WEATHERING AND ERlDSION

GEOMORRHOLOGY OF THE CENTRAL LUNI BASIN, WESTERNRA}ASTHAN*

BIMAL GHOSE, ::;URESH PANDEY, SURENDRA SINGHAND GHEESA LAL

*Paper submitted to the section of Geology and Geography, 53rd, Session ofIndian Science Congress Association, Chandigarh.

INTRODUCTION

Central Arid Zone Research I n8titute, Jodhpur

This region m the Western Rajasthan is a part of the Central Luni Basincovered by the SI.1'I'veyof. Ind:a to po-sheet No. 45 C and is drained by the Lunidrainage system largely from the Aravallis. The n.uni IS th~ main rivet' with theSukri, the JaWai, the Khari, the Bandi etc. as its tributaries. The ap.proximatearea of this region is 11,505 sq. km. The rainfall varies from 29 em in the north-west to 50 em in south-east. The precipitation is erratic, often 10cal1sed andtorren1:.ial. The maximum intensity of rainfall recorded so far was 21.1 em in 24hours in PachlilhadI;a region in extreme north-west of this region .

.Ml the streams are ephemeral with graded and meandering courses andwide flood plains. Besides these streams, there are others radiating from lthe hills.Some channels are either very short and incised or are obliteratedt~runcated Orburied under blown sand. These channels have been referred to as the deadchannels of the Luni system in the subsequent pages of this paper and have beendealt with separately.

The climate being semi arid to arid the breakdown of rocks. by chemicalweathering is slow. This is because of moisture being evaporated before it couldbe penetrated into the rock mass to favour rapid chemical weathering. The effectof diurnal changes of temperature on splitting and 'peeling' of rock masses is evi-den t. Cracks and fissures thus developed are further widened by percola ting waterthat helps to dislodge rocks from the main outcrops. But this process is also slow.

The country rocks are predominantly Malani rhyolite, Jalor granite andErinpura granite. Jalor granites in the region are not foliated or banded whilethe Erinpura granites are. The former weather into exfoliating spheroids while the

GEOMORPHOLOGY OF THE CENTRAL LUNI BASIN 11

latter into domes and 'whale. bucks' or sometimes into rounded hills and torsand are dislodged from the m3in outcrops in big blocks. The latter occur inslightly higher rainfall region of the south-east. In both cases, the hilt slopes (freeface) are steep aud irregular culminating in pediments. The pediment zones arecoveI'd with alluvial fans consisting of the detritus dislodged from the hill slopes.The slope of the ptldiments gradually merges with the plains of aggradationfurther down the slope.

Action of wind is very conspicuous in this region. As a matter of fact for-rpation of yardang and zeugen have not been met with. The deposition of blownsand on the slopes of the hills is a salient feature south of the Nagar Mewa hills,north-e~st of Padru, south of Jalor and Israna hills. The depositions have takenplace on both windward and leeward sides of the ridges. These depositions of blownsand often form minor rigdes orthogonal to the strike of the main rocky outcrops.

DRAINAGE SYSTEM(a) Present Drainage System: The Luni with it:! major tributaries like the

Jawai, Sukri, 'Sandi has attained ma.turity whic:h is cha'racterized by the gradedchannels (Fig. 1). The maximum depth of the channels does not exceed 5 metres.During rains, which are erratic, these ch'annels are somt'times incapable of holdingfull discharge of water from the upper catchments and the flood-waters spill overthe banks and spread inland causing inundation. The first order drainage systemis mostly linear. Such floods are, however, of rare occurrence. Most of the majorchannel beds are filled up with loose alluvial detritus and the channel flow nowbears no relation with the bed rocks .. In places the groundwater potential is veryhigh and water is available in close proximity to the surface.

(b) Prior Drainage System: Examination of recent aerial photographs of theregion has revealed the relics of disorganised channels which are at presentpartly truncated, buried and disorganised. Some channels are either veryshort and incised or are obliterated, truncated, or buried under blown sand. It isnow possible to trace the courses of these channels to facilitate research and toclear away some of the conjectures in the studies of landforms, surface deposits andsub-surface water along with the past trends of climate. These channels are refer-red to as dead channels (Fig •.1:,.

During the summer rains, the run-off as well as vertical percolation aremoderate and, therefore, the evaporation losses are relatively low. Run-off takesplace through channels t.hat remain ordinarily dry for most part of the year. Theduration of run-off as stream flood or sheet flood is short-lived but their dynamiccapabilities are conspicuous in removing the little weathering products that accu-mulate on the hill tOopsand upper slopes.

12 BIMAL GHOSH~ SUREESH PANDY, SURENDRA SINGH ANI). GHEESA. LAL

F""1 . PRESENT DRAINAGE SYSTEM OF CENTRAL LUNI BASIN.

Some of the dead stream channels near Dewalldi JSiwana) a.nd Chandrai(south oL the Panchota hil1) wer.e examined during the survey. It was found thatOn the valley sides there are alternate layers of stone lines (rock fragments) andfiner aggregates. These stone lines s~ggest that they were brought down

GEOMORPHOLOGY OF THE CEN'tRAL LUNI BASIN

RECONSTRUCTED .DRAINAGE SYSTEMS OF CENTRAL LUNI 8ASIN

I/.•.•...•..

13

T,ABLE I :Profile description of vettical stream bank cut' near Purara.

Size of deposits

Rock fragment 25 to 80mm.dia., gravel 5 to 10 mm. dia.

Rock fragments 40-50 mm.dia. pebbles 20-30 mm. dia.

Calcium nodule 3 to 5 mm.dia.

Rounded FOck fragmentsgravels and Goarse sand.

Sub-rounded rock f~ag.ments, small pel!>blesandsilt clay.

Gravelly deposits withalternate layers of cal-dum carbonate.

2 to 3

I~ to 2

I

III

IW More than 3 Silt clay with grits.

At present in most of these channels the upper slopes are incised into theearlier deposits. The depth of incision varies from less than one metre to twometres. It seems extremely difficult to equate the 'phenomena like deep incision inthe upper slopes, long and broad pr.ior channels likt' the Mitri in the east, thePachBhadI:a streams in the north-west, etc. and the formation of kanTcar zonemuch below tIle surface with the present climatic conditions and scanty precipita-tien. SQ dudng the establishment of these drainage system, the climate was wetS"clm~tiJnei the past followed by all environment of rising temperatures and incre-asing dryness when most of these channels ceased to flow and gradua!ly becamedisorganised, truncated and obliterated. Some of the relics of these channelsare so well preserved that it is quite probable that a wet climate prevailed notearlier than the Pleistocene period.

14 BIMAL GHOSH, lJREESH PANDY, SURENDRA SINGH AND GHEESA LAL

GEOMORPHOLOGYOF THE OEN'.i'RALLUNIBASIN 15

TABLE2, Size and shape of sand particles along the stream cut profile n~arDeipura

Total U. S. Standard A. S. r, M. Specification

S. weight ofMesh 20 Mesh40 Mesh 60 Mesh 120 Mesh 200 More than

sampleNo. taken in - 200 mesh

gm. 0.·84mm. 0.42 mm. 0.25 mm. 0.12 mm. 0.07 mm. 0.06 mm.

1. 0.47 0.75 1.50 ,7.77 4.35 0.0914.93gm. 3.15% 5.02% 10.01% 52.02% 29.13% 0.64%

D D,E D,E B-,C,D B,C,D- B, C, D-

2. 1.91 1.87 1.50 6.30 3.29 0.0514.93gm. )2.83% 12.56% 10.05% 42.20% 22.06% 0.30%

C+,D B,C+,D- Ci ,D,E C+,D- B,C A,B,C-

3. 2.00 1.50 1.45 6.80 3.00 0.2214.97gm' 13.35% 10.02% 9.68% 45.41% 20.03% 1.51%

C,D,E- C,D,E C,D C,D- C,D- B,C

4. 1.25 0.85 0.94 4.10 2.25 0.579.97 gm. 12.54% 8.52% 9.48% 41.12% 22.57% 5.77%

C D,+E D,E C,D B,C,D- A-,B,C

5. 0.15 1.37 4.42 11.22 2.40 0.1919.75gm. 0.76% 6.91% 22.38% 56.81% 12.]5% 0.96%

D,C+ D+,E D,E C+,D C+,D- C,D-

6. 2.00 0.50 2,00 11.20 3.80 0.4519.95 gm. 10.02% 2.50% 10.02% 56.13% 19.05% 2.28 .

C,D D,E D,E C+,D C+ ,D- B,C,D-

A, B, C, D and E indicate the shape of the sand particles.A = Angular B = Sub-angular C = Sub-rounded D = RoundedE == Well rounded

In climatic correlation some discrepancy might arise with reference to thesoil and lineal' incision of streams on the upper slopes as compared with thedeposition of alluvial, colluvial or aeolian deposits on the lower riverine plainslike the Takhatgarh-Mitri Plain. Butler (1958) and Van Dijk (1959) are of theopinion that the sediments of the riverine plains of south-eastern Australia werelaid down during a dry climate and the stream incision (with no deposition) took

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

GEOMORPHOLOGY OF THE CEN'i'RAL LUNI BASIN

TABLE 3. The stream length, basin areas and drainage density in. the~. ~:,..-::;

Central Luni Basin

17

RegionApprox. length ofstreams in Km

Approx. area drainedin sq. Km

~t;ainage l?ensitype~ sq. ~m

1 593.5 1155.1 0.512 885.3 1364.8 0.643 994.0 178404, 0.554 695.2 1023.0 0.675 508.6 '657.9 0.746 180.2 468.8 0.387 61.1 227.1 0.228 22.5 116.5 0.109 45.1 181.2 0.25

10 57.9 300.4 0.19

N.B.-The stream lengths and the area dr~ined falling only in 45 C havebeen taken into account, although some of them extend in theadjoining topo sheets. So the values stated above are exclusivelywith referen.ce to the area covered by to po sheet number 45 C.

GEOMORPHIC DIVISIONS AND UNITS

According to the morphology, nllturp. of denu.~a.tion, ~~~thering anddeposition of the present and the past by the erstwhile dr{li.n~ge sys.t~m. thisregion has been divided into seven geomorphic divisions (Fig. 3) and unit~ thatform the basis of land system and land units respectively.

I Siwana DissectedPlateau-I. Klmdal-Ramania intermontane plain (valleyfill). 2. Siwana alluvial plain. 3. Plains of Go}ia-Bhailan. 4. Sandyplain of the west. 5. Hilly tract •.

II Jalor-lsrana-Rewara-Granite-Rhyolite interfluve with intervening plains-1. Western plain with small sand dunes. 2. ·Piedmont zone in the southand west of Israna granite hills. 3. Leta-Bagra. plain. 4. Harji-ManadarLas plain. 5. Piedmont surface of Rewara-Mosal hills. 6. Hills.

III Khari-Bandi-Sagi riverine plain-I. Western sandy plain. 2. Ramsen-Sena plain with granite hills. 3. Khari-Krishaoti plains.

.,'"

:....~

.1'••.. , . 0--

.""" .•..r'"1

..•p'''\~

;~i-

BIMAL GROSE, BURESH PANDEY, SURENDRA SINGH AND GHEESA LAL

GEOMORPHIC DIVISIONS OF CENtRAL l:UNI BASIN

@2

18

GEOMORPHOLOGY OF THE CElIoTRAL LUNI RASIN

IV North and north-east plains-I. Takhatgarh-Mitri plain. 2. Bhadrajangroup of rhyolite hills with intervening plains and piedmonts. 3. Sukri-Bandi alluvial plain. 4. Northern plains.

V Pachbhadra salt basinVI Western plain with dunes-I. Tilwara-Baosin alluvial plain. 2. Sandy

plain with dunes.VI[ F'lo:J:lplain~ of the Luni and Jflw.zi-Sukri drainage system.

19

I. Siwana dissected plateau-This geomorphic division lies almost in thecentre of the region covered by S. O. I. toposheet 45 C and is bounded on all sidesby the 152.40 m contour line. The country rocks are the Jalor granites andMalani rhyolites of the pre-Cambrian period. The Vindhyan sandstone of finegrain has been found below the rhyolite in Siwana outcrop. The southern part ofthis division is occupied by the granite-rhyolite ridges and the northern part isstuded with rhyolite inselbergs of varying relief between 304.80 m to 545.58 mabove the datum. This rhyolite originally formed the plateau surface which waslater on dissected, and the hills on the northern side are all erosional remnants.Warping, ti lting and faulting took place in the region. IIi betwe,en the maingranite and rhyolite hills there is a -rift which is at present occupied by a stream.The western part of this region is covered with blown sand. Tnere are smallpatches in this area where double cropping is practised. The water is availablefrom the aquifers constituted by the net-work of dead and buried stream channels.

LAND UNITS

(i) Kundal-Ram'lnia alluvial inter.montane pZain (Valley fill)-This is coveredwith coarse detritus and sand brought down by the streams. In places this unithas been reclaimed for cultivation. like in Dhiran and Ramania. Short streamsdescend down the steep face of hills whichescarp this unit. This is a tribut<tryplain of the Takhatgarh-Mitri plain. The stream which goes west to east receiveswater from the hills. The dl'a'inage conditions of the eastern tract of this unit aregood. The general depth of wells of the villages of this plain varies from 18.22 m(Jaipur) to 21.23 m (Ramania). The water is found at 15 ~ depth. In the nor-thern portion of this unit there are sand covered alluvial fans which have beendissected by short sub-parallel chaimels. Crops are generally grown in Kharijseason.

(ii) Siwana alluvial plain-It comprises of the flat country of Siwana,Kusip, Thapan-Deora, Rakhi-Devandi and Mawri villages studed with remnantsof granite-rhyolite out-crops that formed a part of the Siwalla plateau.

The major portion of this unit consists of exposed rock surface with thinveneer of detritus transported and spread by sheet floods. The finer materials are

maximum

20 BIMAL GHOSa, SUREESH P.ANDY, SURENDRA SINGH AND GHEERA l.AL,

This division lies between the Jawai and the Khari Rivers in the southelTIJ;

II. Jal€lre-Israna-Rewara granite rhyolite interfluve with interNeningplains

finally t~ken to the valleys w'l.ich act as local base levels. Along the yaUp-ISthe status of dlainage is comparatively good. The general depth or welUs 17.67m (Thamni) to 19.81 m (Siwana). The water is found at 15 ill depth.

(iii) Old alluvial plain of Golia-Bhailan- This lies to the south of theSiwana alluvial plain and comprises of villages Golia-Bhailan, lndrana, etc. Thisdiffers from the above in two aspects.

(a) The former is an er0sional surface situated at higher level thanthe latter.

(b) tI'<l1:e latter is alluvial' fan surface developed by the neaibystreams and is situated at a lower level.

GEOMORPHOLOGY OF THE CENTRAL LUNI BASIN 21

part of the region. Climatically this land unit is wetter than the Siwana dissectedplateau. The country rock here is predominantly granite and some rhyolite.The threemajor hills are theJalOi hills. the Israna hills and the Mosal Rewara hills. The actionof weathering is more conspicuous here and dissections by small streams are promi-n~nt on all sides of the hills. The smaller hills near Nabi, Mailabas, Wan etc.,are the portions of the main hills but apparently isolated by the dissecting streamssome well defined and some disorganised. In between these hills there are inter-vening plains and the surface texture of soil varies from sandy, sandy loam to siltyclay or clay loam. There are saline patches at some places associated with finer.aggregate of soil. As indicated by the orientation of main stream channels thesesaline patches are of local origin due to decomposition of felspars. The thicknessof the soil cover and 'the underlying weathering products exceeds 16 m and thewater is available at the depth of 1 to 15m approximately. The disorganised channelscarry this water from rhe u.?per reaches and it is stored in the weatheredmass below. Where the well is located away from the stream bed the water isbrackish.

LAND UNIT;;I

(i) »'estern plain with small 8and dunes of local origin-This area is devoidof tributary to the main channels and comprises of villages Birana, Reothra,AI: san, Keswan, etc. It extends from 152.40 m contour in the east to the con-fluence of the Jawai and the Khari. The underground water level is 9 m belowthe surface and gradually decreases towards the river beds. The plain is fertileand possesses good drainage status.

(ii) The piedmont zone in the south and west of the Israna granitehills

The western slopes of this piedmont with slopes of 6° to 7° are coveredwith sanl This region has been dissected by numerous channels coming from the

adjacent hills.

(iii) Leta-Bagra plainIt lies in between the Jalor and Israna granite hills and is characterised

by thin veneer of sand and in the middle overlying alluvial deposits. This areais undulated due to the presence of small mounds of sand and incision by channels.

(iv) Harji-Manadar-Las plain

In the northern part of this tract there are patches of dark sticky surfacedeposit (somewhere saline) covered with grasses. This plain slopes on both sidesi.e. to the north and south. The streams drain into the Jawai and the Khari

respectively. '

22 BIMAL GHOSH, SUREESH PANDY, SURENDRA SINOH AND dHEESA LAL

23

3lmetreslfromr,the sprbce. The ~lo.pe ionthe"areJ. is/to the nor~h-west ,Wihich canonlYibe de.t.e!et-edby the[ilPW,of water. The rLv.ers W!.vegraded c,hap.deJs a,nd) wh~nthere i$ liMn l-in"Uleir .c~t.chm~ts •.w~terspreads!()ver their sides. The moisturecontent of surface dap.osits'is m'lointained ~alm3st· throug~)ut the ye'l.r .surfacedeposits are sandy loam and ClAY,.the latter r,~ei¥glc.on:fine,d near.yr to. the streamchannels. The area is usually double .cr~pped.

IV . Notth' and, north-east alluvial plains

This .division lies in t,he north and north-ea~t portion of the surveyedregion in the Luni ba:;in. These plains have i?e~n built up qy t~e t:,ive'rs' lik~ theMitri, the Bandi, the Luni and their tributar:ies an,d consist of ol<;ler and recentalIuyium un<;l~rlain by ~alani voIcllnics ,.,which. stand in the form of hil}s(all,dhillocks near Bhadrajan, Panchota, Khambi and Koma with dissected piedmontveneers to the east and w<:st. The height 9f Bha9raja.n ,~iI1 is 6:1-4.04 metres abovemean sea level. The alignment of hills is aimost north-south except Pan~hota andM\1lewa hills which run from Panchota hHl'(576.31m.} and stands as'inselberg, TheMulewa hills run from Mulewa to Malgarh in north-east ·direotion. 'I'fhehighestpoint is 660.19 m. To the south and south-east oflthe Luni <there are number of'dands' which fall almost on straight lines and in accordance with the ~ivtrvalleys. They are shallow demes$iQns wid?- Qliqim,um d,epth and sticky fine deposits.The piedmont streams are the ~ource of ~ater to the plain. They disap'pe!'lr in thealluviaI'deposits as soon ali they lack gra!lient pull. '

North Qf t!,le Luni is ~n uns:lu,lil~j,n~,plain with oq~a~i9nal ,we~~~~r~1 r~ckyi~l:m.dha.vi})g rnpr,e I!el'qent~ge .of ,lime '~nd f,~Il).q.ll d.qnt;s. The weat)1f;rpd ro1cky.i:;land extf;1nd frpm NiIIl}ge .Khli'jr.i,aji to,]fl.t9nTE::;'R1;I..ani and on-ward .cQv.~1:'eqwi~hlay.er: ofbJpwn,sand,jn\I?~~~' Th,e1deHf'h ot;~t;lls irJ,this flrea,if ~.86 metres. ';J;hegener.<J.l.relief js,mpnQ~J),()Ils j':x~ept hillo~ks ,of. HHr.58]I1. (near~~ra-Ki-ph<l;Di)and 258.16 m. (Samdari) heights exist. There are small tanks (dem.h rfrf?P,11;5~ m.to 4,57 m.) s,cattered here ;}nd there. ';rhey remain dry almost 7-8 months in theyear. ' ''< • "

LAND UNITS(i) The Takhatgarlt:.!Mitri"old alluvial 'plain

It ,e~tendsJ'rpm..,s§l,l,th'l~t',of, 1JaI$llttg~hItq tlW.J;.lWi (flopc;lrw~in in thenOJith.of t~e.$~n.W~1!~l):a,E.ann. TJ1~;:;utfl1('e..4fJpqsi.t~ a.r~ ~n14vium{o,G~he-B.iverWtri anc;lJit&'Jir;i\:ll}t~ies .• T,hed~1'ture ,is, lQ~Y to, j~aJHJYi llpi\m~~~long,;~~aMeliSOall':'lWn;rkl> the. wMer taQw ',is ,5l1to !7"~~rtls. fr.qrp.. ;the, sq f~ce ;'IlPd 1":§l~If\!n ,:byimpevV.iou.s:pllonfOrJml;tiWl, •..

'{ii) IEhfj'Bhadrajau.lgroup1of:,hyoHte mUs'iwilth lIl!liervening ~plains, landpiedmont

VI. Western plain with dune

BIMAL GHt)SE, SUEESH PANDEY, SURENDRA SINGH AND GREESA LAL

The surface is highly saline that limits cropencircled by high dunes except in the eastern portion.

GEOMORPHOLOGY OF THE OEN'fRAL LUNI BASIN 25

VII. Flood plains of the Luni and Jawai-Sukri drainage systems

These are along the course of the m::l.inrivers of the region. These are onlyfound in narrow strips on either side of the rivers. The flood plain is flat andconsists of heterogeneous deposits. The channel beds have coarse sand deposits.The surface deposits are very fine aggregates clay to clay loam. This is a veryproductive tract of the whole region. The distribution of population and concen-tration of settlement are more in this than in other geomorphic divisions.

SUMMARY

This region of the Western Rajasthan is a part of the Central Luni Basinand is drained by the Luni drainage system. The country rocks are predominantlyMalani rhyolite and Jalor granite and Erinpura granite. The Luni witb itstributaries has attained maturity. The relics of disorganised channels identified onthe aerial photographs of the region are at present partly truncated, buried anddisorganised. Along the valley sides of these streams examined near Devandi andChandrai there are alternate layers of stone lines and finer aggregates. During theestablishment of these prior drainage systems the climate was wet but startedgradually dry afterwards.

The region consists of 7 geomorphic divisions and further land units. Theyconsist of (1) Siwana dissE'cted plateau; (2) Jalor-Israna-Rewara granite-rhyoliteinterfluve with intervening plains; (3) Th<:lKhari-Bandi-Sagi riverine plains; (4)North and north-east alluvial plains; (5) Pachbhadra Salt Basin; (6) Western plainwith dunes and (7) Flood plains of the Luni and Jawai-Sukri drainage system. Theplains are fiat and consist of older and younger alluvia with somewhere sandyhummocks. The dunes are longitudinal, transverse and parabolic. The distributionof population and concentration of settlement are more in the flood plains of theJ.uni and Jawai-Sukri drainagoe systems than in other geomorphic divisions.

REFERENCES

Bulter, Ii. E., 1958. Depositional system of the Riverine Plain in relation to soils.C.S.I.R.O. Austrai!a, Soil Publication. 10.

Van Dijk, D. C., 1959. ~oil features in relation to erosional history in the vicinityof Canberra. C.S.I.R.O. Australia, Soil Publication 13.

Bryan, Kirk and Albritton, C.O.Jr., 1943. Soil phenomena as evidence of climaticchanges, Amer. Journ. of Sci. 241. 469-490.