Variations In River Discharge Research Articles

Multiproxy record of suborbital-scale climate changes in the Algero-Balearic Basin during late MIS 20 - Termination IX

High-resolution quantitative analyses have been carried out in samples from the Ocean Drilling Program (ODP) Site 975 in the Algero-Balearic basin through late Marine Isotope Stage (MIS 20)-Termination IX (800–784 ka). The multi-proxy study combines data of planktonic δ18O, δ13C, calcareous plankton (coccolithophores, foraminifera), palynomorphs, alkenone-based sea surface temperature (SST), % alkenone tetraunsatured (% C37:4), and terrigenous biomarkers (C23–C31n-alkanes, C22–C30n-alkanols) with the aim to reconstruct climate-induced paleoenvironmental changes at orbital-submillennial scale, in a crucial time interval of the Early-Midde Pleistocene transition. The surface water δ18Osw has been reconstructed from δ18OG.bulloides and alkenone-based SST as a proxy for salinity changes. The late MIS 20 has been subdivided in several phases based on evidence of (i) meltwater events of polar origin or from surrounding mountain glaciers, (ii) changes in the production rate of Western Mediterranean Deep Water (WMDW) and in deep water ventilation, (iii) variation in terrestrial input and river discharge, and iv) variations in the strength of the north westerlies, and polar front shift. Following a glacial stadial (lasting ca 3 kyr) marked by the strongest WMDW production, coeval with a boreal summer insolation minimum and a marked low sea level, the latest MIS 20 is characterized by a terminal stadial event (lasting ca 3.5 kyr), which is traced by the occurrence of cold-low salinity water, pointing to meltwater advection at the site location. Short-term warm and cool events occurred through Termination IX during sea level rise and insolation increase, preceding the onset of full MIS 19c, characterized by an organic rich layer (ORL) associated with insolation cycle 74. The succession of these climate and oceanographic events has been compared to evidences from other Mediterranean sites, highlighting similar basin-wide patterns, which recall the climate evolution of Termination I. The comparison of our results with the climate proxies from the Integrated Ocean Drilling Program (IODP) Site U1385 located west of Iberian margin made it possible to point at the connection between Mediterranean oceanographic and atmospheric dynamics and the northern hemisphere ice-sheet instability, providing insight on the relationship with the Atlantic meridional overturning circulation and thermal front migration.

Intra- and Inter-Annual Variability in the Dissolved Inorganic Nitrogen in an Urbanized River before and after Wastewater Treatment Plant Upgrades: Case Study in the Grand River (Southwestern Ontario)

External nitrogen (N) inputs originating from human activities act as essential nutrients accumulation in aquatic ecosystems or it is exported elsewhere, where the assimilation capacity is surpassed. This research presents a multi-annual case study of the dissolved inorganic nitrogen (DIN) in an urban river in Ontario (Canada), assessed changes in N downstream of the largest wastewater treatment plant (WTP) in the watershed. Changes in the DIN effluent discharge, in-river concentrations and loads were observed comparing the intra- and inter-annual variability (2010–2013) before, during and after WTP upgrades. These upgrades reduced the ammonium concentration in the river from 0.44 to 0.11 mg N-NH4+/L (year average), but the N load in the effluent increased. In the river, nitrate and ammonium concentrations responded to seasonal variability, being higher during the low temperature (>10 °C) and high flow seasons (spring and spring melt). Among years, changes in the DIN concentration are likely controlled by the effluent to river dilution ratio, which variability resides on the differences in river discharge between years. This suggest that the increasing trend in the DIN concentration and loads are the result of agricultural and urban additions, together with reduced N assimilation, in addition to N loads responding to variable river discharge. Finally, we propose monitoring both concentrations and loads, as they provide answers to different questions for regulatory agencies and water managers, allowing tailored strategies for different purposes, objectives and users.

Representing Human Water Management in a Land Surface Model Using a Supply/Demand Approach

AbstractThe impact of human water management on river discharge is increasingly viewed as a missing process in Earth system modeling. Models which have attempted to include it are generally at coarse resolution and uncoupled to the atmosphere. We propose to describe human water management at high spatial resolution using ORganizing Carbon and Hydrology In Dynamic EcosystEms concept of hydrological‐transfer‐units in the routing parametrization. Irrigated areas are linked to river abstraction points using a minimization process. The directed graphs of river flows and adduction network for irrigation is transposed to propagate water demands upstream. Reservoirs and dams are placed along the graph to balance supply and demands in the four chosen water value classes. Dam regulation is assumed to maximize demand satisfaction and dampen floods while respecting the properties of the infrastructure. The developed human water management module is applied to the Yellow River where irrigation and dam regulation are known to have a strong impact. Results show that the impact of human water management is strongly heterogeneous over space. It propagates along the river channels and can be mitigated by the confluence of tributaries. Moreover, the human impact has a strong seasonality due to time varying irrigation demands and the response of dam regulation. A number of uncertainties still remain and affect the simulated river discharge. Nevertheless, the representation of human water management improves the model's behavior in terms of magnitude and intra‐annual variations of river discharge, and offers the opportunity to implement anthropogenic processes in the water cycle of Earth System Models.

Effects on circulation and water renewal due to the variations in the river flow and the wind in a Brazilian estuary lagoon complex

The Mundaú-Manguaba Estuary Lagoon Complex is located on the coast of Alagoas state in Northeastern Brazil, and consists of two shallow lagoons, Mundaú and Manguaba, that form a system of choked lagoons which are connected to the Atlantic Ocean by a series of narrow channels with a single outlet which dynamically alters its position. This study uses the Hydrodynamic Environmental System, SisBaHiA® to investigate how variations in river discharge and wind influence hydrodynamic circulation, water renewal, salinity and temperature in the lagoons. The free surface positions, obtained by model, were compared with the free surface positions measured at two points of the complex, showing good agreement. The analyses were carried out for dry and wet seasons and extreme events with very high freshwater discharge. The channel system of the lagoons is an efficient filter in reducing tidal variability inside the lagoons. The tidal ranges in the Manguaba and Mundaú Lagoons are 90% and 80% lower, respectively, as compared with the values in the open boundary. The residence time calculated varied between 11 and 365 days and between 2 and 180 days for the Manguaba and Mundaú Lagoons, respectively, making it possible to identify possible stagnation areas. The results from the salt and heat transport model show a prolonged period with low salt concentrations and slow salinity recovery after the rainy season; the water temperature in the lagoons shows little spatial and temporal variation.

Spatio-temporal dynamics of hydrologic changes in the Himalayan river basins of Nepal using high-resolution hydrological-hydrodynamic modeling

The hydrology of the Himalayan region, known as the water tower of Asia, is undergoing rapid transformations due to climate change and growing human influences, and it is known that this region is one of those most vulnerable to climate change. Numerous studies have examined the changes in the hydrology of Nepal, which includes a significant upstream portion of the Himalayas. However, there is a lack of holistic studies on the spatial–temporal evolution of hydrologic dynamics over the entire nation and over long periods. In this study, we present a comprehensive assessment of the changes in river discharge, flood occurrence, and terrestrial water storage (TWS) across all river basins in Nepal using hydrological-hydrodynamic simulations spanning for 40 years (1979–2018) at ~ 5 km spatial resolution, and downscaled flood attributes at ~ 90 m resolution. The spatio-temporal variations in river discharge and inundation extent are examined through mapping of decadal trends using a quantile analysis method. The results indicate that the dynamics of river discharge has evolved varyingly across different river basins. The evolution pattern within a basin generally agrees with that at the basin outlet, but notable exceptions are found, indicating high hydro-climatic heterogeneity within the basins. The decadal evaluation of flood dynamics over major flooded areas suggests that inundation dynamics is strongly influenced by various flow characteristics, including the timing, duration, and magnitude, and that the evolution of flood dynamics is more complex than that of river discharge. Results indicate that the TWS dynamics over entire Nepal is strongly modulated by the variations in subsurface water storage, and groundwater storage has been in continuous decline (-1.74 cm/year) in the recent decades (2002–2016). This study provides a basis to advance the understanding of long-term hydrologic changes in the Himalayan region with important implications for improved water resources management.

Icing - Renewable Water Source and Resource

The icing phenomena occurs in Mongolia every winter, same places where groundwater overflow on ice on surface waterbed, create next ice sheet and create extended ice storage. This phenomenon is important parameters in hydrological cycle and surface water regime for semi-arid, cold regions. The highly continental, semi-arid and cold region has a high variability in river discharge depending on precipitation, with a general tendency towards decreasing water availability due to increasing air temperatures and thus rising potential evaporation. In this study considered understanding natural process of creating icing, due to keep water source as in ice form on surface in dry season. From March to May icing meltwater recharge groundwater and river flow while river is non-flow condition. Some year’s in April riverbed dry without ice in valley under highly mountains, but upper side is cold and water source is still in snow and ice form. Therefore, icing in river valley could recharge surface water by melting where is cold on top mountains river origin but under valley riverbed no snow, ice cover. In this paper written icing process code by MATLAB using energy change between water, air and ice. When we are promoting naturally ice storing or build icing then winter coldness creates ice storage thus artificially recharge surface water resources in dry season like April. The ice storage amount and simulation results shown that recharge groundwater in dry season is icing method one of the possibilities which creates and build huge ice storages in winter. That is new technology keep water in ice form through winter and recharge surface and groundwater in dry season.

Saline intrusion in the Ganges-Brahmaputra-Meghna megadelta

In the fertile Ganges-Brahmaputra-Meghna (GBM) delta, which spans the boundary from West Bengal in India and Bangladesh, the availability of freshwater is crucial to subsistence livelihoods and protected ecosystems. Controlled by large tides and widely variable river discharge, the delta experiences rising river salinity and salt intrusion, as well as seasonal flooding during the monsoon.Future climate change is projected to increase rainfall in South Asia and river discharge in the GBM system. We address how this process might combine with sea-level rise (SLR) to control future river salinity. Model experiments designed using a range of SLR and climate change scenarios are performed to investigate the forces controlling river salinity in the delta. A flexible mesh modelling approach allows us to investigate the impacts at a wide range of time and space scales.In future projections the disparity between wet and dry season salt intrusion intensifies. In the future, SLR acts to increase river salinity in the GBM delta. During the dry season, this effect is worsened by reduced river discharge. In the wet season, this can be mitigated in the eastern part of the delta by larger seasonal river flows. The central and western delta is dominated by SLR, leading to increased salt intrusion all year round, impacting on water resources and agricultural productivity. In the context of an intensifying hydrological cycle, these conclusions have implications for similar tide-dominated deltas, where SLR can increase tidal range, and therefore exacerbate salt intrusion.

Testing hypotheses on signatures of precipitation variability in the river and floodplain deposits of the Paleogene San Juan Basin, New Mexico, U.S.A.

ABSTRACTMuch progress has been made in recent years towards a set of recognition criteria for river discharge variability in river channel deposits, and thus sedimentary proxies for precipitation variability. Despite this progress, there is currently no consensus on how different styles of discharge variability are reflected in river sedimentary records, and whether variable-discharge river records from different climate types can be distinguished. Herein, river discharge and precipitation variability in the Paleogene is investigated using associations between river channel and floodplain deposits across the Paleocene–Eocene boundary from the Paleocene upper Nacimiento Formation and the early Eocene San Jose Formation in the San Juan Basin, New Mexico, USA.The succession is identified as deposits of variable-discharge river systems based on shared channel-deposit characteristics with modern and ancient variable-discharge river systems and the proposed facies models, in addition to alternations of poorly drained and well-drained floodplain deposits and/or slickensides indicating alternating wet–dry cycles. A long-term stratigraphic trend toward increasingly well-drained floodplain deposits is also observed and hypothesized to indicate successively more arid conditions from the Paleocene into the early Eocene. Comparisons with modern rivers from various climate zones suggest a long-term shift from a monsoonal climate in the Paleocene, to a fluctuating subhumid climate, ultimately leading to semiarid to arid conditions in the early Eocene. These observations suggest that floodplain deposits may be a better indicator of ambient climate, whereas channel deposits are records for frequency and magnitude of high-intensity precipitation events. Therefore, the existing facies models for variable-discharge rivers that consider only channel facies may not capture critical information needed to make accurate interpretations of paleoclimatic conditions. This study also adds to a growing body of evidence from geologic records of mid-latitude Paleogene river systems suggesting increases in the magnitude or variability of river discharge coinciding with established climate perturbations.

Morphological behavior of the Magdalena River delta (Colombia) due to intra and interannual variations in river discharge

Morphological conditions of river deltas define the sedimentological processes of this kind of ecosystem, which are strategic points to locate transport infrastructures, such as ports. River deltas can present morphological variations caused by natural or anthropogenic factors, affecting the navigability conditions of cargo ships. In order to guarantee feasible conditions for the navigability of river deltas and reduce economic costs caused by dredging activities, further studies are required to assess the relationship between hydrological and hydrodynamic processes with the morphodynamic behavior along the river basin. This study evaluates the hydrodynamic and morphodynamic conditions of the Magdalena River delta (Colombia) based on river discharges, water levels, and bathymetric information for the period 2006–2012. Moreover, linear-time-invariant systems (LTI) was developed to perform correlation analysis between the climatic oscillations, such as the ENSO, and the water level conditions in the Magdalena River. The bathymetric analysis showed unsteady morphological conditions along the river bed and high erosion rates during the studied period. The delta presented sedimentation conditions during El Niño years, or periods with negative discharge anomalies, and erosion rates during La Niña years, or periods with positive discharge anomalies. For intrannual scales, dry periods (January–April) presented sedimentation trends, whereas wet periods (September–December) exhibited significant erosion trends.

Multi-century tree-ring anatomical evidence reveals increasing frequency and magnitude of spring discharge and floods in eastern boreal Canada

Abstract In eastern boreal Canada, variability in river discharge is poorly understood at the multi-century scale due to short instrumental records. In recent decades, increased magnitude and frequency of spring floods have raised concerns about the potential effects of climate change on flood risk. Unlike tree-ring width, flood rings have a demonstrated dendrochronological utility for reconstructing high discharge in boreal environments. In this study, twelve chronologies of earlywood vessel cross-sectional area (a new hydrological proxy) and ring width were developed from riparian Fraxinus nigra trees periodically flooded in spring. These chronologies were used as predictors of Harricana River spring discharge, which was reconstructed for the period 1771–2016. The reconstruction captured 69% of the variance over a 102-year calibration period. The reconstruction indicates that the magnitude and frequency of spring high discharge has increased since the end of the Little Ice Age (1850–1870 CE) and since 1950. The change from a multi-decadal frequency in the late 19th century to a decadal and then interannual frequency in the late 20th century is associated with an increase in snow cover over much of central-eastern Canada. The association between the reconstructed spring discharge and spring atmospheric circulation indices NINO3.4, AMO, NAO may also have changed in these periods and further work is needed to assess the stability of these associations. The correlation between reconstructed and instrumental spring discharge at the regional scale, as well as the shared features in reconstructed discharge and other paleorecords from subarctic Quebec suggest a common hydrological signal across the study area and for the early 20th to 21st centuries. The unprecedently low and high spring discharge in recent decades compared to the historical natural variability of the last 250 years also suggests that the increase in flood frequency and magnitude originates from climate change.

Evaluation of decadal shoreline changes along the Parnaíba Delta (NE Brazil) using satellite images and statistical methods

This study investigated changes of the shoreline position in the Parnaíba River Delta (PRD), which is in an underdeveloped and sparsely populated area. The general behavior of the shoreline between 1984 and 2017 was analyzed using 12 Landsat satellite images and the Digital Shoreline Analysis System (DSAS) software. DSAS applied statistical methods, such as Weighted Linear Regression (WLR) and End Point Rate (EPR), to define whether the shoreline was retreating or accreting.Data analysis revealed that, on a decadal time scale (33 years), 52% of the PRD shoreline retreated under erosional conditions, while 48% accreted. Accretion mainly occurred at the vicinities of the river mouth, especially eastward where the highest progradation rate was observed (maximum of 29 m/year). Shoreline retreat, up to 9 m/year, occurred predominantly in the western part of the PRD and away from the river mouth.However, changes of the general behavior of the shoreline (retreat/accretion) were observed at an interdecadal time scale, which were positively related to variations in river discharge. Variations of river discharge are directly dependent on the rainfall amount along the drainage basin that, in this region, is controlled by climatic conditions such as El Niño and La Niña. Therefore, the reduced river discharge observed between 1995-1999 and 2009–2012 (El Niño periods), was the major cause the triggered the observed coastal retreat (>6 m/year) on PRD shoreline during these periods.Consequently, the variability of natural factors, such as river discharge and rainfall, are the main drivers of shoreline changes on PRD, since anthropogenic impacts have hitherto only marginal effects on the delta region and on the drainage basin of the Parnaíba river.

Study on Relationship of Land Cover Changes and Ecohydrological Processes of the Tuul River Basin

The Tuul River Basin is the most important socioeconomic and political base area of Mongolia. Therefore, studying the interrelationships between changes in the ecohydrological processes of this basin and its land cover is of great importance for maintaining sustainability and the environment. This study investigated the annual average air temperature, total annual precipitation, and river discharge variability, and land cover changes at selected stations of the basin by using the hydrometeorological analysis, satellite analysis, and land cover determination statistical analysis. During the study period, the average annual air temperature rose from −1.5 °C to +0.3 °C (1.8 °C 361 °C). The average annual precipitation exhibits relatively low change during this period. River discharge varied during the study period. A significant decreasing trend in river discharge was observed at the Terelj (φ = −2.72) and Ulaanbaatar (φ = −5.63) stations, whereas the other stations, Altanbulag, Lun, and Orkhontuul, showed a significant increasing trend. During the study period, changes in land cover were directly related to main hydrometeorological parameters. Between 2000 and 2020, the amount of grassland decreased by 319.67 km2, while the area of water bodies increased by 28.36 km2. In the study area, mainly water bodies and sensitive areas of the land cover types were changed due to changes in precipitation. Studies in the arid and semiarid regions of Central Asia show that changes of ecohydrological processes have a significant impact on land cover changes.

Climate Control of Multidecadal Variability in River Discharge and Precipitation in Western Europe

The influence of large-scale climate variability on winter river discharge and precipitation across western Europe is investigated. We analyze 60 years of monthly precipitation and river flow data from 18 major western-European rivers and its relationship with dominant teleconnection patterns and climate indices in this region. Results show that winter river flow is characterized by large interannual variability, best correlates with (a) the North Atlantic Oscillation (NAO) at the far-northern (R up to 0.56) and southern latitudes (R up to −0.72), and (b) the West Europe Pressure Anomaly (WEPA) at the middle and northern latitudes, from 42° N to 55° N (R up to 0.83). These indices also explain the interannual variability in autumn and spring discharge in rivers characterized by secondary floods. Compared to the other leading modes of atmospheric variability, WEPA increases the correlations with winter precipitation up to 0.8 in many regions of western and central Europe. A positive WEPA corresponds to a southward shift and an intensification of the Icelandic-Low/Azores-High dipole, driving enhanced precipitation and river discharge in these regions. The correlations with precipitation are slightly higher than those with river discharge, particularly in France, with clear latitudinal gradient. This trend suggests that water storage variability and other catchment characteristics may also influence the interannual variability of river discharge. Seasonal forecasting of the WEPA and NAO winter indices can become a powerful tool in anticipating hydrological risks in this region.

Remote Sensing of Spatial-Temporal Variation of Chlorophyll-a in the Jiaozhou Bay Using 32 Years Landsat Data

Wu, M.; Zhao, Y.F.; Sun, L.E.; Huang, J.; Wang, X.H., and Ma, Y., 2020. Remote sensing of spatial-temporal variation of chlorophyll-a in the Jiaozhou Bay using 32 years Landsat data. In: Jung, H.-S.; Lee, S.; Ryu, J.-H., and Cui, T.W. (eds.), Advances in Geospatial Research of Coastal Environments. Journal of Coastal Research, Special Issue No. 102, pp. 271-279. Coconut Creek (Florida), ISSN 0749-0208.The chlorophyll-a concentration (Chla, µg/L) is a vital indicator of water quality and eutrophication, yet optical complexity and significant variability of coastal waters make the accurate estimation of Chla challenging. Monitoring spatial-temporal distribution and variation of Chla and comprehending the correlation between Chla and environmental factors are necessary for long-term water quality assessment. This study calibrated and validated the Chla estimation model with satisfactory performance (R2, RMSE, and MRE values are 0.77, 0.64 µg/L, and 32.5 %) and further characterized the spatial-temporal variation of Chla in Jiaozhou Bay (JZB) based on 381 cloud-free Landsat images of 32 years (1986-2017). The annual mean Chla in JZB reached the highest value in 1997 and decreased gradually in the following two decades. The seasonal variation of Chla is obvious: the highest value of Chla appeared in summer, followed by spring, autumn and winter. Accordingly, the monthly averaged Chla peaked in July, while the minimum occurred in January. The spatial distribution of Chla on different time scales shared a similar pattern. High Chla appeared in the northwestern part of JZB and decreased gradually to the southwest, resulting in the lowest Chla near the water channel connected to the open sea. The spatial heterogeneity mainly arose from river discharge, while the temporal heterogeneity may be caused by seasonal variations in precipitation, temperature, and river discharge. This study indicated that the empirical models for the Landsat data could effectively monitor the long-term Chla variation in JZB.

Temporal Variations in Rainfall and Temperature and their Effects on the River Discharge in the Mara River Basin

The Mara River basin is one of the important transboundary resources in Eastern Africa that not only serve Kenya and Tanzania where it is located as one of the waterheads but also serve the lower countries of Sudan and Egypt. Variations in weather conditions, especially rainfall and temperature in the basin have impacts beyond the basin. The environmental processes that relate to variation in weather conditions include river flow regimes, vegetation cover, agro-calendar and wildlife. This paper looked at how variations in rainfall and temperature affect the river discharge in the Mara basin in order to determine the nature of rainfall and temperature variations in relation to river discharge in the basin. Observed long-term daily rainfall, temperature and river discharge covering 1983 – 2014 period, are used in time series analyses to measure periodicity and trend in rainfall, temperature and river discharge. The relationship between river discharge and the weather elements is determined using linear correlation analysis and multiple regression procedures at ? = 0.05. The results of the data analysis reveal that, the long-term variations in temperature, rainfall and river discharge are such that temperatures are tending toward increase while rainfall and river discharge are tending towards decline. Further, variations in rainfall and temperature conditions indicate un-seasonality in the timing and duration of monthly variations. The variations in rainfall, temperature and discharge series are statistically not significant (Mann Kendall trend test). The relationship between variations in rainfall and temperature with river discharge is that rainfall has stronger linear correlation with river discharge than temperature and therefore declining trends in rainfall are causing reduction in river discharge in the Mara basin. Measures should, therefore, be taken to reduce activities in the basin that are likely to impact on rainfall and temperature such as deforestation and encroachment on the water towers.

A numerical model study of the main factors contributing to hypoxia and its interannual and short-term variability in the East China Sea

Abstract. A three-dimensional physical-biological model of the marginal seas of China was used to analyze interannual and intra-seasonal variations in hypoxic conditions and identify the main processes controlling their generation off the Changjiang (or Yangtze River) estuary. The model was compared against available observations and reproduces the observed temporal and spatial variability of physical and biological properties including bottom oxygen. Interannual variations of hypoxic extent in the simulation are partly explained by variations in river discharge but not nutrient load. As riverine inputs of freshwater and nutrients are consistently high, promoting large productivity and subsequent oxygen consumption in the region affected by the river plume, wind forcing is important in modulating interannual and short-term variability. Wind direction is relevant because it determines the spatial extent and distribution of the freshwater plume, which is strongly affected by either upwelling or downwelling conditions. High-wind events can lead to partial reoxygenation of bottom waters and, when occurring in succession throughout the hypoxic season, can effectively suppress the development of hypoxic conditions, thus influencing interannual variability. A model-derived oxygen budget is presented and suggests that sediment oxygen consumption is the dominant oxygen sink below the pycnocline and that advection of oxygen in the bottom waters acts as an oxygen sink in spring but becomes a source during hypoxic conditions in summer, especially in the southern part of the hypoxic region, which is influenced by open-ocean intrusions.

Influence of Seasonal River Discharge on Tidal Propagation in the Ganges‐Brahmaputra‐Meghna Delta, Bangladesh

AbstractSignificant research efforts have been devoted to understanding river‐tide interactions in estuaries. However, studies on the impact of monsoon‐driven fluctuations of river discharge are limited. Here, the role of varying river discharge on the tidal propagation and tidal limit along the Ganges‐Brahmaputra‐Meghna Delta (GBMD), a macrotidal estuary subject to seasonal and annual river discharge variations, is investigated. The Delft3D hydrodynamic model is validated and applied to an average flood year condition and nine idealized scenarios covering the typical hydrological conditions. Results reveal that the upper limit of the tidal propagation shifts 75 km upstream during the dry season. The residual water level slope and tidal damping rate increase with river discharge beyond 100 km from the estuary mouth. The balance between the generation and dissipation of quarterdiurnal tides shifts spatially as a result of changes in channel convergence and friction and temporally as a function of river discharge, which controls the total friction in the upper tidal river. The balance between tidal dissipation and generation depends on the residual velocity generated by river discharge and the velocity of the principal tides. The maximal generation of quarterdiurnal tides in the upper GBMD depends on the friction generated from the river‐tide interaction. Critical river discharge thresholds produce an optimal condition of dissipation of semidiurnal tides and generation of quarterdiurnal tides through friction at the upper and middle estuary. River discharge above the critical river discharge amount more rapidly dissipates both semidiurnal and quarterdiurnal tides than generates quarterdiurnal tides from nonlinear interactions.

Holocene Climate Modulates Mud Supply, Transport, and Sedimentation on the East China Sea Shelf

AbstractShelf mud is an important sink for fluvial sediment, and it is sensitive to variations in river discharge and ocean circulation, which are significantly influenced by climate change. However, the evolution of shelf mud in response to climate change during the Holocene is poorly understood. Here, we present high‐resolution sedimentary records of heavy minerals and mass accumulation rates (MARs) from the East China Sea shelf to study the response mechanisms of the Holocene shelf mud supply, transport, and sedimentation to the climate‐driven variations in fluvial discharge and ocean currents. The results indicate that the shelf mud primarily originates from the Changjiang (Yangtze) River and has been mainly transported by wind‐driven longshore currents in suspension since approximately 8.0 ka. A comparison of the MARs with several shelf mud sedimentation‐rate records and climate changes during the Holocene on millennial timescales showed that strong (weak) precipitation in the river basin, which is positively linked with Asian summer monsoon and El Niño‐driven storms, could intensify (weaken) the fluvial sediment supply, thereby increasing (decreasing) the shelf mud deposition flux. On multicentennial timescales, changes in the relative intensities of different ocean currents due to climate oscillations during the Holocene could generate frequent migrations of the current shear front (a hydrodynamic barrier), which has trapped an abundance of suspended materials on the shoreward side and resulted in rapid mud sedimentation (~2.3 g/cm2/year) at different sites during different periods. Therefore, our study highlights that the Holocene shelf mud evolution responds sensitively to climate changes on different timescales.

Trends and Variability of Precipitation: Implications for Water Resources in Lake Ziway Watershed, Central Ethiopian Rift

Precipitation is the significant climatic variable that governs the availability of water resources in the country, Ethiopia, but it is highly erratic and variable in spatial-temporal scales. The purpose of this paper was to analyse trends and variability of rainfall at seasonal to annual sales in the Ziway Lake Watershed. The non-parametric Mann-Kendall (MK) and Sen’s Slope (SS) estimation were used to detect the trends and compute the magnitudes of slopes respectively. The Coefficient of Variation (CV) was employed to reveal the variations in rainfall. The spatial interpolations mapping was made by using IDW (Inverse Distance Weighting). The results revealed that the western Ziway Lake watershed had experienced more rainfall variability than the eastern Ziway Lake watershed. The results also indicated that the annual and summer rainfall did not exhibit significant evidence of a monotonic trend. On the other hand, almost all rainfall stations in the spring season revealed decreasing trends (significant and non-significant), for instance, there are three stations (Ogalcho, Butajira, and Koshe) showed significantly decreasing trends at 5% of significant level and the two stations (Kulumsa and Meki) indicates significantly decreasing trends at 10% significant level. Moreover, the magnitudes of slope (changes in mm/year) estimated by SS for stations in the spring season that display significantly decreasing trends were as follows: -8.702, - 6.58, -4.018, and -3.681,-3.667 for Butajira, Koshe, Kulumsa, Ogalcho, and Meki respectively. Droughts can be expected to increase if the decline precipitation trend continues. This could lead to over-exploitation of the water resources. The similarities in patterns of the intra-annual variability of precipitation and river discharges imply that any changes in rainfall pattern would have effects on water availability. The results of this investigation can significantly contribute to guiding water managers and decision-makers for more efficient water resources planning and management. Keywords: Central Ethiopian Rift,, Ziway Lake Watershed, Precipitation, Variability, Trends DOI: 10.7176/JEES/10-10-03 Publication date: October 31 st 2020

Impact of the Monthly Variability of the Trent River on the Hydrodynamical Conditions of the Bay of Quinte, Ontario: A Case Study 2016–2019

The spatial and temporal (monthly) variability of river discharge has a significant effect on circulation and transport pathways within shallow embayments whose dynamics are largely controlled by wind and riverine inputs. This study illustrates the effects of the monthly variation in Trent River discharge on simulated particle transport and settling destination in the Bay of Quinte, Lake Ontario for the years 2016–2019. Observations of Lagrangian surface drifter data were used to derive Trent River discharge forcing for a three-dimensional hydrodynamic numerical model of the Bay of Quinte. Peak monthly flushing was up to three times as much as the lowest monthly flushing in any year, with the Trent River responsible for up to 95% of the flushing in low runoff years. Particle transport simulations showed that particles could be trapped along shorelines, which extended residence times, and Trent River releases suggest that researchers should look for delayed peaks in Total Phosphorous (TP) load measurements in observations between Trenton and Belleville as particles move downstream. Particles with constant settling velocities originating from the Trent River did not move downstream past Big Bay, and particles from the Napanee River were the primary source for Longreach.