Salinity Intrusion into Multi-Port Sea Outfalls

Sea water intrusion into the diffuser system of a long sea outfall is likely to reduce the efficiency of the outfall. Recent surveys have revealed outfalls with a significant proportion of their diffuser blocked, and others discharging through as few as 50% of their diffuser ports. It is suspected that intrusion is the cause of these malfunctionings. Intrusion may be encouraged by the design requirement of low efflux velocities to obtain optimum dilution, or by over-design to cater for future increases in discharge. Although intrusion can only commence at low discharge velocities, when a port Densiometric Froude number falls below about 1, once it has started sea water will continue to enter the diffuser system until a state of balance is reached. Subsequently a considerably greater flow will be required to purge the outfall of all sea water. Intrusion may also be prematurely triggered by wave action, currents, or by reduced flow through a damaged port. Hydraulic model tests at the University of Dundee are leading to an understanding of the intrusion mechanism as it affects the various diffuser systems in current use. A continuing research and site survey programme is aimed at design recommendations to eliminate intrusion or reduce its effects.

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Historic drought and salinity intrusion in the Mekong Delta in 2016: Lessons learned and response solutions

Vietnam Journal of Science Technology and Engineering ◽

10.31276/vjste.59(1).93 ◽

2017 ◽

Vol 59 (1) ◽

pp. 93-96 ◽

Cited By ~ 8

Author(s):

Ngoc Anh Nguyen ◽

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Keyword(s):

Mekong Delta ◽

Lessons Learned ◽

Salinity Intrusion

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Sludge Disposal to Sea in South Africa

Water Science & Technology ◽

10.2166/wst.1982.0013 ◽

1982 ◽

Vol 14 (3) ◽

pp. 93-107 ◽

Cited By ~ 2

Author(s):

D C Macleod

Keyword(s):

Public Health ◽

South Africa ◽

Marine Environment ◽

Industrial Waste ◽

Domestic Sewage ◽

Monitoring Programme ◽

Environment And Public Health ◽

Research Project ◽

Sludge Disposal ◽

Sea Outfalls

The performance of two sea outfalls that have been in operation off the coast of Durban for over 10 years has been monitored for effects on the marine environment and public health. The discharge has been a mixture of domestic sewage and industrial waste from which a large proportion of the sludge has been removed but a 2-year research project, in which the balance of the sludge is also being discharged, has commenced. Performance of the outfalls and details of the monitoring programme are reviewed.

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A Survey for Salinity Intrusion and Pollution Assessment in Maputo Estuary

Water Science & Technology ◽

10.2166/wst.1987.0260 ◽

1987 ◽

Vol 19 (5-6) ◽

pp. 823-832 ◽

Cited By ~ 1

Author(s):

J. M. Salomão

Keyword(s):

Dissolved Oxygen ◽

Industrial Wastewater ◽

Pollution Assessment ◽

Saturation Level ◽

Salinity Intrusion ◽

Pollutant Load ◽

Oxygen Levels ◽

Salinity Gradients

Following surveys recently carried out in Maputo estuary, a survey with the purpose of acquiring data required to characterize the estuary was carried out in December 1983. After reviewing the hydrology of the tributaries to the estuary, the parameters to be monitored - salinity, conductivity, temperature, and dissolved oxygen, are referred. Finally, taking also into account previous information available, an evaluation of the results, and an assessment of the estuary are done. The estuary can be classified as well mixed, since the vertical salinity gradients found are small. The Umbeluzi estuary, however, is partially mixed. Temperature decreases with the depth, and when moving downstream. Some pollution was found along the lower part of the estuary, probably due to the discharge of domestic and industrial wastewater, which brings the dissolved oxygen figures below the saturation level. As for the upper part of the estuary, the dissolved oxygen levels are not only dependent on the pollutant load, but also on the growing of algae, which by photosynthesis under daylight produce oxygen that dissolves into the water. Quite often, the dissolved oxygen figures are above the saturation level. The growth of algae could be due to the input of phosphorus and nitrogen brought in by the tributary streams. A pollutant load discharged upstream could be the reason for some pollution seen in the Umbeluzi estuary.

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Spatio-temporal variability of the salinity intrusion, mixing, and estuarine turbidity maximum in a tide-dominated tropical monsoon estuary

Continental Shelf Research ◽

10.1016/j.csr.2021.104477 ◽

2021 ◽

pp. 104477

Author(s):

Gubash Azhikodan ◽

Nay Oo Hlaing ◽

Katsuhide Yokoyama ◽

Masashi Kodama

Keyword(s):

Temporal Variability ◽

Turbidity Maximum ◽

Estuarine Turbidity Maximum ◽

Salinity Intrusion ◽

Tropical Monsoon ◽

Spatio Temporal

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Supporting Restoration Decisions through Integration of Tree-Ring and Modeling Data: Reconstructing Flow and Salinity in the San Francisco Estuary over the Past Millennium

Water ◽

10.3390/w13152139 ◽

2021 ◽

Vol 13 (15) ◽

pp. 2139

Author(s):

Paul H. Hutton ◽

David M. Meko ◽

Sujoy B. Roy

Keyword(s):

San Francisco ◽

Tree Ring ◽

San Francisco Estuary ◽

Salinity Intrusion ◽

Estuarine Ecosystem ◽

Freshwater Flow ◽

The Past ◽

Decadal Scale ◽

Tree Ring Data ◽

Past Millennium

This work presents updated reconstructions of watershed runoff to San Francisco Estuary from tree-ring data to AD 903, coupled with models relating runoff to freshwater flow to the estuary and salinity intrusion. We characterize pre-development freshwater flow and salinity conditions in the estuary over the past millennium and compare this characterization with contemporary conditions to better understand the magnitude and seasonality of changes over this time. This work shows that the instrumented flow record spans the range of runoff patterns over the past millennium (averaged over 5, 10, 20 and 100 years), and thus serves as a reasonable basis for planning-level evaluations of historical hydrologic conditions in the estuary. Over annual timescales we show that, although median freshwater flow to the estuary has not changed significantly, it has been more variable over the past century compared to pre-development flow conditions. We further show that the contemporary period is generally associated with greater spring salinity intrusion and lesser summer–fall salinity intrusion relative to the pre-development period. Thus, salinity intrusion in summer and fall months was a common occurrence under pre-development conditions and has been moderated in the contemporary period due to the operations of upstream reservoirs, which were designed to hold winter and spring runoff for release in summer and fall. This work also confirms a dramatic decadal-scale hydrologic shift in the watershed from very wet to very dry conditions during the late 19th and early 20th centuries; while not unprecedented, these shifts have been seen only a few times in the past millennium. This shift resulted in an increase in salinity intrusion in the first three decades of the 20th century, as documented through early records. Population growth and extensive watershed modification during this period exacerbated this underlying hydrologic shift. Putting this shift in the context of other anthropogenic drivers is important in understanding the historical response of the estuary and in setting salinity targets for estuarine restoration. By characterizing the long-term behavior of San Francisco Estuary, this work supports decision-making in the State of California related to flow and salinity management for restoration of the estuarine ecosystem.

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