Mean Water Level Research Articles

The relationship between water-level fluctuation factors and the distribution of <i>Carex</i> in floodplain grassland around Poyang Lake

水位波动对鄱阳湖草滩湿地的形成与分布至关重要，但不同要素对湿地植物种的具体影响不尽相同.本研究以湿地优势植被苔草群落为研究对象，通过环湖区样带设置和植被调查得到较大尺度上的苔草分布数据，以不同水文站水文数据结合湖区DEM插值得出各样点水位波动要素数据：年内最大水位差R，年内淹没出露频次F，年平均水位M，最长淹没的出露日期D，年内总出露时间T，用CART模型进行分析.结果表明：1）影响鄱阳湖区草滩湿地苔草群落分布的最直接的水位波动要素为T和R；2）年内总出露时间大于84天（T ≥ 4.619），年极差水位大于11.3 m（R ≥ 10.41）时，苔草群落的综合分布情况最佳.进一步探讨认为：其他水位波动要素未能被CART模型选为分类依据，可能是因为彼此之间存在相关性；高程决定植被分布，实际上是多种水位波动要素综合影响的结果，精度要求不高时，可以用高程替代水位波动各要素进行简略分析.本研究相关结论可以为鄱阳湖控湖工程今后的运行，提供一定的参考，以维持草滩湿地生态系统的稳定，更好地实现其生态价值.;Water-level fluctuations are very important to the formation and distribution of the floodplain grassland around Lake Poyang, and different factors of water-level fluctuations (aspects of water regime) have different effects on wetland plant species. In this study, we used CART model to analyze the relationship between the distribution of Carex and five water-level fluctuations factors (annual water level range,R;annual frequency,F;annual mean water level,M;date of emergency after the longest inundation,D;annual total dewatered time,T), with plant data from sampling around Poyang Lake and water regime date offered by local hydrology bureau. The results showed that:1) the main influence factors of the distribution of Carex were T and R;2) the optimum condition to Carex community should be described as T ≥ 4.619 and R ≥ 10.41,which means annual total dewatered time more than 84 days and annual water level range larger than 11.3 meters. Further discussion indicated that we can use dimension reduction methods in analyzing the effects of water level fluctuations on wetland vegetation in Poyang Lake, because of the inner correlation between the above mentioned five factors. Meanwhile, previously extensive application of elevation in this field is mainly due to the comprehensive influence of different water level fluctuation factors, and only should be used in conditions with low accuracy requirement. This study provided quantitative evidence that water-level fluctuation factors drive the distribution of Carex, and may assist in making decision regarding the dam management, for the purpose of maintaining the floodplain grassland ecosystem, as well as realizing its ecological value.

Prediction of Mean Water Level Rise Behind Low-Crested Structures and Outflow Velocity from Openings by Using a Hybrid Method Based on Two Dimensional Model Test and Hydrodynamic Numerical Modeling

ì €ë§ˆë£¨êµ¬ì¡°ë¬¼ì˜ ì•ˆì •ì„± 및 배후 호안의 월파량은 배후수역의 수위에 영향을 받음에도 단면 수리모형실험수행 시 수위상승량이 ì•Œë ¤ì§€ì§€ 않아 계측 결과가 ì™œê³¡ë ìˆ˜ 있다. 본 연구에서는 ì €ë§ˆë£¨ 구조물 ì œì²´ 배후면의 í‰ê· ìˆ˜ìœ„ 상승량을 예측하기 위해 단면수리모형실험과 í•´ìˆ˜ìœ ë™ìˆ˜ì¹˜ëª¨í˜•ì‹¤í—˜ì„ 수위-ìœ ëŸ‰ 관계식으로 결합하는 결합기법을 시도하였다. 이 기법을 사용함으로써 í‰ê· ìˆ˜ìœ„ 상승량과 ìœ ì†ìž¥ì„ 단면수리모형실험과 동시간대에 얻을 수 있어 이러한 ë¬¸ì œì ë“¤ì„ 상당한 수준으로 í•´ì†Œí• ìˆ˜ 있게 되었다. 또한 구조물의 개구부를 통한 ìœ ì¶œìœ ì†ì˜ 강도에 관해서도 ê°œëžµì ì¸ ì •ë³´ë¥¼ 얻을 수 있어 ì €ë§ˆë£¨êµ¬ì¡°ë¬¼ì˜ ì ì • 평면배치안 ì„ ì •ì—ë„ 도움이 ë ìˆ˜ 있다. 핵심용어: ì €ë§ˆë£¨êµ¬ì¡°ë¬¼, 수위 상승, ìœ ì¶œìœ ì†, ë°©íŒŒì œ 설계, ì´ì•ˆì œ, 결합기법

Seasonal abundance, vertical distribution and life history traits of Mediterranean mud shrimp Upogebia pusilla (Decapoda: Gebiidea) on the Slovenian coast

We studied seasonal abundance, vertical distribution and life history traits of the Mediterranean mud shrimp (Upogebia pusilla) in the mediolittoral zone in Slovenia. At two localities (Strunjan and Lazaret), quantitative samples from three plots (1 m2 each) at (0 cm), below (-50 cm) and above (+50 cm) mean water level were taken once every two months, in alternation. A set of parameters was also recorded, including vegetation cover, sediment type, air and sea temperature, pH, salinity and oxygen levels. Highest abundance was recorded during the warm period of the year, with peak abundance in June 2012 (21 % of total sample). Lowest plots were always occupied with the highest densities of mud shrimps. Males dominated during the winter while ovigerous females reached the peak in June (>40 % of all animals). In June at least 2/3 of females were ovigerous. Estimated mean incubation period was 31 days. We determined four periods in relation to the species’ reproductive activity. Early reproductive period (April) was characterised by emergence of first ovigerous females, while main reproductive period (May–July) was characterised by peak of reproduction. In post-reproductive (August–October), and non-reproductive (November–March) periods, no ovigerous females or newly hatched offspring were recorded.

Do wave heights and water levels increase ocean lifeguard rescues?

ObjectiveTo investigate the association of wave height and tidal water level changes with the frequency of ocean lifeguard rescues. MethodsAll ocean lifeguard rescues recorded by Newport Beach Lifeguards in 2015 and 2016 were linked by time and location to weather and ocean variables contained in other historical databases. We performed separate multivariable analyses using mixed effects negative binomial regression to evaluate the total effects of wave height, mean water level (primarily set by tidal elevation), and rising vs. falling water level, on the frequency of ocean rescue in the study location, controlling for confounding variables. ResultsNewport Beach Lifeguards made 8046 rescues during the study period. In all areas of the beach, rescue frequency increased as waves got larger (IRR: 3.25; 95%CI: 2.91–3.79) but then decreased in large surf (IRR: 0.52; 95%CI: 0.37–0.73). In two sections of beach, lifeguards made more rescues during lower water levels, but in the third section of beach, made more rescues during higher water levels. Rescue frequency increased in two sections of beach with rising water levels, but did not in the other section. ConclusionsWave height, water level, and water level direction were associated with rescue frequency, but the environmental factors included in the analysis did not fully account for most variation in rescue frequency. Other factors need to be evaluated to identify major determinants of rescue frequency.

The effect of tides and storms on the sediment transport across a Dutch barrier island

AbstractUnder natural conditions, barrier islands might grow vertically and migrate onshore under the influence of long‐term sea level rise. Sediment is transported onshore during storm‐induced overwash and inundation. However, on many Dutch Wadden Islands, dune openings are closed off by artificial sand‐drift dikes that prevent the influx of sediment during storms. It has been argued that creating openings in the dune row to allow regular flooding on barrier islands can have a positive effect on the sediment budget, but the dominant hydrodynamic processes and their influence on sediment transport during overwash and inundation are unknown. Here, we present an XBeach model study to investigate how sediment transport during overwash and inundation across the beach of a typical mesotidal Wadden Sea barrier island is influenced by wave, tide and storm surge conditions. Firstly, we validated the model XBeach with field data on waves and currents during island inundation. In general, the XBeach model performed well. Secondly, we studied the long‐term sediment transport across the barrier island. We distinguished six representative inundation classes, ranging from frequently occurring, low‐energy events to infrequent, high‐energy events, and simulated the hydrodynamics and sediment transport during these events. An analysis of the model simulations shows that larger storm events cause larger cross‐shore sediment transport, but the net sediment exchange during a storm levels off or even becomes smaller for the largest inundation classes because it is counteracted by larger mean water levels in the Wadden Sea that oppose or even reverse sediment transport during inundation. When taking into account the frequency of occurrence of storms we conclude that the cumulative effect of relatively mild storms on long‐term cross‐shore sediment transport is much larger than that of the large storm events. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.

An empirical formula for maximum wave setup based on a coupled wave-current model

The present paper proposes an empirical formula for maximum wave setup based on a coupled wave-current model. The wave model is the Simulating Waves Nearshore (SWAN) model; the current model is the Finite Volume Community Ocean Model (FVCOM). This study first evaluates the coupled model system against mean water level data collected from a series of laboratory and field experiments. The model calculation agrees with the measurements. Then, the study uses the model results from simulations with a range of wave conditions to develop an empirical formula for the maximum wave setup as a function of wave height, wavelength in deep water, and beach slope. The formula agrees with experimental and in situ measurements and shows better performance than previous formulas.

Algal bloom prediction of the lower Han River, Korea using the EFDC hydrodynamic and water quality model

The lower part of the Han River, which flows through Seoul, Korea, experienced excessive toxic cyanobacterial growth in 2015. Modeling of algal bloom occurrence patterns in the lower part of this river was performed using the Environmental Fluid Dynamics Code (EFDC) to understand algal dynamics and thus better develop management alternatives. For a 71km long river section, 1175 horizontal 2-D grid elements were developed. This grid system was determined adequate, as the maximum values of the Courant–Friedrichs–Lewy condition and orthogonality deviation were 0.5 and 20.1, respectively. Chlorophyll-a (Chl-a) was chosen as the primary indicator for the likelihood of algal blooms. Calibration and verification of EFDC were performed by comparing the model results to three years of field data collected from 2013 to 2015. Calibration accuracy was verified not only for physical variables, including the mean water level and temperature, but also for other water quality variables in various locations of the study area. To improve the prediction accuracy of Chl-a, three dominant groups of algae were considered: diatoms, green algae, and cyanobacteria. The optimum growth temperature ranges were selected based on field data for the study area. It was found necessary to apply different maximum growth rates for algal groups for the upstream and downstream regions of the study area to appropriately reflect field observations. This result indicates that more than three algal groups need to be included to improve Chl-a calibration accuracy for the study area, yet the current EFDC model can consider only up to three phytoplankton groups. Although this problem could be overcome by assigning different maximum growth rates for different regions, it may be necessary to improve EFDC so that it can include more phytoplankton groups.

Effects of dual wavenumber dispersion solutions on a nonlinear monochromatic wave-current field

An analytical solution for quadratic nonlinear wave-current interactions is derived using a perturbation method. In contrast to existing formulations, it accounts for dual wavenumber solutions of the linear problem for a single frequency and their nonlinear interactions. It is demonstrated that even a small amount of energy present on the second solution will introduce significant quantitative and qualitative differences in the surface elevation. These differences include a shorter wavelength component moving with a lower wave celerity, nonlinear spatial focusing, and a mean water level that varies in space. The second solution is also shown to produce a mechanism which may easily result in localized violations of wave breaking criteria. These weakly nonlinear effects are expected to be relevant to a variety of engineering applications and physical processes.

Coherence Between Coastal and River Flooding along the California Coast

ABSTRACT Odigie, K.O. and Warrick, J.A., 2018. Coherence between coastal and river flooding along the California coast. Water levels around river mouths are intrinsically determined by sea level and river discharge. If storm-associated coastal water-level anomalies coincide with extreme river discharge, landscapes near river mouths will be flooded by the hydrodynamic interactions of these two water masses. Unfortunately, the temporal relationships between ocean and river water masses are not well understood. The coherence between extreme river discharge and coastal water levels at six California river mouths across different climatic and geographic regions was examined. Data from river gauges, wave buoys, and tide gauges from 2007 to 2014 were integrated to investigate the relationships between extreme river discharge and coastal water levels near the mouths of the Eel, Russian, San Lorenzo, Ventura, Arroyo Trabuco, and San Diego rivers. Results indicate that mean and extreme coastal water levels during e...

Effect of Regulation of the Inlet Channel on Tides and Water Levels in Lake Hamana, Japan

Hamanako is an economically and culturally important tidal lake on the Pacific coast of Honshu, Japan. Between 1954 and 1973, entrance works were constructed to regulate the channel to the lake. In a previous paper, the tidal records from Maisaka just inside the lake, prior to regulation, were analyzed to explain the responses of the lake to the ocean tide and other water level changes. The present paper compares water level responses with those following regulation of the entrance. The principal differences are that at Maisaka the tidal range increased up to 1965, following the first stages of regulation, but it has been constant since then. In the inner part of the lake, regulation has increased the tidal range but reduced its variability and has reduced the mean water level in the lake. The southern sand shoal divides the lake into two tidal basins, with Maisaka lying in the smaller outer basin. Studies of the inner basin have shown that its tidal range continues to increase. A hydrodynamic model has been used to show that this increase is primarily due to scouring of the inner channel through the southern shoal. The model has also shown that the constancy of the Maisaka tidal amplitude since 1965 is not a static equilibrium, but is a balance between the effects of the outer entrance channel scouring and increasing the Maisaka tide, offset by the inner channel scouring and reducing the Maisaka tide.

Detection of Trend in Hydrologic Variables Using Non-Parametric Test: A Study on Surma River in Northeastern Bangladesh

An initiative has been taken to investigate the trends in discharge and water level (WL) of the Surma River in northeastern Bangladesh. The daily time series data of discharge and WL from two stations named Kanairghat and Sylhet with a period of 42 years (1973 – 2014) and 35 years (1980 – 2014) respectively have been analyzed. Non parametric Mann-Kendall Test has been applied to detect the trend and Sen’s slope estimator is used to measure the slope of the trends. In Kanairghat station, annual mean WL has significant trend (P: 0.03); while, annual mean discharge, mean monsoon discharge, annual maximum discharge, mean monsoon WL, and annual maximum WL shows insignificant trend (P: 0.24, 0.46, 0.14, 0.05, and 0.12). In Sylhet station, annual mean discharge, annual maximum discharge, and annual mean WL have significant trend (P: 0.03, 0.004, and 0.02). In other hand, mean monsoon discharge, mean monsoon WL, and annual maximum WL in Sylhet station has insignificant trend (P: 0.46, 0.13, and 0.21). According to Sen’s slope statistics, all of the detected trends, except annual maximum WL at Sylhet station, are downward. This study recommends a comprehensive water management scheme should be taken to ensure sustainable use of the river water.

LiDAR Validation of a Video-Derived Beachface Topography on a Tidal Flat

Increasingly used shore-based video stations enable a high spatiotemporal frequency analysis of shoreline migration. Shoreline detection techniques combined with hydrodynamic conditions enable the creation of digital elevation models (DEMs). However, shoreline elevations are often estimated based on nearshore process empirical equations leading to uncertainties in video-based topography. To achieve high DEM correspondence between both techniques, we assessed video-derived DEMs against LiDAR surveys during low energy conditions. A newly installed video system on a tidal flat in the St. Lawrence Estuary, Atlantic Canada, served as a test case. Shorelines were automatically detected from time-averaged (TIMEX) images using color ratios in low energy conditions synchronously with mobile terrestrial LiDAR during two different surveys. Hydrodynamic (waves and tides) data were recorded in-situ, and established two different cases of water elevation models as a basis for shoreline elevations. DEMs were created and tested against LiDAR. Statistical analysis of shoreline elevations and migrations were made, and morphological variability was assessed between both surveys. Results indicate that the best shoreline elevation model includes both the significant wave height and the mean water level. Low energy conditions and in-situ hydrodynamic measurements made it possible to produce video-derived DEMs virtually as accurate as a LiDAR product, and therefore make an effective tool for coastal managers.

Numerical modelling of wind effects on breaking waves in the surf zone

Wind effects on periodic breaking waves in the surf zone have been investigated in this study using a two-phase flow model. The model solves the Reynolds-averaged Navier–Stokes equations with the k − \U0001d716 turbulence model simultaneously for the flows both in the air and water. Both spilling and plunging breakers over a 1:35 sloping beach have been studied under the influence of wind, with a focus during wave breaking. Detailed information of the distribution of wave amplitudes and mean water level, wave-height-to-water-depth ratio, the water surface profiles, velocity, vorticity, and turbulence fields have been presented and discussed. The inclusion of wind alters the air flow structure above water waves, increases the generation of vorticity, and affects the wave shoaling, breaking, overturning, and splash-up processes. Wind increases the water particle velocities and causes water waves to break earlier and seaward, which agrees with the previous experiment.

Land Cover Changes (1963–2010) and Their Environmental Factors in the Upper Danube Floodplain

To analyze the changes in the Upper Danube Floodplain, we used aerial photos to quantify the change of landscape pattern from 1963 to 2010. We focused on typical floodplain habitats, i.e., riparian forest and floodplain grassland. We used landscape metrics and transformation matrix to explore changes in land cover structure and composition. The active floodplain experienced increasing fragmentation from 1963 to 2010. Despite an increase of aggregation, riparian forest suffered a 2.3% area loss from 1995 to 2010. Arable land in the active floodplain declined by 28.5%, while its patch size significantly increased. Elevation, distance to river and soil quality were the most relevant environmental factors for the land cover change in the floodplain. Higher soil quality or longer distance to river led to an increase of conversion from grassland into arable land; grassland patches with poorer soil quality were likely to change into riparian forest; riparian forest closer to the river and with a lower height above mean water level tended to remain stable. This comprehensive understanding of historical land cover change and environmental factors is needed for the enhancement of landscape functions and sustainable development in the floodplain.

Comparing water-level policies in a boreal reservoir: How wave and ice energy can help maintain walleye spawning habitat

ABSTRACTPapenfuss JT, Cross T, Venturelli PA. 2017. Comparing water-level policies in a boreal reservoir: how wave and ice energy can help maintain walleye spawning habitat. Lake Reserve Manage. 00:00–00.Water levels in reservoirs affect the timing and depth of wave and ice forces that help maintain walleye (Sander vitreus) spawning habitat. We studied how changes in a water-level management policy (“rule curve”) in 2000 affected these forces on 3 lakes of the Namakan Reservoir, a large boreal reservoir on the border of Canada and the United States. The 2000 rule curve increased mean water levels (0.1 m) during open-water seasons and caused a significant increase in the amount of time each year that wave energy over suitable spawning substrates suspended <0.2 mm sediments at known spawning locations (6–18%, P < 0.01). Conversely, a decrease in the mean range (0.7 m) of water-level elevations during winter seasons caused an 11% decrease (P < 0.01) in the interaction of ice with spawning substrates at known spawning locations. However, ice scour still affected those substrate elevations that were used frequently by walleye during typical spawning seasons. Our findings suggest that water-level management is important for maintaining suitable walleye spawning habitats, and that policies can be designed to optimize those habitat conditions.

배후수위 저감효과를 가진 신기능 잠제의 개발

Typically, a submerged breakwater is one of the good scene-friendly coastal structures used to reduce wave energy and coastal erosion. However, sometimes, a submerged breakwater also has a negative aspect in that a strong rip current occurring around an open inlet due to a difference in mean water levels on the front and rear sides of the structure leads to scouring. Such scouring has a bad effect on its stability. In order to eliminate this kind of demerit, this study investigated four new types of submerged breakwaters with drainage channels. First, hydraulic experiments were performed the typical and new structures. Then, the wave height and mean water level distributions around the structures were examined using the experimental results. Finally, it was revealed that the new type of submerged breakwater could efficiently reduce the mean water level on its rear side. In particular, in the case of new-type submerged breakwater 2, an average reduction efficiency of 71.2% for the difference between the mean water levels at the front and rear sides was shown in comparison with the typical one.

A 3D Numerical Wave Tank for Coastal Engineering Studies

This paper presents the validation of active and passive, made by a dissipation beach, numerical absorbing methods implemented in RANS-VOF FLUENT® code for modelling long time series of wave propagation interacting with coastal structures. Verification of both numerical techniques was performed in 2D – wave flume, and 3D – wave tank, this one using a multiple active absorption wave makers. The active absorption wave maker allows maintaining the incident wave generation and the mean water level along the time. Good results were obtained for 2D and 3D applications for active absorption wave maker at the generation boundary and both numerical beach and active absorption at the end of the flume/tank.

Wave transformation and hydrodynamic characteristics of wave-breaking models coupled with Boussinesq equations

ABSTRACTThis paper investigates the different wave transformation and hydrodynamic characteristics of three different wave-breaking models – friction-type, eddy viscosity-type and surface roller-type models – coupled with the weakly nonlinear Boussinesq equations with improved linear dispersion characteristics based on comparisons between predicted and measured wave-breaking phenomena. The experimental cases consider not only different breaker types but also different bathymetry conditions, i.e. uniform slopes and a uniform slope with a submerged breakwater. Although all of the properly calibrated wave-breaking models yield equally good predictions of wave heights, mean water levels and trough levels of breaking and broken waves, the models show clear differences in their predictions of the undertow velocity, near-bottom wave orbital velocity profile, wave skewness, and wave asymmetry. The importance of such differences in the predictive capabilities of these widely used wave-breaking models should be highlighted, particularly when extending the model to the prediction of coastal morphodynamics around the surf zone.

Applicability of Multiple Submerged Narrow-Crested Breakwaters for Reduction of Mean Water Level in Rear Side and Flow Control

ABSTRACT Hur, D.S.; Cho, W.C.; Yoon, J.S.; Kang, C., and Lee, W.D., 2017. Applicability of multiple submerged narrow-crested breakwaters for reduction of mean water level in rear side and flow control. In: Lee, J.L.; Griffiths, T.; Lotan, A.; Suh, K.-S., and Lee, J. (eds.), The 2nd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 79, pp. 179–183. Coconut Creek (Florida), ISSN 0749-0208. In this study, to confirm the applicability of multiple submerged narrow-crested breakwaters (SNCBs), a 3-D numerical simulation was conducted. The numerical simulation used the numerical model developed for analyzing the 3-D flow structure around the submerged breakwaters. In addition, to verify the validity and effectiveness of the numerical model, the wave height distribution and mean water level distribution around impermeable submerged breakwater (ISB) and permeable submerged breakwater (PSB) were compared with the results of the numerical model experiment. As a result, the simulate...

Evaluating financial risk management strategies under climate change for hydropower producers on the Great Lakes

AbstractHydropower on the Great Lakes makes up a substantial fraction of regional electricity generation capacity. Hydropower producers on the Niagara River (flowing between lakes Erie and Ontario) operate as run‐of‐river, and changing lake levels alter interlake flows reducing both generation and revenues. Index‐based insurance contracts, wherein contract payouts are linked to lake levels, offer a tool for mitigating this risk. As a potentially useful tool, pricing of financial insurance is typically based on historical behavior of the index. However, uncertainty with respect to the impacts of climate change on lake level behavior and how this might translate to increased (or decreased) risk for those selling or buying the insurance remains unexplored. Portfolios of binary index‐insurance contracts are developed for hydropower producers on the Niagara River, and their performance is evaluated under a range of climate scenarios. Climate Informed Decision Analysis is used to inform the sensitivity of these portfolios to potential shifts in long‐term, climatological variations in water level behavior. Under historical conditions, hydropower producers can use portfolios costing 0.5% of mean revenues to increase their minimum revenue threshold by approximately 18%. However, a one standard deviation decrease in the 50 year mean water level potentially doubles the frequency with which these portfolios would underperform from the perspective of a potential insurer. Trade‐offs between portfolio cost and the frequency of underperformance are investigated over a range of climate futures.