The modell ing study of flow in Vasishta Godavari estuary

The v as islua branch of the Godavari estuary open s into the Bay of Bengal at Antarvedi,Conditions in the estuary arccharacterized by a seasonally varying fresh water discharge and salt water intrusionfrom the Bay resul tingfrom the flow as~oc ia ted with the se.ni- diu rnal t ide. A numerica l model is applied to simulatethe flow and sali nity structures which have also been documented m the literature. The observations duringmonsoon and post-monsoon seasons arc used in a comparison with the theor etical results which are derived froma model in which turbulenceclosure scheme is used.

Controlling the Salt Wedge Intrusion in Shatt Al-Arab River by a Barrage

Shatt Al-Arab River in Al Basrah, Iraq, has recently recorded massive levels of TDS values (Total Dissolved Solids) in the water as a result of reduced fresh water discharge from sources, causing the river to become salinized due to salt wedge intrusion. Therefore, a block dam in the south reach is required to salt intrusion prevention. The main objective of this research is to simulate the hydraulic impact of a suggested barrage in Ras Al Besha on the Shatt Al-Arab River. The HEC-RAS (5.0.7) model was used to develop a one-dimensional unsteady model to gaining an understanding of the proposed barrage's influence on river behaviour. The daily discharges of the Tigris River provided as the upstream boundary conditions, while the hourly water levels of the Shatt Al-Arab River provided as the downstream boundary conditions. The model was initially run on the basis of daily discharges in Aug 2018 and March 2020 for the model's calibration and verification. Then, a model was run with a proposed barrage, Four cases of discharge were chosen which were the low and moderate discharge that equal to (20-50-100 and 250) m3/s with adopted spring tide cycle. The operation scenarios were examined under the influence of three cases of barrage gates (fully opened, 50% open and programmed opening). The results indicate that the investigated discharges will cause a significant problems in navigation depths, especially in the case of the programming of gates opening where the stages drop range between 2.01-3.3m comparing with the normal case. Furthermore, the velocity indicators show that the significant reduction in velocity upstream the barrage led to more sedimentation in the river reach.

Trend and Variance of Continental Fresh Water Discharge over the Last Six Decades

Trend estimation of river discharge is an important but difficult task because discharge time series are nonlinear and nonstationary. Previous studies estimated the trend of discharge using a linear method, which is not applicable to nonstationary time series with a nonlinear trend. To overcome this problem, we used a recently developed wavelet-based method, ensemble empirical mode decomposition (EEMD), which can separate nonstationary variations from the long-term nonlinear trend. Applying EEMD to annual discharge data of the 925 world’s largest rivers from 1948–2004, we found that the global discharge decreased before 1978 and increased after 1978, which contrasts the nonsignificant trend as estimated by the linear method over the same period. Further analyses show that precipitation had a consistent and dominant influence on the interannual variation of discharge of all six continents and globally, but the influences of precipitation and surface air temperature on the trend of discharge varied regionally. We also found that the estimated trend using EEMD was very sensitive to the discharge data length. Our results demonstrated some useful applications of the EEMD method in studying regional or global discharge, and it should be adopted for studying all nonstationary hydrological time series.

Combined geoelectrical and geoelectromagnetic survey for contributing to local hydrogeological regime – The case study of Delfini basin (Chios isl. – Greece)

В данной статье исследуется механизм питания источников, распределенных вокруг широкой области Дельфини на северо-восточной стороне острова Хиос, в попытке найти возможные пути фильтрации пресных вод внутри острова, до того как они будут сброшены в море. Цель. Бурение гидрогеологических скважин для увеличения добычи имеет жизненно важное значение для удовлетворения потребностей в питьевой воде и ирригации широкой территории. Несмотря на то, что в последние годы на острове Хиос интенсивно бурятся скважины, потребность в дальнейших исследованиях связана с увеличением потребления воды в летнее время, с одной стороны, и неэффективностью альтернативных водных ресурсов (например, строительство плотин, опреснительных установок и т.д.), с другой стороны. Методы. Геофизические методы (низкочастотная электроразведка и удельное сопротивление) использовались для детального изучения областей водного потенциала, таких как наиболее широкая область Дельфини, где в зимнее время огромное количество пресной воды сбрасывается через источники до уровня моря. Результаты и их обсуждение. Наличие ограниченного водоносного горизонта, состоящего в основном из известняков, которые перекрыты обломочными непроницаемыми отложениями, а также наличие разрывных зон, несущих водный потенциал, определяют гидрогеологический режим близлежащего района. Это также объясняется наличием солоноватых вод на положительных высотах, обнаруженных в летнее время в близлежащих источниках. По-видимому, боковая протяженность непроницаемых обломочных отложений играет решающую роль, позволяя внутреннему стоку морской воды в летнее время и в сочетании с наличием ограниченного водоносного горизонта пресной воды создавать восходящий смешивающийся поток пресной и морской воды в источниках возвышенностей. В зимнее время огромное количество оттока пресной воды не позволяет внутреннему притоку морской воды In this paper the feeding mechanism of springs distributed around the broader area of Delfini at NE side of Chios Island is explored, in an effort to locate possible fresh water paths inland before they are discharged to the sea. The drilling of hydro wells for more production is of vital importance to cover the drinking and irrigation needs of the broader area. Aim. Although Chios has been extensively drilled in the past years the demand for further investigations comes from an increased water consumption during summer time in one hand and the inefficiency of alternative water resources (e.g. construction of dams, desalination units, etc) on the other hand. Methods. Geophysical methods were used (VLF and resistivity) to explore in detail water potential areas, like the broader area of Delfini, where during winter time huge quantities of fresh water discharge through springs to sea level. Results and its discussion. The presence of a confined aquifer composed mainly of limestones, which are overlain by clastic impermeable deposits, together with the existence of water potential bearing fracture zones determine the hydrogeological regime of the nearby area. It is also explained the presence of brackish waters at positive elevations found during summer time at nearby springs. It seems that the lateral extent of impermeable clastic deposits plays a crucial role in allowing the inland flow of seawater during summer time and combined with the presence of the confined aquifer of fresh water produce an upward mixing flow of fresh and seawater at springs of positive elevations. During winter time the huge amount of fresh water discharges do not allow the inland flow of seawater

Inverse Estuaries in West Africa: Evidence of the Rainfall Recovery?

In West Africa, as in many other estuaries, enormous volumes of marine water are entering the continent. Fresh water discharge is very low, and it is commonly strongly linked to rainfall level. Some of these estuaries are inverse estuaries. During the Great Sahelian Drought (1968–1993), their hyperhaline feature was exacerbated. This paper aims to describe the evolution of the two main West African inverse estuaries, those of the Saloum River and the Casamance River, since the end of the drought. Water salinity measurements were carried out over three to five years according to the sites in order to document this evolution and to compare data with the historical ones collected during the long dry period at the end of 20th century. The results show that in both estuaries, the mean water salinity values have markedly decreased since the end of the drought. However, the Saloum estuary remains a totally inverse estuary, while for the Casamance River, the estuarine turbidity maximum (ETM) is the location of the salinity maximum, and it moves according to the seasons from a location 1–10 km downwards from the upstream estuary entry, during the dry season, to a location 40–70 km downwards from this point, during the rainy season. These observations fit with the functioning of the mangrove, the West African mangrove being among the few in the world that are markedly increasing since the beginning of the 1990s and the end of the dry period, as mangrove growth is favored by the relative salinity reduction. Finally, one of the inverse estuary behavior factors is the low fresh water incoming from the continent. The small area of the Casamance and Saloum basins (20,150 and 26,500 km² respectively) is to be compared with the basins of their two main neighbor basins, the Gambia River and the Senegal River, which provide significant fresh water discharge to their estuary.

ĐẶC ĐIỂM FRONT NHIỆT MẶT BIỂN VÙNG BIỂN ĐÔNG NAM VIỆT NAM

This paper presents an investigation of sea surface temperature front in the Southeast region of Vietnam using daily NOAA satellite images in April (dry season) and September (rainy season) for a period from 1985 to 2009. The method of Cayula and Cornilon (1992) for detecting the thermal front from satellite images was applied to evaluate the characteristics of the sea surface temperature front in the study area. The main features in front distribution, seasonal variations were described, and the relationship between front locations and fresh water discharge from Mekong river was qualitatively analyzed.

Total Biomass and Carbon Estimates in Mangrove Species of Bhitarkanika Wildlife Sanctuary (BWLS), Odisha

We estimated total biomass and total carbon in 18 selected woody mangrove species based on the IVI values along with physico-chemical parameters of sea water and soil. AGB and BGB values were calculated as per the standard protocol in BWLS in five sampling stations namely Dangmal, Bhitarkanika, Habalikhati, Ekakula and Gupti. The highest values of IVI were noted for E. agallocha followed by A. officinalis, A. marina, H. fomes and C. decandra. Total biomass of species range was found to be varying between 0.69 tha-1 in X. molluccensis and 2122.17 tha-1 in A. officinalis. Total site-wise biomass ranged between 0.22 tha-1 in B. cylindrica at Gupti and 1419.26 tha-1 in A. officinalis at Bhitarkanika. Total carbon was considered to be 50% of total dry biomass which varied from 188.45±21.87 tha-1 at Ekakula to 941.31±201.17 tha-1 at Bhitarkanika, respectively. The higher biomass and carbon in A. officinalis proves it to be highly adaptive to the environmental changes in the present geographical locale. The maximum biomass and carbon of all the mangrove species in station Bhitarkanika is due to the fact that this station receives the fresh water discharge of Baitarani river thereby the adequate lower salinity is maintained. The present study reveals that mangroves of Bhitarkanika Wildlife Sanctuary can store substantial amount of atmospheric carbon and therefore needs to be conserved and sustainably managed.

Investigation of Salt Intrusion Condition in the Belat Estuary

Awareness on salt intrusion problem is still lacking in Malaysia due to high precipitation in the region. However, the El-Nino phenomenon that occurred recently has caused extremely low fresh water discharge in the Kuantan River which allowed the sea water to intrude further into its water intake region. Consequently, the Belat River may become potential water resources alternative to build new water intake station for the water supply in the Kuantan River Basin. The aims of this study are to: 1) investigate the salinity distribution in the Belat Estuary; 2) evaluate the applicability of the 1-D analytical salt intrusion solution; 3) determine the calibration parameters in the salt intrusion model. Salt intrusion measurements was conducted during the dry season at spring tide when the fresh water discharge is the minimum. Collection of data such as hydrological data, river cross section and salinity were collected to be used in the salt intrusion analysis. The results obtained show good agreement between the simulated and observed salinity distribution in the estuary with low RMSE and high NSE values. This indicates that the model is reliable and can become an important tool for water manager in conducting salt intrusion study for this area.

SPECIES COMPOSITION AND DIVERSITY OF TIDAL TRAP NET CATCHES IN THE WATERS OF INDRAGIRI HILIR, RIAU, INDONESIA

The coastal waters of the eastern part of lndragiri Hilir, Riau, which are mostly estuarine, are influenced by the huge fresh water discharge and are usually fertile.

Characteristics of meltwater export from Jakobshavn Isbræ and Ilulissat Icefjord

ABSTRACT Jakobshavn Isbræ, which terminates in Ilulissat Icefjord, has undergone rapid retreat and is currently the largest contributor to ice-sheet mass loss among Greenland's marine terminating glaciers. Accelerating mass loss is increasing fresh water discharge to the ocean, which can feed back on ice melt, impact marine ecosystems and potentially modify regional and larger scale ocean circulation. Here we present hydrographic observations, including inert geochemical tracers, that allow the first quantitative description of the glacially-modified waters exported from the Jakobshavn/Icefjord system. Observations within the fjord suggest a deep-reaching overturning cell driven by glacial buoyancy forcing. Modified waters containing submarine meltwater (up to 2.5 ± 0.12%), subglacial discharge (up to 6 ± 0.37%) and large portions of entrained ocean waters are seen to exit the fjord and flow north. The exported meltwaters form a buoyant coastal gravity current reaching to 100 m depth and extending 10 km offshore.