Tailwater Elevation Research Articles

Coordinated optimal operation of hydro–wind–solar integrated systems

The high proportional integration of variable renewable energy sources (RESs) has greatly challenged traditional approaches to the safe and stable operation of power systems. Considering the complementary characteristics of various RESs, an optimization model is proposed in this study for cascade hydropower stations coupled with renewable-energy-based power generation methods such as wind and photovoltaics (PV). Building on the autoregressive moving average (ARMA) model and improved vine-copula theory, a joint distribution model for wind and PV power is built with measured data to capture the spatial and temporal correlations between wind and solar plants, and sufficiently representative scenarios for renewable energy generation are explored. Due to nonlinearities in the forebay elevation vs. reservoir volume, tailwater elevation vs. water flow, and head-sensitive power generation in hydropower stations, several linearization approaches are used to reformulate the optimization model into a more tractable form. The hydraulic relationship and time delay of water flow between cascade reservoirs are established to make full use of the controllable complementarity of hydropower generation. Optimized coefficients of coordinated operations in different seasons are obtained by a heuristic algorithm for cascade reservoirs. A detailed case study is undertaken in a basin with wind farms and solar arrays in Southwest China, and the simulation results demonstrate the potential of a large-scale hydro–wind–solar hybrid system to meet export power transmission demands. Finally, the optimal capacity of wind and PV plants is determined to inform the future planning and construction of actual systems.

Coordinated Optimal Short-Term Operation of Hydro-Wind-Solar Integrated Systems

The integration of high proportion variable renewable energy sources (RES) has greatly threatened the safe and stable operation of power systems. Considering the complementary characteristics of various RES, this paper proposes a short-term optimization model for cascade hydropower stations coupled with renewable-based generations including wind and photovoltaic (PV). Based on autoregressive moving average (ARMA) model and copula function, a joint distribution model for power output of wind and PV is built with measured data and substantial scenarios are produced. Due to the nonlinear curve of forebay elevation - reservoir volume and tailwater elevation - water flow in hydropower stations, several linearization approaches are used to reformulate the optimization model into a tractable form. Hydraulic relationship and time delay of water flow between cascade reservoirs are established to make full use of the controllable complementarity of hydropower generations, and the variability of wind and PV power output can be mitigated. A basin in southwest China with wind farms and solar arrays is chosen as a detailed study case. The simulation results demonstrate the applicability and effectiveness of the proposed approach.

Performance analysis of box and circular culverts using HY 8 software for Aluu Clan, Port Harcourt

This study is on culvert performance analysis carried out in Aluu clan comprising of nine communities. A total of ten culverts located across the roads within the communities were inspected and monitored during rainy season. It entails assessing the culverts to ascertain their functionalities. Amongst all the culverts, one location was observed to be problematic because of the extent and duration of flooding after an incidence of intense rainfall in the area. From field data obtained, the Rational method was employed to determine the peak design flow as 450 ft 3 /s (12.74 m 3 /s). The hydraulic analysis was carried out using HY-8 software (in imperial units) by US Federal Highway Administraion, a powerful tool for analyzing variety of culvert shapes and configurations. From field measurements it was discovered that the existing circular culvert comprising of three barrels of 3 ft (914 mm) diameter, each has a headwater elevation of 115.72 ft (35.27 m) as compared to the roadway elevation of 115 ft (35.05 m). The existing circular culvert was redesigned as box and circular options for comparison and selection. Comparing the two redesigned options, circular and box culverts having headwater elevations of 113.06 ft (34.46 m) and 109.58 ft (33.40 m) while tail-water elevations of both is 106.17 ft (32.36 m), with respect to roadway elevation of 115 ft (35.05 m). Both design options are capable of containing the design flow without any incidence of flooding. However, box culvert has an advantage of lower headwater elevation. Also, both circular and box culverts are outlet control as depicted by culvert performance curves. We stand to gain by redesigning existing culverts observed to experience flooding during heavy storms of short durations. There is need to monitor performance of existing culverts as some were designed with limited field data resulting in under- or overdesign. Keywords: Circular and Box culverts, headwater elevation, HY-8 software, Design flow, Aluu Clan, Port Harcourt

Effect of downstream apron elevation and downstream submergence in discharge coefficient of ogee weir

ABSTRACT Discharge coefficient in ogee spillways is essential factor for producing discharge–head relationship. Discharge coefficient is relevant to the downstream water level submergence and downstream apron elevation. In this study, both submergence and apron effect are investigated using experimental data. To mathematical expression for discharge coefficient, the gene expression programming (GEP) and multiple regression technique were applied using dimensionless parameters. Results showed that GEP is superior to the regression analysis in predicting of discharge coefficient (C s). Performance criteria of GEP are R 2 = 0.967, RMSE = 0.041 and MAE = 0.035. For facility, some design examples are presented that show application of the proposed GEP equation and eliminates linear interpolation using existing graphs. The threshold value for submergence (S = h d/h) is 0.8 in this study. That is for S < 0.8, the discharge coefficient is approximately independent from the tail water elevation. But for S > 0.8, the discharge coefficient is dependent to tail water elevation and reduces rapidly with increasing of submergence. With increasing of submergence from 0.32 to 1, relative discharge coefficient (C s/C0) decreases from 1 to 0.47. Moreover, C s is dependent on P d (vertical distance between spillway crest and downstream apron invert) and P (ogee spillway height).

Evaluating upstream passage and timing of approach by adult bigheaded carps at a gated dam on the Illinois River

AbstractDams are a conservation threat because they function as barriers to native fish movement; however, they may prevent the spread of invasive species. Invasive bigheaded carps (Hypophthalmichthys spp.) threaten the Great Lakes ecosystem and are advancing towards Lake Michigan via the Illinois River. Navigation dams on the Illinois River may deter bigheaded carps' upstream movement. We investigated the permeability of the Starved Rock Lock and Dam (SRLD), the most downstream gated Illinois River dam, to bigheaded carps' migration by examining the timing of individuals approaching and passing through SRLD in relation to gate openness, tailwater elevation, and water temperature. Using acoustic telemetry of (N = ~104 per year) tagged fish, 13 upstream passages of bigheaded carps occurred through SRLD between 2013 and 2016. Eleven passages occurred through the dam gates and 2 through the lock chamber, indicating deterrents (e.g., CO2) placed in SRLD lock chamber may only limit passage of a small proportion of all fish passing through the lock‐and‐dam structure. Passages were documented only in 2013 and 2015. Most of the dam gate passages occurred during high water when gates were completely out of the water. Timing of bigheaded carps approaching SRLD was positively correlated with rising water temperature and high tailwater elevation, and all fish approached during late March through mid‐September. Movement through dams is rare; modifying gate operations to reduce gate openness during late spring and summer could further reduce the permeability of gated dams such as SRLD to bigheaded carps, slowing their upstream advance.

Variability of Saturated Hydraulic Conductivity Measurements Made Using a Flexible-Wall Permeameter

Abstract A study was conducted following the procedures in ASTM E691-14 (Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method) to develop a precision statement for hydraulic conductivity measurement of fine-grained soils using Method C (falling head, rising tailwater elevation) of ASTM D5084-10 (Standard Test Methods for Measurement of Hydraulic Conductivity of Saturated Porous Materials Using a Flexible Wall Permeameter). Twelve laboratories conducted tests on three replicate specimens of three fine-grained soils (9 specimens total per laboratory) from the ASTM Reference Soils Program: Soil ML (silt), Soil CL (low plasticity clay), and Soil CH (high plasticity clay). The data indicated that the measurement variability for hydraulic conductivity is modest but not negligible, and probably contributes to the spatial variability reported in past studies of hydraulic conductivity. No systematic relationships were observed between variability in hydraulic conductivity and testing time (consolidation, permeation), backpressure, B-coefficient achieved at end of consolidation, compliance with the termination criteria, or specimen compaction conditions. Many laboratories did not comply with the test standard or the supplemental instructions, which may indicate that greater oversight of geotechnical laboratories is needed via accreditation and auditing programs. Analysis of the data indicate that hydraulic conductivity can be measured using Method C of ASTM D5084 within a factor of 2 for the 10–6 cm/s range, a factor of 1.5 for the 10–8 cm/s range, and a factor of 4 for the 10–9 cm/s range.

Optimization of Reservoir Operation Using Cuckoo Search Algorithm: Example of Adiguzel Dam, Denizli, Turkey

The Adiguzel Dam is located in Denizli in the western part of Turkey. It was built for irrigation purposes, but it also produces energy at the same time. The dam’s energy-production regime is not regular since there are no reservoir-operating rules. Thus, this study develops a reservoir optimization rule to generate a corresponding gain in energy production. It is well known that operating a reservoir is a complex problem that depends on many parameters such as inflow, storage capacity, water elevation, tailwater elevation, and evaporation. Therefore, in order to optimize energy production, there is a need to use heuristic algorithms such as the Cuckoo Search (CS). This study develops a CS algorithm-based solution to optimize the reservoir’s operational system and generate an optimal operation rule curve. Results show that the CS algorithm improves the system operation, and the energy production will be increased by about 10% to a value of 160000 MWh with a corresponding economic gain of about $12 × 106in total for 183 months.

Effect of Submergence and Apron Length on Spillway Scour: Case Study

Large-scale water resources systems are often managed by an integrated set of hydraulic structures that are vulnerable to wider ranges of discharge and tailwater elevation than envisioned in their original design due to climate change and additional project objectives such as fostering healthy ecosystems. The present physical model study explored the performance of a spillway structure on the Kissimmee River, operated by the South Florida Water Management District, under extreme conditions of drought and flooding with accompanying low and high tailwater levels for both gate-controlled and uncontrolled spillway flow conditions. Maximum scour depths and their locations for two different riprap apron lengths downstream of the spillway stilling basin were measured along with the complex flow fields prior to scour. Effects of tailwater submergence, type of spillway flow and riprap apron length on scour results are interpreted in terms of the measured turbulent kinetic energy and velocity distributions near the bed.

Effects of Jet Flipping on Local Scour Downstream of a Sluice Gate

This study shows that a jet-flipping phenomenon may occur during the scouring process downstream of a sluice gate. The flipping consists of a digging and a filling phase. The former scoured the bed, and the latter refilled the scour hole. The process is cyclical, the phases changed intermittently, and no equilibrium scour condition was reached. The scour depth during digging reached a high of 60% more than the filling phase. Moreover, the scour is more severe with jet flipping compared to no-jet-flip conditions. Generally, the maximum scour depth for the digging and filling phases increases with the increase in the tailwater depth and densimetric Froude number but decreases as the apron length increases. The jet-flipping frequencies increase with the increase in the densimetric Froude number and apron length but decrease as the tailwater elevation increases. The Coandă effect is the most significant factor that triggers the jet-flipping phenomenon. A review of relevant data from previous studies showed that the scouring duration tested for many cases was not long enough to observe the jet-flipping phenomenon. Prediction equations are proposed for the maximum scour depth at the end of the digging and filling phases and for the frequencies of jet flipping. A threshold diagram to predict the occurrence of jet flipping is also presented and could be applied in design to avoid the undesirable phenomenon in local scour below a sluice gate.

Piezometric variations in the basaltic massif beneath the Itaipu hydroelectric plant (Brazil/Paraguay border): Right Buttress Dam

This article describes a case study of the changes in the hydrogeotechnical behavior of a portion of the foundation block of the Itaipu Dam, which is located on the Parana River on the border between Brazil and Paraguay. The study focuses on the foundation buttress blocks of the Right Buttress Dam, where the most permeable regions of the massif are monitored by standpipe piezometers. The behaviors of two features within the basalt layers, a basaltic breccia and a fracture, were evaluated. In general, the uplift pressure distribution models of the foundations of concrete dams only consider the hydraulic loads caused by the presence of the reservoir and the tailwater elevation. However, this study demonstrates that the hydrogeotechnical behavior of the massif in a given period may also depend on the local variation in rainfall. The primary conclusion is that although the rocky massif has received several foundation treatments (waterproofing and drainage work), the natural hydraulic conditions of the massif govern the pressure variations within the monitored features. Studying the behavior of these features is of fundamental importance to all large concrete dams, as a statistical analysis of ruptures in several types of dams conducted by the International Commission on Large Dams has demonstrated that accidents involving this type of dam are primarily caused by foundation collapse, particularly by collapses related to internal erosion problems and low shear resistance.

Hydraulic Analysis and Design of Pipe Culverts: USGS versus FHWA

AbstractCulvert performance curves relate the flow through a culvert to the headwater and tailwater elevations. These curves are calculated differently by the USGS and Federal Highway Administration (FHWA), leading to the possibility of significant discrepancies in predicted culvert performance under some flow conditions. The FHWA methodology generally leads to conservative culvert designs relative to designs based on the USGS equations, and the degree of conservatism is the focus of this paper. The largest discrepancies in estimated headwater elevations for given flow rates occur under high-headwater and low-tailwater conditions, and these discrepancies are due in large part to the uncertainty in whether Type 5 or 6 flow will exist. The results of this paper show that for horizontal culverts with square-edge entrances and smooth surfaces the overestimation in the headwater depth can range from 9–45% for headwater depths in the range of 1.5–3 culvert diameters, with lesser overestimations of 7–30% in case...

CHUM SALMON SPAWNING ACTIVITY IN TRIBUTARIES BELOW BONNEVILLE DAM: THE RELATIONSHIP WITH TAILWATER ELEVATION AND SEASONAL PRECIPITATION

ABSTRACTChum salmon (Oncorhynchus keta) below Bonneville Dam migrate through as well as hold and spawn in both tributaries and mainstem areas of the Columbia River, USA. Whether fluctuations in tailwater elevation influence spawning in tributaries is unclear. We examined the relationship between Bonneville Dam tailwater elevation, seasonal precipitation and chum salmon spawning activities in three tributary spawning areas. In these tributaries, we assessed initial date of entry, time required to enter and length of spawning season, as well as the proportion of the total population that spawned in tributaries and the distribution of spawners among tributaries. Using linear regression, these variables were compared to cumulative hours of tailwater elevation ≥ 3.5 m and cumulative precipitation. Increased Bonneville Dam tailwater elevation was associated with later and longer lasting chum salmon spawning activities, but was not associated with the distribution of chum salmon spawners in tributaries. Increased seasonal precipitation was associated with a more prolonged spawning season and relatively even distribution of adult chum salmon, but was unrelated to the timing of chum salmon spawning in tributaries. The regulation of tailwater elevation downstream from Bonneville Dam can influence the spawning process for chum salmon in tributaries that enter the regulated area. How important this influence is to the decline of chum salmon in the Columbia River is unclear. Published in 2011 by John Wiley &amp; Sons, Ltd.

3D plunge pool scour with protection measures

Plunge pool scour phenomena are well-known for destructive action at the base of hydraulic structures. An experimental study was conducted at the Hydraulic Laboratory of the University of Pisa, Italy, to investigate the hydraulics of 3D plunge pool scour in presence of simple protection measures. The main geometrical scour hole parameters were investigated and various relationships are proposed for different flow conditions. These parameters include the maximum dynamic scour hole depth, the maximum scour hole width and the location of the scour hole initiation point. Equations for all these parameters are presented in terms of the basic scour variables including the jet densimetric Froude number, jet impact angle, tailwater elevation above the originally horizontal sediment bed level and the protection permeability and longitudinal positions of the protection. Moreover, a scour hole typology and relationships for the non-dimensional longitudinal scour hole profile in presence of the protection are also given.

Quantifying the behavioral response of spawning chum salmon to elevated discharges from Bonneville Dam, Columbia river, USA

AbstractChum salmon Oncorhynchus keta that spawn in main‐stem habitats below Bonneville Dam on the Columbia River, USA, are periodically subjected to elevated discharges that may alter spawning behaviour. We investigated behavioural responses of spawning chum salmon to increased water velocities associated with experimental increases in tailwater elevation using acoustic telemetry and a dual‐frequency identification sonar. Chum salmon primarily remained near their redds at base tailwater elevations (3.5 m above mean sea level), but displayed different movement and behavioural responses as elevations were increased to either 4.1 or 4.7 m for 8‐h periods. When velocities remained suitable (&lt;0.8 m s−1) during elevated‐tailwater tests, female chum salmon remained near their redds but exhibited reduced digging activity as water velocities increased. However, when velocities exceeded 0.8 m s−1, the females that remained on their redds exhibited increased swimming activity and digging virtually ceased. Female and male chum salmon that left their redds when velocities became unsuitable moved mean distances ranging from 32 to 58 m to occupy suitable velocities, but returned to their redds after tailwaters returned to base levels. Spawning events (i.e. egg deposition) were observed for five of nine pairs of chum salmon following tests indicating any disruptions to normal behaviour caused by elevated tailwaters were likely temporary. We believe a chum salmon's decision to either remain on, or leave, its redd during periods of unsuitably high water velocities reflects time invested in the redd and the associated energetic costs it is willing to incur. Published in 2009 by John Wiley &amp; Sons, Ltd.

Hydraulics of 3D Plunge Pool Scour

The main flow features of three-dimensional plunge pool scour are explored in this experimental research for steady flow conditions. These include the maximum depth of the scour hole, its streamwise geometry, and the maximum width, the maximum height of the ridge, its shape in plan view, and its profile. Expressions for all these parameters are presented in terms of the basic scour variables, including the approach flow densimetric Froude number, the jet impact angle, the jet diameter, and the tailwater elevation above the originally horizontal sediment bed. This research is based on a previous work relating to two-dimensional plunge pool scour. Differences between the two phenomena are outlined, and the results are discussed in terms of engineering applications. The results of the two works allow for the prediction of the most salient features of plunge pool scour for both the dynamic and the static scour holes.

Performance of Submerged Ogee-Crest Weir Head-Discharge Relationships

Submergence is defined as the ratio of the tailwater to the headwater, both measured relative to the weir crest. The performance of published submerged ogee-crest head-discharge relationships was investigated in this study. Four submerged and one free-flow head-discharge relationship were evaluated relative to a submerged ogee-crest data set covering a range of tailwater elevations, discharges, and weir geometries. For submergence levels 0.8, the accuracies of all but one of the head-discharge relationships were very poor. For such high submergence levels, more accurate methods are needed for predicting submerged ogee-crest head-discharge relationships.

Hydraulics of Plane Plunge Pool Scour

Plunge pool scour involves a significant risk with trajectory spillways because of structural undermining at a dam foot or destabilization of adjacent valley slopes. An experimental program towards the understanding of plane plunge pool scour of a completely disintegrated rock surface was conducted, in which the following items received attention: jet shape, jet velocity, jet air content, tailwater elevation, granulometry, upstream flow to the scour hole, and the end scour profile in terms of the basic scour features. These effects were experimentally investigated based on a systematic variation of the governing scour parameters. The results of this paper allow answering questions that have so far not been addressed. Design equations were proposed to sketch the main tendency of the data sets. The significant effect of the densimetric particle Froude number was substantiated. This research may be used to estimate the prominent scour features for nearly two-dimensional jet arrangements involving a pre-aerated high-speed flow.

Energia Firme de Sistemas Hidrelétricos e Usos Múltiplos dos Recursos Hídricos

This paper presents an optimization model for the calculation of the firm energy of hydropower plants. The model represents the hydro operation in detail (water balance of plants in cascade, storage-dependent production factor, tailwater elevation curve, evaporation as a function of the wet area, etc.) as well as transmission constraints. Results with the model for the existing hydro plants of Brazil show that the calculated firm energy is smaller than the sum of the assured energy certificates of these plants. This means that there will be a new energy rationing in case the worst historic hydrology happens again in the future. A revision of the methodology is proposed, ensuring that the resulting firm energy considers both the hypothesis of the worst drought observed in the past and the decreasing availability of water for energy production, due to other uses.

Short-Term Operation Model for Coupled Hydropower Reservoirs

A short-term operation model is developed for optimal operation of hydraulically coupled hydropower plants. The model uses mixed integer nonlinear programming as an optimization tool. An innovative method is proposed to address the issue of hydraulic coupling through the use of tailwater elevation curves. Binary variables are used in the nonlinear programming model formulation for the selection of the tailwater elevation curves. Sensitivity of operation schedules to time delay due to flow transport is analyzed. The developed model is applied to an existing system of hydropower reservoirs in Manitoba, Canada. Results indicate that operation schedules from the operation model, which considers the aspect of hydraulic coupling, are significantly different from those obtained from a similar kind of model that does not consider this issue in an exhaustive approach. The importance of hydraulic coupling and its effect on generating schedules are emphasized.

VELOCITY FIELD MEASUREMENTS AT AN OVERFALL

The velocities and circulation patterns were measured and characterized for flows in the vicinity of an aeratedstraight drop overfall. The velocity vectors were determined for multiple tailwater levels at a constant flow rate and formultiple flow rates at a constant tailwater level. An acoustic Doppler velocimeter (ADV) was used to acquire three-dimensionalcomponent flow velocities along the channel centerline. The ADV probe performed well in areas of relativelylow flow velocity and low air entrainment, but the probe did not perform well in areas with high flow velocity and high airentrainment. The velocity measurements are presented and the near boundary flow velocities agreed well with previouslymeasured boundary stresses. The velocities near the vertical wall and horizontal floor were observed to be similar inmagnitude for a range of tailwater elevations and discharges. These velocity field measurements provide fundamentalinformation about the velocities and circulation patterns in the vicinity of an overfall. This information enhances ourunderstanding of the forces that cause headcut erosion.