Territory Stories

East Alligator district centre water supply assessment : Kakadu National Park



East Alligator district centre water supply assessment : Kakadu National Park

Other title

D . Pidsley


Jamieson, M.; Pidsley, D.; Paiva, Jerome


E-Publications; E-Books; PublicationNT; Technical Report ; 26/1991




Made available via the Publications (Legal Deposit) Act 2004 (NT).






Water-supply -- Northern Territory -- Kakadu National Park; Groundwater -- Northern Territory -- Kakadu National Park; Kakadu National Park (N.T.)

Publisher name

Power and Water Authority

Place of publication



Technical Report ; 26/1991


1 v. : ill., maps ; 30 cm.

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Check within Publication or with content Publisher.

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Technical Report WRD91026 Viewed at 15:07:48 on 29/07/2010 Page 101 of 107. ~- . t. ' ,: 3 "I , i I 1 , I I I I I I I I I I -, ,I I I I I ./ '/ zowe o~ I I sc.KJjca o.oa /;oj I ~ I I /;-R ... f/' zo_.o,.. I':....J.:..~ a..... ""'~,...... r c>orto CrH ____ ....... j .", P / '\,: , 1--/ n ..~,...,.~11_ ... M ~ .. ,1l1j .. ":" , o o ~ ~ ~ ~ ~ ~ = = r. ........ , _c..~{........u tp4...QIr1! 2 Relat:fombip batlll!J!11 alJcallniq, earlx::n di_ ccntent and !:he oorrasivity of -~ 3. gxpnt: ~ <DRi'C6Ivlfi The deptl' an:! yield of gramdwatar rescurces in t.~ese areas vary =rtling tc locality. Depths of pro:itction bores generally ran;<! fran 10 to SliD wit..., the median depth being in the oroer of 3Qu. Potential yields .fran i"'livi~ prodIction bores can r5'9! fran less t;tw" SO '" Id (0.6 t./s) up 1:0 SOOIiD /d 3(93 t,ls) with the modian yield beL .... sane 150nu /d (17 t./s). A qrpic3l. bore """-lid <:aIt'rise a laterite pref ile to a.ba.lt 2511 (bauxite. red clay an:! sandy clay stratal wi t..~ 1 clean f sarmt.cnu over the balance of the depth. liydro:jeolccally the rescurr.:e areas have the camen:: cca:3ta1 9ramdwa ter fol.la-irg points in l. l!U;h seasonal rainfall, of ten greater than 1 "",t....,. for the period ,Januar{ to March inclusive. This llU;h seasonal rainfall results in the aquile" system being <ed'1arged anrually dJring the Vf!Jr'1 ""t hot llDnsoonal pe ... ..od _ ..aan the"" is rapid growth of ve;;;etation. These con:1l.tions are ideal for wlldirr;; up lti ccncentrations of CO:!. in the soil air as a result ef root. rItSP<raticn with sate ccntril;ution . fran the b!cte~ial decay of organic matter. :bXs and microbes charge 02 in the -soil air to cO2 ' In these envirorm!nts pert:antages of CO2 in soil air up to 25' by vol!.mB halle l:ieen reported ~ared to 1 to 2\ nOCllillly found in soU air and 0.03\ in the free atm::sphera "',. (J .. nni.-x;s. 1971). w -Utrat irg water take~, the Q:l2 into solution, part of ...,ich I'I.ac'".s vert rapidly wi th the wter to proO..lce carbonic acid as disrussed in Section 2. Because of the h i<;h ~ concentratiors in the soil air the inriltratinq ... ter l:::ecares 'Jf!r"l acidic, with a pH often as low as 4.0. 2. ;quifer systems c~risit'Y1 "'cle-an'llt sands cones Where tha cemenc bi ndinq t.."1e quar"".% grains is ,. " CQ'l"OO.Sed entirely of sllie:!.. ~tet" Lntlltratinq thrcuqn the ~turated ~ does not inc .. c4Se in haLe c s (X' salinif:l'{ since the sandstone is ceYOid of 4rr{ chemical sucstance 'oottidl may be dissol'lJEd, with th. ""ceotion of silica .... ich does not aU .. .: the acidl ty of the watar. 0i.u01.Y8d silica >m.ries fr:::m 10 1:0 20 ... /L an:! is thlt predaninant constituent in m:::st of the gram_tars. Thera is also little dlange tc the chaaic3l. quali'l:::1 of water in the aquifer for l:!Ut SalW reason. Thus the dlomic3l. quality of the '.oiater in the aquifer is ~Mrally ver:y -s imilar to that of the oriqinal. raiIWater wi to"l the exception. of t.lte concent...-ations of dissol ..... d CO2 (ani hence acidity) and silica. It can therefore be concluded that the ;>r'..mar'{ reason for t..'1e severe corrcsivity of the coastal groundwaters ,escurces in the NT is b~e h~ CO2 concent...~tions in the soil air 'Which <2USe a . wild up of CO:! and related acidity in 10M graJndW'ater~ 1his catDined with the lade. ?f reactive carbonate material in t!'!.e st...--a.ta 1.n whim the acuifer SYStEms CCOlt" has resulted in lew pat 10;.1 alkalinity grcundwaters. 4.1 (laaera! The general approach has been to adc::t;lt corrcsicn resistant waterials of construction i!S probl-ems have arisen, z:at..'1er than intrcdlcu treacnenl:. Slpply systems typically ~cise a !"Ul'ICer of relatively ",1OO1y spaced bores feeding 1:0 a central grou"'1d level storage frcm ltbich. the ""!ter is lifted by t..-ansfer pu!9 1:0 an elevated storage for distril:ution Generally treatment: at t..~ boreheads is inr;Jrac:ical, the first cppor..unit'l beirq al: tt'.e central storage. Cbnsequently, materials of const.ruction for the 1::cres, rising mains and initial storage tarl<. \IoOJ.ld have to wi t. ... .stand the exuerre corrosion e:f!eC""...s of :he raw water regat'dless of treatment considerations. 4.2 Bores and Bore PIDps Bore casi.rgs, until several years JO, ..ere mild steel (MS) an:! suffered tuberculation ~l .... as well as premature failures at the ~ter-air interlace. Fibre reinforced pl""tJ.C (FPoP) casirr;s at"e new use:i together with stainless :steel (S5) screens .. Galvanized steel (GoSl columns WI."9 found to lase only 1 1:0 2 years. Gals<GUently t..,ey are """ constructed of E1U? with sane in 55.. Adaptoz:s to 'the ~1..lIt9 ard heaCe~ are in 316 SS. GS bore headet3 ha'Je a life of 1 to 2 years.. 55 headet'S are proving suc:ess~~l and FRP is beinq investigated .. Subnersible PunQs are typically in {Gcundfos) , 'Zinc free brcm:elSS Gask. in) and SS cas ings wi til bronze tm;:elle:'s (5a.1t.'1ern Cr::::ss) ~ all 304 55 {Giles -and or plastic In shaft driven ~urtQs rrcstly ~no !:,cog:ress.i~. cavity ;csitive displacerrent um.ts at";~ used Wl.ttl.