38:
718:
A network of 36 monitoring wells at 11 sites was installed around the island to measure the amount of water depleted from the aquifer. By the end of the drought in June 1998, the maximum thickness of the freshwater lens was about 45 feet in some wells, while one site measured a thickness as low as 18
205:
An algebraic model for estimating the thickness of a freshwater lens was developed using groundwater simulations by Bailey et al. 2008. This equation relates lens thickness to geologic and climatic factors such as island geometry, geologic composition, and recharge rate, among others. The equation is
739:
A 40 cm rise in sea level can have a drastic effect on the shape and thickness of the freshwater lens, reducing its size by up to 50% and encouraging the formation of brackish zones. Saline plumes can form at the bottom of the freshwater aquifer when the lens thickness is compromised by drought
714:
observed a noticeable decline in the thickness of the lens. After the reservoirs of the public rainfall catchment system were rapidly depleted following several months of inadequate precipitation, the islands' population began increasing the rate of groundwater pumping to the point that groundwater
735:
on the freshwater aquifer. As more and more of the potable groundwater is salinized, the populations of these islands may see a substantial reduction in available water resources. Smaller islands are at a far greater risk of extensive saltwater intrusion due to a non-linear relationship between
719:
feet. Following the resumption of the rainy season, the thickness of the lens increased by up to 8 feet in some areas, indicating that the recharge rate of freshwater lenses on atolls and small islands responds rapidly to changes in precipitation and groundwater pumping rate.
740:
and saltwater intrusion. Even after a full year of groundwater recharge, the saline plume may not completely dissipate. Sea level rise will likely lead to sustained and possibly irreparable damage to freshwater lenses due to an increase in
191:
is increased, and a thick freshwater lens is maintained through the dry season. Lower rates of precipitation or higher rates of interception and evapotranspiration will decrease the hydraulic head, resulting in a thin lens.
336:
709:
Freshwater lenses rely on seasonal rainfall to recharge the underground aquifer and can drastically change in thickness following drought or heavy rainfall. A USGS report following the 1997/1998 drought in the
603:
831:
Terry, James P., and Ting Fong May Chui. "Evaluating the fate of freshwater lenses on atoll islands after eustatic sea-level rise and cyclone-driven inundation: a modelling approach."
818:
Chui, Ting Fong May, and James P. Terry. "Influence of sea-level rise on freshwater lenses of different atoll island sizes and lens resilience to storm-induced salinization."
371:
535:
Many freshwater aquifers on atolls and small rounded islands take on the form of a Badon Ghyben-Herzberg lens. This relationship is described in the equation below:
461:
116:
786:
MCLANE, Charles. "Effect of withdrawals from a simulated island freshwater lens aquifer system: an analytic element modeling approach." McClane
Environmental, LLC.
679:
652:
181:
699:
625:
525:
505:
481:
431:
411:
391:
158:
138:
211:
527:= time parameter depicting long-term rainfall patterns with the subscripts representing different aspects of this such as region, weather pattern, etc.
540:
727:
Many of the atolls that support freshwater lenses are only a few meters above sea level and as such they are at risk of inundation due to
771:
81:
downward until it reaches the saturated zone. The recharge rate of the lens can be summarized by the following equation:
804:
Effects of the 1998 drought on the freshwater lens in the Laura area, Majuro Atoll, Republic of the
Marshall Islands
65:
that floats above the denser saltwater and is usually found on small coral or limestone islands and atolls. This
17:
791:
86:
74:
767:. Water and Environmental Research Institute of the Western Pacific, University of Guam, 2008.
484:
851:
343:
31:
436:
765:
An atoll freshwater lens algebraic model for groundwater management in the
Caroline Islands
657:
630:
70:
807:
8:
732:
463:= depth to Thurber Discontinuity (the transition between the upper and lower aquifers),
163:
684:
610:
510:
490:
466:
416:
396:
376:
184:
143:
123:
37:
711:
775:
768:
728:
188:
845:
741:
731:. However, an arguably more pressing issue facing these small islands is the
792:
http://us1media.com/PresGalleries/presdownloads/island_freshwater_lens.pdf
331:{\displaystyle Z_{max}={\frac {Y+(Z_{td}-Y)R}{B+R}}\cdot KCT_{r,s,w,y,m}}
78:
62:
744:, rendering many islands uninhabitable with the loss of potable water.
715:
supplied up to 90% of the island's drinking water during the drought.
46:
66:
808:
https://pubs.usgs.gov/sir/2005/5098/pdf/sir20055098.pdf
687:
660:
633:
613:
598:{\displaystyle H=h\cdot {\frac {P_{f}}{P_{s}-P_{f}}}}
543:
530:
513:
493:
469:
439:
419:
399:
379:
346:
214:
166:
146:
126:
89:
763:
Bailey, Ryan T., John W. Jenson, and Arne E. Olsen.
187:(m) of water. With higher amounts of recharge, the
736:island width and thickness of the freshwater lens.
433:= parameters depending on the width of the island,
693:
673:
646:
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597:
519:
499:
475:
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425:
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385:
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330:
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806:. No. 2005-5098. Geological Survey (US), 2005.
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769:http://www.weriguam.org/docs/reports/120.pdf
722:
627:= the depth of the lens below sea level,
654:= the density of the freshwater aquifer,
36:
14:
844:
507:= confining reef plate parameter, and
704:
701:= thickness of lens above sea level.
759:
757:
61:, is a convex-shaped layer of fresh
24:
531:Classic Badon Ghyben-Herzberg lens
200:
25:
863:
754:
140:is the recharge rate in meters,
742:cyclone-generated wave washover
41:A freshwater lens on an island.
825:
812:
796:
780:
265:
243:
13:
1:
747:
373:= maximum depth of the lens,
681:= density of saltwater, and
393:= annual recharge rate (m),
7:
833:Global and Planetary Change
196:Models of freshwater lenses
73:through precipitation that
10:
868:
788:2002 Denver Annual Meeting
160:is precipitation (m), and
77:the top layer of soil and
29:
27:Layer of fresh groundwater
723:Effects of sea level rise
366:{\displaystyle Z_{max}}
733:intrusion of saltwater
695:
675:
648:
621:
599:
521:
501:
487:of the upper aquifer,
485:hydraulic conductivity
477:
457:
456:{\displaystyle Z_{td}}
427:
407:
387:
367:
332:
177:
154:
134:
112:
111:{\displaystyle R=p-ET}
42:
696:
676:
674:{\displaystyle P_{s}}
649:
647:{\displaystyle P_{f}}
622:
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32:Lens (disambiguation)
820:Journal of hydrology
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59:Ghyben-Herzberg lens
30:For other uses, see
822:502 (2013): 18–26.
774:2011-07-22 at the
705:Effects of drought
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206:summarized below:
185:evapotranspiration
176:{\displaystyle ET}
173:
150:
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108:
69:of fresh water is
43:
835:88 (2012): 76–84.
802:Presley, Todd K.
694:{\displaystyle h}
620:{\displaystyle H}
593:
520:{\displaystyle T}
500:{\displaystyle C}
476:{\displaystyle K}
426:{\displaystyle B}
406:{\displaystyle Y}
386:{\displaystyle R}
283:
153:{\displaystyle p}
133:{\displaystyle R}
16:(Redirected from
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712:Marshall Islands
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201:Algebraic model
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55:freshwater lens
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18:Freshwater lens
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729:sea level rise
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189:hydraulic head
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53:, also called
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852:Hydrogeology
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58:
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75:infiltrates
63:groundwater
748:References
79:percolates
580:−
554:⋅
286:⋅
260:−
100:−
71:recharged
47:hydrology
846:Category
790:. 2002.
772:Archived
67:aquifer
607:Where
340:Where
120:Where
413:and
51:lens
49:, a
183:is
57:or
45:In
848::
756:^
483:=
689:h
667:s
663:P
640:f
636:P
615:H
588:f
584:P
575:s
571:P
564:f
560:P
551:h
548:=
545:H
515:T
495:C
471:K
449:d
446:t
442:Z
421:B
401:Y
381:R
359:x
356:a
353:m
349:Z
324:m
321:,
318:y
315:,
312:w
309:,
306:s
303:,
300:r
296:T
292:C
289:K
280:R
277:+
274:B
269:R
266:)
263:Y
255:d
252:t
248:Z
244:(
241:+
238:Y
232:=
227:x
224:a
221:m
217:Z
171:T
168:E
148:p
128:R
106:T
103:E
97:p
94:=
91:R
34:.
20:)
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