Comment
(Comment on the paper 'Evolution of Regional Transmissivity pattern in Adila hasin: . a nested squares finite difference model' by A.IlNarayanpethkar, V.V.S. Gurunadha Rao and K. Mallick published in the Jour.Geol.Soc.lndia, vAl. No.1, 1993, pp.21-32).
The paper uses a computer model to genenlte Transmissivity values over the Adila basin. The modelling appears impressive but is based on certain hydrogeological assumptions which require clarification.
1. 'Lineaments' in Fig.1 (p.22) appear to be straight line stream segments. Is it relevant to present the lineament map if these lineaments have not at all been used in the present study?
2. The paper does not include a hydrogeological map of the Adila basin which would easily have several Deccan basaltic flow/units exposed at the surface. Inspite of standard descriptive terminologies for the Deccan basalts, the authors have preferred to use (p.21) a vague terminology (weathered rock. vesicular lenses associated with red bole, intertrappean beds of weathered, jointed and fractured strata). ~nlcse descriptions are too general to convey the exact nature of the b~lsa1tic flows/units that form the aquifer.
3. loe assumed aquifer thickness of 100m would incorporate several Deccan basaltic units with a distinct set of hydrologic properties. Such a thickness would actually result in a multiaquifcr system rather than a single aquifer. A much sma]]er thickness (15 to 20m) of the unconfined Deccan basaltic aquifer h::IS been visualised for proposing hydrogeological models (Lawrence, 1985; Kulkarni and Dcolankar, 1990).
4. Ihc authors fail to give evidence confirming regional ground water flow. A layered model like the Deccan basalts requires a high Transmissivity lnyer (on a regional scale) Lo accommodate regional ground water movement.
5. Is it practical to use water level data from only 40 of the 1,300 wells (3%) ? Does the data represent the system correctly. particularly in the highly inhomogeneous Deccan basaltic regime?
6. Premonsoon water levels in the Deccan basalts show maximum fluctuation as they arc drastically affected by continuous ~md varied ground water abstraction. Is the assumption of steady state water levels (p.26) therefore justified?
7. In reality ~f unit mesh of eilher one or four sq.km. will include more than one wel1. Using the .method adopted by the authors, every' tested well will give a different T-value due to the inhomogeneous nature of the Deccan basalts. Which of these several T -values is appropriate enough to represent a unit mesh area? This could be the reason for the computed water levels (1st run). using estimated and interpolated values to be higher than the observed values.
8. The T-valucs have been enhanced to compensate the higher computed water levels in the northern part with more lateral ground water flow. Do hydrogeologicrtl conditions HJong the Adita stream allow for such an enhancement of the Transmissivity by almost twice the estimated (field valuc...;;)?
regional scale, through simulation. is rendered easy. Inspite of being aware of the inhomogeneities. there is absolutely no mention of the hydrogeological factors that attribute such inhomogeneity (and anisotropy) to the basalts. Nor is there any reference as to how these factors have been accounted for in ~I rcgional flow model. Further, the authors have failed to convincingly account for the mismatch bctween observed and computed values in
the
light of the inherent inhomogeneity of the Deccan basalts. Instead. they rely on certain adjustments in the T-valucs to arrive at the eventual estimatcs. Such studies may not give correct impression of the Deccm: basaltic aquifer systems.Department of Geology University of Poona Pune-411 007
References
S.B. DEOlANKAR IIIMANSHU KULKARNI
KULKARNI. I-I. and DEOlANKAR, S.B. (1990)Calibrati')n ofpcrmcability fora conceptual hydrogcot~)gicall11oJel of a Deccan basaltic unconfined groundwall;r system from Maharnshtra, India. Modd CARE-90 (Calihnltion andRcliabilily in Ground w,llerModcllillg , the lague.the Netherlands), pp.199-209.
LAwRENCE, A.R. (1985) An interpretation of dugw ~11 performance using a digital model. Ground water, v.23,
No.2, pp.449-454.
Reply
We wish to thank Dr.S.D.Deolankm and Dr.ll.Kulkarni for their interest in our paper (Narayanpethkar et 01 .• 1993a). Clarification:; are given point-wise in the following paragraphs. 1. The lineaments have b{~en used in the modelling. Please refer to the points 2 and 3 on p.28. This oversight has led to points 4 and 8 later in their comments.
2. In order to save spac(: we have not provided the geohydrological map. All the gcohydrological parameters, however, hav{~ been used in the modelling. While describing the basaltic aquifer on p.21 only standard terminologies have been used.
3. lbe assumption of aquifer thickness is problem-specific. ulwrence (1985) had his own reasons to assume 10m in the Nion basin located f<lr awny from our study area. Will this assumption hold good everywhere in tile Deccan basalts? Our basis is as follows:
(i) Water levels have been observed in shallow as well as deeper wells. further, the watcr levels in shallow (phrenlic condition) and deeper (pOSSibly inter-connected multilayer system) wells stand approxim:fltcly at sam(~ elevations.
(ii) T and S values have been estim, ted from shallow as wcll as deeper wells with depths at times in the range of 100m.
4. The groundwater flow can easily be visualised from the water level contour patterns. We have reported this in another communication in a different context (Narayanpethkar ct al., 1993b). As regards high transmissivity layer, once again we wish to refc.r to the points 2 and 3 on p.2S of our paper.
5. Observation well data act as training sets in pattern recognition problems. More than the number of such wells. the emphasis is put on their spatial distribution giving adequate wcightagc to different regions within the basin. The H?-test on p.28 is a measure to indicate how correctly the system is r,epresented.
7. In digital simulation of aquifers every mesh is assigned a specific T-value thereby maintaining continuity in the physical properties and further ensuring the incorporation of anisotropy/inhomogeneity of the formation. TIle discrepancy between the observed and the computed water levels in the first run is due to several factors. Five such factors have been documented on p.26-27 to minimize the difference.
8. This point is related to points 1 and 4 raised earlier by Dr. Deolankar and Dr. Kulkarni.
There has been no oversimplification in the modelling efforts. The relevant parameters-basin boundaries, rainfall, open pan evaporation, groundwater levels, groundwater draft, soil and lithologic conditions, lineaments, transmissivity values, seepage from the reservoir and canal network and the interaction of the Adila stream with the aquifer system among others- have been appropriately taken care of. Inhomogeneity and anisotropy are inherent to geological formations. We rccognize these from the wide variations in physical properties. For instance. the spot T- values range from 2 to 349 m2/day, whereas S-values, from 0.005 to 0.2435. Dcolankar (1980) has also reported T-valucs of basaltic rocks around Pune. Jnste~ld of merely making a mention of it. we hnve accounted for these inhomogeneities in the modelling on the basis of the existing field conditions. This has yielded satisfactory results.
Far from claiming that ours is the last word on nquifer modelling, we shall derive great pleasure. if more and more basins are modelled both under steady-state and dynamic conditions so that our understanding and technology arc fast- forwarded.
Department of Geology
Slu'l'aji Uni1'.Cclltrc of PG Studies
National Geophysical Research Institllte lIydcrabad
References
A.B .NARA YANPETHKAR
V.V.S.GURUNADHA RAO K.MALLICK
DEOLANKAR. S.B. (1980) The Deccan bitsalts of Maharashlra, India- [heir potential as aquifers, Groundwater. 18.
pp.434-437.
LAWRENCE,AR. (1 985) All inlerprctationofdugwell pc rfo nn a nee usinga digilalmodel, Groundwater, 24,pp.449-454.
NARAYANPETllKAR, A.B., GlIRlINADlIA RAo, V.V.S. and Mallick. K.(1993a) Evolution of regional transmissivity pattern in Adila basin: a nested squares finite difference model, Jour. GeoI.Soc.l ndia, v.4l, pp.21-32.
Corrlment 2
(A comment on the Research Note - "t\ note on the l\1iddle Junlssic Strntigruphic succes.. ... ion of Keerd. nome, IKuchchh district, Gujard.ttt by S.Prasad, published in the
Journal of the Geological Society of India, v.4l, No.2, 1993, pp.156-161.)
We appreciate the information brought forth by Prasad. However, we like to make some comments in a wider integrated frame-work:
1. We h~ve taken unambiguous note of the non-g'olden-oolitic basalmost part at Kecra and have even differentiated 33 beds in it. Krishna and Cariou (1988) included this thinner non-golden- oolitic part with the overlying thickcr dominantly gOlden-oolitic part as bed 1
only in
a
broad context ("mostly golden-oolitic" p.152, 1988). Infact. in bed1.
several thicker non-oolitic softer Clays alternate with relatively thin, transgressive hard/pebbly/nodular bands, non-golden-oolitic in the basalmosl part and gOlden-oolitic later. '2. lhe ilIustratcd ammonoidcs are without position. Figure 2 most likely belongs to M.
gr. madagascaricllsis/lrjnngll/nl'is. True AI./ol'J1loSIIS is restricted within a small thickness immediately above bed 1 (Krishna Hnd Cariou 19<)0). Infact. Af.jormoslis as disccrncd only recently is close to distinctly oldcr M. gr, lriangularis/madagascariensis, although bcing phylogcneticllly unrelated. The ncar homcomorphism is linked to rcsponse of the Macrocephalilcs lincages to eustatic cyclicity under limited genetic constraints of morphologicll variation (from comprcssed to depressed to again compressed; Krishna and Cariou 1990 & 1992). The basalmost non golden-oolitic part is dated as earliest Lower Callovian, though extension in the Bathonian is not alLogether ruled out. In the sequence stratigraphic context (Vail el aJ 1(87), the youngcst occurrence of Af.triangularis is placed in the transgressive component of Vail cycle LZA 3.1. while th~~t of !tllormoslis in the transgressive component of the next cycle LZA 3.2 which are separated by several subl' .. oncs.
3. Wc Object to the use of "Jumara Formation" for the older/original Ch<lri Formation
for r~lsons of priority. Further. Pras~ld has wrongly correlated the golden~oolitic part of Lower Callovian age with the Middle Member of "Jumara formation" of Middle Callovian age.
Dcpartmcnt of Gcology BUllaras 1I;"du Unil'!:rsil), lrUralltlsi-221 005
Uderences
CARIOU. E.3nd KRISHNAJ.(1988)The TClhyan ReinedeiinacoL" KUlch.
JAIKRISIINA JAI RAM 0." IA BlNDIlYACHAl PANDEY
KRlSHNA3nd CARIOll (1990) AmlllOlll)id faunal exchange during LowerC:lllovian hctwccllthc Indo-E.1~t·Afric;1l1
and Submcdilerrancan provinces; Implication for Ihe long distance Bisi-Wesl correlations. News!. Straligl' .•
v,23(2). pp.109-122,
KRISHNA ;1 lid CARIOU (l992) The TethY;ln Macron ph:llilin;le: evolutionary. environment'll a nd dispersal stralcgics, Gcobios, M.S.No 15,9 p.
Reply
I am thankful to Drs. Jai Krishna, lR.Ojha and ll.Pandey fOr their appreciation and comments on my research note published in the Journal of GeologiaJl Society of India vAl, No.2, 1993, pp.156-l63. The following are my response to their comments.
The commentators have stated that they have made a note of non- golden oolitic basalmost beds at Keera and have included this sequence with dominantly golden oolitic part as Bed No.I. However, in the reference quoted by them (Cariou and Krishna, 1988, p.152) there is no such mention. I am not aware of any other publication in which they have differentiated "33 beds" in the non-golden oolitic basalmost part of the Kcera. lbere[ore, the author's priority in locating such a sequence stands.
2. The ammonites illustrated were collected from the middle part of the bed no.4 (Member-I) 0.5 km south and SSW of the Keera Dunger.
Some doubts are expressed about the identification of the figured specimen of M.[ormoslls (Sowerby)
.r
morph formosus. I wish to reassure ·that the specimen is a perfectly preserved one and is identical to M.formosus recorded earlier from Kachchh. In the present collection, there arc more than 10 samples of M.[orl1loslis (Sowerby)~
morph formosus collecled from bed nos. 4, 5 and Lower part of bed no.6 (Palaeontology Division G.S.I. Western Region, Registration Nos. 1/188. 190. 194. 196. 200. 201, 203. 208, 210 and 255).The present study of the stratigraphical distribution. of formosus shows that this form is not restricted within a small thickness as stated by the commentators (in Krishna and Cariou, 19(0) but is found not only in bed no.1 of Cariou and Krishna (1988) but also in the succeeding and preceding beds.
As regards the age of the non-golden oolitic sequence (Member-I) reported by me. there is no doubt that it belongs to the earliest Lower Callovian as evidenced by the presence of not only M./ormoslls, M.madagascaricllsis but also M. of triangularis (GSI, Pal.L1b.Reg.No. 11324).
3. TIle only Lithostratigraphic Classification of the Mesozoic of Kachchh which is as per the code of Stratigraphic Nomenclature of India is by Diswas (1971, 1977 and 1981).
It has, therefore. been followed by the author in his work.
Golden oolitic bed (Middle Member of Jumara Formmion of Biswas. 1981. Table-II A, p.64) contains undoubted Lower Callovian ammonites and as such there is nothing wrong in correlaUon given by me.
Geolgical SlIrI'ey of India
Jaipllr
References
SURENDRA PRASAD
DISWAS, S.K. (1971) Note on thc Geology of Kutch, QuartJour.GcoI.Min.MeI.Soc.India, v.43(4), pp.223-236.
--(1977) Mesozoic Rock StratigraphyofKu((·h. QuarUour. GeoI.Min.Met.Soc.lndia, v .49(3&4), pp.1-52.
