Initial Water Level Research Articles

Ultrashort-Term Scheduling of Interbasin Cascaded Hydropower Plants to Rapidly Balance the Load Demand

The short-term scheduling schemes of cascaded hydropower plants are based on day-ahead hydrological forecasting information. Affected by the accuracy of prediction, real-term hydrological information can considerably vary from previously forecasted values, especially for the power load and local inflows. As a result, short-term scheduling schemes are difficult to apply directly in real-time scheduling. To solve this problem, a rolling optimal hourly operation model for interbasin cascaded hydropower plants is proposed to rapidly balance the load demand. The model is deemed an ultrashort-term model, and it has a short-cycle schedule between short-term and real-time schemes. The basic strategy of solving the model is as follows. First, the day-ahead power load and local inflow information are corrected using a statistical method based on the most recent real-time information. Second, the water delay time, defined as the time between when water is released from upstream reservoirs and arrives at downstream reservoirs, is updated based on the most recent real-time information. Third, a heuristic method is proposed to dynamically update the short-term scheduling scheme over the next few hours. The objective is to minimize the maximum relative deviation between the actual water level of a reservoir at the end of 24 hours and the day-ahead forecasted value. This approach can keep the reservoir water level at the end of 24 hours close to the forecasted value and improve the accuracy of estimating the initial water level the next day. The developed method is applied to solve an ultrashort-term scheduling problem involving the cascaded hydropower plants located in Yunnan Province, China. The results indicate that the proposed model can achieve seamless coupling between short-term scheduling and real-time scheduling. The proposed method can provide a scientific basis for the real-time dispatching of large-scale hydropower plants and improve the practicality of short-term dispatching schemes.

Probabilistic tsunami hazard assessment and its application to southeast coast of Hainan Island from Manila Trench

Tsunami is one of the most destructive natural disasters and the probabilistic tsunami hazard assessment (PTHA) has become increasingly popular in both academic and engineering field. However, most methods to carry out PTHA cannot avoid large number of scenario simulations generated by comprehensive assessment of the uncertainties of all seismic parameters. In order to balance the accuracy and feasibility in PTHA, we propose a more efficient approach. Based on the linear assumption of tsunami waves in deep water, the computation of tsunami wave propagation is given by the linear superposition of waves caused by unit sources of water level disturbance, which transforms a large number of seismic tsunami scenarios simulations into a limited number of simulations on wave propagating from each unit source. By placing 5,438 unit sources in Gaussian-shaped waveform with the interval of 0.1° around Manila Trench to approximate the initial water level disturbance under any combination of seismic parameters, we have evaluated 1,380,000 potential seismic scenarios in the Manila trench area. The water level fluctuation process of each target point along 100 m isobaths in every scenario is calculated to estimate whether the maximum wave height of the leading wave exceeds a specific critical value. Combining the probability density of each seismic parameter, the exceedance probabilities of specific wave heights and hazard curves at all target points are given.

Modified models for better prediction of infiltration rates in trapezoidal permeable stormwater channels

ABSTRACTIn stormwater management, it is important to accurately quantify the infiltration rates to solve urban runoff-related problems. This study proposes a method to improve estimates of the infiltration rate in permeable stormwater channels. As part of the analysis, five infiltration models were evaluated: the Kostiakov, Horton, modified Kostiakov, Philip and SCS (Soil Conservation Service) models. Infiltration tests with various initial water levels were performed on channel models with differing base width and side slopes. The results show that the addition of three parameters that describe the trapezoidal cross-sectional area, i.e. the depth, side slope and base width, in the infiltration models yielded better estimates of the infiltration rate. A comparison of the infiltration capacity values obtained from the models after the three parameters were added with those that were experimentally obtained, shows that the improved modified Kostiakov model is the most suitable model to predict infiltration rates in trapezoidal permeable stormwater channels.

Application of BRAHMA hydrodynamic model for flood forecasting

Flood forecasting models are of paramount importance to predict the flood and thereby warning the community living near the floodplains or the vulnerable areas. In the quest for understanding the complex processes of a river, scientist and researchers have given importance to river modeling both analytically and physically by conducting experiments in the laboratory. The numerical model which is basically a mathematical model has gained popularity in the last few decades. BRAHMA (Braided River Aid: Hydro-Morphological Analyzer) is a hydrodynamic model for simulating the spatial variation in water depth, flows, and velocities in the unsteady free surface flow. It is developed by IIT Guwahati in collaboration with Brahmaputra Board, Govt. of India. The BRAHMA 1-D model is capable of simulating both prismatic as well as non-prismatic channel reach. It is also capable of simulating channels with varying width and varying slope. In this paper, an attempt has been made to use the BRAHMA 1-D model for determining the water surface elevation at certain flood-prone areas of Ranganadi River which covers Assam and parts of Arunachal Pradesh, North-East India. The Ranganadi hydroelectric dam is situated in Arunachal Pradesh, India. In this study, the length of the river reach considered is 77.09 km from the Ranganadi Hydroelectric power project. The cross-sectional width of the river in different sections is extracted from Google Earth and depth was obtained by approximate field measurement. The peak release from the dam, the downstream water level and initial water levels are given as input to the model. The water levels at the particular sections of interest are computed as output from the model. From the generated output data set, it is possible to assess the vulnerable areas by the water levels which will be generated from the model.

Dual-purpose winter wheat: interactions between crop management, availability of nitrogen and weather conditions

Dual-purpose wheat has been adopted in many farming systems, but interactions between management, supply of resources, and seasonal conditions are still not clearly elucidated. Two experiments were established in the Loess Plateau of China to measure yield and its components, evapotranspiration, water-use efficiency (yield per unit evapotranspiration), accumulation and apparent remobilisation of stem water soluble carbohydrates (WSC), and economic benefit of dual-purpose winter wheat. Experiment 1 combined factorially three defoliation treatments, i.e. winter defoliation (DC23), spring defoliation (DC29) and untreated control, two seeding rates (currently recommended, and 125% recommended), and over four seasons. Experiment 2 combined factorially two defoliation treatments (spring defoliation and control), two nitrogen rates (low: 120–150 kg N ha−1, high: 180–200 kg N ha−1), three levels of soil water at sowing (low: rainfed; medium: rain +67 mm; high: rain +133 mm), and over three seasons.Defoliation was largely neutral for grain yield and water-use efficiency, and improved translocation of WSC to grain by 8%, harvest index by 7% and net income by 15% across conditions. Grain yield was unaffected by the interaction between defoliation and seeding rate, but significantly impacted by interactions of defoliation × initial soil water level and defoliation × nitrogen rate. Defoliated wheat yield was greater at high than at medium and low initial soil water content, and at low than at high nitrogen rate. Spring defoliation produced similar yield as winter defoliation but the former increased forage income. Increasing seeding rate or nitrogen rate increased forage income but reduced net income due to lower grain income and higher cost. Thus, dual-purpose winter wheat was more profitable (i) when defoliated in spring, (ii) at the lower seeding density, (iii) under the lower nitrogen rate, and (iv) with higher soil water content at sowing. Apparent translocation of stem WSC partially mediated the effect of defoliation on grain yield. It is concluded that dual-purpose winter wheat is feasible under straw mulching in semiarid environment.

Numerical Simulation of Deep Thermal Groundwater Exploitation in the Beijing Plain Area

Thermal groundwater is relatively abundant in the deep-seated bedrock underlying the Beijing plain area. The main geothermal reservoir is composed of dolomites of the Wumishan Group of the Meso–Neoproterozic Jixian System. The thermal groundwater has been developed and utilized since the 1970s and significant declines in groundwater levels were observed. A 3D unsteady flow model of an anisotropic karst-fissure aquifer based on the equivalent continuum is used to describe the flow of thermal groundwater and heat transport. The heat transportation is described by the governing equation including convection and dispersion. The simulation of this paper aims to solve such problems as uneven distribution and thinness of the aquifer, insufficient initial monitoring data, and poor knowledge of the properties of the horizontal boundary. They are solved by considering vertical stratification of the aquifer with equal thickness, replacing initial water level data by surface elevation, and choosing natural boundary far away from the exploitation areas. Through a trial–error procedure, the simulated and measured groundwater level and temperature in the simulation period are well fitted. Three exploitation schemes are proposed to predict the spatial and temporal changes in groundwater level and temperature of the thermal groundwater in the study area. The prediction results show that the reinjection can effectively slow the decline in the thermal groundwater levels. Except for the Dongnanchengqu, Xiaotangshan, and Liangxiang subgeothermal fields, the other six subgeothermal fields have the potential for further development of thermal groundwater.

Numerical investigation on bottom shear stress induced by flushing gate for sewer cleaning.

One of the most common strategies for sewer cleaning is to generate flushing flows using flushing gates to store water in the upstream sewer pipe. Therefore it is important to obtain the flow information on the flushing waves and their eroding effects. In this study, the flow characteristics of the flushing wave and the flushing effect were investigated by a transient flow calculation using a commercial computational fluid dynamics (CFD) code. The values of bottom shear stress were obtained and the effect of several factors are discussed. The water depth and the slope were related to the release rate of the storage volume, while the flushing volume determined the flushing distance at long sewer distances. The initial downstream water level was found to dramatically reduce the flushing effect. Equations based on the storage depth were developed to estimate the flushing effect, and suggestions for the installation and operation of flushing gates are provided.

Dam Break Analysis of Old Aswan Dam on Nile River Using HecRas

The Egyptian segment of the Nile River is controlled from its upstream end by two dams: the High Aswan Dam (HAD) and the Old Aswan Dam (OAD). Nowadays, questions are being raised about the efficiency and safety of the Old Aswan Dam and what will happen if the dam fails? For this regard, a 1D hydraulic model using HEC-RAS package was developed to investigate a number of dam break scenarios, to estimate the outlet hydrograph from the dam site and to route the produced flood wave throughout the first river reach from the dam site up to Esna barrage. A numerical sensitivity analysis was performed to select the relevant values of the implicit weighting factor θ, Δx and Δt. Eight dam break scenarios were developed to investigate the effect of initial water level, inlet flow and dam breach width on the expected inundated area. Results showed that there would not be catastrophic consequences from the Old Aswan Dam failure. The main concern is when large flow values are released deliberately (Q = 605 mm3/sec) from the Aswan Dam.

Roughness Effect of Submerged Groyne Fields with Varying Length, Groyne Distance, and Groyne Types

Design guidelines were developed for a number of in-stream structures; however, the knowledge about their morphological and hydraulic function is still incomplete. A variant is submerged groynes, which aim to be applicable for bank protection especially in areas with restricted flood water levels due to their shallow height. Laboratory experiments were conducted to investigate the backwater effect and the flow resistance of submerged groyne fields with varying and constant field length and groyne distance. The effect of the shape of a groyne model was investigated using two types of groynes. The validity of different flow types, from “isolated roughness” to “quasi smooth”, was analyzed in relation to the roughness density of the groyne fields. The results show a higher backwater effect for simplified groynes made of multiplex plates, compared to groynes made of gravel. The relative increase of the upstream water level was lower at high initial water levels, for short length of the groyne field, and for larger distance between the single groynes. The highest roughness of the groyne fields was found at roughness densities, which indicated wake interference flow. Considering a mobile bed, the flow resistance was reduced significantly.

A new approach in evaluation of a spillway capacity preserving the safety requirements

The 23 m tall Bawanur dam is a multipurpose project currently being constructed on the Diyala River, Iraq. The project provides storage, flood control, irrigation, power production and recreational uses. The dam body is embankment with clay core. In the initial design the spillway was provided with 9 bays equipped with 14 m span tainter gates capable to discharge 11460 m3/s, corresponding to 10000 years return period outflow. The discharge from the Darbandikhan Dam (H = 128 m, V= 3 bil.m3) located 52 km upstream was the main contributor to design inflow hydrograph into Bawanur reservoir. In the improved design the outflow from Darbandikhan spillway was reviewed by considering both the inflow discharge and the reservoir initial water level as independent random variables. The variability of initial reservoir level was defined based on recorded maximum annually reservoir water levels during the period 1962 – 2013. The outflow from the Darbandikhan dam corresponding to 1:10 000 years return period was reduced to 5298 m3/s, significantly less than the one in the previous approach that was 11000 m3/s. The spillway has now only 6 bays.

A novel stochastic modelling approach for operational real-time ice-jam flood forecasting

Forecasting ice jams and their consequential flooding is more challenging than predicting open water flood conditions. This is due to the chaotic nature of ice jam formation since slight changes in water and ice flows, location of the ice jam toe along the river and initial water levels at the time of jam formation can lead to marked differences in the outcome of backwater level elevations and flood severity. In this paper, we introduce a novel, operational real-time flood forecasting system that captures this stochastic nature of ice-jam floods and places the forecasts in a probabilistic context in the form of flood hazard maps (probability of flood extents and depths). This novel system was tested successfully for the ice-cover breakup period in the spring of 2018 along the Athabasca River at the Town of Fort McMurray, Canada.

Coping with Extreme Events: Effect of Different Reservoir Operation Strategies on Flood Inundation Maps

The need of addressing “residual flood risk” associated with structural protection measures, such as levee systems and flood-control reservoirs, has fostered actions aimed at increasing flood risk awareness. Structural measures have lowered risk perception by inducing a false sense of safety. As a result, these structures contribute to an underestimation of the “residual risk”. We analyze the effect of different reservoir operations, such as coping with drought versus coping with flood events, on flood inundation patterns. First, a hydrological model simulates different scenarios, which represent the dam regulation strategies. Each regulation strategy is the combination of an opening of the outlet gate and of the initial water level in the reservoir. Second, the corresponding outputs of the dam in terms of maximum discharge values are estimated. Then, in turn, each output of the dam is used as an upstream boundary condition of a hydraulic model used to simulate the flood propagation and the inundation processes in the river reach. The hydraulic model is thus used to determine the effect, in terms of inundated areas, of each dam regulation scenario. Finally, the ensemble of all flood inundation maps is built to define the areas more prone to be flooded. The test site is the Casanuova dam (Umbria, central Italy) which aims at: (i) mitigating floods occurring at the Chiascio River, one of the main tributaries of Tiber River, while (ii) providing water supply for irrigation. Because of these two competitive interests, the understanding of different scenarios generated by the dam operations offers an unique support to flood mitigation strategies. Results can lead to draw interesting remarks for a wide number of case studies.

A Joint Sedimentation-Flood Retention Assessment of a Small Water Reservoir in Slovakia: A New Hope for Old Reservoirs?

The intensification of agricultural production brings problems related to water erosion, even to the upper parts of river basins. Soil particles that have eroded from unprotected agricultural land are often deposited in small water reservoirs, the efficiency or function of which might be compromised. This study presents an analysis of changes in the retention capacity of a small water reservoir over a period of 8 years. Within the study, a detailed bathymetry of the reservoir was conducted using an acoustic Doppler current profiler. The results, when compared to a 2008 geodetic survey, showed that the retention volume of the reservoir was reduced by only 2%, which was also confirmed by mathematical modeling. The possibility of strengthening the reservoir’s role in flood protection was also investigated. A flood wave with a return period of 100 years was estimated using a design storm approach. A simple numerical model was proposed to transform the flood wave through the reservoir by considering four different scenarios of the elevation of the initial water level. The model, which is based on a water balance equation, uses simple hydraulic relationships to control the discharge through the reservoir’s outflow objects. The results demonstrate that by reducing the initial water level, significant improvements in terms of the flood peak’s attenuation and a longer time to peak values could be achieved.

Influence of reservoir shape upon the choice of Hydraulic vs. Hydrologic reservoir routing method

The objective of the paper is to compare the hydrologic and hydraulic reservoir routing methods in term of assumptions, equations, numerical computation procedures, necessary data and advantages-disadvantages of their use. To test the results provided by the two methods, a set of two reservoirs from Romania was chosen: one long and narrow and the other one roundly shaped. Corresponding inflow hydrographs were chosen, and similar conditions were imposed for the outflow dam control structures, namely the initial water level in the reservoir to be at the Spillway Crest Level (SCL) and no outflow control. For the hydrologic method the Puls procedure was used and a program was written in Scilab to solve the continuity equation in finite differences. For the hydraulic method HEC-RAS software was used to solve the 1D Saint-Venant equations. Outflow and stage hydrographs at the dam were compared together with the stage hydrograph at the reservoir tail for the hydraulic method. Results show that the hydraulic method should be used for the long and narrow reservoirs, as it considers the backwater effect, whereas the hydrologic method can be efficiently used for all other reservoirs where this effect is negligible.

基于起调水位上限优化策略的水库弃水控制方法

基于起调水位上限优化策略的水库弃水控制方法

Thermal performance analysis and optimization design for LNG submerged combustion vaporizer

Submerged combustion vaporizer (SCV) is an efficient and energy-saving liquefied natural gas (LNG) heat exchange facility, which is developed by multiphase flow heat transfer combined with supercritical fluid heat transfer technology. This paper adopted the computational fluid dynamics (CFD) approach to investigate thermal performance of a real-life SCV with the designed handling capacity of 202 t/h. The numerical results and monitoring industrial data were in good agreement, indicting the feasibility of present method. Results displayed that two typical physical processes, namely, hot flue gas and water flowing across stagger tube bundle wall and supercritical LNG gasification, occurred inside the SCV system. The shell-side heat transfer capacity was mainly affected by the initial water level and volume rate of flue gas. Higher inlet LNG velocity could effectively enhance local tube-side heat transfer coefficient, and the maximum value may depend on the inlet LNG pressure. Furthermore, the Han models could be used to predict the overall thermal performance of SCV with a higher accuracy. Eventually, an optimization design method for SCV system was provided.

Reflood experiments at elevated pressures using intact and deformed rod bundles to simulate small and medium break loss-of-coolant accidents

Abstract Reflood experiments at elevated pressures for small and medium break loss-of-coolant accidents were performed to investigate the influence of fuel deformation on the peak cladding temperature and local quenching behaviors. The typical experimental parameters such as initial water level, power, reflood rate, system pressure, initial wall temperature, and fluid temperature were varied to cover a wide range of flow conditions under a medium and high pressure. The experimental results showed remarkable differences in the peak cladding temperature and local quenching behaviors between the intact and deformed rod bundles due to the flow blockage effect. The present results implied that the fuel rod deformation can enhance the coolability of fuel rods by the flow blockage in the present fully blocked channel. Any bypass in a partially blocked channel may change those results due to a crossflow between intact and deformed rods. The experimental results were then used to validate the system analysis code, Multi-dimensional Analysis of Reactor Safety-KINS Standard (MARS-KS). The MARS-KS code showed good prediction of the present experimental data for most of the flow conditions.

Hydroclimatological Drivers of Extreme Floods on Lake Ontario

AbstractThis study examines the hydrologic and climatic conditions that precede major flood events on Lake Ontario, with the purpose of understanding the potential for seasonal forecasts to inform lake level management. Seven late spring/early summer flood events are identified since 1949, including the record‐breaking flood of 2017. The surface climate, atmospheric circulation, and antecedent lake levels for the preceding winter and spring seasons are examined. Results suggest that flood events are caused by different combinations of high, initial wintertime water levels across all of the Great Lakes, anomalously wet winters across the entire Great Lakes basin, and wet spring conditions, particularly in the eastern part of the basin. Wet winters that precede flood events are often associated with La Niña conditions, while wet springs are often associated with a westward shift of the North Atlantic Subtropical High. As the critical drawdown period for Lake Ontario occurs in the fall, before the onset of anomalous winter or spring/summer inputs, a generalized additive model was used to predict April–August maximum monthly average Lake Ontario water levels using November levels for all Great Lakes, a nonlinear response to the wintertime Niño 3.4 index, and scenarios of April–May overbasin precipitation. The Niño 3.4 index significantly improves lake level predictions, suggesting that an El Niño‐Southern Oscillation signal may be useful for lake level management. Future work needed to verify the use of El Niño‐Southern Oscillation for Lake Ontario flood forecasting and to link the North Atlantic Subtropical High to predictions of springtime Great Lakes climate is discussed.

Development of an integrated hydrological-irrigation optimization modeling system for a typical rice irrigation scheme in Central Vietnam

In Central Vietnam, farmers report an increasing occurrence frequency of water shortages for irrigation during dry seasons. Particularly during the summer-autumn rice season, water is often insufficient to irrigate the entire rice production areas, and thus restricting rice productivity significantly. In this study, a coupled hydrological-irrigation optimization modelling system is developed to optimize irrigation strategies for a typical rice irrigation system in Central Vietnam. The model consists of a fully distributed hydrologic model, which simulates the inflow to a reservoir, and an irrigation model, which optimizes the rice irrigation technology, i.e. Alternate Wetting and Drying (AWD) or Continuous Flooding (CF), irrigation schedule and cropping area under given water constraints. Irrigation strategies are derived based on different initial reservoir water levels at the beginning of the cropping season as well as different maximum water releases. The simulation results show that the initial level of water in the reservoir is crucial: Water levels of less than 90% do not provide sufficient water to irrigate the entire cropping area, whereas a level of 70% restricts the cropping area to 75%. AWD is able to reduce the water input, ranging from 4% to 10%. The adoption of AWD therefore has the potential to irrigate a larger area and may help to increase the profit of the farmers. However, the benefits of AWD can only be achieved after significant investment in the canal system and the reservoir outlet. Since the robustness of the optimization results (performance variability) is crucial for decision support, we estimated the impact of different computing environments on the solutions. Only limited performance variability is found, giving confidence in the robustness of the model for decision support.

Horizontal Circulation Patterns in a Large Shallow Lake: Taihu Lake, China

Wind induced hydrodynamic circulations play significant roles in the transport and mixing process of pollutants and nutrients in large shallow lakes, but they have been usually overlooked, while environmental, biological, and ecological aspects of eutrophication problems get the most focus. Herein we use a three-dimensional model, driven by steady/unsteady wind, river discharge, rainfall, evaporation to investigate the spatially heterogeneous, large-scale hydrodynamic circulations and their role in transporting and mixing mechanisms in Taihu Lake. Wind direction and velocity determines the overall hydrodynamic circulation structure, i.e. direction, intensity, and position. A relative stable hydrodynamic circulation pattern has been formed shortly with steady wind (~2 days). Vertical profiles of horizontal velocities are linearly correlated to the relative shallowness of water depth. Volume exchange between subbasins, influenced by wind speed and initial water level, differs due to the complex topography and irregular shape. With unsteady wind, these findings are still valid to a high degree. Vertical variations in hydrodynamic circulation are important in explaining the surface accumulation of algae scums in Meiliang Bay in summers. Vorticity of velocity field, a key indicator of hydrodynamic circulation, is determined by wind direction, bathymetry gradient, and water depth. The maximum change of velocity vorticity happens when wind direction is perpendicular to bathymetry gradient. Furthermore, Lagrangian-based tracer transport is used to estimate emergency pollution leakage impacts, and also to evaluate operational management measurements, such as, the large-scale water transfer. The conclusion is that the large-scale water transfer does not affect the hydrodynamic circulation and volume exchanges between subbasins significantly, but succeeds to transport and then mix the fresh, clean Yangtze River water to a majority area of Taihu Lake.