embayment. The general flow for this kind of semi open embayment is from upstream entrance to downstream entrance. The exceptional of flow in the embayment is characterized by a limited configuration of downstream entrance in carrying the momentum into the embayment.
We estimated relative bubble density and flux based on the ultrasonic echo intensity and the upward velocity. We derived a relational expression between the relative bubble density and the ultrasonic echo intensity, after assuming that the (a)bubbles can be replaced by simple rigid spheres with a constant radius, (b)the radius is enough larger than the wavelength of the incident wave of the acoustic current meter, and (c)the sound absorption by the sea water can be regarded as the constant. At high tide, at erupting state the relative bubble density had large value, while at halting state it had quite small value. At low tide, however, the relative bubble density had almost always positive value, thus the bubbles always were present in the sea water. And the similarity between the relative bubble density and the upward velocity confirmed that the bubbles in the sea water were transported by the fluid discharged from the underwater geyser.
Our main instruments for collecting current flow velocity data are acoustic Doppler sensors. An inherent issue with application of this type of instrument is that the observed data are contaminated by spurious records. Detecting and replacing becomes important in turbulence studies. In the present paper we introduce two effective approaches for detecting multipoint spikes effectively by applying wavelet decomposition. Moreover, by taking advantage of time series modeling a reliable method for replacing multipoint spikes is presented. This method is able of predicting future points while keeping the trend and high-frequency fluctuations. Applying the introduced detecting- replacing outliers algorithms to different samples and comparing the results with other approaches confirms reliability and accuracy of them.
This paper presented a 3D model for substance transport in river and its application for simulation of pollutant transport in Mekong river due to floating cages-raising. 3D flow-field was solved by logarithmic distributing 2D flow-field of averaged height. Pollutant transport is calculated by solving its full 3D transport equation. The 2D continuum and momentum equations were solved by finite difference method with ADI scheme of Ponce-Yabusaki. The 3D transport equation was solved by finite volume method with ADI scheme of Douglas-Gunn in "sigma" transformed co-ordinate. The model was tested over analytical solution. Some preliminary results of simulation for pollutant transport of Myhoahung floating cages area (Angiang province) are also presented.
The effect of sludge on water quality has big problems in Hori River, Nagoya, Japan. An observation is carried out to find out the relationship between the sludge and water quality at Naka Bridge of Hori River. Observations have done in the spring and neap tides using salinity, dissolved oxygen, turbidity, water temperature and ph as indicators. Moreover, experiment on the chemical parameters of water quality such as TN (inorganic form i.e. NH4-N, NO3-N, NO2-N) and TP were done in order to find out the impacts of sludge on the water for the improvement of better habitants of Hori River. Overall, TP and TN for the different two tides did not show any large variations and were fairly comparable. The pattern of water quality changed with the tides. For example, during spring tide, high DO levels were recorded and vice versa. At spring tide, the DO levels increased due to wave action and sea water intrusion. The sludge flushed into the river during spring tide of high velocity and exposure in the middle layers. Therefore, it noted that the water quality of the Hori River was greatly influenced by the tidal changes and the deposition of sludge.
The present study is concerning bottom boundary layer beneath solitary wave over smooth beds condition. A new generation system was proposed to generate an oscillatory motion similar to solitary wave in a closed conduit water tunnel using a mechanical system. This generation system facilitates easy measurement of periodical oscillatory motion to replace solitary wave motion with a sufficient tranquil period. The velocities were measured by using a Laser Doppler Veloci-meter (LDV) at 17 to 22 points in the vertical direction. The experiments were accomplished with different velocities under single and periodical oscillatory motion conditions and validations have been done in some various terms of experiment relevant to solitary wave boundary layer. A good agreement is achieved in validation of free stream velocity and also both single and periodical oscillatory motion measurements methods. Furthermore, validation of velocity distribution in time variation obtains a critical Reynolds number which has a good agreement with the finding of previous researchers.
Solitary wave run up phenomenon has been studied widely. Its similarity to tsunami has magnified the importance of the study. Bed stress will have significant influence during this stage. Nevertheless, it is unclear where the bed stress dominant flow regime will occur. In this study, SWE model is coupled with k-w model, to achieve a more accurate bed stress assessment. The conventional Manning method approach for bed stress is replaced with a direct assessment from the boundary layer using the k-w model. Numerical experiment is conducted to estimate proper criteria to define the demarcation line for bed stress dominance regime. Bed stress effect is investigated by analyzing each of the momentum terms. It is found that the run up process can be classified into five phases based on the bed stress importance. Furthermore, a new parameter is proposed as a demarcation line for bed stress importance region.
In this study, a simple statistical method is developed to correct bias in the precipitation simulated by GCM20, an atmospheric general circulation model with 20 km spatial resolution developed by the Meteorological Research Institute. The method primarily aims to correct intensity of GCM20 daily precipitation samples to express both seasonal patterns and extreme values appropriately. The basic idea of the bias correction is to adjust the probability distribution of GCM20 daily precipitation to that of its observed counterparts. To examine the correction performance the proposed method is applied to the Yoshino River basin in Japan. The results show that it appropriately corrects the GCM20 bias in both monthly and extreme daily precipitation.
Previous studies have used low-resolution models to investigate the potential predictability of river discharges. The present study conducts a preliminary investigation of this predictability based on a dynamical seasonal prediction method using an atmospheric general circulation model (AGCM) and studies its dependency on the AGCM’s horizontal resolution. I performed 60-km and 180-km mesh AGCM simulations forced with the observed sea-surface temperatures and sea-ice concentration and simulations performed by converting the 60-km mesh simulation results to 180-km mesh ones and vice-versa. The global geographical distributions of the potential predictability resemble those of previous studies; in addition, the river basin correction effect is reconfirmed and found in basins exceeding 104km2 in area. Comparisons of the potential predictability among the multiple simulations demonstrate that upscaling loses the detailed features of the potential predictability, while downscaling retains the details. Dominant sources of the difference in the potential predictability of river discharge between the 60 km and 180 km mesh AGCMsimulations are their atmospheric potential predictabilities.
Several reports have assessed water scarcity globally using a widely accepted index on an annual basis, namely, withdrawal-to-water resources ratio (WWR). Here, we ask whether it is appropriate to use the WWR to assess the impact of climate change. Global warming is projected to increase the temporal and spatial variability of precipitation, decrease snowfall, and change the timing of snowmelt. To assess the impact of climate change on global water resources incorporating sub-annual time-scale phenomena, this study applies a new water scarcity index on a daily basis termed the cumulative withdrawal-to-demand ratio (CWD) . Our results indicated that global warming increased the mean annual runoff in 61% of the total land area globally. However, in 22% of the area where runoff increased, the CWD showed increased water stress. Those regions included India, northern China, and Europe. For India, the increase in water stress was attributed to the seasonal gap between runoff and water demand. The increased runoff was concentrated in a few months, while the high irrigation water demand months differed and were much longer. For Europe, the change was attributed to the shift in the timing of snowmelt, which occurred a few months earlier than at present, causing water shortages in early summer.
Bioenergy is regarded as clean energy due to its characteristics and expected to be a new support of world energy de¬mand, but there are few integrated assessments of the potential of bioenergy considering sustainable land use. We esti¬mated the global bioenergy potential with an integrated global water resources model, the H08. It can simulate the crop yields on global-scale at a spatial resolution of 0.50.5. Seven major crops in the world were considered; namely, maize, sugar beet, sugar cane, soybean, rapeseed, rice, and wheat, of which the first 5 are commonly used to produce biofuel now. Three different land-cover types were chosen as potential area for cultivation of biofuel-producing crop: fallow land, grassland, and portion of forests (excluding areas sensitive for biodiversity such as frontier forest). We attempted to estimate the maximum global bioenergy potential and it was estimated to be 1120EJ. Bioenergy potential depends on land-use limitations for the protection of bio-diversity and security of food. In another condition which assumed more land-use limitations, bioenergy potential was estimated to be 70-233EJ.
Train operation is stopped to ensure safety when the precipitation observed by a rain gauge exceeds a predetermined value. This paper proposes a method to determine the installation interval of rain gauges for railroads suitable for hourly precipitation which is often used as the index of rainfall intensity. The installation interval of rain gauges is evaluated from viewpoint of both safety and reliability of train operation, based on the spatial distribution of precipitation observed by rain gauges. The results is that when the installation interval of rain gauges is reduced from 10 km, the current standard in JR East’s, to 5km, the rate of increase in safety exceeds the rate of decrease in reliability. The conclusion is, therefore, the installation interval of rain gauges should be set at 5 km.
Outliers in flood frequency analysis have bothered us to examine the goodness-of-fit to the model of extremes. Too large value of the return period will be thought ridiculous even for the extraordinary magnitude of record maximum. We are just faced to the question: whether the outlier is a special case, or the model is not appropriate. The problem will arise often though the rest of data seems to be fitted very well. We, engineers have tried to do by employing numerous candidates of mathematical functions of population, though there is also the possibility of extrapolation in another point of view of this problem. This study proposes the method of drawing a window with the limits to view the data and models in the Gumbel plot. The outliers beyond the frame of window are inconclusive to judge the goodness-of-fit to the model. The window will release us from the fateful behavior of outliers in the extreme values, as well as the obsession of testing more than enough candidates of population, provided that we make the possible efforts by employing the special techniques, e.g. regional analysis etc. and continuing the observation ordinarily.
The objective of this study is to estimate the daily extreme precipitation distribution in an Asian monsoon region considering orographic precipitation in mountainous areas. For this purpose, the APHRODITE (the activities of the Asian Precipitation Highly Resolved Observational Data Integration Towards the Evaluation of Water Resources) dataset and precipitation observations from 150 rain gauges throughout Thailand were used as the main input. Firstly, a bias-correction for undervalued precipitation in the APHRODITE dataset was conducted compared with the rain gauge data. Secondly, a frequency analysis for estimating the extreme precipitation for return periods was performed based on the bias-corrected APHRODITE dataset and the rain gauge data. For taking orographic precipitation effect into account, a regression relationship among the calculated extreme precipitation, elevation and latitude was developed using the 150 rain gauge data. Incorporating the effect of orographic precipitation, the extreme precipitation distribution was improved to show the characteristic of precipitation in mountainous areas. The improved precipitation distribution was validated reviewing past studies about orographic precipitation in Thailand.
In this study, availability of global datasets, such as rain gauge data, satellite observations (GPCP and GSMaP) and reanalysis data (APHRO and H08) were discussed and analyzed in the Mekong River basin. First, spatial distribution and monthly precipitation data in 2000 were compared by each datasets. APHRO and H08 datasets were identified as better representing for wide areas like the whole basin. Secondly, precipitation intensity frequency was compared. Extreme event at lower-basin area could be estimated by GPCP and GSMaP. It is suggested that GPCP and GSMaP are useful for short term event such as flood simulation. Finally, using calculated annual water balance within the catchment, precipitation at several sub-catchments were compared and discussed. H08 was closest to estimated precipitation at each sub-catchment. And APHRO could represent characteristics of precipitation at sub-catchment.
Rain-gauge stations have been operated by many agencies, thus temporal and spatial characteristics of rain-gauge network have not been studied. We studied the observation density of rain-gauge network over Japan using available data observed by Japan Meteorological Agency (JMA), the River Bureau under Ministry of Land, Infrastructure, Transport and Tourism (RB-MLIT) and local governments (L-Gov). As a result of analysis of elevation, rain-gauge stations have been installed at a constant rate by each elevation class of the topography, and Japan has no rain-gauge stations over altitude 2500m. As a result of observation density by mesh analysis, approximately 70% of rain-gauge stations could observe rainfall data. In addition, we analyzed between DID and flood/drought disaster in recent years and observation density over Japan.