Analysis on the mode of depletion of water reserves contained in the Locoli aquifer (Monte Albo - northeastern Sardinia)

Seasonal ecological changes and water level variations in the Sélingué Reservoir (Mali, West Africa)

This paper presents the impacts of frazil ice jams on the variation in water level at the Hequ Reach of the Yellow River in China. Based on both field observations and experimental studies, it is found that both the evolution of frazil ice jams and the associated variation in water level depend upon an interesting interaction between hydraulic variables during the ice-jammed period. In particular, the critical Froude number governing the formation of river ice jams and their upstream propagation is about 0.09. The water level during ice-jammed periods depends not only on the slope of the water surface and the water level under open-water conditions with the same discharge, but also on the length of the ice jam and the ice concentration in the water. Moreover, the field investigations show that the thickness of river ice strongly influences the variation in water level during ice-jammed periods. Empirical relationships are derived to quantify the relationship between the highest water level during ice periods and related physical parameters. To confirm the field results, and to explore the influence of ice discharge on the variation in water level, experimental studies were also conducted. These results confirm that the ice concentration plays a key role in the variation in water level and the jam thickness. Given the complexity of the jamming processes, surprisingly good agreement is observed between field and experimental investigations.

Monitoring water volume changes of a given lake needs precise estimation of water level and water surface variations. The water level of the lake might be erroneous due to multi reflections, called multi peak waveforms, from the illuminated area inside the radar footprint. Bathymetry data are also not available everywhere to measure the absolute water volume storage. To derive optimized ranges and consequently more precise water level, corrupted waveforms need to be analyzed. We developed a new approach to select an optimal peak in a given waveform to be retracked with the threshold retracker. We selected a peak, which provides a water level closest to the in situ gauge. In another scenario, we involved all meaningful peaks in a given waveform and considered the average of retracking corrections obtained from all sub-waveforms/peaks. The water surface of the lake was estimated from analyzing SAR images. To distinguish water from non-water surfaces, the threshold algorithm based on the histogram has been used. The surface time series was validated against external data. Finally, relative water volume changes were estimated from the water level and surface variations according to the Heron method. In this study, we used L2 and L1b data of Sentinel-3 A SRAL and SAR images from Sentinel-1 A and B from June 2016 to May 2018 to monitor Lake Vanern in Sweden. Our analysis in water level determination shows an improvement of 50% for our novel optimized peak selection method compared to L2 data in front of in situ gauge measurements. We also found that for more than 90% of the waveforms, the first peak, called the first sub-waveform, leads to a better result. The second scenario, i.e. involving all meaningful peaks, called mean-all sub-waveforms, has almost the same performance as the optimized sub-waveform, which shows the effectiveness of this scenario for water level monitoring. We found a correlation of 97% and 71% for the water level with respect to the water volume and surface variations, respectively. A 78% correlation was achieved for water surface-volume variations. There is also a correlation of 83% and 88% for our water surface and volume variations with respect to that of the Hydroweb database, respectively. An RMSE of 5 cm in water level variation is a significant achievement for the Sentinel-3 SAR altimeters over the inland waters, i.e Lake Vanern.

We present an analysis of the long-term trends and variability of extreme water and tidal levels and the main tidal constituents using long-term records from two tide gauges in the wider region of the Rio de la Plata estuary: Buenos Aires (1905–2013) and Mar del Plata (1956–2013). We find significant long-term trends in both tidal levels and the main tidal constituents (M2, S2, K1, O1, and the overtide M4) from a running harmonic analysis in both locations. The tidal range decreased on average 0.63 mm y−1, as a result of an increase of the low water levels and a decrease of the high water levels. We also find a secular decrease in the amplitude of the semi-diurnal constituents and an increase of the diurnal ones, but of different magnitudes at each location, which suggests that different processes are producing these changes. In Buenos Aires, an increase of river discharge into the estuary seems to reduce the tidal range by hampering the propagation of the tidal wave into the estuary, whereas no influence of river discharge on water and tidal levels can be detected in Mar del Plata. We believe that other factors such as thermohaline changes or the rise of mean sea-level may be responsible for the observed tidal range decrease. Despite the tidal long-term trends, we find no significant trends in the meteorological component of the tide-gauge records other than an increase in the mean sea-level. In addition, we explore teleconnections between the variability of the meteorological component of the tide-gauge records and climate drivers.

Subtidal water level and current variability in Barataria Bay—a microtidal bar‐built estuary within the Mississippi Delta—and its relation to local and remote wind forcings were analyzed using three different methods: (1) statistical analysis of in situ observations, (2) an analytical model with idealized wind field, and (3) a barotropic numerical model. Remote wind effects (i.e., the coastal water levels imposed by Ekman transport) are dominant at forcing currents at the bay mouth and thus control estuary‐shelf exchanges. In contrast, subtidal water level variability, which ranges from 0.35 m at the bay mouth to 0.55 m at the bay head, is mainly associated with local wind effects, especially at the head of the bay. This occurs because the local wind‐induced water level tilting within the bay is larger than the coastal sea level pumping, i.e., the spatially uniform variations in water levels forced by remote winds. This result contrasts with (1) most coastal plain, fjord, and tectonic estuaries and (2) with other bar‐built estuaries in the region, in which remote wind effects dominate water level variability within the estuary. These differences are due to geomorphological features unique to Barataria Bay, such as its limited estuarine‐shelf connectivity and its orientation relative to local shoreline.

Coseismic response of groundwater level in the Three Gorges well network and its relationship to aquifer parameters

Long-term water level dynamics in the Red River basin in response to anthropogenic activities and climate change

Abstract. The forecasting of inundation levels during typhoons requires that multiple objectives be taken into account, including the forecasting capacity with regard to variations in water level throughout the entire weather event, the accuracy that can be attained in forecasting peak water levels, and the time at which peak water levels are likely to occur. This paper proposed a means of forecasting inundation levels in real time using monitoring data from a water-level gauging network. ARMAX was used to construct water-level forecast models for each gauging station using input variables including cumulative rainfall and water-level data from other gauging stations in the network. Analysis of the correlation between cumulative rainfall and water-level data makes it possible to obtain the appropriate accumulation duration of rainfall and the time lags associated with each gauging station. Analyses on cross-site water levels as well as on cumulative rainfall enable the identification of associate sites pertaining to each gauging station that share high correlations with regard to water level and low mutual information with regard to cumulative rainfall. Water-level data from the identified associate sites are used as a second input variable for the water-level forecast model of the target site. Three indices were considered in the selection of an optimal model: the coefficient of efficiency (CE), error in the stage of peak water level (ESP), and relative time shift (RTS). A multi-objective genetic algorithm was employed to derive an optimal Pareto set of models capable of performing well in the three objectives. A case study was conducted on the Xinnan area of Yilan County, Taiwan, in which optimal water-level forecast models were established for each of the four water-level gauging stations in the area. Test results demonstrate that the model best able to satisfy ESP exhibited significant time shift, whereas the models best able to satisfy CE and RTS provide accurate forecasts of inundations when variations in water level are less extreme.

Spatial and temporal variations of the epiphytic algae assemblages associated with roots of macrophytes in 14 sampling sites, seven zones with lentic and seven with lotic conditions of the Ayapel flood plain was evaluated. It was determined that the degree of connectivity between the river, the streams and swamp increased in high waters which produced physico-chemical uniformity conditions and limited the development local conditions. Thus, the most isolated bodies reach a greater degree of independence from the main body due to the formation of horizontal gradients. This individualization of the physico-chemical conditions is most evident in the low water phase. Diversity and richness of species variation at the spatial level was found, as well as lower floristic similarity (30%) between the periphytics assemblages which favored the recorded high species richness. Diatoms predominated in the system, being favored by ammonium concentration; their abundance decreased with precipitation increase. Chlorophyceae are favored by the precipitation increase, variation in water level, low concentrations of nitrates, nitrogen ammoniacal and electrical conductivity. Low concentrations of nutrients and the decrease of precipitation favor the development of the cyanobacteria. Finally, Euglenophyceae, Dynophyceae and Chrysophyceae are considered as minority algal groups within the epiphytic assembly.

The investigation of freshwater lake water resource changes in arid regions is crucial for understanding the evolution of regional lake dynamics under climate change, given their value and limited availability. This study aims to overcome the limitations of traditional water level monitoring methods and address the practical need for monitoring water level changes in Lake Bosten, located in the arid and semi-arid regions of China. To this end, we employed ICESat, ICESat-2, and CryoSat-2 altimetry data, as well as Landsat 8-OLI optical remote sensing data, to obtain the water level information for Bosten Lake from 2003 to 2022. We analyzed the temporal variation of the lake level and discussed the response of the lake level to climate and human activities in the context of temperature, precipitation data, and human water use. The water level of Lake Bosten exhibited a decreasing and then increasing trend, with three rising and three falling intervals, respectively. The intra-year variation of the lake water level exhibited bimodal characteristics, and the fluctuation range of water level during abundant water periods was greater than that during dry periods. Finally, we correlated the extracted lake water level with the measured water level at the hydrological station and found a significant positive linear correlation between the observed water level of Bosten Lake based on satellite altimetry and the measured water level at the hydrological station, with an overall correlation coefficient of 0.896 and 0.934 (P < 0.01), indicating high accuracy of the water level results obtained in this study. The dynamics of Lake Bosten are influenced by a combination of climate change, hydrological elements, and human activities, with a relatively weak relationship between climate change and lake volume and a strong influence of human activities. Multi-source altimetry satellites provide a powerful tool for monitoring lake water levels over a long time scale, which is critical for studying lake water level changes and their response to climate and the environment.

The flood pulse is a key factor in the ecological processes of the varzea. This study aims to describe water level variation at a varzea site in the Middle Solimoes river region (Amazon River). The study took place in Mamiraua Sustainable Development Reserve from 1990 to 2008. During this period, water level varied between a minimum of 21,71 and a maximum of 38,55 meters above sea level. Average annual amplitude was 10,60 meters (n =17, s.d. = 1,84). The three highest water levels were registered in 1997, 1998, and 1999, whereas the lowest were registered in 1991, 1992, and 1995. The study showed that high water level periods, or floods, occur from May until mid-July, whereas low water levels, or dry periods, occur in the months of September, October, and November. Flooding periods begin in the end of November and end in the beginning of May, whereas, drying periods - when water levels fall - start mid-July and end in the beginning of September. The annual flooding pattern has followed a similar model created from monthly water level averages. Markedly different oscillations were observed in 1992, 1995, 1997, and 2004. Through the monitoring of water level variations in the Mamiraua Reserve it was possible to characterize the flood pulse in the middle Solimoes river region - a variable to be compared with other environments in the Amazon basin.

Bandwidth modulation and centre wavelength shift of a single FBG for simultaneous water level and temperature sensing

The principal factors that control the character of deformation variations in water level in mouth areas of rivers are considered. The role of wind regime and the sea level variations in the formation of positive and negative setups is assessed. River mouth zones are classified in terms of the predominance of positive or negative variations in water level. Specific features of the positive or negative setup regimes in the mouth zones of the Neva, Don, and Volga rivers are discussed.

Various abiotic and biotic factors may determine the spatial distribution patterns of Cladocera in a lake. The aim of this study was to examine the horizontal distribution of Cladocera in a lake connected to a river during low and high water phases and the abiotic factors that determine variation in their populations. Microcrustaceans were collected in integrated samples at 40 sites distributed on a lake. The mean abundance of Cladocera was around five times higher in the low water phase than in the high water phase. Only populations of <em>Bosmina hagmanni</em> Stingelin, 1904 and<em> Bosminopsis deitersi</em> Richard, 1895 predominated in the low water phase, while in the high water phase, <em>B. hagmanni, Ceriodaphnia cornuta</em> f. <em>rigaudi </em>(Sars, 1896)<em> Diaphanosoma spinulosum </em>Herbst, 1975 and<em> Moina micrura </em>Kurz, 1875 predominated at some sampling stations. The majority of cladoceran species showed an aggregated distribution in the low water phase, except <em>B. longirostris</em> and<em> D. fluviatile</em> and, <em>B. longirostris</em>, the only ones which presented a uniform distribution pattern in the high water phase. Most of the aggregates of cladoceran species predominated in both the dry and rainy periods on the east side of the lake due to intense easterly wind. Some cladoceran populations formed isolate aggregates in other parts of the lake and near the lake-river connection site. Canonical Correspondence Analysis (CCA) showed that the variables phosphorus, nitrogen and suspended matter (eutrophic conditions) determined distinct patterns of horizontal distribution in some cladoceran populations at some stations in the low water phase, while in others, the patterns of horizontal distribution were determined by environmental conditions as alkalinity, pH, oxygen, depth and water transparency. In the high water phase, CCA revealed that phosphorus and water transparency were positive determining factors in the distribution of some cladoceran species, while alkalinity, depth and suspended matter were negative. Our study showed that the distribution of cladoceran species may vary somewhat between the two distinct water phases depending on the micro-scale variation patterns of environmental factors.

The importance of elucidating the effects of small periodic influences on the behavior of complex systems is well acknowledged. In the present research, a possible impact of regular water level variations in large reservoir as an example of small external influence (comparing to tectonic forces) on the dynamics of local seismic activity was investigated. In general, large reservoirs located in the seismically active zones are often considered as a factor which quantitatively and qualitatively influences the earthquakes generation. It was many times reported that during impoundment or immediately after it (namely from several months to several years), both the number and the magnitude of earthquakes around reservoir significantly increased. These changes in earthquake generation are named the reservoir induced seismicity (RIS). After several years of regular seasonal load/upload of the reservoir, the seismicity essentially decreases down to the level when lesser earthquakes occur with lower magnitudes. To explain this decrease, the authors of the present paper recently proposed a model of phase synchronization of local seismic activity by the periodic variation of the water level – the reservoir-induced synchronization of seismicity (RISS). Generally speaking, RISS presumes a kind of control of local seismic activity by synchronizing small external periodic influence and hence an increase of the order in dynamics of regional seismic activity. To reveal these changes in dynamics of phase-synchronized seismic activity around a large reservoir, field seismic and water level variation data were analyzed in the present work. Data sets of laboratory stick-slip acoustic emission, under a weak influence imposed as a model of natural seismicity influenced by periodic water level variation, also were analyzed. The evidence is presented showing that an increase of the order in dynamics of daily occurrence, as well as temporal and energy distribution of earthquakes took place around Enguri high dam water reservoir (Western Georgia) during the periodic variation of the water level in the lake. It is shown that when the water level variation in a reservoir is close to periodic, monthly frequency of earthquake occurrence reveals two maximums: in spring and autumn. There is a clear asymmetry in the seismic response, possibly due to load/unload response ratio (LURR) effect; the maximal release of seismic energy is during loading, i.e., in the spring.