Increase In Water Level Research Articles

A Novel Method for Analyzing Sandbar Distribution in Shelf-Type Tidal Deltas Using Sediment Dynamic Simulation

Shallow marine shelf sedimentation is a hot and difficult topic in today’s reservoir sedimentology research, and it is widely present in the world. The shallow marine shelf sedimentation is not only affected by complex hydrodynamic effects such as tides and waves, but also controlled by bottom tectonic features, forming a complex and varied sedimentation pattern. During the Middle Jurassic period, the northern part of West Siberian Basin was characterized by a shallow marine shelf sedimentary environment. In the central reion of this basin, a typical tectonic uplift zone developed, forming a tectonic background of “one uplift zone between two depressions”. Simultaneously, the dominant influence of tides in the shallow marine shelf environment facilitated the formation of a typical shelf-type tidal delta sedimentation system in the Jurassic strata of the northern part of West Siberian Basin. This sedimentation constitutes a significant natural gas reservoir, and it is important to investigate the sedimentary evolution of shelf-type tidal deltas and to clarify the internal structure and distribution of sedimentary sand bodies and interlayers in shelf-type tidal deltas, which is the basis for the fine development of this type of reservoir. This paper takes the Jurassic strata in the Y region of northern part of West Siberian Basin as the research object, and conducts numerical simulation based on sedimentary dynamics for the shelf-type tidal delta sedimentation formed under the tectonic background of “one uplift zone between two depressions”. In addition, tidal amplitude and initial water level were selected for different hydrodynamic factors to study the main controlling factors of shelf-type tidal delta sedimentation. The simulation results show that tidal amplitude is positively correlated with three-dimensional configuration characteristic parameters of the sedimentary sand bodies, and the development of tidal bars becomes more and more limited as the initial water level increases. This paper systematically investigates the sedimentary evolution of shelf-type tidal delta under the tectonic background of “one uplift zone between two depressions” by the sedimentary dynamics method, which deepens the understanding of the shelf-type tidal delta sedimentation process and provides a new thinking for the development of this sedimentary reservoir type (School of Geosciences China University of Petroleum (East China)).

Seepage and Stability Analysis of Earth Dams’ Downstream Slopes, Considering Hysteresis in Soil–Water Characteristic Curves under Reservoir Water Level Fluctuations

Fluctuations in reservoir water levels have a significant impact on the seepage and slope stability of earth dams. The varying rate of the water level and soil–water characteristic curve (SWCC) hysteresis are the main factors affecting the seepage and the stability of dam slopes; however, they are not adequately considered in engineering practices. In this study, the SEEP/W module and the SLOPE/W module of Geo-studio were employed to analyze the seepage features and the stability of downstream slopes, taking into account the water level fluctuation rate and the SWCC hysteresis. The results reveal that the pore water pressure of the representative point forms a hysteresis loop when the water level fluctuates, which becomes smaller as the water level variation rate increases. Within the loop, the pore water pressure with a rising water level is greater than the value when the water level is dropping, and the desorption SWCC derives greater pore water pressures than the adsorption SWCC. Similarly, the safety factor (Fs) curves under the condition of water level fluctuations also form a hysteresis loop, which becomes smaller as the variation rate of the water level increases. When the water level fluctuation rate increases to 4 m/d, the two curves are tangent, meaning that the Fs with a rising water level is always greater than the value when the water level is dropping. The desorption SWCC derives a lower Fs value than the adsorption SWCC as the water level draws up, but this initiates no evident difference in the Fs value when the water level draws down. These findings can be used to inform the design and operation of earth dams under fluctuating water levels.

Integrated geochemical and microbiological assessments of Astroni lakes reveals Campi Flegrei unrest signatures

Astroni volcano in the Campi Flegrei caldera (southern Italy) is a 2 km wide, densely vegetated tuff ring and hosting several volcanic structures, including tuff cones, scoriae cones, lava domes, and three small lakes. Geochemical data of waters and dissolved gases from the lakes, coupled with microbiological analyses on lake water and sediments, were used to shed light on the possible relationship between the lakes and the hydrothermal fluid circulation system as suggested by previous geophysical surveys. Water chemistry was dominated by solutes, mainly Na+ and HCO3−, deriving from fluids and CO2-rich gases typically found in discharges located at the periphery of hydrothermal-volcanic systems. Lago Grande (LG) lake showed an anoxic hypolimnion with abundant non-atmospheric dissolved gases, consisting of biogenic CH4 and CO2, the latter having a twofold origin, biogenic and hydrothermal. The occurrence of anaerobic methanotrophs coupled with the lack of hydrogenotrophic methanogenic archaea along the whole vertical profile of LG suggested that CH4 was mostly produced from degradation of abundant terrestrial organic matter within the deep lake sediments, and then consumed during its diffusion through the lake. Notwithstanding, the output rate of CH4 from LG surface was anomalously high relative to those commonly measured in lakes. Carbon dioxide from the hydrothermal source and produced by CH4 oxidation was partially fixed in the lake via the acetyl-CoA pathway. Accordingly, the CO2 fluxes from the LG surface were relatively low, in the range of those measured in volcanic lakes dominated by biogenic CO2. The dependence of the chemistry of the Astroni lakes on inputs from the Campi Flegrei hydrothermal system, besides on biogeochemical processes, offers a possible explanation for the anomalous increase of the LG water level occurred in the last years, which was not consistent with the recorded local rainfall but likely caused by an increasing hydraulic pressure related to the enhanced hydrothermal activity recorded at Campi Flegrei in the last decades. According to this hypothesis, the future evolution of the current volcanic unrest may govern the fate of the lake water level with important implications for the functioning of the precious Astroni ecosystem.

HYDROLOGICAL REGIME OF THE IKVA RIVER (SOUTHERN BUG BASIN)

This article reveals the issue of a detailed study of the hydrological regime of small plain rivers in the presence of data from regular observations. The Ikva River, the object of our study, belongs to the Southern Bug basin and is its small tributary, on which a hydrological indicators monitoring station has been operating since 1939. Since 1955, a continuous series of observations has been available, which allowed us to carry out a detailed analysis and description of the main hydrological characteristics – levels (H, cm) and water flows (Q, m3/s), to evaluate their fluctuations in time, cyclicity and the relationship Q= f(H). The construction of the corresponding graphs confirmed that the Ikva River is characterized by cyclic flow fluctuations, and since 1965 we have already observed two complete cycles of fluctuations in water level lasting about 30 years. At the moment (2022), the flow indicators record the minimum of the low-water phase of the second cycle, so we can expect an increase in the flow in the near future and the transition to a new cycle. We have also determined that the amplitude of water level fluctuations of the Ikva River at the post in the village of Stara Sinyava over many years is 60 cm, and varies from a minimum of 75 cm (1957) to 135 cm (1981), that is, a little more than 0.5 meters in total. This agrees quite well with the literature data and estimates of other authors, considering the plain nature and small size of this object. The long-term course of the water levels of the Ikva River is characterized by a slight increase, while the long-term fluctuations of the average water flow at this station also do not have a large amplitude: from 0.66 m3/s (2020) to 3.64 m3/s (1979) i.e. 2.98 m3/s. At the same time, the general trend line for multi-year cost fluctuations shows, on the contrary, a tendency to decrease them. Therefore, we can state that the graphs of multi-year costs and levels are not synchronous, which is evidence of the manifestation of vertical channel deformations in the area of the post. As the water level increases, the decrease in water consumption is a direct sign of siltation of the riverbed in this area and the raising of the bottom level due to accumulative processes over a long period. The largest amplitudes are characterized by the parameters of the maximum runoff, that is, the amplitudes of the maximum levels (∆Нmax = 168 cm) and maximum flows (∆Qmax = 92.9 m3/s), which is not surprising, because we are talking about the characteristics of the period of floods and inundations, which are always marked by significant fluctuations in time. An interesting fact, identified for us for the first time, is that the characteristics of the minimum flow of the closed period of the channel are characterized by higher amplitudes than the characteristics of the open period. Therefore, the summer low water is more pronounced than the winter low water, which means that in the warm period (summer), the lack of precipitation more clearly provokes a decrease in water levels and flows in the channel system than during the winter period. The reason can be both winter thaws and the specifics of the groundwater regime. Key words: hydrological regime; water level; water flows; hydrological cycle; low water phase; high water phase; relationship Q=f(H).

Investigation of the microfracture and damage characteristics of dam during impoundment at Sanhekou hydropower station

Dam stability is one of the most important issues in hydraulic engineering. Microfractures and damage commonly occur during impoundment, which might lead to serious dam problems. In this study, based on the engineering background of the Sanhekou hydropower station, microseismic monitoring and numerical simulation were employed to systematically investigate the microfracture and damage characteristics of the dam body. First, the microseismic monitoring system was established to capture the microfractures inside the dam. The results indicated that the rise in water level elevation has a significant effect on the microfracture and damage characteristics of the dam body, especially during the early stage of impoundment. This can be reflected by the variation in the derived source parameters, i.e., the b value, daily energy release, daily apparent stress and daily apparent volume. In addition, the failure mode of the microfractures could be determined by using the ES/EP value of microseismic events and the moment tensor inversion method. The cracking orientation of the failure surfaces could also be determined by the moment tensor inversion method. Subsequently, numerical simulation was conducted where the initial damage of the dam was considered by integrating the microseismic monitoring data. The simulation results suggested that dam deformation under impoundment considering microseismic feedback agrees well with the real field measured results. The stress level of the dam toe was larger than that of the dam heel, and both the dam toe and dam heel were under compression before impoundment. However, with increasing water level elevation, the stress status of the dam heel area changes from compression to tension. The findings in this study will provide a better understanding of the damage and failure mechanism of dams during impoundment, which might be helpful for the design and support of dams in hydropower stations.

The impact of drought duration on two Potamogeton species with different growth forms

When facing new climate extremes, aquatic plant communities may experience more frequent or increasing durations of water shortages. Aquatic macrophytes of permanently inundated habitats (true hydrophytes) may lack the physiological or morphological characteristics that protect terrestrial plants from drying out. Aquatic hydrophytes with floating or emergent leaves are expected to be more resilient to droughts than completely submerged plants, as they have morphological characteristics adapted to air-exposed conditions. Therefore, we expected the latter to survive longer periods of air exposure and perform better with increasing drought than a completely submerged growing species. Here, we conducted a microcosm experiment and exposed two Potamogeton species—the completely submerged growing Potamogeton perfoliatus and the areal leaf producing Potamogeton nodosus—to different drought conditions (1, 5, and 15 days). We aimed to detect how two species with different growth strategies cope with and respond to increasing air exposures with waterlogged sediment. Both species showed a resistance to 1–5 days of drought but showed high mortality after 15 days. They displayed significant differences in all measured morphological responses (shoot length, side shoot, and leaf counts), plant chemistry (carbon, nitrogen, and phosphate), and the produced biomass (shoot, root, leaves), and reacted significantly to increasing drought durations. Differences in their resistance were observed based on the mortality rate and morphological responses. To prevent long-term droughts and keep mortality low, we recommend to the water managers to identify areas of risk and increase water levels during dry periods.

A new framework for quantifying alongshore variability of swash motion using fully convolutional networks

Waves running up and down the beach (‘swash’) at the landward edge of the ocean can cause changes to the beach topology, can erode dunes, and can result in inland flooding. Despite the importance of swash, field observations are difficult to obtain in the thin, bubbly, and potentially sediment laden fluid layers. Here, swash excursions along an Atlantic Ocean beach are estimated with a new framework, V-BeachNet, that uses a fully convolutional network to distinguish between sand and the moving edge of the wave in rapid sequences of images. V-BeachNet is trained with 16 randomly selected and manually segmented images of the swash zone, and is used to estimate swash excursions along 200 m of the shoreline by automatically segmenting four 1-h sequences of images that span a range of incident wave conditions. Data from a scanning lidar system are used to validate the swash estimates along a cross-shore transect within the camera field of view. V-BeachNet estimates of swash spectra, significant wave heights, and wave-driven setup (increases in the mean water level) agree with those estimated from the lidar data.

Characteristics and causes of water level variations in the Chenglingji–Jiujiang reach of the Yangtze River following the operation of the Three Gorges Dam

ABSTRACT Water level adjustment downstream of dams significantly impacts river regimes and flood control. However, due to constant strong scouring, our quantitative understanding of the characteristics of water level variations and their causes in the Chenglingji–Jiujiang Reach of the Yangtze River remains limited. Here, we analyzed the water level change trend via the Mann–Kendall method and analyzed geomorphic change and river resistance using 406 cross-sectional profiles as well as data on discharge and water levels from 1991 to 2022. Results showed that the critical conversion discharges (CCD) in the Chenglingji-Hankou Reach and the Hankou-Jiujiang Reach were approximately 35,000 and 30,000 m3/s, respectively, after the operation of the Three Gorges Dam. The water level exhibited an overall decline mainly due to river erosion when the discharge was lower than the CCD. The water level exhibited a nonsignificant upward trend mainly due to increased river resistance (7–20%) when the discharge was higher than the CCD. The obvious increase in the floodwater level in individual years was caused by the effect of downstream water level increase. Our findings further the understanding of downstream geomorphic response to dam operation and their impacts on water levels and have important implications for flood management in such rivers worldwide.

Wave setup estimation at regional scale: Empirical and modeling-based multi-approach analysis in the Mediterranean Sea

Wave setup is a physical process that induces a temporal increase of the mean water level due to wave dissipation by bottom friction and breaking in the surf zone, extending over tens to hundreds of meters in the cross-shore direction. Wave setup contribution to coastal sea level solely induced by wind and atmospheric effects can increase by more than 100% under extreme events and conditions favoring its formation. It is therefore crucial to consider this phenomenon when assessing sea-level-related coastal hazards. Previous studies estimated the wave setup effect by means of numerical modeling and empirical formulations at regional and global scale. Such analyses require either high computational capacity to implement high-resolution numerical models over large domains, and/or accurate information on coastal morphological features from global or regional databases. Although the Mediterranean Sea is a fetch-limited environment, waves generated from extra-tropical cyclones are powerful enough for wave setup to develop, and subsequently for a potential significant wave setup contribution to extreme coastal sea level. Through the use of both numerical and empirical methods, we investigate the uncertainty associated to wave setup representation on the frequency and magnitude of coastal extreme sea levels occurring on sandy beaches in the Mediterranean Sea. Wave setup values are compared at beach scale between process-based modeling and empirical approaches, showing highly variable results. We also quantify the impact of wave setup on return levels of coastal sea level extremes using reconstructed sea levels. We employ various methods to calculate the wave setup component. Results show high spatial dispersion, with clear differences between the numerical and empirical approaches, especially in regions prone to the development of energetic waves. The total inter-method dispersion of 100-year return levels is often higher than 30 cm for average values of 62.4 cm. We emphasize the important limitations related to wave setup modeling (i.e., its underestimation) at large scale, and call for caution when applying empirical formulations (generally developed from local studies) at regional to global scale, which can lead to unrealistic wave setup values.

An initial assessment of mobile dam efficiency in raising low-flow water levels in the Vietnamese Mekong Delta

In recent years, the Tien and Hau rivers have experienced a downtrend in water levels during the low flow season. This decrease has led to detrimental effects on agricultural production and ecological health in the VMD’s upper regions, such as the Long Xuyen Quadrangle (LXQ) and the Plain of Reeds (PoR). This research employs a numerical hydraulic model for a preliminary assessment of the potential effectiveness of mobile dams in increasing water levels in the VMD’s upper part. A calibrated 1D hydraulic model was utilized to evaluate the performance of the proposed mobile dams: one situated near the My Thuan bridge on the Tien river, and the other near the Can Tho bridge on the Hau river. Initial results indicate that setting the crest of mobile dams at -1.0 m could raise minimum and maximum water levels in the Tien river near Tan Chau by 1.0 m and 0.15 m, respectively, and in the Hau river near Chau Doc by 1.1 m and 0.07 m, respectively. Furthermore, these mobile dams could significantly enhance the minimum and maximum water levels in An Binh channel within the PoR and Ba The channel in the LXQ, by up to 0.55 m and 0.26 m, and 0.42 m and 0.29 m, respectively. These findings provide an essential foundation for initially understanding how mobile dams can improve water resource management in the VMD. However, additional investigation is required to assess the effects of mobile dams on salinity intrusion, ecological balance, hydrological dynamics, sediment deposition, and erosion.

Experimental investigation on the characteristics of seepage failure of landslide dams with strongly permeable zones

Landslide dams are formed by river blockages caused by landslides or other slope instability bodies. They exhibit loose structure, poor stability and strong permeability. Large water head caused by water-level increase can trigger seepage deformation of soil and influence the stability of landslide dams, possibly leading to dam breach and catastrophic damage. Various landslide dam structures also result in differences in seepage characteristics. In this study, multiple physical model tests for seepage failure of landslide dams with strongly permeable zones were designed. The influence of the location and gradation of the strongly permeable zones on the seepage of landslide dams was studied. The characteristics and modes of seepage failure of landslide dams with strongly permeable zones were analysed. The experimental results showed that the cyclic evolution failure of piping and downstream slope collapse was an essential failure mode for the seepage-induced failure of landslide dams with strongly permeable zones. Compared with the strongly permeable zone at the bottom of a landslide dam, the piping caused by seepage evidently promoted the slope erosion of the dam with the strongly permeable zone in the middle. As the permeability coefficient of strongly permeable zones increased, piping was faster and easier to form, and piping failure, slope erosion, and slope collapse were more severe. The seepage failure of landslide dams mainly included the emergence of seepage water, piping, slope erosion, and downstream slope collapse. Piping was caused by the erosion and migration of some fine particles of soil in seepage channels in the dam. When the flow drag force could overcome the resistance force among the soil particles, some fine particles and even large particles on the downstream slope surface were continuously eroded. This study provides new insights into the evolution process and breach mechanisms for the seepage-induced failure of landslide dams with strongly permeable zones.

Wave and Roller Transformation Over Barred Bathymetry

AbstractThe cross‐shore transformation of breaking‐wave roller momentum and energy on observed barred surfzone bathymetry is investigated with a two‐phase Reynolds Averaged Navier Stokes model driven with measured incident waves. Modeled wave spectra, wave heights, and wave‐driven increases in the mean water level (setup) agree well with field observations along transects extending from 5‐m water depth to the shoreline. Consistent with prior results the roller forcing contributes 50%–60% to the setup, whereas the advective terms contribute ∼20%, with the contribution of bottom stress largest (up to 20%) for shallow sandbar crest depths. The model simulations suggest that an energy‐flux balance between wave dissipation, roller energy, and roller dissipation is accurate. However, as little as 70% of the modeled wave energy ultimately dissipated by breaking was first transferred from the wave to the roller. Furthermore, of the energy transferred to the roller, 15%–25% is dissipated by turbulence in the water column below the roller, with the majority of energy dissipated in the aerated region or near the roller‐surface interface. The contributions of turbulence to the momentum balance are sensitive to the parameterized turbulent anisotropy, which observations suggest increases with increasing turbulence intensity. Here, modeled turbulent kinetic energy dissipation decreases with increasing depth of the sandbar crest, possibly reflecting a change from plunging (on the steeper offshore slope of the bar) to spilling breakers (over the flatter bar crest and trough). Thus, using a variable roller front slope in the roller‐wave energy flux balance may account for these variations in breaker type.

Exploring the relationship of the winter-spring crop’s rice yield with meteorological drought and water resources in Ben Tre province

Recent environmental changes have significantly impacted rice cultivation in Ben Tre province, the Vietnamese Mekong Delta (VMD) coastal province. This research employed the Mann-Kendall (MK) non-parametric method and Sen’s slope (SS) technique to detect trends in the rice yield of the winter-spring crop (WSC) in Ben Tre province and environmental parameters from 2009 to 2020. These environmental parameters include the meteorological drought index and key water resource metrics, potentially affecting the region’s rice yield. Furthermore, it established the relationship between these environmental parameters and rice yield using multiple linear regression. The results indicated an average decrease of 0.13 ton/ha/year in the WSC’s rice yield, with a severe reduction to 2.86 ton/ha in 2016. This decline in rice yield is likely attributed to environmental shifts, particularly during years with extreme hydrological events. The study found that during the months of dry season, from January to April, there was a decrease of 0.14 per year in the minimum Standardized Precipitation Evapotranspiration Index (SPEI-4min) at the Ben Tre meteorological station; an increase in the minimum daily discharge at the Tan Chau station (QTCmin) by 81 m3/s/year; a decrease in the mean daily water level at the My Thuan station (QMTmean) by 0.22 cm/year; and an increase in the maximum daily water level at the Ben Trai station (HBTmax) by 0.67 cm/year. However, the maximum daily salinity concentration at the Tra Vinh station (STVmax) showed no significant trend, oscillating between 6.5 and 15 g/l, potentially because the three-hourly monitoring intervals might not have fully captured peak salinity levels. The regression model identified SPEI-4min (with a Correlation Index (CI) of 0.450) and STVmax (CI = 0.372) as the primary factors influencing rice yield. Additionally, QTCmin and HBTmax were also significant, though to a lesser extent, with correlation indices of 0.310 and 0.303, respectively. Conversely, QMTmean had a relatively minor influence, with a correlation index of 0.136. These findings are crucial to developing adaptive strategies and policies for improving the resilience of rice production in the study province and throughout the VMD.

Hydrological variability of middle European peatland during the Holocene, inferred from subfossil bog pine and bog oak dendrochronology and high-resolution peat multiproxy analysis of the Budwity peatland (northern Poland)

Subfossil pine and oak tree trunks were excavated during exploitation of the Budwity peatland in Northern Poland. Based on dendrochronological analysis, the woodland successions in peatland were reconstructed and correlated with moisture dynamics of the peatland ecosystem inferred from the high-resolution multi-proxy analysis of the peatland deposits. From the results of dendrochronological analysis and the 14C wiggle matching methods, four floating pine chronologies (5882–5595; 5250–5089; 3702–3546; and 2222–1979 mod. cal BP) and two oak chronologies (4932–4599 and 4042–3726 mod. cal BP) were developed. The organic sediments of the peatland (6 m thick) were deposited over approximately nine thousand years. The lower complex (525–315 cm) comprises minerogenic peat, while the upper complex (315.0–0.0 cm) is composed of ombrogenic peat. Subfossil tree trunks are distributed across various peat horizons, which suggests multiple stages of tree colonisation followed by subsequent dying-off phases. Multiproxy sediment analyses (lithological, geochemical and δ13C stable isotope, pollen, plant macrofossils, Cladocera, diatom, and Diptera analyses) indicate that the two earliest phases of pine colonisation (5882–5595 and 5250–5089 mod. cal BP) and the two stages of oak colonisation (4932–4599 and 4042–3726 mod. cal BP) were associated with periodic drying of the peatland. Conversely, tree dying-off phases occurred during periods of increased water levels in the peatland, coinciding with stages of increasing climate humidity during the Holocene. The two most recent phases of pine colonisation occurred during the ombrogenic stage of mire development. Remnants of the dead forest from these phases, marked by subfossil trunks still rooted in the ground, were preserved and exposed presently during peat exploitation, approximately 2.5 m below ground level. The identified phases of tree colonisation and subsequent dying-off phases show correlation with analogical phenomena observed in the other investigated European peatlands.

Overtopping Reduction By Artificial Reefs

Artificial or Engineered reefs are primarily developed for enhancing the ecological system. In Guidelines for the Placement of Artificial Reefs (UNEP, 2009) they are described as "An artificial reef is a submerged structure deliberately constructed or placed on the seabed to emulate some functions of a natural reef such as protecting, regenerating, concentrating, and/or enhancing populations of living marine resources." Often these artificial reefs have either a complex shape inspired by biomimicry (e.g. Coastruction) or a more regular shape, designed to function as modular blocks that can be easily placed on top of each other (e.g. Reefy). In many parts of the world, application of these engineered elements on top of existing shallow reefs may be a solution to not only enhance the ecosystem but also to increase the safety level of the hinterland. Also, in light of climate change and further increasing water levels, the artificial reefs may be a valuable alternative to reduce wave overtopping and prevent the land for extreme flooding. To quantify the possible effect of such artificial reefs in more shallower areas, physical model testing have been performed in which both overtopping was measured with and without the use of engineered elements. Shallow water depths have been chosen here, since the reef should induce wave breaking, resulting in the wave energy to decrease. The performance of these engineered elements in relation to its submergence has been investigated and a reduction coefficient has been developed.

English English

River diversion is a procedure carried out prior to constructing a dam. It is conducted by diverting water from the main river so that the main dam construction work can be executed at a specifically dry area. In Meninting Dam, the diversion system consists of two main structures, namely cofferdam and diversion tunnel that is equipped with a navigation structure at the upstream part of the tunnel. During the construction, cofferdam experienced overtopping on June 17, 2022. The overtopping most likely occurred because of the diversion tunnel’s inability to divert the actual flood effectively during the construction. Therefore, this research aimed to analyse the effectiveness of Meninting Dam’s proposed diversion tunnel against design flood discharge for a return period of 25 years. The data used in this research were the updated version of the ones used to design the whole construction of Meninting Dam’s diversion system, while the flow conditions along the diversion tunnel were analysed using HEC-RAS. At the same time, the analysis was also carried out using the Level Pool Routing Method as a comparison. The analysis results show that the design flood discharge for a return period of 25 years in Meninting Dam Watershed is 265,62 m3/s. This causes the water level along the diversion tunnel reach el. +165,95 m above sea level. Taking into account that the cofferdam crest elevation is at +170,00 m above sea level, it could be concluded that Meninting Dam’s proposed diversion tunnel, which is 4 m wide and 4 m tall is able to divert the design flood discharge for a return period of 25 years effectively. The investigation results in Meninting Dam Watershed show that the main cause of the overtopping was heavy precipitation. This caused the increasing water level at the upstream part of the cofferdam that resulted to its inability to function properly, taking into account that it was still under construction when it occurred

Water Level Fluctuation Effect on Fish Reproduction Success

Alteration of water levels of the lake/reservoir due to changes in river discharges, upstream abstraction, and drawdown regulation due to hydropower generation has been reported as among the major challenges to fish physiology and ultimately reproduction. Variations in lake/reservoir water levels influence biodiversity and the abundance of lake/reservoir biota. Variations have the greatest impacts in the littoral zones hence, interfering with fish spawning, incubation, and hatching of eggs, as well as the development of larvae, postlarvae, and juveniles. This particular paper reviews the literature available on the effect of the reservoirs/lakes’ water level fluctuations on fish reproduction success using the documentary view method. The literature argues that water level fluctuations have both positive and negative impacts depending on frequency, magnitude, and duration and the species exposed. Extreme fluctuations tend to bring more adverse impacts. It further indicates that extreme and untimely water level fluctuation has direct impacts on the aquatic habitats and ultimately impacts fish assemblage and their populations. Few articles indicate the range of decrease or increase of water level, duration of such events, and effects they have on reservoir/lake ecosystem functions and fish physiology. Nevertheless, quantification of moderate and extreme water level fluctuation and associated effects is lacking. Although water level fluctuation is an important environmental cue for aquatic organisms, literature shows that the reduction of extreme water level variations especially multiannual variations is vital for fish reproduction. Therefore, upstream water use and reservoir operations should take into consideration the effects of water level fluctuations on reservoir structure, biological functions, and ultimate effects on fish reproduction.

Natural Climate Protection through Peatland Rewetting: A Future for the Rathsbruch Peatland in Germany

Draining peatlands to create agricultural land has been the norm in Europe, but in the context of climate change and the loss of biodiversity, these rich ecosystems may reactivate their functions as greenhouse gas sinks and retreat spaces for animals and plants. Against this background, the National Moor Rewetting Strategy was put into effect in Germany in 2023, together with the Natural Climate Protection Action Plan. This article examines the methodology of peatland rewetting from scientific, administrative, social, and technical perspectives. The article focuses on an example of moor rewetting in central Germany: the Rathsbruch moor near the municipality of Zerbst, Saxony-Anhalt. To illustrate the importance of rewetting projects for degraded peatlands, five scenarios with different target soil water levels were considered, and the associated greenhouse gas emissions were calculated for a period of five years. For the planning solution, an estimate of the medium-to-long-term development of the habitat types was made based on current use and the dynamics typical of the habitat. The results for the Rathsbruch moor area showed that increasing the water level in steps of 1, 0.8, or 0.5 m has no significant influence on reducing the CO2 emissions situation, while a depth of 0.3 m has a slight influence. When the water was raised to 0.1 m below the surface (Scenario 5), a significant CO2 reduction was observed. The calculated avoided CO2 costs due to environmental damage show that the environmental benefits multiply with every decimeter of water level increase. The rising groundwater levels and extensification favor the establishment of local biotopes. This means that two of the biggest man-made problems (extinction of species and climate change) can be reduced. Therefore, this research is applicable to the development and planning of recultivation work at municipal and regional levels in Germany and beyond within the framework of EU restoration policy.

Design of adsorption chillers under rolling conditions in naval applications: Experimental and numerical approaches

International shipping is one of the major contributors to the overall greenhouse gases emissions and therefore its decarbonization is a key priority worldwide. Among the possible energy efficiency measures, the use of waste heat for cooling through adsorption chillers has gained significant attention. However, the proper integration of such kind of chillers on board needs to consider the effect of the rolling movement of the ship. In the present work, two different sorption modules (i.e the couple of adsorber + evaporator/condenser) are experimentally tested in horizonal position and at different inclinations, considering permanent tilting or continuous moving. The results were subsequently used for the implementation in a dynamic simulation model and the design of the chiller for application on passengers’ vessels. Results showed that operation under constant inclination of 30° resulted in a reduction of the cooling energy supplied by 22.5 % for the module with zeolite and by 55.8 % for the module with silica gel. The highest specific cooling energy (SCE) is 0.26 kWh/kg for the zeolite module and 0.18 kWh/kg for the silica gel module. The main issues underlined under tilted operation is the progressive reduction of the water level in the evaporator, which causes incorrect operation of capillary-driven evaporation. Accordingly, the increase of water level in the evaporator was suggested as mitigation strategy. It was however found out that the issue is only relevant if prolonged operation in a tilted condition is foreseen, but not under typical rolling operation with continuous movement.

Rewet without regret? Nutrient dynamics in fen peat exposed to different rewetting degrees

All over the world, peatlands have been drained, often for agricultural purposes, resulting in CO2 emissions, soil subsidence and biodiversity loss. To combat these negative effects, drained peatlands are being rewetted, but knowledge of the effects of rewetting on peat biogeochemistry is still incomplete, especially since a variety of rewetting methods and rewetting degrees exists. We conducted a mesocosm experiment in which we exposed 100 intact agricultural fen peat cores (80 cm, 20 cm Ø) to five different water levels (0, 20, 40, 60 cm and variable—surface), two nutrient application levels to mimic continued agricultural use, and two water origins. Over an eight-month period, we harvested above-ground plant biomass five times and sampled pore water at two depths each month. Samples were analysed for nutrients. Our results show increased phosphate and ammonium availability upon fully rewetting (0 cm—surface) and less so under partially rewetted circumstances (20 cm—surface). Above-ground biomass was strongly affected by nutrient application, especially in the high water level treatments. Vegetation was primarily N-limited, and N in the vegetation decreased with increasing water levels, indicating stronger nitrogen limitation upon rewetting. We conclude that nature restoration under fully rewetted conditions will likely be challenging as a result of the large release of nutrients from the system which may also affect surrounding nature areas. Furthermore, we conclude that partial rewetting combined with low-intensity agricultural use can be a solution to slow down the adverse effects of drainage, although this will lead to decreased agricultural production.