High Water Levels Research Articles

Interactions between foredune morphologies and vegetation: Exploring the occurrence of arbuscular mycorrhizal fungi

Vegetation is a key trait for understanding the foredune morphologies. However, the rhizosphere in coastal dunes imposes high levels of water and nutrient stress on plants. In these conditions, arbuscular mycorrhizal fungi (AMF) are prominent root symbionts that play a crucial role in improving to abiotic stress and promoting plant growth. On the south coast of the state of São Paulo, foredunes were studied for their floristic composition, relative frequency of AMF and grain size of rhizosphere. Foredune was classified regarding the morphology as terrace, ridge I, and ridge II. The terrace has a low height (<0.5 m) and is composed of native species canopies low (<0.2 m) and high (0.5–1.5 m) characterized by AMF colonization close to 60%. In contrast, ridge I showed wavy crests that were about 1 m high and ∼30 m wide, with a predominance of plant species with low canopy and 68% AMF colonization. The morphology ridge II reaches the greatest height (3 m), to the detriment of a smaller width (up to 15 m) and the plants present high canopy (>0.5 m) with close to 75% AMF. The increase of the relative frequency AMF from the terrace to ridges I and II may indicate that the increase of sand accumulation with continuous burial of roots is rather positive to plant growth. Yet, varied canopy heights of the plants species control the verticalization and horizontalization of the foredune. Low-canopy species, gradually slow down wind flow, causing spatialized deposition and widening. Conversely, species with highest canopies swiftly reduce wind flow due to the density of their aerial portion (leaves), resulting in deposition just below their structure fostering foredune vertical growth.

Source apportionment of suspended particulate organic matter in a shallow eutrophic lake of Southwest China using MixSIAR model

Eutrophication has become prominent in many lakes of the world, resulting in a continuous rise of suspended particulate organic matter (POM) that can be of vital consequence for water quality and carbon cycling. While the accumulation and decomposition of POM can enhance nutrient cycling at a rate depending on the property of lake-water organic carbon, it is important to identify the source of suspended POM for evaluating eutrophication and carbon burial. Here we analyzed the distribution of stable isotopic ratios (δ13C and δ15N) and the carbon/nitrogen ratio (C/N) in suspended POM in a shallow eutrophic lake of subtropical China, for apportioning the POM sources using Bayesian mixing model. Specifically, we collected seasonal samples of lake-water POM (>0.7 μm) from 20 sites in Yilong Lake from September 2020 to June 2022, as well as six types of modern samples covering the main carbon sources in the catchment. The spatial surveys showed that in the dry year (low water level) the δ13C of POM was more enriched in the western basin than those in the central and eastern basins, while the seasonal surveys showed the most enriched δ13C of POM in September. However, this spatio-temporal heterogeneity disappeared in the wet year (high water level). It was also found that the δ13C, δ15N and C/N values of POM varied significantly with those of phytoplankton across sites and seasons. Application of the MixSIAR model further showed that phytoplankton was the predominant source of POM in Yilong Lake (79.8 ± 13.4 %), but with large annual difference, 68.9 ± 10.3 % in the dry year and 90.7 ± 3.7 % in the wet year. In comparison, the contribution of the other five endmembers was much more moderate. In particular, the proportion of allochthonous organic carbon in POM was relatively low, with terrestrial plants and soils contributing 6.1 ± 4.8 % and 4.3 ± 2.5 % of POM, respectively. Our quantitative evidence for the dominance of the autochthonous source (i.e., phytoplankton) in lake-water POM over time and space suggested a determining role of eutrophication in the composition of lake organic carbon. Therefore, the coupling of algal blooms with organic carbon cycling in inland waters can be enhanced with continuous catchment development and regional warming.

Flow patterns at river bends and its response to surrounding infrastructures

On January 6, 2023, high-intensity precipitation occurred in the Babon River watershed, causing the river overflow and flood in several areas. Severe impact in the surrounding area was observed, such as in the Dinar Indah Housing Complex. Hydrodynamic complexity around a river bend points out the importance of understanding the flow patterns at a river bend. Therefore, this study aimed to describe the flow pattern of the river bend and analyze its response to the surrounding infrastructure using the HEC-RAS 6.3 model. Furthermore, improvement to structural mitigation was also designed. Field observations were also conducted to gather field data on the flood impact. The model results indicate that the highest water level within the river bend is 1.9 m, and the highest velocity is 5.85 m/s, which is on the outer bend. A dyke was then planned to be about 3.75 meters high, accompanied by a retaining wall to protect the river bank using the interlocking permeable revetment (IPR). Dyke and retaining walls provide stability against shear, overturning, and collapse.

Vegetation types and flood water level are dominant factors controlling the carbon sequestration potential in Dongting Lake floodplain, China

Wetlands are important carbon sinks. However, the carbon sequestration potential of flooded wetlands may be weakened owing to water regime changes induced by anthropogenic disturbances. Using the eddy covariance technique, this study quantified the effects of the water level and vegetation types on the net ecosystem CO2 exchange (NEE), gross primary production (GPP), and ecosystem respiration (Reco) from a reed marsh (Miscanthus sacchariflorus) and a sedge meadow (Carex spp.) in the Dongting Lake floodplain from 2014 to 2016. Our results indicated that the sedge meadow (−89.49 to −186.47 g C m−2 y−1) and reed marsh (−246.12 to −513.94 g C m−2 y−1) were carbon sinks on the interannual timescale. However, the sedge meadow changed from a carbon sink to a carbon source during the flooding season. The effect of flooding on the carbon sink function in the reed marsh was dependent on the water level. The carbon sink function of the reed marsh was enhanced by moderate flooding (water level under 30.5 m in Chenglingji) owing to the inhibition of Reco, but was weakened by extremely high-water levels (over 33 m in Chenglingji) during the flooding season. Seasonal variations in NEE, GPP, and Reco were closely related to photosynthetic photon flux density, soil water content, water level, soil temperature, and air temperature. We can conclude that the increase in reed area combined with the decrease in flooding days in the sedge meadow can potentially enhance the carbon sink function of the Dongting Lake floodplain.

Numerical study on the effect of the PI-controller type on the quasi-steady reactor pressure in MAAP 5.04 code

Abstract In this work, the boiling water reactor (BWR) was adopted as a physical model to study the influence of PI-controller type on the quasi-steady reactor pressure in MAAP 5.04 code. The designed reactor pressure can be simulated through the open area of a valve modified by PI controller. The proportional gain (k p) is equal to one in all cases. For the integral gain (k i) smaller than or equal to 100 (i.e., k i = 0.1, 1, 10 and 100), a scrammed reactor incurred by the high reactor water level (Level-8) that is due to the large reactor pressure drop does not occur in the simulation. Compared to k i = 1, 10 and 100, for k i = 0.1, the reactor pressure modified by the PI controller is more close to the designed reactor pressure; however, the time to meet the designed reactor pressure is longer. The reason is that k i = 1, 10 and 100 incur a larger overshoot in the modified reactor pressure through the feedback system; although the time to meet the designed reactor pressure can be shortened, the amplitude of the reactor pressure varying with time is obvious. To exactly simulate the reactor pressure of a nuclear power plant under the normal operation, our results can offer MAAP code users an important reference to design the PI controller.

Research on the Influence of Deep-Water Drilling Risers on Drillstring Motion Trajectory and Vibration Characteristics

The swing of the riser in deep-water drilling can significantly impact the drill string. In this study, we establish a riser model that considers the combined disturbance of periodic dynamic wind and wave loads. By coupling it with the drill string model, we develop a dynamic model for deep-water drilling systems. Through analyzing multiple sets of different drilling parameters, we examine displacements and impact forces at various positions along the drill string system. Specifically, our focus lies on velocity, acceleration, and rotational speed information of BHA. We investigate how WOB and rotational speed influence motion trajectory and vibration characteristics of the drill string within the dynamic model of deep-water drilling systems. Simulation results reveal slight differences in whirling trajectories between inside the riser and below mud line for the drill string. Rotational speed has a greater impact on the drill string compared to WOB; higher rotational speeds lead to increased collision forces between the drill string system and both riser and wellbore. Our findings identify specific combinations of WOB and rotational speed parameters that can stabilize drilling operations within dynamic models for deep-water drilling systems. These research results provide valuable insights for adjusting WOB and rotational speed parameters in deep-water drilling.

Diazotrophic community in the sediments of Poyang Lake in response to water level fluctuations.

Water level fluctuations (WLFs) are typical characteristic of floodplain lakes and dominant forces regulating the structure and function of lacustrine ecosystems. The sediment diazotrophs play important roles in contributing bioavailable nitrogen to the aquatic environment. However, the relationship between the diazotrophic community and WLFs in floodplain lakes is unknown. In this paper, we carried out a comprehensive investigation on the alpha diversity, abundance, composition and co-occurrence network of the sediment diazotrophs during different water level phases in Poyang Lake. There were no regular variation patterns in the alpha diversity and abundance of the sediment diazotrophs with the water level phase transitions. The relative abundance of some diazotrophic phyla (including Alphaproteobacteria, Deltaproteobacteri, Euryarchaeota, and Firmicutes) and genera (including Geobacter, Deferrisoma, Desulfuromonas, Rivicola, Paraburkholderia, Methylophilus, Methanothrix, Methanobacterium, and Clostridium) was found to change with the water level phase transitions. The results of ANOSIM, PerMANOVA, and DCA at the OTU level showed that the diazotrophic community structure in the low water level phase was significantly different from that in the two high water level phases, while there was no significant difference between the two high water level phases. These results indicated that the diazotrophic community was affected by the declining water level in terms of the composition, while the rising water level contributed to the recoveries of the diazotrophic community. The diazotrophs co-occurrence network was disrupted by the declining water level, but it was strengthened by the rising water level. Moreover, redundancy analysis showed that the variation of the diazotrophic community composition was mostly related to sediment total nitrogen (TN) and total phosphorous (TP). Interestingly, the levels of sediment TN and TP were also found to vary with the water level phase transitions. Therefore, it might be speculated that the WLFs may influence the sediment TN and TP, and in turn influence the diazotrophic community composition. These data can contribute to broadening our understanding of the ecological impacts of WLFs and the nitrogen fixation process in floodplain lakes.

Advanced Quantitative Precipitation Information: Improving Monitoring and Forecasts of Precipitation, Streamflow, and Coastal Flooding in the San Francisco Bay Area

Abstract Advanced Quantitative Precipitation Information (AQPI) is a synergistic project that combines observations and models to improve monitoring and forecasts of precipitation, streamflow, and coastal flooding in the San Francisco Bay Area. As an experimental system, AQPI leverages more than a decade of research, innovation, and implementation of a statewide, state-of-the-art network of observations, and development of the next generation of weather and coastal forecast models. AQPI was developed as a prototype in response to requests from the water management community for improved information on precipitation, riverine, and coastal conditions to inform their decision-making processes. Observation of precipitation in the complex Bay Area landscape of California’s coastal mountain ranges is known to be a challenging problem. But, with new advanced radar network techniques, AQPI is helping fill an important observational gap for this highly populated and vulnerable metropolitan area. The prototype AQPI system consists of improved weather radar data for precipitation estimation; additional surface measurements of precipitation, streamflow, and soil moisture; and a suite of integrated forecast modeling systems to improve situational awareness about current and future water conditions from sky to sea. Together these tools will help improve emergency preparedness and public response to prevent loss of life and destruction of property during extreme storms accompanied by heavy precipitation and high coastal water levels—especially high-moisture laden atmospheric rivers. The Bay Area AQPI system could potentially be replicated in other urban regions in California, the United States, and worldwide.

Tracking Centimeter‐Scale Water Level Changes in Swedish Lakes Using D‐InSAR

AbstractLakes are valuable water resources that support aquatic and terrestrial ecosystems and supply fresh water for the agricultural, industrial, and urban sectors worldwide. Although water levels should be tracked to monitor these services, conventional gauging is unfeasible in most lakes. This study applies Differential Interferometric Synthetic Aperture Radar (D‐InSAR) to estimate small water level changes, less than 2 cm, in Swedish lakes over 6‐day intervals. We validated the method across the shores of 30 Swedish lakes with gauged observations in 2019. We used Sentinel‐1A/B images with a 6‐day temporal separation to construct consecutive interferograms and accumulated the phase changes in pixels of high coherence to build a time series of water levels. We find that the accumulated phase change obtained by D‐InSAR replicates the magnitude of water levels in seven lakes in Southern Sweden, where water levels change slowly, less than 2 cm per 6‐day period, as validated by in‐situ gauges. In addition, this study demonstrates the application of D‐InSAR to estimate the long‐term direction of water level change (i.e., increase or decrease) in all 30 lakes. This work reveals the utility of high temporal resolution water level observations in support of other satellite water level instruments such as conventional altimeters and the recently launched Surface Water and Ocean Topography Mission.

Effects of birch encroachment, water table and vegetation on methane emissions from peatland microforms in a rewetted bog

This study investigated the influence of vegetation and microforms on methane (CH4) balances of a rewetted bog in north-west Germany. The two study sites are in close proximity on the same former peat extraction area, one dominated by Sphagnum-mosses and the other one by a dense Betula pubescens stand with a high Eriophorum vaginatum cover. The contribution of microforms (hummocks/hollows) to CH4 emissions and the effect of Betula encroachment has been studied. Transparent and opaque chambers were used to measure CH4 fluxes every 3–4 weeks during daytime for one year. For the estimation of annual balances, three methods were compared and the method using water level and soil temperature as explanatory variables was selected. Fluxes were scaled to the site level. The annual emissions per site are and 7.1 ± 1.5 g CH4-C m−2 year−1 at the treed site and 36.1 ± 3.5 g CH4-C m−2 year−1 at the open site, mainly controlled by higher water levels. Highest annual emissions originated from hollows at the open site, but in the vegetation period, hummock emissions tend to be higher. At the tree site, emission differences between the microforms were less pronounced. There were no differences between fluxes from transparent and opaque chambers.

Quality of drinking water and risk to the health of the population of the south Baikal region (Russia)

Providing good quality water in sufficient quantities is a major challenge in the world. The purpose of the study is to assess the quality of drinking water and the health risk of various population groups in the southern Baikal region (Siberia, Russia) under changing hydrological conditions. Lake Baikal is the largest freshwater body of water and is one of the sites protected by UNESCO. Materials and methods. An analysis of centralized and non-centralized water supply was carried out in the south-eastern part of the Irkutsk region, adjacent to Lake Baikal. The data used are from the Baikal (regional) Information Center for 2011–2022, and they include the results of monitoring the water quality of the centralized domestic and drinking water supply (CDW) with 140 thousand samples, and non-centralized domestic and drinking water supply (NDW) with 108 thousand samples. In all samples, 17 substances were determined. In addition, during the flood period, accompanied by additional water disinfection, trihalomethanes were determined in populated areas exposed to negative impacts. The quality of drinking water was assessed in comparison with the maximum permissible concentrations of substances (MPCs) approved by regulatory documents of Russia. An assessment of the characteristics of drinking water consumption by the population of the Baikal region was carried out, based on interview data from sample groups of the population. The assessment of the risk to public health, due to chronic oral intake of chemicals, was carried out using the values of the hazard coefficient (HQi), the hazard index (HI), individual carcinogenic risk (ICR), and population carcinogenic risk (PCR).Village residents more often use underground water sources (centralized and non-centralized). Residents of cities are provided with water from surface sources (Lake Baikal and the Angara River). Significant concentrations of iron, nitrates, and manganese were found in drinking water used by villagers. Average concentrations of iron - 2.25 mg/dl, manganese - 0.6 mg/dl, nitrates - 135 mg/dl were recorded in the water of underground springs in villages of the Irkutsk region. Among rural residents of the Irkutsk region, 60.8 % live in settlements with non-water supply systems, 28.4 % have mixed water supply.The non-carcinogenic risk for the adult and child population was calculated; HI > 1 was identified for the population using underground water sources. the non-carcinogenic hazard for the adult population, it was found that HI in the Irkutsk region slightly exceeded the standard value (1), amounting to 1.3, and for the child population - 1.6, the main contribution to the hazard index is represented by nitrates. For children of individual rural settlements of the Angarsk region HI = 1.38. The carcinogenic risk for water from underground sources reached in the range 1.56 × 10−5- 2.1 × 10−4 (in some settlements). Priority carcinogens were identified: arsenic (the contribution of which is 56.3–100 %), hexavalent chromium (29.9–35.8 %). A carcinogenic risk for city residents arises from increased disinfection during periods of microbiological contamination (floods, rains, high water levels), and it is associated with the formation of halogen-containing compounds. ConclusionThe need to strengthen the drinking water quality monitoring system in risk areas has been proven by increasing the number and frequency of sampling during flood periods.

Experimental and numerical study on the breaching mechanisms of landslide dams with non-uniform structures

Landslide dams often exhibit non-uniform structures due to the rapid and dynamic accumulation of various types of landslide materials. These variations in dam composition significantly impact breach progression, causing significant errors in current model tests and numerical simulations with uniform structure assumptions This adversely affects peak flow predictions and decisions related to risk prevention and control. This study conducted a series of flume tests to examine the influence of non-uniform structures on the failure mechanisms of landslide dams. A 3D dam breach model was used to replicate these flume experiments and obtain more detailed information. Large Eddy Simulation (LES) captures the hydraulic features of dam-break flow, while equilibrium equations model morphological changes in landslide dams amid complex terrains using suspended and bed load transport. The findings indicate that in a uniform dam, the presence of coarse particles shifts erosion characteristics from layered erosion to step-pool development. Furthermore, as the content of coarse particles increases, the number of steps also rises. In the vertically non-uniform structure, the upper layer affects the formation of the breach, the middle layer affects the dam break and the breach flow, and the bottom layer affects the remaining dam height. The presence of an armor layer results in a higher water level and accelerates breach formation with a larger breach flow. In the horizontally non-uniform structure, the upper part of the overflow side is the core area of the breach, the lower part of the overflow side and the upper part of the opposite side affect the downcutting and widening rates of the breach, respectively. Preferentially, the breach tends to develop towards the relatively weaker of the two sides.

Dynamics of beach scarp formation behind detached breakwaters

Detached (offshore) breakwaters are widely used as beach stabilization measures. However, there is potential for erosion at the openings between detached breakwaters, which may result in the formation of beach scarps. This study evaluated the formation of beach scarps around breakwaters using field surveys and numerical simulations. The evaluation was conducted using a combination of a recent advanced field survey method and a numerical modelling system combining GPV-MSM, SWAN, and XBeach. The unmanned aerial vehicle photogrammetry results revealed the height of the beach scarp generated behind the detached breakwaters to be approximately 3.0 m at Aoyama beach, Niigata coast, Japan, although sand deposition occurred below sea level towards the detached breakwaters. The numerical simulation using the results of the field survey showed that a combination of high waves and increased water level owing to radiation stress between the shoreline and breakwaters resulted in a steeper slope in the beach morphology. Second, avalanching occurred on the beach, leading to the formation of beach scarps. This study showed that detached breakwaters may lead to high water levels, resulting in the generation of beach scarps behind the breakwaters. This study implied that large beach scarps can be generated even when detached breakwaters are constructed.

Variable pressure foaming on functionality and structural properties correlation in flexible polyurethane foam

The production cost of flexible polyurethane foam is significantly dependent on the cost of polyol, which constitutes the largest percentage of materials used in foam production with the characteristics to induce superior mechanical properties. Suitable fillers that are relatively cheap can be introduced in the foam as replacement for polyol. Certain compositions of filler have deleterious effect on some relevant mechanical properties of the foam. This paper investigates the Effects of Variable Pressure Foaming on functionality and structure property correlation in polyurethane foam using different percentage of inorganic fillers at different pressure in flexible polyurethane foam for the dual purposes of achieving sustained mechanical properties of polyurethane foam and reduction in the production cost by using the VPF Technique. Government restricts the use of certain auxiliary blowing agents like chlorofluorocarbon, trichloroethane, carbon dioxide, methylene chloride, acetone, pentane and water. VPF machine, in which we can make different densities of foam without adding auxiliary blowing agents which are banned in the Europe and other countries. These blowing agents are highly carcinogenic and ozone depletors, which are also harmful for human beings’ health and greenhouse effect. Water is a natural blowing agent, producers have tried to raise the water level substantially as an ABA agent, With the high exotherm associated with high water level formulations, there is so much urea formation that it is difficult to make flexible PU foams and inferior foam quality and durability, scorching in the foam and pose a fire hazard during foam manufacturing. For the rapid cooling process, it required excess Toluene Diisocyanate usage and allowed excess TDI vapour to be released into the atmosphere. In VPF, enclosed chamber and the exhaust is vented through carbon beds, it filters the TDI fumes which are very harmful for human beings’ health and for the environment. Foams can be achieved by foaming under vacuum, thus substantially reducing the water level and TDI usage. VPF technique offers a unique combination of environmental friendliness, superior product consistency and unique foam properties. It provides us with a platform for new product technology and a reliable process to meet the increasingly stringent environmental regulations.

Comparisons of Different Machine Learning-Based Rainfall–Runoff Simulations under Changing Environments

Climate change and human activities have a great impact on the environment and have challenged the assumption of the stability of the hydrological time series and the consistency of the observed data. In order to investigate the applicability of machine learning (ML)-based rainfall–runoff (RR) simulation methods under a changing environment scenario, several ML-based RR simulation models implemented in novel continuous and non-real-time correction manners were constructed. The proposed models incorporated categorical boosting (CatBoost), a multi-hidden-layer BP neural network (MBP), and a long short-term memory neural network (LSTM) as the input–output simulators. This study focused on the Dongwan catchment of the Yiluo River Basin to carry out daily RR simulations for the purpose of verifying the model’s applicability. Model performances were evaluated based on statistical indicators such as the deterministic coefficient, peak flow error, and runoff depth error. The research findings indicated that (1) ML-based RR simulation by using a consistency-disrupted dataset exhibited significant bias. During the validation phase for the three models, the R2 index decreased to around 0.6, and the peak flow error increased to over 20%. (2) Identifying data consistency transition points through data analysis and conducting staged RR simulations before and after the transition point can improve simulation accuracy. The R2 values for all three models during both the baseline and change periods were above 0.85, with peak flow and runoff depth errors of less than 20%. Among them, the CatBoost model demonstrated superior phased simulation accuracy and smoother simulation processes and closely matched the measured runoff processes across high, medium, and low water levels, with daily runoff simulation results surpassing those of the BP neural network and LSTM models. (3) When simulating the entire dataset without staged treatment, it is impossible to achieve good simulation results by adopting uniform extraction of the training samples. Under this scenario, the MBP exhibited the strongest generalization capability, highest prediction accuracy, better algorithm stability, and superior simulation accuracy compared to the CatBoost and LSTM simulators. This study offers new ideas and methods for enhancing the runoff simulation capabilities of machine learning models in changing environments.

Performance of rotational speed controlled small-scale head-dependent hydroelectric power plant

Small scale or micro scale hydroelectric power production is characterized by high investment costs compared to operation costs. In addition, the repayment time is often long, more than ten years (if not subsidized heavily) which requires that a small-scale hydropower plants can be profitable only if both the investment costs and the running costs are low. The performance and efficiency of a plant is very important because having long repayment time means that the efficiency improvement of one percentage unit often means the ten percentage unit improvement in profit. The most economical way to control the flow is sometimes a two point control where generators are switched on and off depending on high water level used as control variable. The water level cannot be kept constant using this method, but the traditionally used mechanical blade angle adjustment system is too expensive in very small (approximately &lt;100 kW) units. The new method of controlling the upper water level (head) is the use of rotational speed control of turbine, implemented by a four quadrant frequency converter. The efficiency of a 4-quadrant frequency converter is approximately 97 %, which reduces the income compared to the situation where the generators are directly connected to electricity network. However, when the head is kept constant using a frequency converter, it is not required to switch off the generator circuit breakers which have a finite life time and the head height can be kept optimal in terms of performance. In this paper, a system structure, a pilot plant installation and example calculations on the feasibility of a frequency converter driven fixed blade hydro power turbine is given.

Assessment of Shoreline Change from SAR Satellite Imagery in Three Tidally Controlled Coastal Environments

Coasts are continually changing and remote sensing from satellites has the potential to both map and monitor coastal change at multiple scales. Unlike optical technology, synthetic aperture radar (SAR) is uninfluenced by darkness, clouds, and rain, potentially offering a higher revision period to map shoreline position and change, but this can only be feasible if we have a better interpretation of what shorelines as extracted from SAR imagery represent on the ground. This study aims to assess the application of shorelines extracted from SAR from publicly available satellite imagery to map and capture intra-annual to inter-annual shoreline variability. This is assessed in three tidally controlled coastal study areas that represent sand and gravel beaches with different backshore environments: low-lying dunes and marsh; steep, rocky cliff; and urban environments. We have found that SAR shorelines consistently corresponded to positions above the high-water mark across all three sites. We further discuss the influence of the scene geometry, meteorological and oceanographic conditions, and backshore environment and provide a conceptual interpretation of SAR-derived shorelines. In a low-lying coastal setting, the annual change rate derived through SAR presents a high degree of alignment with the known reference values. The present study contributes to our understanding of the poorly known aspect of using shorelines derived from publicly available SAR satellite missions. It outlines a quantitative approach to automatically assess their quality with a new automatic detection method that is transferable to shoreline evolution assessments worldwide.

Research on the Deformation Law of Foundation Excavation and Support Based on Fluid-Solid Coupling Theory.

To investigate the impact of underground water seepage and soil stress fields on the deformation of excavation and support structures, this study initially identified the key influencing factors on excavation deformation. Subsequently, through a finite element simulation analysis using Plaxis, this study explored the effects of critical factors, such as the excavation support form, groundwater lowering depth, permeability coefficient, excavation layer, and sequence on excavation deformation. Furthermore, a comprehensive consideration of various adverse factors was integrated to establish excavation support early warning thresholds, and optimal dewatering strategies. Finally, this study validated the simulation analysis through an on-site in situ testing with wireless sensors in the context of a physical construction site. The research results indicate that the internal support system within the excavation piles exhibited better stability compared to the external anchor support system, resulting in a 34.5% reduction in the overall deformation. Within the internal support system, the factors influencing the excavation deformation were ranked in the following order: water level (35.5%) > permeability coefficient (17.62%) > excavation layer (11.4%). High water levels, high permeability coefficients, and multi-layered soils were identified as the most unfavorable factors for excavation deformation. The maximum deformation under the coupled effect of these factors was established as the excavation support early warning threshold, and the optimal dewatering strategy involved lowering the water level at the excavation to 0.5 m below the excavation face. The on-site in situ monitoring data obtained through wireless sensors exhibited low discrepancies compared to the finite element simulation data, indicating the high precision of the finite element model for considering the fluid-structure interaction.

Compound flood impacts from Hurricane Sandy on New York City in climate-driven storylines

Abstract. High impact events like Hurricane Sandy (2012) significantly affect society and decision-making around weather/climate adaptation. Our understanding of the potential effects of such events is limited to their rare historical occurrences. Climate change might alter these events to an extent that current adaptation responses become insufficient. Furthermore, internal climate variability in the current climate might also lead to slightly different events with possible larger societal impacts. Therefore, exploring high impact events under different conditions becomes important for (future) impact assessment. In this study, we create storylines of Sandy to assess compound coastal flooding on critical infrastructure in New York City under different scenarios, including climate change effects (on the storm and through sea level rise) and internal variability (variations in the storm's intensity and location). We find that 1 m of sea level rise increases average flood volumes by 4.2 times, while maximised precipitation scenarios (internal variability) lead to a 2.5-fold increase in flood volumes. The maximised precipitation scenarios impact inland critical infrastructure assets with low water levels, while sea level rise impacts fewer coastal assets though with high water levels. The diversity in hazards and impacts demonstrates the importance of building a set of relevant scenarios, including those representing the effects of climate change and internal variability. The integration of a modelling framework connecting meteorological conditions to local hazards and impacts provides relevant and accessible information that can directly be integrated into high impact event assessments.

Hedge fund fee structure and risk exposure

We provide a closed-form solution for the optimal investment strategy of a hedge fund manager compensated by a management fee and a high-water mark (HWM) contract. The fraction of the assets under management (AUM) allocated to equity is an increasing and convex function of distance to the HWM, with the size of the incentive fee rate enhancing the convexity effect. Importantly, the management fee induces more risk-taking behavior because it provides insurance to the fund manager. Beating the HWM by small amounts is optimal because it mitigates the ratchet feature of the HWM and smooths revenue. The decomposition of revenues between the two fee types is also examined. An extension introduces fund termination triggered by a large AUM drawdown. Risk exposure is either a decreasing or a hump-shaped function of the distance to the HWM.