Floods frequently occur in the world, which cause serious damage of properties and loss of lives. It is thus important to identify flood vulnerability in flood-prone area. This study identified flood vulnerability in the Lower Mekong Basin of Cambodian floodplain and developed flood vulnerability indices for the average and extreme floods in order to avoid big damages and cope with flood in their life. The flood vulnerability was defined as amount of potential damages. The agricultural and house damages were considered to develop flood vulnerability indices, because both are major income and stocks. The agricultural damage was defined as the function of flood water depth during the cultivation period and its duration. The house damage was defined as the function of maximum flood water depth.
An environmental impact assessment (EIA) that provides the means to measure and compare project impacts, and which can easily be re-evaluated, is highly useful in the strategic planning of structural flood mitigation measures (SFMM). SFMM are essential in the sustainable development of flood-prone urban centers. In Metro Manila, Philippines, the EIA methods for planned SFMM do not provide sufficient tangible results, which make it difficult to compare and re-evaluate the impacts between SFMM alternatives. Thus, this study proposes the use of the rapid impact assessment matrix (RIAM) technique to systematically and quantitatively evaluate the environmental impacts of planned SFMM in Metro Manila. The RIAM was slightly modified to fit the requirements of this study. Results indicate that the EIA by RIAM can provide a clear view of the impacts associated with the implementation of SFMM projects.
The development of new water sources to ensure more stable water supply for Metropolitan Manila is urgently needed especially with the changing climate. The objectives of this study are: 1) to develop hydrological models in 3 river basins (Angat, Kaliwa and Pampanga) surrounding Metro Manila; 2) to assess basin-scale hydrological impacts of climate change in terms of a) flooding trends and b) drought trends. Calibrations of the basins were performed in Angat dam inflows for Angat basin; and Pantabangan dam, Cabanatuan, Zaragoza, San Isidro and Arayat stream flows for Pampanga river basin. Soil moisture verification of Pampanga river basin utilized monthly surface soil moistures from both the LDAS-UT and hydrological model outputs in short vegetation areas. Incorporating bias corrected rainfall and other parameters from GCMs showed future flooding trends is virtually certain to increase while drought trends are as likely as not to increase in the uplands but very likely to increase in the flood plains.
Basin-scale climate change impact studies mainly rely on general circulation models (GCMs) with various emission scenarios. Bias in GCMs should be removed for regional or local scale circulation study. This study describes selection of appropriate GCMs over a focused region to decrease analysis uncertainty. An efficient and comprehensive statistical bias correction method is developed that covers extreme rainfall, normal rainfall and frequency of dry days. Heavy rainfall is corrected by fitting a generalized Pareto distribution (GPD) to peak over threshold series. We used a gamma distribution for normal rainfall correction on a monthly scale and frequency by rank order statistics. Validation was done via long-term seasonal climatological rainfall, ranking extreme rainfall, and return-period estimates by the GPD. In this way, we analyzed climate change impacts at the basin scale in the Philippines.
The objective of this study was to investigate climate based observation and satellite based indices in order to monitor agricultural drought in Thailand and to study the effect of agricultural indices on major economic crops. Standardized Precipitation Index (SPI) and remotely sensed Vegetation Condition Index (VCI) were introduced to observe drought in the central region of Thailand. Integration of SPI and VCI has demonstrated the potential of geospatial technology to analyze and identify agricultural drought areas in macro scale at near-real time. The spatial analysis of 3-month SPI distribution indicates that it was the largest area of exceptional and extremely drought in 2010. VCI time series can be used to monitor vegetation condition correlating with moisture condition and landuse type. The frequency, area extent and severity of drought assessed from SPI and VCI could be benefit for the development of mitigation strategies of drought events.
In this study, we investigated the impact of climate change on hydrology and sediment load in the Be River Catchment using SWAT hydrological model. The calibration and validation results indicate that the SWAT model is a reasonable tool to simulate the impact of environmental change on hydrology and sediment yield for this catchment. Based on the calibrated model, the responses of hydrology and sediment yield to climate change were simulated. Climate change scenarios (A1B emission scenario) were developed from four GCM simulations (CGCM3.1 (T63), CM2.0, CM2.1, and HadCM3). Under the climate change impacts, the simulated results exhibit that the annual streamflow is expected to decrease by 2.4% to 4.4%, and the annual sediment load is projected to change by -1.4% to 4.5% in the future. It is indicated that changes in sediment yield due to climate change are larger than the corresponding changes in streamflow. In addition, climate change causes increases in annual evapotranspiration (0.8% ~ 2.8%) and decreases in groundwater discharge (4.4% ~ 6.14%) and soil water content (2.0% ~ 4.8%).
River discharge in Indochina Peninsula region was projected using a distributed flow routing model (1K-FRM) with kinematic wave flow approximation for three climate experiments: the present climate (1979-2008), the near future climate (2015 - 2044), and the future climate (2075-2104). Topographic data used for the flow routing model is 5-minute spatial resolution data which was processed from scale-free global stream-flow network dataset. The flow routing model 1K-FRM was fed with general circulation model (GCM) generated runoff data for three climate experiments. The GCM dataset used was the latest 20km spatial resolution general circulation model (MRI-AGCM3.2S), which was developed by Meteorological Research Institute, Japan Meteorology Agency. The changes of flow in Indochina Peninsula region under climate change were analyzed by comparing simulated river discharge for the present climate, the near future climate, and the future climate experiment. Analysis results show clearly changes of annual mean discharge, mean of annual maximum discharge and mean of annual minimum discharge with the degree of changes different according to location. The changes, which were detected in the near future climate conditions, become clearer in the future climate conditions. In some locations, the increase of flood and drought risk was found.
The Thailand’s Great Flood in 2011 resulted in the great calamity causing tremendous losses impacting livelihood, social and economic of the nation. A better understanding of the basin hydrological processes is necessary for studying and predicting a future flood. Consequently, this study aims to develop a regional distributed hydrological model for water resources situation prediction. The regional hydrologic model was composed of a runoff generation model with a concept of the variable infiltration capacity and a flow routing model using the kinematic wave equation. The effects of dam control were also included in the flow routing model. The model was applied to the Chao Phraya River basin to reproduce floods in 1995, 2008, 2010, and 2011. By using the model, the effect of the existing dams operations and the new dam construction on flood control is numerical evaluated.
Flood simulation by using a distributed hydrological model (DHM) has been implemented to support dam operation. This study aims to investigate the applicability of Satellite Based Precipitation (SBP) combined with local rain gauge network as input for flood forecast at Chao Phraya basin, Thailand. DHM was set-up at contributing area to Bhumipol dam for inflow forecast in order to protect lower region. As input data, SBP was combined with local gauge network targeting effect of monsoon. DHM was run during 2007-2010 to validate the spatial and temporal accuracy of corrected SBP. The approach showed reduction of the large overestimations of SBP. Then, the accuracy of discharge simulation was successfully improved. The results indicate feasibility to estimate inflow of Bhumipol dam using corrected SBP with local gauge network. Moreover, this method can be useful not only for risk assessment of flooding, but also support proper dam operation.
Climate changes induced by global warming are a worldwide concern. In some regions, the risk of serious floods is expected to increase under a changing climate during the 21st century. This study examined the potential impacts of climate change in the Chao Phraya River Basin (CPRB), Thailand, using the MRI-AGCM3.1 and 3.2 datasets, developed by the Meteorological Research Institute (MRI) of the Japan Meteorological Agency, as inputs to a watershed hydrologic model. The results indicated that future river discharges will increase owing to increased rainfall in the upper mountainous region and in the Nan, Yom, and Wang river basins. Furthermore, a significant increase in annual inflow to the Bhumibol reservoir was projected in the late 21st century, whereas drought conditions may occur in the Pasak River Basin in the future.
A box groyne is composed of various types of single groyne to satisfy the different river ecological requirements. In order to create an appropriate watery and sedimentary environment for aquatic life in the groyne zone during flooding, the exploration of three-dimensional flow structure around the box groyne under the submerged condition is necessary. The flow velocity around submerged box groynes with a longitudinal block, which is composed by straight and L-shape groyne, are measured by PIV (Particle Image Velocimetry) on the horizontal plane (x-y) and vertical plane (x-z). The interaction effects between the vertical vortex detached from the crest of the first groyne and the transverse vortex detached from the lateral of the first groyne cause the complex three-dimensional flow characteristics in the box groyne zone. The longitudinal block set in the lateral side of box groyne definitely affects the development of transverse vortex associated with the inflow condition and reduces outflow passages in the lateral interface of box groyne. As to the upper flow, the inlet and outlet of fluid, and also the flow direction are greatly changed by the longitudinal block.
To study the turbulence characteristics of open channel flow, an analytical solution for the standard k-ε model is proposed. The primary concern of the research is to improve the velocity distribution in depth-averaged model that failed to reproduce well by Engelund model. Additionally, the effect of damping function on velocity distribution is checked by comparing the analytical result including and excluding the damping function in uniform flow. However, very negligible effect of the damping function on velocity distribution is observed; in spite that the model reproduced the flow properties reasonably. The validity of the model is also tested using numerical results of the finite difference scheme. In addition analysis is also performed for non-uniform flow. The analytical results of varied flows are checked in comparisons with uniform flow results. The analytical results showed that the nature of the distributions of hydraulic variables satisfied the conditions of (accelerated and decelerated) non-uniform flows.
A predictive theory to study the nonlinear development of the perturbations in a channel with a lateral gradient in the streamwise velocity due to the presence of bank vegetation is presented. The ratio between the undisturbed parallel velocities in the vegetated and non-vegetated zones is taken as the expanded parameter at the weakly nonlinear stability analysis, along with its corresponding wavenumber at a critical condition where the perturbations nor grow nor decay. In most cases evaluated herein, we have supercritical bifurcation, where the amplitude of the perturbations is found to reach an upper bound as time tends to infinity. We find reasonable agreement between predicted and experimental results for the time-averaged velocity profile, kinematic eddy viscosity, shear layer width and maximum friction velocity.
Forced submerged jumps within a non-prismatic stilling basin, named in-ground stilling basin, were experimentally investigated. An in-ground stilling basin (ISB) is a newly popular concept for stilling basin downstream of flood mitigation dams (FMDs). In FMDs usually one bottom outlet is located in the centerline and the width of the stilling basin is much wider than the width of the bottom outlet, which leads to a small expansion ratio, k, for the outflow. This study experimentally investigates the flow patterns and velocity reduction, within ISB downstream of FMDs, under different hydraulic and geometric conditions. Finally, an innovative design guide-line is proposed considering downstream flow requirement.
The paper presents experimental and numerical investigations for understanding the mechanism of mass transport by internal wave propagation over a flat bottom in two-layer stratified fluid. The mass transport velocity has been estimated from the horizontal excursion of water particle. The water particle trajectories were obtained from PIV results in an experimental flume and also computed by a two-dimensional non-hydrostatic numerical model. We confirmed the numerical model reasonably reproduce the measured wave profile as well as the measured mass transport of the internal waves. A series of numerical experiments showed the dependency of mass transport on the layer thickness ratio and the wave height. We found that the maximum mass transport velocity is highest when the upper and lower layer thicknesses are equal and it becomes smaller as the thickness of lower layer exceeds that of the upper layer. For all thickness ratios, the mass transport velocity gets larger with increase of internal wave height.
In the present study, the variations of the salinity and water discharge in the main branches of the Ota Estuary were investigated using the Fluvial Acoustic Tomography System (FATS). The Ota Estuary has a branched section of the Gion and Oshiba. The response of the salinity variations at the branches can be described as a power-law of river discharge. The exponents -0.53 and -3.86 at the Gion and Oshiba implied significant differences in the salt intrusion variations in these branches. The mechanisms of the salt intrusion at the site study were analyzed using the salt decomposition method based on the FATS data. The results indicated that the advection is the dominated seaward mechanisms at the both branches. However, the variations in the landward directed mechanisms were influenced by the triple correlation between the salinity, water velocity and water level fluctuations.
Debris flows are very dangerous phenomena in mountainous areas throughout the world. Debris flow causes damage of lives and properties. To prevent or mitigate debris flow disaster, various kinds of the Sabo dams have been constructed. Control function of such Sabo dams have been reported through a lot of studies. In recent studies, experimental and numerical works have been performed for definition of general design criteria of Sabo dams. Nevertheless, there are few studies discussing the arrangement of Sabo dams. The objective of this study is to improve the sediment capturing capacity by the arrangement of Sabo dam. The numerical simulations and experiments have been carried out to investigate the debris flow deposition volume of a series of Sabo dams. The constitutive equations of Takahashi1) et al. are used for debris flow deposition at upstream of a Sabo dam. Results indicate that a decrease in distance of between dams will increase equilibrium bed slope due to upper located Sabo dam.
This work presents detailed morphodynamics modelling of the bedform under variable discharges and simulates the conditions in which the bed of the river is flattened out in upper plane bed regime. This scenario is simulated by detailed hydrodynamics, sediment transport and morphodynamics models, which is an extension for the model developed by Nabi1. Several discharge hydrographs are examined here. In the first case, the discharge increase linearly, and then stay constant. We found that dunes are generated before the condition reaches the upper plane bed regime. As the flow condition fall in the upper plane bed regime, high frequency ripples generate and they flattened the bed out. As the discharge stay constant, the bed remains smooth with small high frequency ripples. Later, four different scenarios are simulated, in which the discharge decreases again after a certain period. It is observed that the bed regenerates again in the case the discharge decreases. The model shows its capability in simulating the flood wave events.
Recently, there have been a lot of numerical models for prediction of urban inundation damage due to heavy rainfall by using the combined drainage system. Although it is important to estimate inlet and overflow discharge through the storm drain, calculation method and formula are not clarified. Hence, in this study, the numerical model of storm water interaction between the ground surface and drainage system we have previously used is improved and validated based on physical experiments. From the comparison, they showed agreement in all the cases of steady state condition. In the unsteady state cases, it was found that simulation results agreed well with experimental results of the ground inundation start time and the maximum inundation depth as well as the water level increase process. However, piezometric head reproduced small differences when the downstream water level was decreased. It was judged that was caused by inadequate consideration of exit and entrance head loss between the tank and pipe.
Microwave Satellite data has become very useful in weather prediction through data assimilation for improving Numerical Weather Prediction (NWP) initial conditions. By assimilating 23GHZ (sensitive to water vapor) and 89GHZ (sensitive to cloud water) brightness temperature, the predictability of an extreme rain weather event over Lake Victoria, East Africa is investigated. The assimilation of AMSR-E brightness temperature (TB) through a Cloud Microphysics Data Assimilation (CMDAS) into a NWP considerably improves the spatial distribution of this event. Assimilating cloud water, water mixing ratio and other ice cloud components inserts clouds, triggers weak surface convergence and consequent convection. The spatial distribution of the simulated event is comparable to observed satellite rainfall. Through assimilation, smaller events missed by the downscaling experiment are introduced into the model state and this leads to a better forecast. The integrated cloud condensate follows a similar pattern to observed cloud top temperature with the probability of detection improving as well. However, even though the system is able to reproduce a reasonable distribution of this event, there still remains overestimation especially over the regions of maximum precipitation.
Increasing surface temperature has resulted in significant changes in rainfall patterns. This paper presents the projection of the future extreme rainfall based on a statistical downscaling model for a global super-high-resolution climate model output. The downscaling model is formulated with the consideration of physical processes that govern heavy rainfall patterns. A case study is examined for nine observation sites in the Vu Gia-Thu Bon river basin in Central Vietnam. Results show that by the end of this century (2075-2099) heavy rainfall is projected to increase for the entire basin. Especially in elevated locations, it is very likely that extreme rainfall will increase about 30% relative to the present-day climate (1979-2003); the future rainfall with 10-yr return period will greatly exceed those with 25-yr under the present-day climate conditions. Meanwhile, a slight increase of extreme rainfall is projected for low-lying places along the coastline.
This study aims exploring the characteristics of extreme precipitation corresponding to surface air temperature in Bangladesh. Analysis for each seven division of Bangladesh has been accomplished separately using observation dataset. In the next step, calibration of historical extreme precipitation from GCM model MIROC simulation has been performed comparing with observation. Model simulated dataset is obtained from the scenario of RCP8.5 of MIROC version-5. Bias correction has been taken into consideration while using model output. Finally, model simulation is applied to analyze projection of future changes of extreme precipitation in the targeted region. Results show that there are fair agreement among observation, MIROC present and MIROC projection simulations. An increase in extreme precipitation intensity is found in six divisions among seven divisions in Bangladesh for MIROC future projection simulation.
Downscaling plays a major role in evaluating future changes of precipitation and setting up appropriate adaptation strategies at regional and local scale. Hence, this study evaluates statistical bias correction and Dynamical Downscaling (DD) approaches by applying them to reproduce present climate of precipitation and discharges in Shikoku Island, Japan. DD captured well spatial and temporal distributions of precipitation owing to influence of the spatial resolution enhancement. Statistical bias correction has limitations in estimating extreme rainfall intensity as well as frequency with seasonal consistency. In particular, bias corrected GCMs failed to reproduce extreme rainfall events and corresponding discharges in July and August. This is a limitation from the statistical bias correction. As DD results were reasonable with observation, the inconsistency resulted in bias correction method can be eliminated by performing Pseudo Global Warming Down-Scaling (PGW-DS) for future climate. The identified systematic biases in DD will be corrected by statistical method and transferred to PGW-DS. This method aims to provide better science-based information of future changes of precipitation and discharges.
In this study, a prediction model of paddy thermal condition was developed, which solved heat balance in two layers of crop and water to describe heat balance change with different water management. To calibrate and evaluate the applicability of proposed model, field experiment was conducted. Calculated water and vegetation temperature showed good agreement with observed data. Then by using the proposed model, the changes of paddy thermal condition with different water managements were simulated. Continuous irrigation was effective to cool down the water and soil temperature, and water depth control was also effective when relatively cool irrigation water was not available.
India is rich in water resources being endowed with a network of rivers that can meet water requirement of the country. However, with the rapid increase in the population and increasing demands of water for irrigation purposes, the available water resources are getting depleted and the water quality is deteriorating. Humans have strongly impacted the global water cycle including its quantity and quality. In the present work, we have discussed the water availability in major river basins and have described both the quantity and the quality of water resources in India. In water quantity, we compare the relationship between groundwater withdrawal and precipitation that shows the highest groundwater withdrawal in the northern region. We have also discussed the future expectations of water quantity in India. In water quality, we examined the relationship between cereal production and high consumption of nitrate in agricultural water and have discussed the extensively high consumption in the northern state of Punjab in India.
Assessment of storm is accomplished by the storm area and duration rather than a simple analysis using the rainfall data of the ground rain gauge stations. One of the best expressions for assessing storm is Depth-Area-Duration (DAD) analysis. The DAD analysis provides a powerful, objective, easy-to-understand three-dimensional perspective of storm rainfall, and is applied to estimate probable maximum precipitation (PMP) for the design of hydraulic structures. However, a general DAD analysis is prone to generate subjective errors to divide and accumulate sub-basins. Further it is difficult to understand the impact of recent localized and intensive storms due to the climate change. This research carried out to obtain DAD analysis of high accuracy in the small basin and relieve errors that occur in the analysis. Methods to estimate areal rainfall are the inverse distance weight (IDW) and ordinary kriging (OK), while methods to accumulate area are the box-tracking and the point-tracking. The merits and demerits of these methods are discussed.
Probable maximum precipitation (PMP) is one of the keys for the designing of probable maximum flood (PMF) and flood disaster management. A basin-scale spatial distribution analysis of the extreme rainfall and PMP in the Yodo river basin are presented. The maximum 24-hour rainfall data from 1881 to 2011 were used. Spatial PMP and its isohyetal lines produced using Hershfield and Spline interpolation method agrees with the historical flood records. Highest PMP is observed around the Hikone and Shimogahara stations (above 900 mm), while the least at Yanagase and Torahime (below 500 mm). Estimation of the return periods (RPs) using non-linear regression and the generalized extreme value (GEV) distribution for the historical maxima suggests that the GEV overestimates RPs and non-linear regression (NLR) with PMP as upper bound stabilizes the estimates of RP by GEV. Spatial distributions of the 4000 years return periods extreme rainfalls show some similarities with the PMP's distribution.
The largest-ever flood event was recorded at the Kumano River in the Kii peninsula of Japan from August 31 to September 4, 2011. Water level data exceeded the observation range in many places except in the Ouga water stage station at downstream. This study aimed to estimate the peak discharge of the event by using the estimation method, which is a 2D dynamic wave model combined with particle filters, and by considering the water level observed at the Hitari and Ouga stations and a river discharge estimated by a hydrological model. The estimation method was applied to the three historic flood events for quantifying the uncertainties of the Manning roughness coefficient(Manning n) of the subject river channel. Based on the optimized range of Manning n, the filtering method was applied to estimate the largest peak discharge of the 2011 flood using the discharge estimated by a hydrological model. The possible range of the largest peak discharge was successfully evaluated through the comparison of the observed flood marks. Finally, a rating curve established by the estimation results at the Ouga station is examined.
To assess the vulnerability of urban water supply systems, in regions even with limited accessible data, a proper index is required. Therefore, we developed a method to assess the drought risk using basic flow characteristics. Here, we suggested calculating water shortage index using intake volume, daily discharge, water demand, inhabitants served and water source type at each river basin. This method was applied in major rivers in Japan but considering its applicability in developing countries. The results show Yoshino River with the highest drought risk while Yodo River with the lowest risk. Actually, Yoshino River was found more vulnerable against change of intake amount for agricultural use. On the other hand, Arakawa and Abukuma Rivers were sensitive due to change of water demand depending on population change. The obtained water shortage indices were compared to actual reported droughts in Japan, and logic connection was found. Thus, water shortage index might be useful to analyze drought risk in other rivers.
A physically based distributed biosphere hydrological model with three layered energy balance snow melt module (WEB-DHM-S) has been implemented at point scale at Yagisawa dam site to evaluate the long-term simulation of snow depth from 1948 to 2006 using high resolution JP10 reanalysis data. The time series of snow depth, its averaged value and anomaly and the snow cover durations are evaluated. The model is able to capture the seasonal and inter-annual variability of snow depth well with average bias at 0.013 m and root mean square error at 0.29 m. A continuous negative anomaly was well simulated from 1985 to 1994. Long-term analysis showed that the decadal change was more apparent for snow cover days with snow depth above 50 cm and the number of snowfall days had a decreasing trend. In addition, the snow depth values from 1948 to 1963, an outcome of this research, can be used as the reference dataset by the scientific community.
Tropical glacier Huayna Potosi located in Cordillera Real in Bolivia was the main object in this paper. This study obtained two main parameters related to atmospheric conditions, i.e. diffuse fraction and atmospheric transmissivity, to evaluate the solar radiation distribution for the study of tropical glacier melts. The parameters were calculated by physically-based solar radiation formulas and then refined with observed data at ground level. These deduced parameters were conversely applied as input to GIS solar radiation model to obtain monthly spatial distributions of solar radiation considering atmospheric conditions and topographic from June 2011 to May 2012. Spatial distribution of glacier melt was finally simulated by applying glacier melt model considering air temperature and solar radiation.
An enhanced temperature-index model including albedo and shortwave radiation has been applied to the tropical Zongo glacier. The model satisfactorily simulated the daily discharges and their seasonal variations with an efficiency of 0.71 (Nash-Sutcliffe). The energy balance analysis revealed that three factors mainly control melt on this glacier: incoming shortwave radiation, incoming longwave radiation and sensible heat flux. Accordingly, the model differentiates between temperature-dependent and temperature-independent components moving towards a more physically based but still simple model. Modelling was improved with respect to the traditional degree-day method in the wet season characterized by simultaneous accumulation and strong melting while capturing the low melt rates found in the dry season. However the model missed some peaks in discharge due to the underestimation of precipitation at the low elevation meteorological station.
Digital Elevation Model (DEM) is the most fundamental input to flood inundation modeling. Satellite based topographic data, such as SRTM (Shuttle Radar Topographic Mission) DEM, has made a significant contribution to inundation modeling and other hydrological studies, particularly in data scarce countries. Nevertheless, most of DEM products suffer from artefacts caused by data acquisition or processing. For example, the SRTM DEM suffers from striping artefacts that can cause significant errors in inundation simulations. This study developed Fourier Transform based de-striping techniques to identify and mitigate the striping artefacts. The de-stripped DEM is compared with a reference DEM and the result proved promising. We also attempted to understand the effect of striping artefacts on flood inundation modeling in the Mekong Delta. When the de-striped DEM was integrated in flood inundation modeling, significant improvement was observed in simulated spatial flood extent.
This study addressed potential climate change impacts within the Atbara Basin upstream of the Nile River. A Distributed Hydrological Model (DHM) was integrated with prediction scenarios from two General Circulation Model (GCM) outputs. The DHM model was validated using historical gauge records at Atbara Kilo3 station. Then, the model was forced with GCM outputs to investigate potential changes in the flood characteristics for the years 2011-2030. In terms of water resource management, the key conclusion was that natural stream flows of the Atbara Basin will not change significantly during the next 20 years, but that peak flow may increase from 2021 to 2025. The results suggest the need for careful flood management in the basin.
Sediment load can provide very important perspective on erosion of river basin. The changes of human-induced vegetation cover, such as deforestation or afforestation, affect sediment yield process of a catchment. In this study, a new sediment rating curve considering vegetation cover was developed to evaluate the impact of vegetation cover changes on sediment yield in Da River Basin. The Normalized Difference Vegetation Index (NDVI) and leaf area index (LAI) can be used to analyze the status of the vegetation cover well. Thus long time series NDVI from satellite was applied to represent vegetation cover in the past years. Potential LAI from ecosystem model (Biome-BGC) was used to explain the vegetation cover without human activities. Finally, standardized NDVI and LAI were inputted into the new sediment rating curve to evaluate human-induced vegetation cover change effect on sediment load.
Based on the sensitivity analysis at annual, monthly and daily scales, a multi-step optimization scheme is designed to optimize parameters in Xinanjiang model with the help of SCEM-UA algorithm. In this scheme, parameters are classified into three groups and optimized group by group at different time scale. In this paper, the attention is focused on the parameters for data adjustment, Cp and Cep, which are optimized in the first step. Instead of optimizing Cp and Cep directly in two dimensional spaces, the concept of aridity index (the ratio of annual potential evaporation to precipitation) is introduced into the optimization process, and proposed a relationship describing Cp and Cep as a function of annual runoff coefficient and pan aridity index (the ratio of annual pan evaporation to precipitation). In this way, the feasible parameter space is narrowed and efficiency of sample points which generated for optimization in SCEM-UA algorithm is improved. In addition, it provides a simplified and quick way to get acceptable values of Cp and Cep when the request of precision is not so strict.
Groundwater management at many arid areas in the world has been difficult to be properly performed due to the limited availability of hydrogeological data. Recent development of Kharga Oasis, as an arid area located at western desert of Egypt, has been mainly depended on groundwater of Nubian Sandstone Aquifer. During the last two decades, the excess pumping of groundwater at Kharga Oasis brought about a significant drawdown of groundwater table. To implement an optimal groundwater management, temporal and spatial variation of groundwater table should be investigated first as an indispensable factor in groundwater flow analysis. In the current study, temporal change of groundwater pore pressure for arbitrary target points is analyzed using Geo-statistics and Genetic Algorithm models. It was found that Genetic Algorithm technique produces good performance compared with Geo-statistics model and can be available to analyze the temporal change of groundwater table with limited data.
Source identification of nitrate contamination in groundwater is an important first step for groundwater management and quality prediction. Therefore, a small scale field research was conducted in an agriculture-dominated alluvial fan in Kofu, Japan, where nitrate contamination was found in the groundwater. Methods used in this study were combining isotopes, ions (biochemical process) and precipitation data (physical process) to understand the nitrate source and process leading to the groundwater nitrate contamination. Our investigations suggest that the nitrate from manure source gave significantly larger contribution than fertilizer. In winter period, there was no strong evidence that anthropogenic nitrate exist in the groundwater. It also found that denitrification process might occur during the recharge process, hence reducing the nitrate concentration. As a preliminary step to describe groundwater dynamics, isotopes and ions provide effective tools to trace sources of contamination and to study processes affecting nitrate.
Even though run-of-river hydropower dams are a widespread, only a few studies have tried to clarify their impact on the downstream ecosystem. The current study aims to clarify the mechanism of ecosystem degradation in the downstream of a run-of-river hydropower dam due to water diversion for energy purposes. Field investigations were conducted in summer days at high and low flow stages to investigate the impact of discharge on downstream ecosystem represented by benthic attached algae in particular. Having this categorization of the collected data and with the help of 2D hydraulic simulations the influence of water diversion on the downstream hydraulic properties and patterns of ecosystem change were clarified
Behavior of an invertebrate, Isonychia japonica, was investigated based on their response to approach flow velocity. Without refugia, the behavior has been categorized into four, walking or crawling, passive walking (or no walking), washout and enduring behavior. The critical depth-averaged velocity for no walking is 0.20 m/s and for washout is 0.40 m/s for the specie. The corresponding local velocity calculated from PIV analysis at the invertebrate height for no walking and washout is 0.12 and 0.22 m/s, respectively. The blocks were placed as refugia for the invertebrates and were successful in providing refugia to the invertebrates. With blocks as refugia, washout behavior was not observed. The local velocity around invertebrate habitat after placement of blocks was reduced to less than 0.10m/s during high flow conditions which is less than the critical velocity conditions without refugia.
To reveal factors relevant in controlling stream temperatures in summer season in the Tama River, field measurement, water and heat budget analysis as well as model development were performed in this study. Detailed information on water temperature, flow rate, meteorological variables as well as water-sediment heat flux was obtained through the intensive field measurement. Water and heat budgets analysis indicated that the wastewater effluents contributed to mitigate stream temperature at one middle stream site. A 1-D dynamic model for river flow and heat transport was developed, taking the effect of groundwater-stream water interaction processes and wastewater effluents into accounts. We concluded that the current stream temperature regime in the Tama River downstream reaches is maintained by the heat dispersion in the riverbed sediment and also the effluents of treated wastewater.
Certain part of wash load which entered a reservoir is settled on the bed as sediment. Sediment occupies the storage capacity of reservoirs and reduces the amount of available surface water resource. Especially in North Africa which has the low vegetation land cover in the catchment and long retention time due to the clear precipitation difference between summer and winter, the wash load inflow and the sedimentation ratio is very high. In order to discuss managing the sedimentation, the behaviour of the wash load in the water body of a reservoir have to be grasped. In this study, sediment traps and auto recording thermometers were placed in the different depth in order to know what depth the floodwater enters. The amount of trapped sediment is equivalent to average sedimentation ratio. In addition, the bed area which might receive the sedimentation is estimated by numerical simulation. The volume of sediment estimated from the trapped sediment and the bed area is almost equivalent to the sediment volume which was estimated by the bathymetric survey.
EL-Burullus lagoon is a brackish water coastal lake on the Mediterranean Sea, Egypt. Lake ecosystem has been deteriorated since Aswan High Dam construction, 1965. Lake salinity has been suffered from significant decrease due to excess unregulated drainage water effluent into the lake, which affected the lake flora and fauna. This study presents a modeling study to investigate the impact of climate change on salinization process in the lake. A calibrated two-dimensional depth-averaged mass transport model with finite volume in dicretization is used to simulate salinity distribution under two IPCC climate change scenarios (SRES B1 and SRES A2). Although results reveal with increase salinity values to double the current values, they are still obviously lower than those before constructing Aswan High Dam. A dynamic discharge system is proposed to re-originate lake's salinity under climate change conditions.
This paper describes the improvements of the 3D model proposed by Trieu et al. (2010). The model was applied to simulate the pollutant transport from fish cages (group of cages located closely together that was assigned as the single point source of pollution discharge) in the river system. In contrast, the pollution discharge from both the pond culture and the cage culture was considered in the present study. Moreover, the complete suspension was modeled by calculating the concentration of particle wastes load from riverbed. Furthermore, the conservation of simulation was ensured by using the finite volume method instead of the finite difference method to solve the 2D flow field. The improved model simulated nutrient discharge from the intensive Pangasius farming in the Mekong Delta, Vietnam. The simulated output was verified with the observed data. A good agreement between the observed and simulated data proves that the improved model could help decision makers for better planning and monitoring purposes.
The river mouth morphology changes in the Samegawa river mouth during its recovery following The Great East Japan Tsunami of 2011 was investigated in this study by analyzing the water level data and aerial photo. The aerial photos provide valuable information on the changes. However, their availability is limited. The correlation coefficient and the linear gradient between the water level data in the river and the tidal level were analyzed. The river mouth narrowing, as well as the river mouth opening has been successfully detected. The assessed parameters correspond well with the condition obtained from the aerial photo analysis when available. In addition, these parameters also provide information on the river mouth condition when there are no aerial photo data. The proposed method in this study will provide an efficient way for analyzing and evaluating the morphology changes at a river mouth.
Prediction interval for a successive occurring extreme is derived. The well-known confidence intervel for a return level of precipitation has been sometimes, or frequently in our mind, misused by misunderstanding what the interval stands for. Return period and encounter probability, which has been employed in many previous literatures, are indirect to handle our target against the extremes. Not only predicting a future extreme but anticipating the past extraordinary events, such as the daily amount of precipitaion in the Tokai heavy rain can be also examined in the view of statistical test by the derived prediction distribution function, in which the degree of experience plays an important role.
This paper describes new findings about probable maximum precipitation (PMP) in Japan on the basis of spatial analysis of radar rainfall provided by the Japanese Meteorological Agency (JMA), Ministry Land,Infrastructure, Transport and Tourism (MLIT). The depth-area-duration (DAD) analysis provides PMP estimates for all over Japan. This paper has renewed the DAD relationship for the area of 0 to 32400 km2 as well as rainfall duration of 1 to 24 hr. A case study for the Kii Peninsula, which was much damaged by severe storm, floods, landslides and debris flows brought by Typhoon Talas that attacked Wakayama, Nara and Mie Prefectures in September 2011, shows an example of PMP estimation in the region and verifies the flood took place in the Kumano (Shingu) River in the Peninsula in terms of probable maximum flood.
This study aims to develop a method for forecasting the water level of the Kahayan River in Indonesia. In recent years, peatland in that basin has been drying as a result of agricultural development, and such drying has led to more frequent large-scale wildfires there. By incorporating the sea surface temperature, which is affected by the El Nino event, into a Nearest-Neighbor Method (NNM), the water level forecasting accuracy was improved even in case that the lead time of prediction was extended. In addition, highly accurate water level forecasts were obtained by using predicted rainfall calculated by NNM and a tank model that can reproduce the hydrological cycle in the basin. Accordingly, a method for forecasting the water level even when data are missing was proposed. The results promise to be useful for basin management to prevent peatland wildfires.
Economic growth of the Greater Mekong Subregion has been drastically increasing in the past few years. Especially as the role of the Mekong River and its tributaries become more important, therefore the evaluation of hydrological data will be necessary for infrastructure development in the future. The time-series variation of long term hydrological data such as daily precipitation and discharge which are available in Mekong River Commission was evaluated by using the method of regression analysis, excess threshold analysis and probability analysis. As a result, the annual precipitation and the average of discharge have been on a declining trend in southern region of the Lao PDR especially rainy season. On the other hand, the average of discharge in the tributary which has hydro power dam such as NamNgum, Sekong, Sedone has been increasing trend in the dry season. It is also understood that fluctuation range of flood and drought discharge is increasing compare with last 40 years.
This study analyzed the spatial representativeness of heavy rain and the capture performance of heavy rain observed by the rain gauges installed discretely at 347 sites in Kanto Plain and 287 sites in the mountainous area of Koshin-etsu region. The spatial representativeness is evaluated by the percentile of precipitation ratio between two sites. The spatial representativeness of 1-hour precipitation and 24-hours precipitation becomes lower, when the precipitation increases. The spatial representativeness is lower in 1-hour precipitation than in 24-hours precipitation and in the mountainous area than in the plain. The capture performance is evaluated by the capture rate of heavy rain, and relation between the capture rate of heavy rain and distance of two sites is formulated. The capture rate of 1-hour precipitation and 24-hour precipitation becomes lower, when threshold of heavy rain increases. The capture rate is lower in 24-hours precipitation than in 1-hour precipitation and in the mountain area than in the plain.