1,720,983 research outputs found
Satellite data as complementary information for hydrological modelling
No full textHydrological models at river basin scale are needed to predict floods, droughts, available water, and effects of future changes, caused by climate and land cover change. However, in many river basins, there is not enough data available to construct these models. Fortunately, it becomes more and more attractive to use earth observations from satellites as complementary data to construct hydrological models in these river basins. This thesis describes the development and application of methods that allow one to combine the scarce ground data, available in such poorly gauged catchments, with expert knowledge and modern satellite data, with the purpose to conceptualise, calibrate and validate hydrological models. Case studies show that satellite-based rainfall, space-based gravity observations and remotely sensed evaporation estimates are of great value in the improvement of our models.Water ResourcesCivil Engineering and Geoscience
Propagation of weather forecast uncertainties in flood forecasting. A case study on Rhine discharges at Lobith
No full textWater ResourcesWater ManagementCivil Engineering and Geoscience
Estimation of predictive hydrological uncertainty using quantile regression: Examples from the National Flood Forecasting System (England and Wales)
No full textIn this paper, a technique is presented for assessing the predictive uncertainty of rainfall-runoff and hydraulic forecasts. The technique conditions forecast uncertainty on the forecasted value itself, based on retrospective Quantile Regression of hindcasted water level forecasts and forecast errors. To test the robustness of the method, a number of retrospective forecasts for different catchments across England and Wales having different size and hydrological characteristics have been used to derive in a probabilistic sense the relation between simulated values of water levels and matching errors. From this study, we can conclude that using Quantile Regression for estimating forecast errors conditional on the forecasted water levels provides a relatively simple, efficient and robust means for estimation of predictive uncertainty.Civil Engineering and Geoscience
Modelling ungauged lowland basins: Does complementary groundwater data add value to topography driven conceptual modelling?
No full textA common practice for hydrologists to determine the performance of a hydrological model and its parameter values, is by calibrating the model parameters on observed discharge data, but this data is not always available. For this reason, other data should be used as complementary data in order to reduce the uncertainty of outflow and processes in the ungauged basins. This thesis presents a case study on an area in Baden-Württemberg, Germany, to see whether groundwaterlevel data can be used as complementary data for hydrological models of ungauged basins. It has been divided into two Hydrological Response Units (Lowland and Hillslope) with use of the surface slope and the height above the nearest drainage (HAND) algorithm. The main result is that a combined addition of groundwater level measurements and constraints did show reduced uncertainty, and thus improvement, of the internal model processes, especially the fluxes towards and out of the slow responding reservoir. Validation of these processes still remains difficult in ungauged areas, but it is believed that valid results can be made on the outflow out of the lowland areas with a combination of constraints and groundwater measurements to determine internal processes, and evaporation estimates obtained from satellite imagery to reduce the uncertainty of the total runoff out of the area.Water ResourcesWater ManagementCivil Engineering and Geoscience
Remote river rating in resource constricted river basins: Exploring opportunities for ungauged basins through low-cost technological advancements
No full textThe unavailability of consistent accurate river flow data is a significant impediment to understanding water resources availability, and hydrological extremes. This is particularly true for remote, difficult to access, morphologically active and therefore rapidly changing rivers. The state of global river discharge monitoring with respect to water infrastructure and frequency of data collection has been on the decline over the past few decades. This is despite the significant importance of these data for river flow predictions. Fortunately, rapid advancements in technologies open up possibilities for water resource authorities to increase their ability to accurately, safely and efficiently establish river flow observation through remote and non-intrusive observation methods. Low-cost Unmanned Aerial Vehicles (UAVs) in combination with Global Navigation Satellite Systems (GNSS) can be used to collect geometrical information of the riverbed and floodplain. Such information, in combination with hydraulic modelling tools, can be used to establish physically based relationships between river flows and permanent proxies. This study attempts to monitor flow in volatile, dangerous and difficult to access rivers using only affordable and easy to maintain new technologies. This thesis consists of three main components: i) generating a workable framework for monitoring rivers using low-cost technologies; ii) establishment of river geometry using a combination of airborne photogrammetry and low-cost GNSS equipment iii) and physically based rating curve development through hydraulic modelling of surveyed river sections.The first three chapters of this thesis provide an introduction in the form of a literature review, justification for the study and a description of the study area. In chapter 4, a framework is developed through an intensive review of traditional river monitoring processes. Uniquely effective and low-cost individual components are selected and placed within a framework. The ideal outcome is an interconnected framework which clearly presents the steps which are necessary for river monitoring in remote locations. The manner in which each critical step is related to the other is explained. Furthermore, the method by which modern technologies are assimilated into the method is described. Within the framework, critical thresholds are set up in order to signal the to the water manager whether the proposed model in its current state continues to perform as required.Chapter 5 investigates how low-cost technologies such as UAVs in combination with low-cost GNSS devices can be used to generate river geometry for the purposes of application in a hydraulic model. Furthermore, performance of the open-source photogrammetry software substantiated the claim that, free and open-source available packages are capable of producing results which are as good as proprietary alternatives as shown by the RMSE analyses. A novel approach to generate a seamless bathymetry through merging and volumization was successfully tested. Results presented in this chapter encourage future studies to investigate the impact of variations in the number of Ground Control Points (GCPs) on discharge estimations in a hydraulic model with different hydrodynamic boundary conditions. This follow up was instituted in Chapter 6.In this sixth chapter we accept that uncertainties in the data acquisition may propagate into uncertainties in the relationships found between discharge and state variables. This uncertainty prompts the need to understand the impact of varying geometries on hydraulic models. Specific attention is placed on variations caused by differing GCP numbers since the task of GCP placement is time consuming, potential dangerous and resource intensive in certain location and instances. We are successfully able to determine the minimum number of control points required to reproduce geometry. Overall, we successfully develop and test a workable method for water resources authorities to estimate river flows accurately through the application of advanced, low-cost technologies with minimal contact with measured variables.The development and application of low-cost technologies for river flow monitoring has led to the following important conclusions:• For the purpose of flow estimation, there is no need to use more than seven GCPs to establish accurate UAV-based geometry. Rather, it is more crucial to distribute the available markers to be maximally representative of the terrain elevations. Furthermore, it may be necessary to place more markers in close proximity to locations where one may expect the largest challenge for photogrammetry software (e.g.: water, thick forest/vegetation)• In order to limit the impact of the “doming” effect on terrain geometry measurements, one of the most effective, yet easily implementable mechanisms is to measure a river line using Real Time Kinematic (RTK) Global Navigation Satellite Systems (GNSS) equipment. This data can then be used to correct the terrain post photogrammetry processing.Water Resource
Evaluation of the usability of a rapid flood model
No full textFloods are one of the most devastating natural disasters, hitting various regions in the world each year. In the last decades the potential damage caused by floods has increased. The need for tools, like flood maps and flood models, for real time monitoring and forecasting of floods has also increased. When an upcoming flood is expected, and these preparatory tools are not available, giving an insight into how and when the flood will proceed is difficult. A rapid flood model can assist in decision making and emergency response during threatening flood situations. The concept of a rapid flood is a model which makes prediction of a flood event in 1) a short period with the use of 2) publicly available data 3) for any flood prone area in the world. This thesis evaluates the usability of a rapid flood model for river flooding and crisis management. This study consists of three parts. The first two, a 1D and 2D schematization, determine the most influential parameters and conditions of a flood for different types of river areas. Publicly available data is used for these most influential parameters and conditions to simulate the third study case, the 2011 Thailand flood event. The rapid model can be setup for any flood prone area in the world in 1 or 2 days by an experienced modeler. The publicly available data needs to be supplemented by chosen methods and equations to set up the model. This study shows that the most influential parameters and conditions for the rapid flood model are site specific. For a relative flat area the type of land use is an influential condition, while in a mountainous area the river geometrics are the main influential parameters. The analysis gives an insight into which data the available resources, both time and money, should be spend on, if they are not publicly available. Over all, this evaluation shows that a rapid flood model can provide a reasonable estimate of a flood event in a short amount of time by using only publicly available data. The proper use of the rapid flood model depends highly on the type of river area and using the correct data for the most influential parameters and conditions for these river and area types.Hydraulic Structures, Flood RiskHydraulic EngineeringCivil Engineering and Geoscience
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Silenced Rivers: Modelling and assessing the impacts of large-scale hydropower projects on the ecohydrology of the Myitnge and Myittha rivers in Myanmar
No full textHydrological modifications to the natural flow regime through the regulation of a river threaten the integrity of river ecosystems. In Myanmar, the exponentially growing hydropower sector poses a threat to the ecohydrology of some of the last large free-flowing rivers in the world. This study investigates to what extent the natural flow regime of the Myitnge in Myanmar has been hydrologically altered by the Yeywa dam, which is currently the largest hydropower dam in Myanmar. The study furthermore examines which ecological processes have been or could potentially be most affected by these hydrological modifications. This is done by modelling the natural flow regime of the dammed Myitnge river in Myanmar using the distributed hydrological rainfall-runoff Wflow\_sbm model, which consists of a set of python programs to perform hydrological simulations. The suitability of this model as a tool for environmental flow management in Myanmar is simultaneously investigated. The model uses PCRaster, which in turn makes use of a dynamic modelling language within a GIS framework. It was forced using static and dynamic data which is mostly globally available from different satellites, and derivatives of this, and calibrated and validated on data collected during field visits in 2018 as well as some secondary data sources. The field data collection focused on river bathymetry and soil properties such as infiltration capacity. Furthermore, scenarios were developed and simulated that varied in dam operational capacity (29\% and 80\%), reservoir management (for flood mitigation), and irrigation demand. Using modelled discharge results, multiple environmental flow assessments were carried out, comparing pre- and post-dam scenarios. The results demonstrated that different elements of the flow regime can be altered slightly depending on the Yeywa operational scenario. For the irrigation scenario, the high water uptake to meet the crop demand alters the magnitudes and duration to the largest extent of all the scenarios. According to the results, the dam alone does not alter most of the components of the natural flow regime (and hence presumably the associated ecological factors) to a very large extent, regardless of the capacity it is operated at. This is because the attainable operational capacity is limited by inflow: raising the capacity at which the dam is operated can only be done for a limited amount of time due to the extreme seasonality. For the current operation and in the simulated scenarios, habitat availability for different species of plants and animals, as well as the river's ability to structure the channel morphology are the elements most at risk due to the Yeywa dam. This is mostly because the occurrence of large floods has significantly reduced or completely disappeared from the flow regime, as also demonstrated by a habitat inundation analysis for the Myitnge. There is potential for the optimisation of the operation of the Yeywa reservoir, but it remains limited to the availability of inflows, which in turn is dependent on the natural seasonality and the size of the reservoir. Therefore, one of the main recommendations is to avoid keeping the outflow below the natural inflow in the dry season, and to run the turbines at maximum capacity during the monsoon period. This is advised in order to protect the downstream channel area from dewatering in the dry season, and to maximize the electricity generation during the wet season, while simultaneously keeping the released discharge very close to the natural flow regime.Water Managemen
Rainfall – runoff model of the Huangpu River in Shanghai
No full textShanghai is a city located in a coastal region and to understand the flood risks it is exposed to, it is of most importance to first understand the processes that control the water levels for the different flood scenarios. Historically, the Huangpu River has reached its highest levels during landfalling typhoon events, which create a combined scenario that involves high sea water levels due to storm surge, and high river water levels consequent not only of the storm surge at the river mouth, but also of the runoff generated by precipitation in the upstream regions. This research project will focus on the later, assessing the impact of torrential rainfall during tropical storms on the water levels along the Huangpu River in Shanghai city. By studying the hydrological regime of the area of interest, three main watershed regions are identified for the Huangpu river basin; the Taihu lake basin situated upstream regulates the yearly discharge on the downstream areas of the river and is controlled by means of a flood gate which remains closed once a certain flood risk is identified, an agricultural area covered in its majority by an interconnected lake system, and the river basin which encompasses the remaining contributing regions to the system. A hydrological model is built for the Huangpu river basin following the rational method, identifying from satellite databases the dominant land cover classes of the region, the hydrological soil group based on the different soil contents, and the average slope around the area based on a digital elevation model. Using the precipitation data from typhoon Fitow, the hydrological model was used to estimate the corresponding discharge time-series from the storm to be used as input on a hydrodynamic model of the Huangpu river. The hydrodynamic model of the river was built using D-Flow Flexible Mesh, it was used to assess different scenarios of the river system configuration, allowing to understand not only the overall contribution of rainfall-runoff to the river discharge but also the effect of each of the catchments on the river system. The performance of this model, as well as of the hydrological model was observed by comparing the predicted values with the site measurements at two hydrological stations, one midstream at Huangpu Park which highlighted the strong influence of the tide on the water levels for the river sections closer to the sea, and one upstream at Mishidu where the influence of the rainfall runoff to the water levels could be observed. The hydrological model was then validated using the precipitation data from typhoon Haikui, taking the corresponding discharge time-series for it to the DFM river model and comparing the estimated water levels to the actual measurements. Finally the river profile with the maximum water levels along it as predicted by the DFM model was compared to the scenario modelled with no rainfall-runoff discharge and the measured embankment height to understand the contribution to flood risk of the torrential rainfall during tropical storms on the water levels along the Huangpu River.Additional thesi
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