1. › bitstream › 10070 › ...Technical Report WRD81049 Viewed at 14:07:24 on 29/07/2010 Page 3...

Technical Report WRD81049

Viewed at 14:07:24 on 29/07/2010 of 28.

III 1. 1

I

'. I I

f' II

'. ~I ,

II II :1

'.

•

I I I I I I

NORTHERN TERRITORY

COASTAL PLAINS HYDnOLOGY

By D. Kingston.

0)


Viewed at 14:07:24 on 29/07/2010 of 28.

tUbject:

J I I I I I I I I I I I I I I I

,--, ~"..~ > " 4 ~

"-"

DEPARTMENT OF TRANSPORT AND WORKS DK:JA:331

MINUTE

DIRECTOR

COASTAL PLAINS HYDROLOGY REPORT

In response to a request from you a paper on the hydrology of the coastal plains has been written by D. Kingston for the book 'Northern Heritage' being editted by Dr. H. Ridpath and Professor H.A.J. \"/illiams.

since the paper presents material which has derived from activities in the area by the former Water Resources Branch and the Investigari~ Branch of Water Division it is appropriate that it is also made available as a Division report. It is felt that the hydrological zoning of l~~d presented in the paper is an important contribution to the planning of land use in the area, not only for buffalo and cattle management but also for land drainage, road construction, flood plain management and irrigation. The report is attached hereto recommended for publication.

N.A. WATSON ~hief Engineer Investigation

~------------------~


Viewed at 14:07:24 on 29/07/2010 of 28.

I I I I I I I II ,

·1 1. il 1. II ,

II

I I I I I I

COASTAL PL~INS HYDROLOGY

Synopsis

The formation of the Northern Territory coastal plains is discussed in the context of the action of the sea and the various river catchments dr.aining on to the plains. Areas are classified according to the dominance of river action, rainfall or tidal action in an attempt to explain the (' .... ccurenc.e and durat ion of ;'<lat er on dif f erent 2.rcas.

D. KINGSTON Nov. 1981.

(iii)


Viewed at 14:07:24 on 29/07/2010 of 28.

I il l ,

II I il I

;. I, I II i

•• II 11 i

i.

.'"

I I I I I I I I

CONTENTS

Section

1 Hydrology and landform

2 Role of the sea in landform

3 Rainfall, streamflow and landform

4 A hydrological classification of the wetlands plains

5 'Surface and groundwater transfer

6 Cyclic salt

7 Water movement and its ~fmplications

(i v)


Viewed at 14:07:24 on 29/07/2010 of 28.

• I il ;

:. ; List of Figures

'. Figure 1 Hydrological factors in wildlife

" • • 2 (a) Concept of tidal marsh emergence

• • 2(b) The coastal barrier

,I • • 2(c) Tidal meanders

· . 3 Rainfall and runoff

il · . 4 (a) Adelaide River to Alligator River area

I · . 4(b)

• • 4(c)

Adelaide River plains

South Alligator plains

II • • 4(d) ~1est Alligator - Wil<1man plains

· . 4(e)

1t · . 4{f)

East AlJ.igator - 11agela plains

Mary River plains , , 4 (g) '. · . 1.<Jes t coas t of N. T.

I I I I I

• I (v)

•


Viewed at 14:07:24 on 29/07/2010 of 28.

I I I il i

1. i it :, 1. t

il , ,

i.· l !

II , ,

!I 1

;1 ,

~I I I I I

• I

1. H¥drology and landfo~ It 1S not possible to think of the hydrology of the coastal wetlands without thinking about the origin of the landform on or through which the <later moves. It is helpful to form a picture of the role that water has taken in the formation of the plains because it leads us to expect water to occur and move in certain ways before making detailed water surveys.

l'ihilst we are considering land composed of materials very recent (in geolpgical terms) vie may consider the coastal plains to be determined by functions of weather, land and sea which h~ve persisted for practical purposes, as we now knoH them. F'igure I suggests the interaction of these .elements leading towarc1s Lhose aspects of the coastal wetlands which at these latitudes make them hospitable or not for wildlife. These are feed, shade, drinking water avail~bility and flooding. .

The processes indicated in Figure 1 are individually studie(1 by specialists amongst whom we may count themeteorologist, geologist, oceanographer, hydrologist, geomot'phologist, harbour engineer, pedologist and biologist. Here we will attempt to draw together concepts of hydrology arld geomorphology with a view to forecasting the occurcncc of surface 'V'.1ater and shallow grOUt1Cl\'lat or, fresh or sal t as , f~ 'ld1 'C It may a Lect Wl~ _lLe.

2. Role of the sea in landform ~ J:'hcre -have been conflicting ViC\(lS on sea le\'el history

during the past 6000 years (FeLl p37l). Some bclic;ve that the sea attained a higher level, about three metres above the present, before falling back during a 1Recent emergence'; others consider that sea level attained the' present level within the past 6000 years Hithout a higher Holocene stand. The problem remains controversial but. has a bearing on the origin of much of the [lorthern wetl.ands whose elevation is only becoming knOVln in tIle last 15 years in th(~ course of surveys for ri.ce development, road bui.l(1ing and the c!1vironmental studies associated with ura!lium mining. Referring to the South Alligator flood plain Hilliams has stated (EeL2) that l'Ie are still in no posi.tion to eva]uCll:e the procise role of past and present geomorptlic processes in the evolution of the South Alligator flood plain~ No data are available on coastal sed~!nent budgets, on alluvial stratiaraohv, or on currellt sedi!itellt 'j~ields from the basin.

~ . -There is an urgent need for c;n integrated fieJd stu(ly of 21Juvial and estuarine coastal dynamics.

•

Technical R

eport WR

D81049

View

ed at 14:07:24 on 29/07/2010P

age 7 of 28.

--* -

f-I I ,

- - -

WEATIIER

LAND

~

- - - - - - - - - -- - - --

HYDROLOGICAL FACTORS IN WILDLIFE

/tAINFALL ~uNjHINE

(U'C4JC $I'Ia) " RWIOFF FEED

WATER

".- "-CATCHMENT w'DLUME/ TIME >-- WATER

< \ /'J5IU-'OItMAN(li {JYNAM(C5 QuANTiTY'

'" "-sEDIMENT \ --\,PLANr SHADE /WNOFP ECOLQ(;Y /

" MATER-IALS ~ LAnOFORM f-nYNAMICS AllfJ SOILS

/ I /1 /

KUR"cE,"n lJRINKING MArSRIAL3 ~H"'LL6wCJJ,OJ./HtJWAr£R JlYIJ/tOI.O(.,Y WATER

/ TIDE /WtJ WAyE VOLUMe/TIME ;-- W~T£R. V HAFOflMANCF 1JYNAMICS QUAliTY

'" / SEA '- FLOODS

WATER

FIGURE I

, I


Viewed at 14:07:24 on 29/07/2010 of 28.

,

II 11 j

II i

,

II ,

II I. I. i ,

II i

..

I I I I I I I I I

Unfortunately even a barely adequate survey of some of the components of sediment movement on the coast would req uire resources of manpower, technical expert is e and equipment that is far beyond the resources of an area so thinly populated as northern Australia. Thus we are restricted to qualitative statements derived from references to other parts of the world augmented by local information on \Vater behaviour (Ref 3), soils (Ref 4) and topography (Ref 5). Harine sediments and soils may come from nearby land areas, transported by local streams and rivers, transported from far inland by major rivers such as the Victoria River, from offshore coral reefs, old deposits offshore and from erosion of the shoreline itself (Ref 6). Johnson & Eagleson examin€d the various currents active along coastlines, the modes of sediment transport and in the coastal engineering context, showed that as a general rule the longshore movement (known as 'littoral drift!) is by far the most important. j·'leA.surements on the California coast showed rates of drift UD to 800 000 cubic metres per vear. This would have been only the coarser iractions of th~ moving sediment since the measurements involved would have been particles OVE'r 62 microns. Huch more would be in the silt and clay particle size range, the fine particles movi.ng in Sl1SpdlSion, \,hich is the material deposited in the auiescent zones behind the coastal barriers. Just hm, much niore material is mobilised in the susPended sediment port:ion than the b~~d movement could not b0 guess cd at J but suspended sediment movefilent far exceeds in distance a corresponding bed load mo\rernent in a given :c.ime and ther:efor(: rClc.kes up in

-distance for what it lacks in concentrd!-,ion. Inspect-ion of Stephens Creek reservoir near Brokel1 Hill which is silted from an arid zone source ShO"\dS thilt the fine mdt:~ri.s.ls completely dominate the volume of infilling. Looking to the posstble alluvial source of material in the northern ~lE~tlands where the: littoral drift is 'i,..,rest to east', rivers such as the Daly. Vi.ctoria and Ord seem Ekely sources. Seen from the air in flood time the suspended sediment load of the Victoria can be seen staining the 'i,v~atcr fot· many kilometres out to sea.

Exami.ning the map of the coastal plains [rom the Adelaide to the Allit,ator River.s I Fig1Jre 4(a), the extept of many of them is seen to be out o[ proportion to the rivers reeding them. For example east of \;JooloeT the Hary tZivcr looks incapable of creating with alluviQl sedi.ment, the plain in this ared. Furtber-wot·o Cd letd aciou of me(.-~nder on the various rivers sho;,~ed a common rat io [or Lhe lot.,rer reaches of cdch regardless of catchment size. This is intet'p!~etcd as the characteristic of tide ra.ther thDn streamflo\·J. These ratios revc:rted to more individual values ill the headward reaches of the plains, therefure it is concluded that:. coastal ;and tidal proc.e.sses \'lere the dominant~ factors in much of the plains creatioTI$ Furthcr'i1iore it ~Jas found thp~t. ,Ground le\:els in the lo~"er reac~1Es of the


Viewed at 14:07:24 on 29/07/2010 of 28.

II j

l' I II ;

II ;

!I I. I I I I I I I I I I

• I

~ I I I

Adelaide River plains were frequently in the range of one or two metres above Australian Height Datum (ABO) whilst Mean High Water Spring tides at Danvin is 2.97 metres pRO, almost a metre higher than the plains. Likewise high tide in the East Alligator is half to one metre higher than large parts of the Mageia Plain. It appears that estuarine plains can remain lower than sca level but cease to be covered at high tides.

Prevailing north westerly I"inds cause west to east longsho~e currents and littoral drift on the northern aspects of this coast, spit formation and subsequent sand acretion on the seaward side builds the coastal barrier that will constrict the r,iver mouths if it can. The channel resistance created in the mouth will lo",er the height to which the tide rises on the landward side in response to the harmonic motion in the open sea. (The electrical alterriating currcnt circuit is analogous to this, increased resistance \v'ill reduce the amplitude of the voltage in a capacitance in series with it). Figure 2(a) illustrates this dynamic depression of high tide and the· forlnation of the tidal marsh such as the ~'iildman River estuary now is seen to be. (Ref.7, p 1080).

Further constriction by the gro;,vth of the coastal barri(~:r_· l 1FJY inhibit tidal penetration .almost completely, the tidal Hl(.=anders becoming relics. This is now seen on the lower Mary River. The lower Adelaide River was also Jjke

""" this onco upon a time as can be seen just wost of v-;oolnel'. However a channel in Tr.:he,t is no'.".· Tbe Na.rrows on t.ho .~dolaide (sec' figure 4 (b)) cut back and captured the flow of the river t'(~jlJvenating the tidal porformanc8 i<n the lo~'ler Adelaide and re-establishing the tidal meaIlder system as far back as Beatrice Hill and dry season saline: intrusJon even further.

The Soutl, and East Alligator Rivers have substantial catchments of high runoff country, trH= (>scarpment country, and enough DC t se<SJ.wcn:d [low to keep dO\,ln the sand bar formaLic)~ which is the progenitor of the closure by tile coastal b<~rrier. Hovinq round to the \,:estern aspect of the Northern Territory coasfline, this Catl also l)e said of the mouths of the Daly and Vict.ori2 Riv(:rs I sources, as previously mentioned; of much sediment for dj,slribution by thE' coas tal processes.

The barrier across the j\-~agela plains embayment W2S

formed ... not so much by littor2tl drift directly, C:8 by the spill of the East Al.Jigator. With a high tide of 3.8 metres, this is the level to \'lhi.ch the! ground has bt:?en raj sed at tile Magela outlet by sediment of either marine or fluvial origin. Wherever the cotlstraint on tidal movement is effective fresh Ir,'ater E-H-".'amps may be expected to persist.


Viewed at 14:07:24 on 29/07/2010 of 28.

PERSPECTIVE

SEA

SUBMERGENCE COASTliNE. I ITIAt.,.

SPUR FORMATION dt SETTLING f, BASIN.

~Jt.~::~~~,~,~ Beach Line· or Une:s

"MUlliple Outlets due to Surcharqe of Sand Ridgf:.

Marsh

CWSURE.J. EXPOSURE' OF PLAIN BY YNAMIC DEPRESSION OF HIGH TID

M-ecndc:rs u-ndczr Fluvial Rt9im-E

Floodin\! by bl~h rainfall only.

M~nd~rl undtr Tidal Rang" /Capaclly Rf:q'm<:.

SECTION

Tid~ RQ~9C

NO DEPOSIT

MQrin~ Mud to bf:low High Waler

SPUR ~ PONDAGE DEPOSIT !

Expond

River -

High Tide Grodj~nt due to Otann.f R~sit.ttnce:.

(I.r. Dynamic Dcpre-ssion ot HiSh Tides).

PI\ i. ~ --- .. ~,~\.~':~

EXPOSURE.

Fluvial Flood If. somcz AiJuvie ..

RAIN AGE PATTERN OF MARSH MODIFIED RELATION OF ALLUVIA TO MARINE MUD. AFTER DEPRESSION OF HIGH TIDE

D. kiNGSTON. (AFTER THORNBURY)

, I ! t I

I I ,

I.&J

"* ~ Q ar:

~ ... ~ 4Iit .... Q.

..... ~

9 ~


Viewed at 14:07:24 on 29/07/2010 of 28.

I I , I I I I I I I I I I I I I I .. - --,

I I

II 1_:

I


Viewed at 14:07:24 on 29/07/2010 of 28.

I I I I I I I I I I I I I I I I I I I I I


Viewed at 14:07:24 on 29/07/2010 of 28.

I I I I I I I I I I I I I I I I I I I I I

RAINFALL AND RUNOFF

RAINFALL .co'(? DARWIN IlllNal=l= IlE6loNALlSElJ F=ON t: SniT/allis IN T~

AlJ£J.AliJE Ii'IVGIt .BASIN

ZONJ?> SkoW IhMI&I' ~RaM :507. 71> 70 % l'-to~.l./7Y

'-.

UP. otT. NOV. JJG&. JAN. FEA MA~ JlPR. MAY JUN. JUl. AJl6.

FIGLlRE 3


Viewed at 14:07:24 on 29/07/2010 of 28.

II i i

II 5

il 1

II ,

II I ,

II i

il '. :. 11 11 ,

11 '11 , i

II I.

~

I I I I I I

may start to pond water well ahead of major stream flow coming in the rivers or in the creeks draining on to;' the fringes of the plain. The general pattern for these maritime plains is for the coastal reaches (example:, Beatrice Hill to The Narrows) to be inundated by direct rainfall. and the head,vard reaches to be inundated by local runoff and periodically by overflow from the principal river. Thus the materials to be found in the upper reaches include areas of alluvial sediments. sands and silts' and in these areas channels and depressions created and seasonally replenislled by streamflow may occur. This is the area to look for perenial fresh \,yaterholes and in some cases' these may be water table windows as at Acacia Gap, Leaning Tree, Red Lily and Nourlangie waterholes. Hhen rivers overflo'" their banks, the v.later, running at shal1o\ver depth, runs at lower 'velocicy and therefore deposits its sedim~nt load. This causes the formation of river levees, the coarser silt laid clow"TI first, the finer silts on the flood plain outside the levees and clays at the downstream end of the reach of alluvial plain. The poorer drainage of the dm('nstrearn end of the alluvial plain may be reflected in the ve;"retation

- ~ Q

type such as the north I.-lest corner of \V"ooll.-}onga F,eserve (Figure 4c), in this case probably inhibited by levee format Jon on the main channel of the South .A.lligator ~

4. ~ hy-d~,gJ_~g~_£2~ __ C l?~?_~_ifi~n t ion of the vl€'t 12~n?s p 12~ins Figures 4(a) and 4(g) sho\v the coast;,d. wetlands from the

~. Adeld:Lde to Alligator Rivers and from the Ora to Charles Point respcoctively. Figures 4(b) to 4(f) sho<! those from the Adelaide to the Alligator in more detail using the land system interpretations of Scory ot al (Ref .4) as an indication of perennial sW8.mps or high water table. The I

planform of the ',mtercourses bas been used as a guide to the domi.nant hydrological factor influencing permanence of "/Bter in the area. The symbols used are:

hydrological factor S - streamflow dOlllinated P - precipitation dominated T - tide domi~~tcd

gcomophology factor S - streamflo\] domi.llatcJ lar-ldform T - dominaLed by coastal and tidal

P"-o~~~Se" in l"n~ ~nrma-l·"[1 1. .... 1;..::::;._ Q _ _c ..... .)..~ __ L L C, •

Thus PIT represents an area whc~e pre.cipitf~tion is tbe main _guarantee of !'vctness on an area of land cl'cated by coa.stal processes.


Viewed at 14:07:24 on 29/07/2010 of 28.

I I

11 I

.1 :. • ;1

I I I I I I I I I I I I I

4. t The South Alligator River With a substantial catchment of high runoff terrain the river is competent in maintaining its channel (Figure 4(c». North of the highway coastal procesSes are probably the dominant landform agent and direct precipitation the earliest inundat ion source. l-lith an open channel these plains drain overland so perennial water is restricted to pockets at the margins. Soil salinity and treelessness can be expected in most of the area marked (PIT).

From the highway bridge to Jim Jim Creek landform is alluvial overlaid on estuarine (ST) and \-later occurence from streamflow (S/ST). The overflovl of the main river creates levees '''hich have occluded the entrances of Jim Jim and Nourlangie Creeks causing the s\Vamps as indicated, the \(oolwanga being most noted for its extent and constant wetness.

Upstream of Jim Jim confluence and Hooh,ranga boundary on Nourlangie Creek landform of the plain is alluvial and inundation is from str0amflo,;·;r and perennial. No salt problem and adequate tree gro\'lth may be expected.

4.2 The Hest A~ligator and Hildman RiVers 111ese are shown on Figure 4«l) and a si;nilar sequence of symbols P/'l', S/ST and SIS provides a similar pattern of landform, hydrology and salinity expectations. The VJildman Eiver outlet shot.rs a more advanced stage of occlusion than the South Alligator. The river is dying in the area marked SIST with insufficient catchment runoff co overide the silt supply. As tidal capacity is lost to siltation the semidiurnal tidal flow ~ill ~ecrease and the tidal chaonel will, in turn, fai] to main:::atn itself. Tidal meanders \-1ill becocne relics as on the l-.fary I{iver plains. The alluvial deposits of the loJildman in this dying zone have creat ed a barrier across A lli.gator Creek resulting in the extensive sHamps there (marked SjS). The Hest Aliigator River apf-lears to have died in the corresponding zone (31ST) blocking itself and creating the sldar:.1py zone (marked SIS).

4.3 The Mary River Bloekage-ottl1e--mouth of the 1'-1.sry is .... rirtually cCJrapletc (Figure 4(£)). The stllall \vdterCOl1rses that crOBS the coastal barrier arc merely the overflo'i;'is of the vlhole coastal l[!goon sysccm and probably onl.y have significant aggregAte flow in ahove average \-.Jet seasons. In fdct the most likely outflo\'J of the system does not even enjoy the name of the Hary but is Called Sam~)an CreE>k. The coastal bo..rrier has creat ed the large s;;.;anlp rEarkeJ PiT v;b.ich has its inundation quaranteed by precipitation. The coastal barrier is coarser t:natcri,ql than t.he plD.in behind it and probably ",llo"s grouIldvJater flo,,, to t11,,, sea. Il may be expected that connate and cyclic salt is ~urged from the


Viewed at 14:07:24 on 29/07/2010 of 28.

I I I I 'I

1)1

•• 11 ,I ,. ,

il '.1 :1

..

I I

• I I I I I

area and tree growth possible. The other zones marked 51ST and SIS may be described as before. The dying zone extends to within 20 kilometres of the high'way bridge.

4.4 The Adelaide River This is shown on Figure 4(b). As mentioned earlier this system was similar to the Mary before the river capture occurred through the Narrows. The semi-diurnal tide flows have re-cstablished the channel with the characteristic tidal channels evident to Beatrice Hill. The influence of the tide rise is recorded to I,ithin five kilometres of Harrakai crossing. The open river channel provides for the area to drain overland seasonally and hence the virtual absence of perennial swamp in the plains north of Beatrice Hill. The area marked T/T is nOll subject to tidal inundation attributable to the opening of the Narrows channel but the land here would have been crea ted by coastal processes frorn its nor tIl east. It is now living its second tidal life as the dO'lleg in one of the tidal channels sho~m. The sub-soils of most of the plain probably fail to transr.lit ground,vater so cyclic and connate salt result in a lack of tree growth.

4.5 The Bast Alligator and Magela system The East Alligator itself h~s adequat~ runoff and tidal. capacity for channel maintenance (Figure 4(e)). As mentioned in Section 2 its flood overflow deposits scclimcnt across the mouth of the Magcla ofJ.baymcnt to a sufficic:nt depth to occlude the system and Jock in the swamps as shown (PIT). The overflow of the Magela basin has beel) studied in some detail in what haPPBoB to have been a series of good years. The system overflows the alluvial barrier in above average wet seasons. If a below average wet season occurs with a uniform intensity through the summer, the outflo;, could conceivably faiL The lagooned area when full has an area in tIle order of ],70 square kilometres from which the eva\Jorative output during February will be about 30 million cubic metres or ten cubic metres per second. With the lagoon systems Eull, a steady flow of this rate could enter and not emerge at the other end6 The flow balance is, unfortunately, not gUit0 so simple as that since there are surface slopes, storage challgcs al1d infiltration compotlcnts to be considered but the figure illustrates the phenomenon of river occlusion by littoral or alluvial sediments .

4.6 The Victoria River With a catchment of 86,000 square kilometres, llCStly arid and subject to C)7clonic rains, this river is a source of much sediment for the Northorn Territory coastline. Studies in the catchment in 1968 i ndic.-:itccl the annual sediment yield from the catchment to b(:; between 1000 ancl 9000 tonncs per square kil~netrc. The lowest figure th~rcforc is eighty six million tonnes per year and it could be over seven hundred


Viewed at 14:07:24 on 29/07/2010 of 28.

I I I I 'I ;. 1

:1 :1 ,I -

II ,

I, ;

,J 1 I I I I I I I

l1lillion tonnes per year. The map sho\vs vast shoal formation in the mouth of the Victoria River and land systems maps for the coast (Reference 8) indicate large plains of estuarine soils between the Victoria River and Charles Point.

4.7 The Hoyle, Dilke, Reynolds and Finniss Land system mapping has not been done in similar detail to the northern coast of the t.rr but for each of these a pattern similar to the Hary River is anticipated. On this, the west coast, the mechanism creating the coastal barrier is different as the monsoon wind direction is more directly on-shore. An expert on shoreline processes would probably find a different type of beach configuration. Aerial inspection of the coast leaves no doubt about the existence of the coastal barrier. It may be anticipated that the exposure to the north west monsoon would result in cyclic salt affecting the ~oils of these plains.

4.8 The Daly River This has a catchment of 54,000 square kil()metres and, in addition to the large su=.er discharges, it has the added honus of a substantial dry season flo"1 emanating from the Tindal limestone system. Tile river is capable of maintaining its channel and putting down alluvidl sediments over tile esluarine materials at lease to Wooliar8 and probably further. I-ii.th a flared estuary mouth facing thE' prevailing '"Iinds, it is not surprising to find a tidal bore on this river and witnesses have recorded a bore of 2 metres in the ctlannel. It is interesting ~o speculate whether the bore is Elorc inf]uential than the normal tical f10\'1 in determining the meander paLterll. Soil loss

··studies at one point in the catchment indicate at least 3 million tonnes of sediment pe'r year come dot'Tn this river and this may prove to be much more vmen the arid south tributm-ies are studied (i. e. Dry River).

5. Sur face .and Grounduater Trans fE'_Y

The combination of slop'eot'~th-e~land vith the rate or int:ensity of rain£all decides '1"7hcther most rain~'Jater £10\>/5 ah~.ay or lingers long enough for evaporatiot:. into t.he atmosphere-or infiltration illtO ttle ground to use a large proportion of the vlater. The saJ;~e applies to water that flo"ls on to the land from oUler land areas (run-on), floodouts and floodplains. The texture of. the upper fe\v metres or centimetres of soil dete"rmine to ~·}hal extent ~ater, eitller rainfall or 'run-on' will i;-lfiltrate arId then, as soil moisture, will be availa.hle l~ithet" Lo percolaLe furt her to augment groundwat er: res erVeS or be taken up by plants and returned to the atnlosphere by evapo-transpiratiotl through the leaves.

J~ ______________________ __


Viewed at 14:07:24 on 29/07/2010 of 28.

11 ~ I ,

11 1. i ,

11 j

il 1. 1

I. i.1 i i

:. 1.

, i i

11 :. :1 :, I I I I I I I

There is little doubt that in the flatter plains, particularly where the clay content of the soil is highest, the lions share of infiltrated water is taken up by evapotranspiration. Recharge of groundwater storage in shallow alluvial aquifers (phreatic aquifers; we are not considering deep rock and confined aquifers in this context) may become significant only near to the point where rivers enter floodouts or overflow on to floodplains laying relatively coarse alluvial material deposits.

Transfer bet'.veen surface and ground"ater also may occur to or from the rivers. watercourse itself depending on the water level difference between the river and the water table and the length of time the difference is maintained. [This time factor is very important, in the drainage equation -' which represents the:process mathematically, time appears in the exponent of the pmver function used to express the rate of accretion. It is also a reason why good vegetation cover or mulch on soil is a good help for infiltration.) The presence of floodouts or perennial ,·;atercourses is therefore an important association l"lith water table aquifers.

In the arid zone the water table frequently lies below the river bed and transfer from the river is through uns aturat ed do\-m\"ard f 10\>J be 1m'] the ri. ver to a recharge mound in the -v.. .. ater table belo~ . .;. (0 situation notably changed in recent years on the Todd River in Alice Springs) .. In humid zones generally, as in the northern i,'7etl~nds, the ~.,7ater table is frequently above river bed level, the

-incision of the river in the land may be described as a window on the \-later table. Hhen the river level is higher than the (,ater table water flows into the surrounding ground and when the river level falls the reverse occurs. Water that resides in the banks temporarily is referred to as bank storage and is of interest to the vegetation along the river banks. If in the course of a full cycle of seasons, the sum of £lO;'-;8 out from and back into the river is a nett f 10\,v

out, the river 1.8 descri.bed a.s a losing river, if it is a nett flow into the river it is a gaining river.

In gcner21 it is expected that £ low betVt7eCn surface and groundwater is confitled to flooc!out zones and the banks.of perennial watercourses. Ho,\·vever, lhere is reason to bl~lieve that some swampy areas of the plain not in a floodout zone or along percnni.al ri vcr banks, do f low into the phre.:J.tic ground,-:''!aceJ~, notably' the lAnd. syst8::n described by St01:Y, \.Ji lliarHB and Hooper (Ref .Lt ) 93 Pint·link le east. of \,Joolner .. The presence of papcrbark indicates tl1at connate and cyclic sp_l.t 1.S being pUTged and an adequate grcundvlater movement must occur from tllis area to the seae The association between salinity and tile failure of drainage to occur down,,;arus through the soi 1 is as true in the natural state as in irrigation practice.


Viewed at 14:07:24 on 29/07/2010 of 28.

-11 i , 1. I i'

il I

·jl

il I

i

II !

II . , i

II I , 1. , j ~I , J j

\1 -j I

i. II 1 ! -

I I I I I I

6. Cyclic Salt Resildents on the coast know that sea air contains enough salt to affect their gardens and the painD-70rk of their houses. Indeed the salt content of rainfall can be measured up to sixty milligrammes per litre. for onshore rainbearing airflows, decreasing as you go inland. The salt cycle is completed by water flowing over or through the land back to the sea. In some hydrological environments water flow back to 'the sea is very low and evaporation very high. The cyclic salt being thus left behind at the point of evaporation (salt lake) or in the zone of root osmosis leading to evapo-transpiration. (soil salinity). This is the reason salinity problems affect arid and semiarid areas where onshore weather prevails such as SA and WA in the forties latitudes, subject to westerlies, and northwest IVA subject to the north westerly monsoon rains. ,Even if only a 4

fraction of orie milligramme per litre. persists in the high level north westerlies that are the moisture source of relatively light rains in central Australia, it is enough to build up over the centuries the salt ,"hich is found in the closed drainage systems like: Lake Eyre, Amaedus, Hackay and Woods. .

In parts of the coastal plains drainage off or through the soil is inhibited, by low grades or low hydraulic conductivity respectively. Cyclic salt must claim our attention, if not as the original (connate) source, then at least as a possible maintaining supply of salinity in plains soils of marine origin. The pattern in many of the these plains is heavy inundation by rain'tTater and local runoff yet

- salinity persists at one or D-W metres depth. (example: Cyperus land system. (Ref. 4). Before the wet season commences these black clays are cracked and the first hundred or so millimetres of rain penetrates before the clays close up. This amount is taken up as' evapc:transpiration leaving its salt-contribution behind. Parts of the plains (both ,.;ith or without any recent marine heritage) may still receive cyclic salt, but better grades and hydraulic conductivity may purge them sufficiently for tree growth to occur.

7. Hater 110vement and its implications Movement between surface and ground",ater 'was discussed .in section 5 and cyclic salt behaviour in secton 6. These concepts may assist in the follo'V.'ing evaluation of plains lands when combined with the concept of the hydrological classification of the area in question.

7.1 Streamflmv dominated landform The levee soils will be free draining and depending on moisture supply from rainfall, bank storage or periodic overflow abundant vegetation is to be expected. In the flood channels or back plains finer soils are to be expected. depending on longit:udinal grade which may range from 1 in 1000 to 1 in 5000. Drainage efficiency will range from good to poor and so will soil quality. No doubt prolonged inundation of the deeper parts of the back plains will inhibit tree grmvth. Shallow groundwater of _ fair quality may be anticipated whever the alluvium is deep enough and not too fine~


Viewed at 14:07:24 on 29/07/2010 of 28.

:,·'1 . , .~

-J <J

tl , ! j. i

II !

II I

1. 11 II , , . ,

\1 i

1

jl ,

II

0<

I I I I I

7~2 Landform with alluvial material overlaid on e'stuarine mat erial.

In most respects, a similar pattern to 7.1 may be expected. The draining qualities of the back plains are likely to be inferior due to the proximity of the estuarine soils and the low altitude relative to the drainage destination. A botanist may recognise this feature in the vevegation found in these areas. Shallow groundwaters are likely to be of poor quality and of 10,,] yield although ponded surface water will be of good quality "hile it las ts.

7.3 Landform dominated by coastal process Inundation is substantially provided by direct rainfall followed in some years by flood streamflow depending on how far down the plain the area is. Poor subsoil drainage probably accounts for the lack of trees on large areas and where overland drainage can occur fresh water either as soiL· moisture or "aterhales is liable to be absent for part of the year. The shallow groundwaters are likely to be brackish. .

Hhere surface drainage is inhibited by one of the various processes discussed in section 4, swamping conditions prevail. If subsoil drainage is lacking, treeless sedge sW'amps may be expected. If under drainage can occur sufficient to control salt levels then paperbarks will be in evidence except where the surface water depth is excessive. An example of this adequate drainage occurrence was the coars .er mat erials of the coas tal barrier on the Mary plains .. Another case could be by ,'Jay of old infilled watercourses (vlashouts) depending on the circumstances (and therefore sediment type) of their infilling.


Viewed at 14:07:24 on 29/07/2010 of 28.

j

II i I

II i

'I , ,

: 1-' :. :1

il I

I , ':1 I ,

11 II I

'I I I I

References

1. Bird,. E.C.F., Coastal Lagoons of South eastern Australia (Landform S~udies from Australia and New Guinea -Jennings, J.W. and Mabbutt, J.A.) Australian National University Press (1967).

2. Williams, ~l.A.J., Geomorphic Evolution of the South Alligator Floodplains, Darwin ,,)etlands Workshop (August 1980).

I

3. Purich, P., Study OTI Flooding on the Sub-Coastal Plains of NOrth Australia, !Water Resources Branch, Northe= Territory Administration (1965):

I

4. Story~ P., Williams, M.A.J., Hooper, A.D.L., o 'Ferrall, R.E., and NcAlpine, J.R., Lands of the Adelaide -Alligator Area, Northern Territory, Land Research Series No. 25, C.S • .L.R.O., (1969).

5. Transport and \-Jorks, Department of, Uranium Province gydrology, Water Division (1980 Volumes 1 to 10) (1981 Volume 11). '

6. Johnson, J.W., Eagleson,P.S., Coastal Processes, Estuary and Coas t line Hydrodynamics, f'lcGraw Hill (1966).

7. van'Veen-, J., Coasts, Estuaries and Tidal Hydraulics, (in Civil Engineering Reference Book, edit. Probst, E.H., and Comrie, J.), Butterworth (1951).

, 8. Stevlart, G.A., Perry, R.A., Paterson, S.J., Traves, D.M.,

Slatyer, R.O., Dunn, P.R., Jones, P.J. and Sleeman, J .R., Lands of the Ord - Victoria Area ,Jestern Australia and Northern Territory, Land Research Series No. 28, C.S.LR.O. (1970).


Viewed at 14:07:24 on 29/07/2010 of 28.

-

I

I I

\

I

\

J

\

\

~ \1

!\ [,

:J II

I \ I

~

------- -

"'---T i I ! i \-" ..!!. l"t

\

\

I

\

\

,J I

\

I I

Technical R

eport WR

D81049

View

ed at 14:07:24 on 29/07/2010P

age 23 of 28.

I I I I I I I I I I I I I I I I I I

,

ADELAIDE RIVER PLAINS

I """'::':'.-:-1 COAS'Y'AL PLIHN .. , .. '-J lJRAlNING

r;r/777) c.eAS'TAL PLAtN LCL/--LLJ SWAMPY

.. K..LfJ'll/YIIJ./

FICURE

""'''''IE'''

--------~~.--~

CIIIIM}1,;;/tS flAY

4(h)


Viewed at 14:07:24 on 29/07/2010 of 28.

-

1 1

I I I I :3 ;

I J

I -:r- --- -- ---------- --


Viewed at 14:07:24 on 29/07/2010 of 28.

! 'J

1 I 1

I 1 ,I

I i

) o

D

___ · .... ···.,il_-__ -___ -__ -__ .-__ -__ .-__ -__ .-•• -••• -•• -••• -••• -• ..:..;..;.;. -


Viewed at 14:07:24 on 29/07/2010 of 28.

-

I ~

I ~ ~ _.g~ - ---- -

t I

- - ---

.. .. ---~ i '*' .\,

I:l

~ ~ ~~ • I :::, 41 <..:>

~i ~

~' \J! "11

10

I : •

-------


Viewed at 14:07:24 on 29/07/2010 of 28.

P 4 ~ ~

\ ..

I ~~ • I ~i .. "'0

~ ,

.., i ~ "" ~,

~i 3 ~. < 'I ..

II ~

JI" .. " ~~ 1-" "'~ ~Q

" • 0 ~ ....

-----------------


Viewed at 14:07:24 on 29/07/2010 of 28.

~

~ <: ';;1~l

~ ~ 1)1

t-~

<TO

;:1 '" a <.l "-I- S '" '-'l "'. 4l $ '" l-

"" ~ ~ CJ ttl

\\ ::t ct '-" VJ Cj -,

~ .. 0:

~ ,. ~ ~

'. ~ ;: 0 ;,; i '" "

~ s

~

--------------

1. › bitstream › 10070 › ...Technical Report WRD81049 Viewed at 14:07:24 on 29/07/2010 Page 3...

Documents

Transcript of 1. › bitstream › 10070 › ...Technical Report WRD81049 Viewed at 14:07:24 on 29/07/2010 Page 3...