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

Water ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 647
Author(s):  
Luc Descroix ◽  
Yancouba Sané ◽  
Mamadou Thior ◽  
Sylvie-Paméla Manga ◽  
Boubacar Demba Ba ◽  
...  
Keyword(s):  
West Africa ◽  
Fresh Water ◽  
Water Discharge ◽  
West African ◽  
Water Salinity ◽  
Dry Period ◽  
Senegal River ◽  
Inverse Estuary ◽  
Fresh Water Discharge ◽  
Rainfall Level

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.

scholarly journals Analytical approach for determining the mean water level profile in an estuary with substantial fresh water discharge

2016 ◽  
Vol 20 (3) ◽  
pp. 1177-1195 ◽  
Author(s):  
Huayang Cai ◽  
Hubert H. G. Savenije ◽  
Chenjuan Jiang ◽  
Lili Zhao ◽  
Qingshu Yang
Keyword(s):  
Water Level ◽  
Fresh Water ◽  
River Discharge ◽  
River Flow ◽  
Water Discharge ◽  
Value Theory ◽  
Velocity Amplitude ◽  
Mean Water Level ◽  
The Mean ◽  
Fresh Water Discharge

Abstract. The mean water level in estuaries rises in the landward direction due to a combination of the density gradient, the tidal asymmetry, and the backwater effect. This phenomenon is more prominent under an increase of the fresh water discharge, which strongly intensifies both the tidal asymmetry and the backwater effect. However, the interactions between tide and river flow and their individual contributions to the rise of the mean water level along the estuary are not yet completely understood. In this study, we adopt an analytical approach to describe the tidal wave propagation under the influence of substantial fresh water discharge, where the analytical solutions are obtained by solving a set of four implicit equations for the tidal damping, the velocity amplitude, the wave celerity, and the phase lag. The analytical model is used to quantify the contributions made by tide, river, and tide–river interaction to the water level slope along the estuary, which sheds new light on the generation of backwater due to tide–river interaction. Subsequently, the method is applied to the Yangtze estuary under a wide range of river discharge conditions where the influence of both tidal amplitude and fresh water discharge on the longitudinal variation of the mean tidal water level is explored. Analytical model results show that in the tide-dominated region the mean water level is mainly controlled by the tide–river interaction, while it is primarily determined by the river flow in the river-dominated region, which is in agreement with previous studies. Interestingly, we demonstrate that the effect of the tide alone is most important in the transitional zone, where the ratio of velocity amplitude to river flow velocity approaches unity. This has to do with the fact that the contribution of tidal flow, river flow, and tide–river interaction to the residual water level slope are all proportional to the square of the velocity scale. Finally, we show that, in combination with extreme-value theory (e.g. generalized extreme-value theory), the method may be used to obtain a first-order estimation of the frequency of extreme water levels relevant for water management and flood control. By presenting these analytical relations, we provide direct insight into the interaction between tide and river flow, which will be useful for the study of other estuaries that experience substantial river discharge in a tidal region.

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

2017 ◽  
Vol 7 (1) ◽  
pp. 47
Author(s):  
Badrudin Badrudin ◽  
Bambang Sumiono ◽  
T.S Murtoyo
Keyword(s):  
Species Composition ◽  
Fresh Water ◽  
Coastal Waters ◽  
Water Discharge ◽  
Fresh Water Discharge

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.

The tidal circulation and flushing capability of the outer Tay Estuary

1980 ◽  
Vol 78 (3-4) ◽  
pp. s33-s46
Author(s):  
J. A. Charlton
Keyword(s):  
Exchange Rate ◽  
Fresh Water ◽  
Water Discharge ◽  
Hydraulic Model ◽  
Tidal Currents ◽  
Tidal Circulation ◽  
Fresh Water Discharge ◽  
Outer Estuary ◽  
Tay Estuary

SynopsisMeasurements of tidal currents in the outer Tay Estuary, and from the hydraulic model of the estuary, are used to present a tidal atlas of the area and to deduce residual tidal circulation. Additional tests on the model show that the volumetric exchange rate with the sea of the outer estuary can be as high as 58 per cent per tide, but may be lowered to about 35 per cent if multiple tide recirculation is considered. Fresh water discharge into the estuary does not materially affect this exchange rate.

Evidence of the recent decade change in global fresh water discharge and evapotranspiration revealed by reanalysis and satellite observations

2012 ◽  
Vol 48 (2) ◽  
pp. 153-158 ◽  
Author(s):  
Ki-Weon Seo ◽  
Duane E. Waliser ◽  
Baijun Tian ◽  
Baek-Min Kim ◽  
Seong-Chan Park ◽  
...  
Keyword(s):  
Fresh Water ◽  
Water Discharge ◽  
Recent Decade ◽  
Satellite Observations ◽  
Fresh Water Discharge

Prediction of salinity intrusion in Danshuei estuarine system

2008 ◽  
Vol 39 (5-6) ◽  
pp. 497-505 ◽  
Author(s):  
A. Etemad-Shahidi ◽  
A. Dorostkar ◽  
Wen-Cheng Liu
Keyword(s):  
Fresh Water ◽  
Water Discharge ◽  
Eddy Diffusivity ◽  
Turbulence Closure ◽  
Estuarine System ◽  
Salinity Intrusion ◽  
Closure Scheme ◽  
Fresh Water Discharge ◽  
Vertical Eddy Diffusivity ◽  
Vertical Eddy

The main parameters that affect the flow conditions and intrusion of salt water in an estuary system are tides and the seasonal variation of water discharge. A laterally averaged two-dimensional numerical model called MIKE 11 XZ is used to simulate the hydrodynamics and salinity intrusion of Danshuei River estuarine system. This model can simulate hydrodynamics and water quality in estuaries, reservoirs and lakes. MIKE 11 XZ solves the Reynolds-averaged Navier–Stokes equations by using Abbott–Ionescu finite difference scheme in a non-dimensional vertical σ-coordinate. Vertical eddy diffusivity in the model can be determined by a constant value, a mixing length theory and a k or k−ɛ turbulence closure scheme with Richardson number correction. A series of comprehensive field data obtained from Danshuei estuarine system is used for evaluation, calibration and verification of the model. The friction coefficient was calibrated and verified using water surface elevation and velocity measurements, respectively. Then the vertical eddy diffusivity was calibrated and verified through comparison of salinity measurements in different layers of several stations. Reasonable agreement was obtained between the model results and the observed data using k−ɛ turbulence closure scheme. The model application was investigated with different discharges and the effect of discharge variation on salinity intrusion was determined. The results showed that the fresh water discharge is the main parameter that affects the salinity intrusion in this system. Finally, simple power equations are suggested to predict the salinity intrusion due to the fresh water discharge in different tributaries of the system.

Some Aspects of the Ecology of Lake Macquarie, N.S.W., with Regard to an Alleged Depletion of Fish. II. Hydrology

1959 ◽  
Vol 10 (3) ◽  
pp. 279 ◽  
Author(s):  
RS Spencer
Keyword(s):  
Sea Level ◽  
Fresh Water ◽  
Oxygen Tension ◽  
Heavy Rainfall ◽  
Salt Water ◽  
Water Discharge ◽  
Narrow Channel ◽  
Mean Sea Level ◽  
Lake Temperature ◽  
Fresh Water Discharge

Lake Macquarie is a marine-dominated drowned valley connected to the sea by a shallow narrow channel which damps tidal oscillations from 5 ft on the coast outside to about 3 in. in the like. Superimposed on the semi-diurnal tides are changes in level in response to changes both in the external daily mean sea-level and in the volume of fresh water discharge into the lake. Temperature and chlorinity cycles are closely linked. Discharge from the creeks supplies phosphate but little nitrate for the lake. Prolonged heavy rainfall in both 1955 and 1956 produced stratification of the water associated with lowered oxygen tension in the underlying salt water. There is evidence of a wind-generated circulation within the lake.

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