Page images
PDF
EPUB

The Harnow river apparently has a perennial flow. It has a very steep gorge which should be easy to dam below Jhafar without inundating any land of value. Whether the capacity of such a dam (provided the extent of the flow of the Harnow would be sufficient to replenish the supply) would suffice to provide power for the Hazara district is a matter for the engineers concerned.

In Dr. Coulson's opinion, however, recourse could very easily be made to the more suitable stream, the Kunhar, along the course of which, no doubt, suitable alternative sites could be found for dams which would supply the whole of the Hazara district with power.

62. In response to a request by the Engineer-in-Chief, Army Headquarters, Dr. A. L. Coulson was deputed in December, 1936, and January, 1937, to

investigate the waterWater-supply, Balu

supplies of certain tactically important areas chistan.

in the Zhob district of Baluchistan, and also an area in the Quetta-Pishin district. Dr. Coulson's stratigraphical notes are published elsewhere in this Report (see pp. 80-83).

63. In January, 1937, Mr. W. D. West examined the site of the reservoir and dam for the Pench River (Surera) Hydro-electric Scheme. Pench River Hydro

This scheme is for the generation of electrical electric Scheme, Nag- energy for use at Nagpur, and involves the pur district, C. P.

construction of a reservoir on the Pench river below Kandlai, at a point some 36 miles in a direct line N. by E. of Nagpur, on sheet 55-0/2 where it flows south through hilly country.

The dam and reservoir sites are located on folded Archæan rocks, the strike of which is parallel to the alignment of the proposed dam. These rocks, which comprise three stages of the Sausar series, namely banded granulites, calcitic marbles, and muscovite-biotite-schists, considerably veined by aplite, are disposed in the form of an anticline and syncline overturned to the N. N. E. The dam site is located on one limb of the banded granulite, which forms a prominent ridge through which the river has cut its way.

The banded granulite is a very tough rock, though considerably jointed. Mr. West, however, is of opinion that the joints will be found to be tight in depth, but suggests that preliminary excavation along the site of the dam should be undertaken to settle the point. Apart from this, the site selected for the dam may be considered to be a good one, provided certain precautions are taken.

To obtain the necessary storage, the dam at this site will require to be about 116 feet high, which will maintain a reservoir extending about six miles up the river to Kandlai, with a capacity of 3,600 million cubic feet. The site appears to be quite suitable for a reservoir, and in view of the thickly forested nature of the catchment area, silting of the reservoir is not likely to become a serious problem.

The scheme as a whole may present certain engineering difficulties, but from the geological point of view the site is considered by Mr. West to be a reasonably good one.

64. In February, 1937, Mr. W. D. West was deputed to report on the geological aspects of the Tons River Hydro-electric Scheme, in Tons River Hydro

the northern part of Rewah State, Central India. electric Scheme, Rewah This part of the State is situated mainly on State, Central India.

an elevated plateau, averaging about 1,000 feet in height. It is bounded on the south by the Kaimur range, and on the north and east by the escarpment that overlooks the plains of Allahabad and Mirzapur. The Kaimur range gives rise to a number of streams flowing northwards across the plateau, of which the most important are the Tons and Bihar rivers. On reaching the northern edge of the plateau, these streams descend abruptly to the plains by a series of waterfalls, and it is proposed to utilise this drop for the production of hydro-electric power.

The possibilities of such a scheme have long been recognised, and they have been referred to in the reports of the Hydro-electric Survey of India. Closer examination, however, has generally revealed that the conditions are not altogether ideal, and it is for this reason, no doubt, that little progress has so far been made.

The rainfall of this area averages about 42 inches a year, which must be accounted quite good. Owing, however, to the scarcity of vegetation in this part of the State, the rain, as soon as it falls, rapidly runs off the ground into the streams and rivers, and is thus quickly lost. It is for this reason that the flow of water in the Tons and Bihar rivers rapidly decreases after the monsoon, and soon falls below the volume required for the production of the minimum amount of power. The construction of a reservoir on the top of the plateau is the obvious way of controlling the flow of water, but this is made impracticable by the fact that, owing to the very level nature of the plateau, the formation of such a reservoir would flood large tracts of cultivable land, and thereby prove uneconomic on account of the compensation that would have to be paid to the large

number of villages affected. In view of these difficulties, a scheme is under consideration which makes use of the combined waters of the Tons and Bihar rivers. This involves utilizing the flow in the Tons river until about the beginning of February, thereafter supplementing it with water from the Bihar river. Even so the latter will be insufficient during the hot weather, and it will be necessary to conserve its waters by the construction of a reservoir. By thus combining the waters of the two rivers, such a reservoir would not require to be so large, and the amount of flooded land would be kept to a minimum.

The details of the scheme are as follows. It is proposed to build a storage reservoir in the upper reaches of the Bihar river about four miles south of Rewah. The waters of this reservoir, when required, will gradually be released down the Bihar, and a diversion weir in the Bihar somewhere above the Chachai Falls will divert the water across the Bihar-Tons watershed into the Tons river. A pick-up weir in the Tons, a short distance above the Tons Falls, will feed the power channel leading to the power house forebay, which will be situated about a mile and a half downstream of the falls. In this way it is calculated that a minimum flow of at least 300 cusecs can be maintained throughout the year.

The geological structure of the area is simple and consists of a very shallow syncline of Vindhyan rocks, comprising the Upper Rewa sandstone,

sandstone, the Ganurgarh shales, the Bhander limestone and the Lower Bhander sandstone, in ascending order. It is the Upper Rewa sandstone which forms the escarpment over which the Tons and Bihar rivers descend in waterfalls to the Gangetic plain.

The site of the dam of the proposed reservoir on the Bihar is located on the Bhander limestone. This is a massive, fine-grained limestone, which is well bedded and jointed. It is, possible, therefore, that a certain amount of leakage may occur, which must be considered from two aspects, (1) loss of water from the reservoir, (2) the safety of the dam. Regarding the first point, a certain amount of leakage will not greatly matter, since the Bhander limestone is underlain by the impervious Ganurgarh shales. And since the latter crop out in the river below Rewah City, any water that may be lost from the reservoir will be collected further downstream, and ultimately utilised.

Regarding the safety of the dam, which will only be about 40 feet high, Mr. West considers that if adequate precautions are taken to protect the floor of the reservoir immediately upstream of the dam, and if the dam be given fairly deep foundations, any possible danger to the dam should be provided against.

Mr. West also examined several sites for the diversion weir on the Bihar, and considered that the site at Simon Ghat would be suitable provided that the weir is designed with gates that would let the excess water through with little or no fall on to a protecting apron.

The site suggested for the pick-up weir in the Tons river is located on Upper Rewa sandstones, which extend most of the way across the river. The site appeared to Mr. West to be a good one, provided precautions are taken to prevent leakage by sealing up conspicuous joints in the bed of the river above the weir.

Two sites were examined for the pipe line and the power house. . Mr. West considered one of these to be quite satisfactory, as the pipe line would be founded on solid rock practically the whole way down, while a convenient ledge, just above high flood level, offered a suitable site for the power house.

65. While in Rewah State, Mr. West was also asked to give an opinion as to whether the subscil strata in Teonthar tahsil, the northern Tube-well irrigation

tahsil of the State, are suitable for tube-well

tahsil, irrigation. This tahsil is situated at the foot Rewah State, C. 1.

of the ghats, and forms the southern edge of the Gangetic alluvial plain ; and the question considered was whether there is likely to be sufficient water in the alluvium of this area to enable tube-well irrigation to be conducted in the manner adopted in the more northern part of the United Provinces.

General considerations suggest that the floor of the alluvium of the Gangetic trough slopes very gently northwards, and that the alluvium is shallow on the southern side of the trough. This view is supported by the fact that Vindhyan rocks are seen in the bed of the Tons river at Chak ghat, where the main road from Rewah to Allahabad crosses the river. There can thus be little doubt that the alluvium of the whole of this tahsil is quite thin. The possibility, therefore, of a deep reservoir of water existing in this area, suitable for extensive irrigation, is considered by Mr. West to be out of the question.

in

Teonthar

same

66. Mr. West also examined the dam site for the Nindeh reservoir, which it is proposed to construct on the Nindeh river, a tributary

of the Karmnasa river in the southern part Nindeh reservoir dam site, Mirzapur dis- of the Mirzapur district. This scheme has trict, U. P.

been drawn up with a view to utilizing the energy available from the water that is let down from the Dongia reservoir for the irrigation of the Garai canal system. It has been estimated that about 130 cusecs on an average are let down for 123 days in a year. It is proposed that during the rest of the year the necessary supply of water should be obtained by building a reservoir on the Nindeh river.

The whole of the area under consideration is situated on the Kaimur sandstone. On account of the damage done to the rocks in front of the spillways of the Dongia reservoir during the high flood of 1936, it was considered desirable to determine whether the

weakness existed in the rocks at the proposed site for the Nindeh dam. At the Dongia reservoir the Kaimur sandstone is highly jointed, and moreover the joints are deeply weathered. In consequence, during the flood of 1936 the weathered portions of the joints were washed away and large flags of the rock were uprooted and moved bodily downstream. Examination of the rocks at Nindeh showed at once that the sandstones, although belonging to the same series, are markedly less jointed, both at the surface and in depth, and Mr. West considered that, provided the usual precautions were taken to grout any prominent joints that exist along the dam site and for a short distance above and below it, there was no objection to the site.

67. By desire of Surgeon-General Goil I visited the Darjeeling catchment area on 8th October 1937. It has been in the past a popular

saying that the common intestinal troubles of Water-supply, Darjee. Darjeeling in the monsoon

were due to in the water”. Previous to my visit I had examined in Calcutta two samples of the Darjeeling water drawn during the monsoon, one of the water as it flowed into the storage reservoirs (“ Senchal Lakes '') and one as it flowed out of them towards Darjeeling. Both were entirely free from mica or kaolin, but contained an infinitesimal amount of chloritic matter, and a surprising amount of vegetable debris. Mica in any quantity would no doubt, be an irritant to the intestines, while kaolin would act as the reverse. The latter is, like chalk, used in medicine, I believe, as an internal

mica ling, Bengal.

« PreviousContinue »