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Groundwater-Seawater Interactions: Seawater Intrusion, Submarine Groundwater Discharge and Temporal Variability and Randomness Effects
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Fresh groundwater quality and availability in coastal areas is affected by seawater intrusion into coastal aquifers, and coastal water quality and ecosystem status may be significantly affected by groundwater pollutants that are transported into coastal waters by submarine groundwater dis-charge (SGD). This thesis uses an overall regional perspective for investigating: i) seawater intru-sion and its possible control in sustainable coastal groundwater management; ii) SGD and its relevant quantification as one interacting part among the diverse main regional pathways of freshwater and tracer/pollutant inputs from land to sea; and iii) the integrated system functioning of both i) and ii) as main components of the same coastal groundwater system.

Results show that intensive pumping rates may be maintained for a long time before major re-gional seawater intrusion problems are recognized by too high salinities in pumped groundwater. After such late recognition, pumping wells are no longer useful and a common strategy of mov-ing groundwater pumping further upstream from the coast only increases the extent of the salt-water intrusion zone into the aquifer. An alternative strategy may be to control seawater intrusion through artificial groundwater recharge, for instance by sufficiently treated wastewater, which may considerably reduce long-term trends of salinity increase in pumped groundwater, even for small artificial recharge rates compared to pumping rates. In general, account for natural spatial-temporal variability and randomness may be essential for relevant prediction of groundwater dynamics for management purposes. Spatial and temporal randomness effects, however, may not be additive, but rather largely overlapping, with either spatial or temporal randomness being the dominating part that must be accounted for in predictive groundwater dynamics calculations. Aquifer depth is identified as an important control parameter in this context, yielding much greater temporal randomness effects in shallow than in deep aquifers.

Combined simulation results suggest a simple, approximately linear regional relationship between total SGD and its hydrologically determined freshwater component. Tidal oscillation may signifi-cantly affect such linear dependence of steady-state SGD, but primarily for low SGD conditions. High SGD appears to depend mainly on a dominant freshwater component, which effectively counteracts density-driven flow of seawater into the aquifer and thus decreases also effects of sea-level oscillation on the seawater component of total SGD. Comparative analysis between different SGD estimation methods in different reported high-SGD regions of the world indicates possible anomalously large regional SGD estimation from tracer concentrations in coastal waters, by confusing different main pathways of groundwater flow and pollutant inputs to the sea.

Place, publisher, year, edition, pages
Stockholm: KTH , 2005. , x, 21 p.
Series
Trita-LWR. PHD, ISSN 1650-8602 ; 1019
Keyword [en]
Hydraulic engineering, Seawater intrusion, submarine groundwater discharge, coastal groundwater management, coastal zone management, temporal variability, temporal randomness
Keyword [sv]
Vattenteknik
National Category
Water Engineering
Identifiers
URN: urn:nbn:se:kth:diva-222ISBN: 91-7178-027-0 (print)OAI: oai:DiVA.org:kth-222DiVA: diva2:7944
Public defence
2005-06-01, sal D3, KTH, Lindstedtsvägen 5, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20101012Available from: 2005-05-25 Created: 2005-05-25 Last updated: 2010-10-12Bibliographically approved
List of papers
1. Seawater intrusion in coastal aquifers: Effects of seasonal variations in extraction and recharge rates
Open this publication in new window or tab >>Seawater intrusion in coastal aquifers: Effects of seasonal variations in extraction and recharge rates
2001 (English)In: SWICA M3 Cyber Proceedings of First International Conference on Saltwater Intrusion and Coastal Aquifers - Monitoring, Modeling and Management / [ed] Ouazar, D. and Cheng, A.H.-D., 2001, 1-11 p.Conference paper, Published paper (Refereed)
Abstract [en]

Over-exploitation of coastal aquifers causes seawater intrusion and eventuallycontamination of groundwater wells in many parts of the world. Artificial recharge oftreated wastewater can be used to avoid or control seawater intrusion. A commoncharacteristic of many coastal areas in Southern Europe is that most of the annualwater demand, and hence the amount of water that can be used for artificial recharge,is concentrated to a few summer months, whereas natural groundwater recharge takesplace during the winter months. This paper addresses the effects of seasonal variationsin pumping, as well as in artificial and natural recharge rates on the dynamics ofsaltwater intrusion and especially on the evolution of salinity in extractedgroundwater. Specifically, numerical simulations are performed to examine theseasonal variability effects for a given set of extraction and recharge locations, but forscenarios with different artificial recharge rates. Parameter values for describing theaquifer and its hydraulic-hydrological properties are taken from a coastal aquifer inIsrael. We show that predicted salinity in extracted groundwater under assumedtemporally constant pumping and recharge conditions differs from the mean value ofsalinity under seasonally variable conditions. For long-term predictions, theassumption of temporally constant conditions may yield relatively small (less than10%) over- or underestimation of average salinity during the periodic steady-statestage that results from seasonally variable conditions. For short-term predictions, upto the common planning period of 25 years after starting a new groundwatermanagement practice, the same assumption may lead to considerable (50-55%)underestimation of maximum salinity values under seasonally variable conditions.

Keyword
Seawater intrusion, seasonal variability, artificial recharge
National Category
Water Engineering
Identifiers
urn:nbn:se:kth:diva-5140 (URN)
Note
QC 20101012Available from: 2005-05-25 Created: 2005-05-25 Last updated: 2010-10-12Bibliographically approved
2. The influence of temporal hydrological randomness on seawater intrusion in coastal aquifers
Open this publication in new window or tab >>The influence of temporal hydrological randomness on seawater intrusion in coastal aquifers
2006 (English)In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 330, no 1-2, 285-300 p.Article in journal (Refereed) Published
Abstract [en]

We investigate general effects of temporal hydrological randomness on seawater intrusion in coastal aquifers, using a 2D conceptuatization and model parameterization of three coastal aquifer zones on the Mediterranean Sea. These three aquifer cases represent quite different examples of hydrogeological conditions and temporal hydrological and groundwater management variability and statistics. A general result for all aquifer cases is that the effects of temporal randomness on expected salinity in pumped groundwater are greater for spatially homogeneous than for spatially heterogeneous aquifer representations. We quantify also prediction uncertainty around expected groundwater salinity, in terms of the salinity standard deviation and coefficient of variation (CV) in the different aquifer cases. In general, the salinity CV appears to depend much more on the aquifer depth than on the input temporal fluctuation statistics of each aquifer case. Aquifer depth may thus be a main indicator for resulting prediction uncertainty in salinity of pumped groundwater due to temporal hydrological randomness.

Keyword
seawater intrusion, temporal randomness, natural recharge, heterogeneity, Monte-Carto simulations, expected salinity, coefficient of variation
National Category
Water Engineering
Identifiers
urn:nbn:se:kth:diva-5141 (URN)10.1016/j.jhydrol.2006.03.024 (DOI)000241716300020 ()2-s2.0-33749683725 (Scopus ID)
Note
QC 20101012Available from: 2005-05-25 Created: 2005-05-25 Last updated: 2017-12-04Bibliographically approved
3. Intensive groundwater development in coastal zones and small islands
Open this publication in new window or tab >>Intensive groundwater development in coastal zones and small islands
2003 (English)In: Intensive Use of Groundwater: Challenges and Opportunities, Lisse: Balkema , 2003Chapter in book (Other academic)
Place, publisher, year, edition, pages
Lisse: Balkema, 2003
National Category
Water Engineering
Identifiers
urn:nbn:se:kth:diva-5142 (URN)9789058093905 (ISBN)
Note
QC 20101012Available from: 2005-05-25 Created: 2005-05-25 Last updated: 2010-10-12Bibliographically approved
4. On the possibility for generic modeling of submarine groundwater discharge
Open this publication in new window or tab >>On the possibility for generic modeling of submarine groundwater discharge
2003 (English)In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 66, no 1-2, 171-186 p.Article in journal (Refereed) Published
Abstract [en]

We simulate large-scale dynamics of submarine groundwater discharge (SGD) in three different coastal aquifers on the Mediterranean Sea. We subject these aquifers to a wide range of different groundwater management conditions, leading to widely different net groundwater drainage from land to sea. The resulting SGD at steady-state is quantifiable and predictable by simple linearity in the net land-determined groundwater drainage, defined as total fresh water drainage minus groundwater extraction in the coastal aquifer system. This linearity appears to be general and independent of site-specific, variable and complex details of hydrogeology, aquifer hydraulics, streamlines and salinity transition zones in different coastal systems. Also independently of site-specifics, low SGD implies high seawater content due to seawater intruding into the aquifer and mixing with fresh groundwater within a wide salinity transition zone in the aquifer. Increasing SGD implies decreasing seawater content, decreased mixing between seawater and fresh groundwater and narrowing of the salinity transition zone of brackish groundwater in the aquifer.

Keyword
coastal aquifer, coastal zone, groundwater-seawater interactions, seawater intrusion, submarine groundwater discharge
National Category
Water Engineering
Identifiers
urn:nbn:se:kth:diva-5143 (URN)10.1023/B:BIOG.0000006101.12076.10 (DOI)000186894700010 ()
Note
QC 20101012Available from: 2005-05-25 Created: 2005-05-25 Last updated: 2017-12-04Bibliographically approved
5. Quantifying hydrological and tidal influences on groundwater discharges into coastal waters
Open this publication in new window or tab >>Quantifying hydrological and tidal influences on groundwater discharges into coastal waters
2005 (English)In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 41, no 12, W12427- p.Article in journal (Refereed) Published
Abstract [en]

[1] In coastal aquifers the dynamic mixing zone between intruding seawater and fresh groundwater constitutes a zone of salinity transition that may supply brackish groundwater along with chemical tracers and nutrients to coastal waters. Tidal influence has been proposed as a possible mechanism for enhancement of recirculated seawater, total submarine groundwater discharge (SGD), and associated tracer loading through salinity transition zones into coastal waters. We show that tidal oscillation may, for relatively low SGD cases, considerably increase the average recirculated seawater component of total SGD relative to nontidal conditions. High SGD cases, however, are dominated by and require large fresh groundwater flow components also under tidal conditions; this result is obtained from a wide range of different groundwater simulation scenarios and is supported by direct comparison with field data from different reported high-SGD sites in the world. For cases with hydrologically limited fresh groundwater flow directly into the sea we propose that observed excessive coastal loading of groundwater-derived tracers may be the result of large groundwater flow and transport into unmonitored coastal stream reaches, in addition to SGD.

Keyword
sea-water, seepage, transport, aquifers, system, model, flux
National Category
Water Engineering
Identifiers
urn:nbn:se:kth:diva-5144 (URN)10.1029/2004WR003920 (DOI)000234370500001 ()2-s2.0-31544439143 (Scopus ID)
Note
Uppdaterad från "In press" till published: 20101012. QC 20101012Available from: 2005-05-25 Created: 2005-05-25 Last updated: 2017-12-04Bibliographically approved
6. Resolving the diverse pathways of freshwater and pollutant inputs to coastal waters
Open this publication in new window or tab >>Resolving the diverse pathways of freshwater and pollutant inputs to coastal waters
Show others...
2005 (English)Article in journal (Other academic) Submitted
National Category
Water Engineering
Identifiers
urn:nbn:se:kth:diva-5145 (URN)
Note
QS 2010 QS 20120319Available from: 2005-05-25 Created: 2005-05-25 Last updated: 2012-03-19Bibliographically approved

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