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RIVER METAMORPHOSIS DUE TO HUMAN INTERVENTION IN THE NEYYAR BASIN, KERALA

BY THRIVIKRAMAJI. K.P.

DEPARTMENT OF GEOLOGY, UNIVERSITY OF KERALA TRIVANDRUM-695 581

INDIA MAY, 1985

2ND TECHNICAL REPORT OF PROGRESS OF WORK SUBMITTED TO THE DEPARTMENT OF ENVIRONMENT, GOVERNMENT OF INDIA, NEW DELHI, GRANT

NO.9(6)/4/83/ENV-2/dt: 15/03/1983

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PREFACE

This annual report for the second year of the project on River Metamorphosis due to Human

Intervention, Neyyar basin, Kerala includes the results of various studies carried out during

the second year. The sections in this report document, describe and discuss landuse,

geomorphology, surficial geology and slope studies carried out in the filed area as well as the

results of the studies carried out on air-photos and topographic sheets. A section deals with

the load characteristics of water samples collected from the Neyyar at specific site. The

results of the continuing studies on the hydrology of the Neyyar also finds a place in this

report. Further metion is made of the bedstead type exosion monitor to record the periodic

accumulation or removal of soil from the slopes. Though the instrument was devised and

fabricated during the period covered by this reported actual field monitoring will take place

only during the period of 1985-86. In addition several data tables and diagrams have been

included in this report.

K. THRIVIKRAMJI

Department of Geology,

2nd May, 1985

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ACKNOWLEDGEMENT

I take this opportunity to place on record the continued help, co-operation and support

rendered by the Department of Environment, Govt. of India, New Delhi in the implementation

of the Project on River Metamorphosis due to Human Intervention in the Neyyar Basin. The

Department of Geology of the University of Kerala and the University of Kerala and the

University of Kerala (especially Prof.P.O. Habeeb Mohammed, the Vice-Chancellor) readily

offered a helping hand at times of need. The Survey of India, Bangalore and Secretary,

Department of Defence, Govt. of India, New Delhi granted permission for study of the

Airphotos of the Neyyar basin. A band of young and illustrios research staff relentlessly

offered their whole-hearted co-operation in the realization of the projected targets of work in

the difficult terrain of the Neyyar basin, without which the implementation of the field

programme would have certainly suffered. However, the errors and omissions or lapses in the

content of the report soley mine.

K.P. THRIVIKRAMJI

Department of Geology

University of Kerala

Kariavattom 695 581

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ABSTRACT

The Neyyar River net is mostly carved out a Precambrian crystalline terrain, which bad undergone considerable deformation. The drainage pattern of the basin is dendritic to sub-dendritic and at some places. It assumes a rectangular nature. The inter-relations of the dominant lithological units, viz. Charnockite and Khodalite have not been examined in detail for the purpose of the investigations reported in the following pages. Tertiary sedimentary rocks are noticed along the coastal plain. Laterite-derived soil cover is noticed in most part of the basin along with soils formed out of alluvial deposits. Generally speaking, the upstream parts of tributaries are under crystalline rocks: the middle reaches under laterite: and the down stream portions of the master stream in ancient channel fill deposits.

The dominant landuse in the basin is more of a rural nature. The modification of tributaries has its own intrinsic relation to the landuse pattern of the region.

Air-photo studies of the Neyyar basin have been under-taken to assess the role of lithology and structure of the bed-rock on the development of river-net. Major control of structure is noticed in the midland region, where the joints, foliation and lineaments influence the topography. The Charnockites seem to be more massive than the gneisses anyway.

The landuse pattern of the Neyyar basin (interpreted from airphotos) is fast changing and hence very dynamic. It is interesting to note that the land that was once under rice paddy gave way to tappiocea or plantain: and the land once under mixed crons is now converted to rubber plantations. Large scale exploitation of flood plain mud and channel sand most of the time reaches menacing proportions leading to bank caving, and out offs of channel bends.

A slope map prepared from toposheets demonstrate the spatial variations of slope values across the basin, especially in the lowland (below 200 m), midland (between 200-600 m.) and the highland (more than 600 m.). A major portion of the basin classifies under lowland (86.56% or 425.8 Km2). Midland portion is only 11.17% or 54.96 Km2, where as the high land is 2.27% or 11.17 Km2. The left-bank portion of the basin shows a much rugged topography and hence a variety of slope class distributions than the right-bank portion.

Valley fills have formed due to inability of the streams to transport all the load supplied to it by hill slope processes and fluvial action by headward erosion and/or extension of streams. The terracing of fill material for cultivating rice paddy or similar crops reduces the overall length of the slopes and allows the flood waters to be trapped in them temporarily, resulting in the deposition of most of the load. Though terracing action tantamounts to reduction in sediment supply to the main stream, such actions stand as lone example of a positive human action. Terracing of hill slopes also have led to similar results.

The study of temporal and spatial variations of suspended load and dissolved load in the network at several points have been carried out by collection and analysis of water samples. Any meaningful contribution can be expected only after accumulation of such data for at least a period of one year covering the monsoons and baseflow season.

Rainfall data is being collected from six of the subbasins of the Neyyar network, and will be used in the experiments conducted in the field on soil erosion rates and quantities.

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Contents

I Preface

Ii Acknowledgement

Iii Abstract

Chapter I Surficial Geology of Neyyar Basin

Chapter II Neyyar Basin Landuse and soil

Chapter III Photogeology of Neyyar Bsin

Chapter IV Neyyar Basin: Photo-Interrupted Geomorphology and Landuse

Chapter V Slope Studies in Neyyar Basin

Chapter VII Hydrochemical and Hydrologic Studies

Chapter VIII Bed-Stead Type Erosion Frame

List of Illustrations

1. Surficial Geology Map

2. Landuse Map

3. Soil Map

4. Geologic Map: Photointerpreted

5. Landuse Map: Photointerpreted

6. Slope Map

7. Map of gauging stations in Neyyar Basin

8. Rain Gauge sites

List of Tables

1. Slope data, Neyyar Basin

2. Hydrologic Data for Master Stream, May 1984

3. Hydrologic Data for Master Stream, Nov. 1984

4. Hydrologic Data for Master Stream, Feb. 1985

5. Water Chemistry of Tributary Streams, Nov. 1984

6. Water Chemistry of Master Stream, Nov. 1984

7. Water Chemistry of Master Stream, Feb. 1985

8. Rainfall Data for Neyyar Basin: Oct. 1984 to Feb. 1985

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CHAPTER I

SURFICIAL GEOLOGY OF NEYYAR BASIN

Introduction

Surficial geologic mapping subbasins of fifteen tributaries of Neyyar river, eight in left bank and seven in right bank has been carried out on Survey of India Toposheets (Nos.58 H/2, H/3, H/6) of 1:50,000 scale.

Quartzo

feldspathic gneiss, biotite gneiss and garnet-sillimatite gneiss belonging to the

Khondalite group are the predominant rock types exposed in Neyyar basin. The strike of foliation of gneissic rocks is generally in a NW-SE direction with local variation to N-S, NE-SN and E-N. The dip of foliation varies from 50 to nearly vertical; Local opposing dips are also noted. Laterite and charnockite are the other rock types exposed.

The interrelationship between charnockites and Khodalites is not clear. In many places there are intercalations or rather interlayering of one within the other. The demarcation of these rock types is done by the preponderance of one over the other.

Laterite is observed as a capping, over gneissic rocks as well as Tertiaries.

Major part of the river basin is covered by soil. Lateritic, clayey loam, poorly drained and well drained soil, loam (yellowish brown) and alluvium are the main soil types.

The tributaries of Neyyar river exhibit subdendritic as well as rectangular drainage patterns. Two major tributatries on the left bank (Chit Ar and Aruviyodu thodu) chiefly exhibit a rectangular drainage pattern. The order of feeder streams varies due to abstraction as well as due to development of minor first order streams.

Generally the upstream parts of all the tributaries are underlain by crystalline rocks, the middle reaches of the stream course by laterite, and the downstream portions by soil cover lying over alluvium.

Surficial geology of each subbasin from the dam site is described separately.

Sl.No. Tributary Drainage area

1 Tributary joining at Kallikad (RB) 4.9 Km2

2 Tributary joining of Puduvittumuri (Puzhanad) (LB) 3.5 Km2

3 Tributary joining at Ottasekharamangalam (LB) 49.2 Km2

4 Tributary joining at Ariyankod (LB) 5.3 Km2

5 Tributary joining at Kizhavur North (RB) 1.35 Km2

6 Tributary joining at Kizhavur South (LB) 2.5 Km2

7 Tributary joining at Parachal (RB) 9.9 Km2

8 Tributary joining at Aruvikkara (RB) 1.8 Km2

9 Tributary joining at Perumkadavila (LB) 7.65 Km2

10 Tributary joining at Aruvippuram (LB) 48.00 Km2

11 Tributary joining at Aruvippuram (RB) 13.4 Km2

12 Tributary joining at Amaravila (LB) 2.7 Km2

13 Tributary joining at Olathannai (RB) 20.68 Km2

14 Tributary joining at Pazhayakada (RB) 11.00 Km2

15 Tributary joining at Vlathankara (LB) 22.1 Km2

RB : Right bank, LB: Left bank

Surficial Geology

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(1) Tributary joining at Kallikad (W 532821)

This third order tributary joins the mainstream from the right bank.

Geniss and garnet bearing charnockite to a very small extent, dipping NE together with lateritic soil and soil rich in humus, cover the upstream area of this tributary basin. Laterite showing parental rock structures especially foliation are also exposed on the head water portion of this tributary (near kokkuti, W 517853).

Lateritic soil, clayey soil and soil with humus cover the downstream part of the stream (Viranakavu, W529711). Flood plain silt covers either banks just near the vicinity of the confluence with the main channel.

Tributary at Puduvittumuri (Puzhanad, W 544794)

This second order tributary joins the mainstream from the left bank.

Quartzo-fledspathic gneiss with biotite, striking NW-SE is the only rock type exposed. It is observed for more than half the length of stream after which lateritic soil covers the banks up to the confluence with the mainstream.

A knickpoint is noticed along the stream course where gneissic foliation strikes NW-SE. Isolated exposures of gneiss also occur on either banks surrounded by lateritic soil and soil with humus.

Tributary joining at ottasekharamangalam W 539752 (Chit Ar)

Chit Ar , a tributary, enters the mainstream on the left bank. This tributary possesses the largest drainage network, and drainage area (49.2 Sq.km.) in this river basin. Rectangular andsubdendritic drainage patterns (heopold, L.B, Wolman, M.G and Miller, 1964) are exhibited by this 4th order stream due to structural control of the underlying rocks. Lower reaches show crudely developed meanders. This tributary crosses three knickpoints before entering the stream.

Gneisses are the predominant rock types exposed in the subbasin. Garnetiferous biotite gneiss and Biotite gneiss are the two main types. Foliation of gneissic exposures on the northern part of the rectangular network of streams strike NW-SE and dip towards NW and the rest of the gneissic exposures show a foliation strike of E-N, and ENE

WSW and dip northerly. The strike and dip directions vary locally. Gnessic rocks also show, crude foliation and intra-folial folds. Laterite exposures are comparatively few. Gneiss-charnockite intercalation (Soman, K 1980) is observed on the upper reaches and northern portions of the rectangular drainage network (as at Kuttappu W 640768). Here the preponderance of one over the other is difficult to interpret. Gneissic exposures continue southward upto the end of the southern tip of the rectangular drainage network is due to structural control of the underlying rocks. The strike of foliation of the rock exposures on the northern end swings to NW-SE from E-W and ENE-WSW of the southern end.

Chit Ar shows almost a straight course for 3 Kms. Upto the confluence with the main stream. After its confluence with Neyyar river, the master stream also shows a straight course for 8 kms. This may be due to a lineament control (samsuddin, 1980) trending in this direction (ENE-WSN) as revealed from the attitude of rick exposures.

About 4 Kms. Upstream of the commencement of the straight course of Chit Ar, two knick points are noticed. Gneissic rocks are exposed on both points with an E-W trend. Lateritic soil, loamy and clayey soil and soil with humus are the soil types exposed along the stream course from the upstream part.

A knickpoint occurs at about 2/2 Kms. Upstream, from the confluence of Chit Ar with Neyyar. The rock type exposed is pink coloured gneiss (with garnet) with foliation strike of ENE-WSW and northerly dip. The rock is highly jointed. Quartzo feldspathic gneiss, without garnet occurs in association with pink gneiss showing a similar trend. The exposure displays effects of differential eresion.

Aspect of meandering is exhibited by Chit Ar for a distance of about Kms. Upstream of the straight section. At the confluence with the master channel, gneissic rocks are observed.

Loamy soil with humus and alluvium are also developed in the subbasin.

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Tributary entering at Ariyankod (W538752)

This third order stream joins the ainstream at Ariyankod from the left bank. Restricted exposures of Charnockite, striking NW-SE is exposed on the upper reaches (Mundanad W582710) of the stream. No other rock types are exposed, except laterite near the confluence with the masterstream. Lateritic soil of the transported type, loam and alluviu are the soil types developed on the stream banks. Charnockite is garmetiferous. Alluvium occurs at the near Victinity of its confluence with the main stream.

Tributary at Kizhavur North (W524753)

This second order tributary joins the master stream from the right bank subbasin.

No exposures of hardrock is seen throughout the course of the stream. Only laterite is exposed and is observed for almost half of the length of stream. Then upto the confluence of the tributary with the mainstream laterite soil covers the banks. Laterite soil is of the transported type.

Tributary joining at Kizhavur South (W525747)

This stream has changed from first order to second order-due to development of a minor first order stream. It joins the master channel from the left bank.

Quartzo feldspathic gneiss with biotite and garnetiferous sillimanite gneiss are the rock types exposed on the head-waters (Anavur W553720) of the tributary and downstream portions of the stream respectively. Gneissic exposures and gneissic boulder rich talus form the ridges on either side of the tributary. As we reach the middle part of the stream course, gneiss becomes weathered. Also, gneiss on slopes get deeply lateritised. Laterite and loamy soil, cover both the banks of the stream upto the exposure of garnet-sillimanite gneiss. Garnet-silli anite gneiss or laterite is exposed alternatively upto the confluence of this tributary with the mainstream. Floodplain silt also covers the banks on the confluence of this tributary with the masterstream.

Tributary at Parachal (W515757)

This stream is of third order. It enters the mainstream from the right bank. The stream has two main branches which join about ½ Km. upstream of its confluence with the master stream.

Both gneiss and laterite are the rocks exposed on the upper reaches of the two branches of the tributary. Gneissic foliation shows a north easterly dip. The northern branch of the stream shows gneissic exposures with foliation diping towards south west but on the southern branch of the stream, gneissic foliation dips towards northeast.

The two branches of the stream have more or less the same category of rock exposures. Gneiss and laterite occur alternatively towards downstream from the upper reaches. Gneiss to laterite alternation is observed in the upstream parts of the two branches of the stream. Depth of weathering of gneiss is deeper as we go downstream. There is a knickpoint near its confluence with the other branch. The cock exposed is gneiss with foliation striking NW-SE, and dipping SW. After the merging of the two branches, gneiss is seen exposed upto the near vicinity of the confluence with the main stream. Here gneissic foliation dips toward NE and it is marked by intrafolial folds. On the confluence with the master stream alluvium and lateritic soil occur.

Tributary joining at Aruvikkara (W494746)

This right bank tributary joining the main channel at Aruvikkara (near Aruvikkara temple is of third order). The order of the stream has changed from second to third by the development of minor first order streams.

Gneiss with foliation striking NW-SE, and NE ly dip is exposed to a negligible extent on the upper reaches (Pongumud W475746) of the minor tributary. Lateritic soil, loamy soil and clayey soil are the soil types noticed on the stream banks upto its confluence with the mainstream where gneiss is exposed. At this point the bed and banks of the master channel are made of quartzo feldspathic gneiss.

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Tributary joining the mainstream at Perumkadavila

This left bank tributary is of third order. Gneissic rocks with foliation striking NW-SE are exposed for almost half of the stream length from the upstream part towards downstream direction. The valley is confined within two gneissic ridges. In the down-stream direction gneiss become more weathered and lateritised and is covered by topsoil and lateritic soil. Banks, near the convluence of the tributary with the mainstream, are composed of lateritic soil.

Tributary at Aruvippuram from the left bank

(Aruviyodu Thodu)

Aruviyodu thodu, a tributary on the left bank, has second largest drainage area (48 Sq.km.) in the Neyyar basin. A very wide drainage network is displayed by the stream. It exhibits rectangular as well as subdendritic drainage pattern interpreted as the result of structural control of bedrock. The stream is of fourth order and shows a meandering course. There are two knickpoints along its course.

Quartzo-feldspathic gneiss with garnet showing crude foliation, saprolite and laterite are the rock types exposed on the upper reaches Tattiyur W 68055 of the stream. Gneissic foliation trends in NWW-SSE direction with north easterly dip, is clearly exposed in the bed rock. Isolated exposures of gneiss surrounded by loany soil with or without humus and by lateritic soil also occur on the upstream part of the stream.

A knickpoint occur just upstream of the merging of the rectangular network of streams with the main tributary. The rock exposure is gneiss-charnorkite association, but gneiss is the dominant type. Foliation trends in NW-SE but it varies locally. Charnockite is garnetiferous when associated with gneiss. At this point, river channel is fairly wide. Bank materials are loosely consolidated and partly drained soil and floodplain silt.

Occasionally bed rock gets lateritised on the upstream part of the tributary basin. Latorite shows well preserved structures of parent rock namely foliation (dip NE).

As we move to the central part of the subbasin, the areal extent of exposure of gneiss becomes negligible. Loan lateritic soil and alluvium cover the remaining areas.

From the central part of the subbasin upto the confluence with the master stream, the tributary displays prominent meandering. Gneissic rock and lateritic soil are exposed at the confluence with the mainstream. Loan lateritic soil and alluvium constitute the anks between the central part of the stream course and the confluence with the master stream.

Tributary at Aruvippuram from the right bank

The stream is of fourth order and joins the mainstream from the right bank.

Gneiss and laterite the insitu type are the rocks exposed on the upper reaches (Maranallur W471734 of the stream, shows a north easterly dip. As we go downstream, lateritic, and lateritic soil increasingly occur.

Towards the middle reach (Vandanur W476712 of the stream, weathered gneiss is observed in contact with laterite showing well preserved structures, especially foliation, dipping NE. Lateritic soil, clayey soil and well drained soil are the soil types developed in association with the above rock types.

Alluvuyn and clavey soil cover the banks near the confluence of the tributary with the master channel.

Tributary joining at Amaravila (W519653)

The tributary is of third order. It is a left bank tributary.

Gneiss and lateritised gneissic rocks are exposed on the upper reaches (Mekkolla W552656 of the left bank of the tributary. Laterite constitutes the headwaters of the right bank of the stream. Lateritic soil overlain by coarse grained soil and clayey soil overlain by dry soil constitute both the stream banks alternatively, from the upstream portion to the near vicinity of

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the junction of the tributary with the master stream. Floodplain silt is exposed on either banks of the tributary near the confluence.

Tributary at Olathanni

This tributary is of fourth order and enters the main stream from the right bank. It shows a wide drainage network.

Hardrock exposures are not observed throughout the course of the tributary. Clayey soil overlain by dry soil, lateritic soil and alluvium form the upper reaches (Kuttappana W640768) of the tributary. Well drained red loan underlain by clayey soil and alluvium constitute both the banks of the tributary.

Clayey soil increasingly cover the banks, as we go from the headwater portion to the middle part of the course of the tributary. Floodplain silt is observed on both the banks near the confluence of the tributary with the master channel.

Tributary at Pazhayakda (W486619)

This tributary joins the master stream from the right bank. It is of second order.

Bedrock is not exposed throughout the course of the tributary. Laterite and clayey laterite and observed on either banks of the tributary.

Laterite and clayey soil constitute both the banks of the tributary in the handwaters. Hardrocks are not exposed either in the channel bed or along the banks.

Lateritic soil of the transported type and soil similar to teri sands are observed towards downstream.

On either banks near the neighbourhood of the confluence of the tributary with the mainstream, floodplain silt is observed.

Tertaries are exposed in the neighbourhood of the merging of the tributary with the master stream.

Tributary at Vlathankara (W494608)

This left bank tributary is of second order. The tributary has shifted its past course and joins the mainstream at a point south of the previous channel (Gregory, K.J, 1977). The paleo-channel is still preserved as an abandoned one, having discharged only during the higher stages.

Quartzo feldspathic gness, garnetiferous gneiss, biotite gneiss and laterite are the rock types exposed on either banks along the course of the tributary upto its confluence with the mainstream. Gneissic foliation strikes roughly NW-SE and dips Towards NE. Laterite displays structures of parent rock (gneiss), such as foliation.

The channel bed and banks of the upstream portions (Parasuvakkal) of the tributary is rocky, sometimes with a cover of laterite or sediment. Biotite moiss and garnet biotite gneiss show foliation dipping in W-S and 50 N 110 directions. The laterite cover as well as the top soil cover increase in thickness in the downstream direction. The channel be also shifts from rocky to lateritic in the same direction. Along the down-stream parts the contact between laterite and bedrock can be observed.

The channel is lined with boulders and channel bottom is highly seoured and rockfloored due to break in level (rapid) along slopes specially in the upper reaches of the tributary.

Isolated exposures of meiss, particularly of biotite gneiss, are noticed on the upstream part of the left bank of the tributary. Fresh exposures of gneiss with foliation dips to NE are also seen on the right bank of the tributary.

Laterite is exposed as cappings over gneissic rocks as well as in slopes. The banks of the tributary are mostly of lateritic soil of the transported type (ie. Rarely with any primary structure). Lateritic exposures tend to the clayey as we reach the confluence of the tributary with the master stream. Floodplain silt is observed to be capping the laterite near the confluence with the mainstream.

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Summary

This Neyyar river net is carved out in a terrain, which had suffered intense tectonic activity

the reflection of which is observed in the form of dislocation of which is observed in

the form of dislocation of the river net in the highlands as well as midlands. Right angled bends along the course of the river indicate that structural features have a control over the spatial pattern of river net. It is evidenced by the swinging of the strike of foliation of rock exposures from NW-SE to ENE-WSW and E-W.

The drainage pattern of the Neyyar river basin is dendritic to subdendritic and rectangular at some portions.

The interrelationship between charnockite and khodalite, the two predominant rock types of the basin, is not clear.

Laterite occurs as capping over gneissic rocks as well as Tertiaries.

Chapter II

NEYYAR BASIN: LAND USE AND SOIL

Introduction

A study of human intervention and river channel changes cannot be complete without a detailed look at the current land use and soil types of the area in question.

Neyyar basin is a small network of 492 Sq.Km area. The Neyyar flows through an undulating terrain of different types of soil in different land surfaces, but all evolved from more or less the same type of parent material. The type of soil has major role in agricultural productivity and the type of cultivation of a certain region. This fact has very easily been recognized in this river basin also. Tributary development and/or its disappearance has its own intrinsic relation to the land use pattern of the region.

Land Use

L.B. (1)

This second order tributary originates from the area surrounding Kannumamuda (W583638) near Karakonam. Lying near to the mouth area the Neyyar, it has only one tributary though it is lengthy. It has a typical meandering nature connecting small and large stock ponds in the low lying plain.

According to the need and grend of the people over land and cultivable space, people resist any encroachment of their land. So people have a tendency to divert/abstract small and sometimes even larger tributaries. This small tributary used to have its junction more or less half a km. above the present confluence. This has been noticed in the study of S.O.I. 1914 map and S.O.I. 1969 map. And field inspections proved that this change in the confluence is due to land management, according to the will and wish of the local people. At the confluence of the stream the main river also shows a considerable shift purely man made.

Along the stream channel, at bends the banks are protected by masoney work and at places by growth or planting of Kaitha (Pandanus syrs). Either banks of the stream near the confluence area is fully covered by conconut (cocus nucifera) Arecanut (Area catechu) mango (Mangifera indica) plantain (Musa Sps: ) and other trees. Tapioca (Lanihot utilisima) seems to be an inter crop to coconut gardens. The paddy fields are in a transitional state to crops like lantain, tapioca and several pulses. This is due to the declining value of rice and increasing labour charges and high expenses for paddy cultivation but not because of lack of irrigation facilities. Again the basin area as a whole shows a typical change in hill slopes. Most of the hill slopes are now under intense rubber Hevia braziliensis cultivation. These lands were previously under tapioca or mixed crops. Rubber cultivation has a remarkable impact on the land use pattern of this region.

L.B. (2) Land Use of

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This tributary presently is a third order one and has two main branches converging litter above the confluence. Near the confluence land is under intense degradational process. The soil is ideal for brick making and the people look more to the paddy fields near to the tributary as well as the main stream than any other part of the land. The lead to sudden fall of valley walls. Brick making is the main occupation of the local people. This activity is so intense that with in few years or so a part of the valley would be widened and in a subsequent flood there would be more destruction of banks leading to soil erosion.

The paddy fields on either sides of the stream are fastly giving way to new crops viz. Tapioca, plantain, pulses, vegetables and so on. The development of new first order streams indicate that this area has a very good supply of water, initially meant for paddy. But farmers find it difficult to grow paddy, instead they cultivate more profitable crops and let the excess water to flow over to the near by stream.

In the upper reaches of this tributary (Mekolla) Rubber has captured the lion s share of the will slopes. But poor farmers still stick to tapioca. Land under tapioca is not well terraced, soil erosion in these places leads to the reduction in productivity or profit of the farmers. Wealthy farmers do terrace their land with boulders of laterite or by arranging rubbles to check soil erosin. Coconut and other mixed crops also share their part in this area which would given considerable importance. Of this, coconut; due to escalating value has a very great consideration by the people.

L.B. (3) Aruviodu thodu

Aruviodu thodu is the second largest tributary in the basin after chittar. This fourth order tributary covers a pretty large area in the basin. The basin of Aruviodu thodu has a very high rate of soil erosion. Expecially at bends, bank erosion is intense. In the flood plain region paddy and coconut are the chiefcrops cultivated. But because of bank erosion coconut palms on the bank face severe threat to their very existence. A chute cut development is identified at a place marked (c) on the map. This strongly presents the erosional, capacity of the stream. The hill slopes near chattan para (Sathan para, W552705) area also show poor land management in tapioca cultivation leading to soil loss. Terraced tapioca cultivation is also practiced in may places. The local people have a better consciousness about soil loss from their property and dig the stream bed for sand. Sand borrowing is active in this tributary also.

In the upper reaches, Kuttakkada (W561699) the stream branches out in a rectangular net because of structural control of underlying rocks. Rubber is the main attraction of the growers. Tapioca has been replaced by rubber. Valleys and low lying areas are devoted for paddy plantations, vegetable and tapioca.

L.B. 4 Parumkadavila

The left bank of the stream in the flood plain region of the main river is sloppy and is under paddy and mixed crops. Before it flows down to the flood plain a major portion of the tributary washes rock out crops and steep land surfaces. But even an inch of the land where soil is present is not left uncultivated. For example a rock out crop wounded with soil at shoulders under intense tapioca cultivation is located and is marked ® on the man. Rubber with its high value seems competing with tapioca. A dense growth of mixed trees (natural also cover this hilly tract. A major portion of the soil is well drained and is good for under cultivation.

L.B. 5

The is small second order stream, five kms. In length. More than ¾ of the stream runs through paddy fields, the confluence as well as the place of origin is rocky. The sloping face of the rocks with soil is under cultivation of one or another type of crops, especially Tapioca. On the right bank of the stream where U is marked on the map after a paddy field, the hill slope is unterraced. Tapioca cultivation is done on newly tilled surface. Rills developed on it and is further developing into rather big gullies. There are chances for a good amount of soil to creep down to the paddy fields and then into the streams. Cultivation of plantain and tapioca in paddy fields seems to be an additional income for the local farmers

L.B. 6

Originating from a rubber plantation near Mundanadu (W582710) this third order stream extends up to Ariyenkod (W 538752) where it merges in the Neyyar. Mundanadu and

13

adjoining elevated p;aces are fast moving into the sway of Rubber plantation. These plantations seem to the well productive with a well drained gravelly soil.

The head waters of small first order streams (Kaithodu) join together in a zig zag way to form the flow of the stream. This is due to land management; Farmers always avoid excess water from their land for a particular type of cultivation, where the water table is comparatively high, Rubber, Tapioca, Coconut and other mixed trees are the main items in the dry slopes of this stream. Paddy and plantains predominate near the confluence and in low lands.

L.B.7

Chittar

Chittar is the most conspicuous tributary to Neyyar. Being the largest tributary it covers and area larger than any other tributary, the net work has. This 4th order stream has a trellis pattern unlike most of the other tributaries. The valley is wide and at places chittar equals the Neyyar in width.

Then the filed inspection was executed in April-lay season of 1984 the stream was in a braided stage, inspite of the intermittent rainfall that occurred in this period. The sediment carrying capacity of the stream was very low due to sedimentation outwitted discharge. It was astonishing to notice that from he mouth of the stream, a distance of 5 to 8 Kms. there was loose seniment 2 to 3 feet in thickness present in the stream bed. The aforesaid fact invariably shows that the poor management of cultivated or cropped land produces high rate of soil movement from the banks of streams into them.

The head stream area of this tributary lies between 200 and 600 mts, from sea level, these hills in the high contours are devoted for Rubber plantations. But well planned Rubber cultivation check the run off of soil down to the valley floor. The hill slopes that are previously cultivated with Tapioca, are turning fast into Rubber platations. The places like Kuttappu (W840768) Kudappanamudu (W613757) Kovillur (W614740) Vellare a (W617711) & Chilumpara (W594740) are most excellent examples for rubber cultivation. One of the reasons for the development of first order streams in this tributary is the drains from Rubber plantations, since rubber needs well drained slopes.

Other than rubber, tapioca shares the slopes and in the level lands, Areccanut, coconut and other trees like Mango, Jackfruit etc. have fairly dense growth. Albesia (Alpasi), a soft wood tree which can be used pretty well in match box industry, seems to be a special variety in cultivation, at certain location in this basin.

Sand borrowing is active at places show S.B. on the map. Inspite of large quantities of sediments in the bed of this stream sand borrowers look more into the main river than the tributary stream. This is due to the coarse texture of sand in this tributary which has little value. Toward the flood plain of Neyyar the land use changes. Here coconut and tapioca predominate and paddy fields remain in transition to tapioca.

L.B. 8

This small second order stream originates from the paddy fields near Vazhichal (W566796). Many first order channels join this stream. Rubber and tapioca are the main crops. Brick making activity is intense at the confluence with Neyyar and this spot resembles itself to a large Industrial quarrying set up. Men, Women and even children are indulged bery much in this occupation. This activity erodes either banks of the Neyyar as well as the tributary.

R.B. I

This tributary has its confluence with the main stream at Pazhayakada (W486619). Since this tributary lies almost in the flood plain region of the Neyyar, stream bed has a very good amount of flood plain silt and soil has a very good amount of clay. This clayey soil is ideal for brick making. Hence brick making very intensively done in the vicinity of its confluence with the main stream.

The main cultivation in the sub basin is coconut, tapioca, plantain and paddy. Albesia (Alpasi) (for Match Box Industry) cultivation in open area as well as in paddy fields is practiced in this sub basin.

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Minor irrigation authority has a well planned project on the tributaries of Neyyar to widen the Valley as well as construction of dikes along weak points in order to check water from spilling out to paddy fields and adjoining plots and at places the banks are lined with rubbles and wild Kaitha (pandanus syrs) to prevent bank erosion.

R.B. 2

Maruthur thodu

Maruthur thodu is a fourth order stream and is one of the largest tributaries of Neyyar in the right bank. About 3 Kms of the thodu from the confluence towards upstream lies in the flood plain area of Neyyar. The left bank borders the flood plain area of Neyyar. The left bank borders the flood plain area and the right bank is a slope. In the confluence area between Brayinmoodu (W487642) bridge and the main river the soil is clayey. Excavation of clay is a very wild activity in this place. This clay is then transported to nearby small scale pottery making units. Mud borrowing for brick making is the chief occupation of the people in this part. Land owners consider it as a monetary income but they do not realize the havoc which would happen in the near future.

Along the tributary further upstream the main cultivation is paddy. Thus tributary has very good dikes on either sides (planted coconut) built by the minor irrigation authority. Plantains and Tapioca are the other noticeable crops in the basin. A small tributary between Kodangavila (W474676) and Manalur (W478669) lost its in-coming gullies into a stock pond at its place of origin due to the pressure of population on land. Construction of hourses and management of coconut gardens are the reasons for this. Again, near the kuttappana bridge, Balaramapuram (W478682) another stream disappeared after the construction of Trivandrum Kanyakumari Rail track. Now water creeps away through paddy fields into the stream.

R.B. 3

Though this tributary drains a small area it has a very good spread. The frequency of first order streams is comparatively high. This area is well productive and no waste land is seen any where except the rocky part in the place of origin. Along the stream, paddy fields predominate but plantain and Tapioca are extensively grown in the paddy fields. Thus a small first order gulley disappeared due to the diversion of water into the tapioca and plantain-fields. On hill slopes rubber and tapioca are the chief crops. People have a tendency to replace tapioca with rubber. The Maranallur

Pongummudu (W497752) area from where the stream originates has a very good amount of rock out crops. But the need of the people in rubble as an essential building material is increased the exploitation of this rock out crop.

R.B. 4

This is a small tributary of 3rd order, though it is shown as first order in the S.O.I. 1969 map. Near Pongummudu in 1914 (S.O.I. maps 1919) there was a small gulley formation, now it has developed into a stream and joins the present stream to make it a second order on; the reasons being land management to drain the waters from the slopes (sheet wash) where coconut and rubber are the main crops. The Neyyar irrigation canal crosses the stream where it branches out. But is has no connection with the formation of the new stream. There is an escape for the canal to the stream at this spot. Near the confluence on the left bank a new gulley develops fastly forming into a new first order stream. Still another gulley develops in the right bank along paddy field.

Soil erosion in this area is considerably high because of unterraced cultivation of tapioca and other crops.

R.B. 5

This third order stream has its confluence near Pulimuttom (W497752). Just above the confluence with Neyyar, it branches out into and drains the low lying valley between Kulangara (W482780) & Amachal (W520780). The elevated land between the two branches are under Rubber, Tapioca and coconut cultivation in accordance with the nature of slope and type of soil.

Land management here is typical, according to the type of crop cultivation, the change in the valleys differ. If rubber is the crop, gulley development results, because rubber does not grow well in excess water, so the excess water is being channelised to the near by tributary and

15

thus a new stream of 1st order develops. But in the case of vegetable gardens or plantain crop the need of water is acute. Farmers grow these items, in or very close to first order streams and then divert the water into nearly rectangular intricate channels to serve every corner of their field and they plug the out let of the tributary, thus the first orders no longer join the main stream.

The valley widening in this tributary is attributed to the work that has been done by the Minor Irrigation Department. The poor management of hill slopes head to the run down of top soil from the cropped land. Thus two examples were located in this tributary area where Hill erosion is severe. Unterraced tapioca cultivation promotes soil creep from slopes. Other than coconut and other mixed crops, paddy tapioca, plantain and rubber are the chief crops cultivated here.

R.B. 8

Metamorophosis because of human intervention is well depicted in this sub-basin. This tributary has its confluence with Neyyar at Kallikadu, 3 Kms from the Neyyar dam.

This tributary basin had many small first order gulleyes about 50 years back, which were independent, (1914 S.O.I. map). But in 1969 any of these tributaries disappeared and new first orders developed to join the tributary bordering paddy fields. It was very much interesting to see a new first order stream developed in between the coconut and mixed crops garden to join the main tributary near Kallikadu junction (W532821) which is not shown in the 1969 map. Again another first order stream just after the N.I.P. W.B. Canal grew into a second order one. Though the left bank runs the Kuttichal-Kallikadu road, on the left side of the road is a ridge more or less uncultivated. Gulleyes which develop in slopes drain into the tributary cutting across the road through culverts.

In the head waters this tributary is found extended the valley beyond the main road into a rubber plantation. In the elevated hills the land is fast moving into the sway of rubber Paddy and coconut are other crops in this basin.

Summary

When the land use of a particular region is studies we have to consider the type of soil, amount of rainfall, topography of the land, poor or richness of the people of the region and the Government policy to develop agriculture and industry.

This river basin is more rural than urgan in land use. In a poor economy management of land against soil crosion and fortilising the arable land are not much easy. People here are not illiterates but they need more counseling to save their land and to improve productivity in a better way. The economic potentiality of the region is considerably high. But tapping the resources of the nature should be rational if the need of the age is a better environment.

SOIL CHARACTERISTICS OF NEYYAR BASIN

Introduction

Soil is the loose weathered material on the surface of the earth. It is the end product in the process of weathering of parent material. According to the nature and type of underlying rocks, soil in a particular place differs from another. In the genesis of soil we have to take into account many factors like parent rock, climate of the place (ie, Temp. rainfall) vegetation, organisms and the amount to exposure of the rock to the agents of weathering.

The agriculture department (soilsurvey) of Kerala categories the soils of the Neyyar basin into nine major divisions, viz. (1) Kazhakuttom

Poovar association (2) Karaman

Chriayinkil association (3) Neyyattinkara vellayani association (4) Vilappil Vizhinjam association (5) Trivandrum

Thonnackal

Varkala association (6) Amaravila

Urikil association (7) Nedumangad

Palode association (8) Vembayam Kuttichal Kunnathukal association and (9) Kottur

Kallar association (Ref. Map). The affore said map was taken as the base map for the soil study and soil map ploting of the basin.

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The down stream area of the Neyyar basin has an area of 284 Kms. The soils in this area has been classified under six divisions viz. (1) clayey soil (2) clayey loam (3) Loamy soil (4) Lateritic soil (5) sandy soil and (6) Soils on rocks and pure rock out crops (figure). Lateritic soil accounts for the lions share in the basin. It covers an area of 106.78 Sq. Kms (37.60%). 30.30% of the basin is loamy soil (86.04 Sq. Kms). 16.59% is cads classified as soils on rocks and rock out crops (47.122) Kms). Clayey woil with riverine alluvium accounts for 7.18% (20.392 Kms). 10.72 Kms is covered by clayey loan soil showing 3.77% of the basin. In the mouth area sandy soil represents 4.49% with an area of 12.752 Kms.

Tables showing total area and percentage of different Soils in the individual basins and of the whole

Basin are given below:-

Total down stream area

Cls Clm Lmy in Sq. Kms.

Las Ro Sas

2842 Kms 20.397 10.7 86.04 106.78 47.12 17.75

Percentage of various soils present in the whole down stream area of the basin

Total area Clayey Soil

Clayey Loan

Loamy Soil Latritic Soil Outcrop Sandy Soil

2842 Kms 7.18 3.77 30.30 37.60 16.59 4.49

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PERCENTAGE OF VARIOUS TYPES OF SOIL IN THE SUB BASINS OF THE NEYYAR BASIN

Basin No.

Total area in Sq. Km

Cls Km2 % Clm

Km2 % Lmy Km2 % Las

Km2

% Ro Km2 % Sas

Km2 %

LB 1 40 Nil Nil Nil 23.00 57.50 Nil Nil Nil 4.25 10.62 12.75 31.87

2 22 2.00 9.09 1.00 4.55 16.00 72.72 Nil Nil 3.00 13.63 Nil Nil

3 3 0.80 26.66 0.20 6.66 2.00 66.66 Nil Nil Nil Nil Nil Nil

4 16 1.22 7.62 Nil Nil 4.00 25.00 8.60 53.75 2.25 14.06

5 48 2.62 5.46

5.37 11.19 28.00 58.33 12.00 25.00

6 8 0.25 3.13

1.50 18.75 2.75 34.37 3.50 43.75

7 3 0.30 10.00

1.95 6.50

0.75 25.00

8 5 0.32 6.40

2.23 4.46 0.95 19.00 1.50 30.00

9 50 1.18 2.36

0.25 5.00 37.87 75.74 10.80 21.60

10 4

4.00 100.00 Nil Nil

11 2

2.00 100.00

PERCENTAGE OF VARIOUS TYPES OF SOIL IN THE SUB BASINS OF THE NEYYAR BASIN

1 2 3 4 5 6 7 8 9 10 11 12 13 14

LB 1 11 2.08 18.91 Nil Nil 8.92 81.09 Nil Nil Nil Nil Nil Nil

2 21 4.50 1.00 7.90 37.61 8.55 40.71

3 13 0.13 6.00 1.60 12.30 10.39 79.22

6.88 6.76

4 2 0.12 14.70 Nil Nil 1.88 94.00

5 10 1.47

Nill Nil 7.16 71.60 1.37 17.70

6 19

13.75 72.36 5.25 27.63

7 5 74.0 74.60

1.27 25.40

8 2

1.70 8.50 0.3 15.00

Total 284 20.397 7.18 10.7 3.77 86.04 30.30 106.73 37.60 47.12 16.59 12.75 4.49

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CHAPTER III

PHOTOGEOLOGY OF NEYYAR BASIN

Introduction

Study of geological fabric of Neyyar basin, has been carried out with the aid of aerial photos of 1:25,000 scale, photographed between 1979 and 1982. A phtogeologic map of the river basin has been generated from the photogeologic data. Geomorphic expression of ridges, trends of lineament, faults, joint systems and foliation pattern have been identified. Contacts between crystalline rock exposures and soils, crystalline rock and saprolite and crystalline rock Vs. Crystalline rocks have been traced. Dependence of geomorphic elements on rock types like massive charnockite, ridge gneiss, plateau laterite are brought out. Forest land covering the catchment area is discernible from rock exposures. Drainage control over translithorelations such as breaks in slopes, density of drainage, drainage pattern and variation of which of stream have been noted.

Correlation with toposheets

Preparatory to air study, aerial photos were correlated with toposheets (No.58H/2, H/3 & H/6) based on stream junctions irrigation canals, towns and roads. From airphotos the entire river not including merging of subsequent streams has been traced along with various geological features.

Photolithology

Inspection, and stereoscopic viewing of photos show that a major part of the catchment area is forest covered. Wherever, rock exposures are noticed examination of exposures suggested that the dominant rock type in the reservoir catchment is mainly charnockitic. Specially in the northern northwestern and western parts of the reservoir catchment the charnockite outcrops are covered by patches or continuous patches of grass. Charnockite occurs as massive, subspherical, dome like hills with variable summit elevations and steep sided slopes. Gentle slopes on the massifs are noted trending in a southwesterly direction. Charnockitic exposures trend roughly in a NW-SE direction. Gneissic rocks are also exposed as ridges in the catchment area. Compared to charnockite massifs, gneissic ridges show steeper slope. Well developed foliation and joints reservoir catchment variations in shape, size, tone and structural features like joint systems, foliation patterns, enable one to distinguish between dominantly charnockitic portions from the gneiss dominated portions. It is suggested that the foliated and jointed aspects of gneisses and the massive domical appearance of charnockites can be extreme value in air photo analysis of similar terrains, in the tropical environments with alternating wet and dry spells.

Photogeology Downstream of Dam

Though with subdued relief on the left bank of the master stream, photo expression of gneissic rocks are frequently noticed.

Downstream of dam, charnockite exposures are very much restricted in occurrence, with the exception of Pongumoodu, on the right bank. On the left bank, charnockite dees occur in the sector between Mandapathinkadavu and Kallikad.

Rock expressions are noticeably absent in the photos, downstream of Aruvippuram. Compared to the upstream of the damsite photo relief is comparatively low in this sector. Exposures of gneiss-charnockite intercalation are noticed on the summits of hills. The outcrops show roughly circular outlines.

Further in this sector, gneiss, charnockite and laterite are noticed to occur with an order of decreasing abundance.

Eaterite and soil (derived out of it) cover gentler slopes of hills. On steeper slopes mostly scree or talus instead of laterite or soil, occurs, Rock-rock, Rock-laterite and rock-soil contact can be fairly easily discerned from the photographs.

Structure

With the aid of air photos sometimes, it is easier to observe and identify strucral make up of the surficial rocks than rock lithology itself.

19

At the foot of Agasthyamala and at the confluence of Neyyar and Kallar subsequent streams are noticed to follow straight line courses, which might be reflecting the structural control on stream net. Perhaps the streams would have taken advantage of lineaments trending along NW-SE and NE-SW directions. With a NW-SE orientation. This lineament control of stream course finds its expression in the S.O.I. toposheet too.

A second instance of structural control on river net development is noticed in the sector at the confluence of Neyyar and Chit Ar (Fig. ). The disposition of the stream course (downstream of confluence) indicates that the channel beds twice at right angles with intervening straight courses. Structure controlled stream net development is visible in the photographs as well as to a lesser degree in the S.O.I. toposheets. The straight channel course upstream and downstream of the confluence can be traced over a distance of about 8 Km.

Down stream of the confluence with Chit Ar, the Neyyar follows WSWerly course between Aryankod and Aruvikkara. At the latter place, the channel follows a SEly course and maintains the same, until it reaches pasuyannara. Further downstream the river channel occupies a water gap at Aruvippuram across a WNW

ESE trending ridge. Through the water gap the river cascades downstream and crosses the 50 contour.

Foliation

Orientation of gneissic foliation was estimated from air photos. The estimates of strike direction in catchment area as well as downstream of dam are given in Table 1

Joints

An attempt was also made to recognize the orientation of joint system in charnockite and gneiss. The strike of major joint systems, estimated from air photos, for charnockites and gneisses are listed in Table 2

Fault

Offset of a step like rock terrace, trending along N340, in the Chit Ar sub basin (which falls in the eastern side of Neyyar) is of special interest. The two separate blocks of the step like terrace occur on the northern side of the course of Chit Ar. The blocks seems to have been offset by a dextral strike slip movement along N250 direction. Though the fault zone is not expressed topographically, the anifestation of this feature in the stereoscopic view, indicates the development of the step like terrace. This conjecture should be seen in the light of the fact that the Chit Ar does follow a course parallel to the proposed faul zone even outside the Chit Ar subbasin beyond the confluence with Neyyar.

Water gap at Aruvippuram

A very prominent ridge with a water gap, trending roughly northerly is noticed at Aruvippuram. Two minor ridges almost parallel to this trend are noticed at Kuttiyanikad and further NE of the latter at Ottasekharamangalam. The dominant trend of foliation and orientation of the ridges are fairly close to each other. However only the Aruvippuram ridge is cut across through by the Neyyar in the water gap. On the slopes, only a thin layer of soil is developed. Laterite is not very prominent. The southwestern flank of the Aruvippuram ridge is much steeper than the opposite slope.

Table I

Strike of foliation of gneissic rocks in catchment area

(1) N 324 (5) N 34

(2) N 325 (6) N 33

(3) N 300 (7) N 36

(4) N 286 (8) N 35

(9) N 66

(10) N 70

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Table II

Strike of joint systems of charnockites and gneisses downstream of dam

N 21 N 60

N 22 N 62

N 24 N 287

N 204 N 286

N 205 N 288

N 275

Photoexpression of CHarhockite, Gneiss and Laterite

The geomorphic expression of laterities crystalline rocks, laterite and crystalline rock boundaries have definite and distinctive characters, phototonal variations and fabric expressions. In low lying areas the crystalling rocks and laterite cover disappear under the flood plains and the secondary clay. The pattern of these covered crystalline features are mostly determined by the fluvial processes of the area. In such areas, the chances of a crystalline outcrop or a crystalline derived laterite to occur are remote. The terraces are gently undulatory and are mainly single in nature.

The midland has a geomorphic expression of multiple terraces. A lower fluvial process dominated terrace separated from an upper plateau type terrace, with escarpments and dipside slopes are noticed. This configuration differs in degree in all the directions. Formation of the saprolite, and degree of lateritisation, disposition of groundwater, etc. change the form, from the lower terrace to the upper; the lower section with thicker laterite than upper one. Thus the thickness of laterite increases from on either side the stream. There is a hump at the intersection of this wedge with the weathered crystallines. This represents a high seepage horizon resulting in the absence of any streamflow above the hump. This contact can be wedge shaped or circular depending on the dimensions of the area lying between streams. So a profile been marked from the intersection of laterite and the crystalline rocks.

The distance from the midstream to this hump, the gradient of the surface and phototonal characteristics of the area are indicative of the nature of crystalline rocks.

A charnockite massif will leave steeper slopes than the gneissic columns. The contrast between the laterite derived from the charnockite and charnockite itself are distinct. The contact between the laterite derived from the charnockite and charnockite massifs show a more or less uniform appearance and pattern of distribution from the summit and down the slope. Thus the break will have the contour like configuration on the ridge. On the other hand on gneissic ridges such contacts are more linear around the ridges.

Among the two rock types anistropism of large scale fabric elements dominate the gneisses. The deformation during earlier episodes across the terrain resulted in the modification of S, foliation to coincide with the regional grain. Most of the streams have a tendency to align themselves parallel to this regional grain resulting in a trellis type drainage, whereas charnockite with the general isotropic character implanted a dendritic drainage.

Summary

The airphoto studies of the Neyyar basin has been undertaken to assess the role of structure and lithology of the crystalline rocks on the development of the river net.

It is seen that major influence of structure is noticed in the midland region where the joints, foliation and lineaments criss cross the charcnockites and gneisses. The charnockites seem to be more massive than the gneisses any way. In the low land sector ( 200m elevation) due to the development of thick saprolite cover, the structural control of stream net appears to have vanished.

The watergap at Aruvippuram is perhaps the result of erosion of saprolite by the stream, exhumation of the underlying crystalline rocks. The zig zap bends at right angles and straight

21

stream courses in Chit Ar subbasin and the point downstream of the confluence with Neyyar are further examples of structure influencing the stream course.

The photo expression of massive, domical charnockite and well foliated gneisses are unique and for the very same reason identification of these rocks are farly easy for a trained eye. It has also been possible to estimate strike of foliation directions, joint systems and lineaments from the air photos.

Dendritic to subdendritic and lineaments from the air photos the highland, and in midland. In the low land area the stream courses are parallel, mainly following the regional grain of the bedrock.

We certainly agree that any measurement made out of air photos are subject to errors due to the very fact of relief displacement and scale variation across the photograph.

CHAPTER IV

NEYYAR BASIN

PHOTO INTERPRETED GEOMORPHOLOGY AND LAND USE

Introduction

Security of aerial photos of any terrain is complementary to the field investigation, whether it be in geomorphology or any other branch of geology. Further, serially taken air photos are considered to be best media for monitoring short term changes undergone by various land form elements, like slopes, channels and alluvial deposits. The main purpose of airphoto study in this project is to asses the area of the forest cover, to examine the status of various land segments and land form elements under different category of crops, to verify the data on shifts of channel confluences and of the main channel itself like under cutting of river bends, abandoning of earlier channels and to get a glimpse of the extent of different sorts of man induced modification of the landscape of the Neyyar basin.

Setting

Neyyar, a sixth order stream, is a network with a basin area of 492 Km2. It is situated in the southernmost part of Kerala State. The Neyyar rises from the Agasthyamala (W685925), at 5550 ft above MSL. The stream flows a south southwest course in the highland ( 600 m elevation) and continuous the same trend in the midland region (between 600 m 200 m) elevation. After entering the low land ( 200 m elevation) the stream takes a North westerly course interepted by channel segments oriented in a south westerly direction. Such a shift pushes the stream course to the left half of the basin axis. Further a south westerly trend prevails until it enters the laccadives sea, at Puvar (W465567). Aerial photos depict a picture of the rural landscape on either banks of the river. A mountainous abode, a hilly midland and a rolling low land are easily demarcated. In this basin an irrigation dam was built in the year 1959 at Kallikkadu (W532821). Up stream of the reservoir, a major portion of the catchment area is under reserve forest. Rubber and Eucaliptus plantations are also rained in the rugged foot hills.

Aerial photo study of Neyyar basin was carried out in the survey of India southern circle office at Bangalore. Stereopairs of 1 : 25, 000 scale (photographed between 1979 and 82) were examined using mirror stereoscopes. A total of 226 photos covering Neyyar basin which fall under S.O.I. topomaps No. 58H/2, 58 H/3 and 58 H/6 were studied in 22 man days between 31st December, 1984 and 11th January, 1985. Aspects of land use, geomorophology, features of stream banks and stream channels and cultural features were examined during the study. A pencil sketch of various features of interest has also been generated from the air photos.

GEOMORPHOLOGY

Catchment area

The catchment area of Neyyar is a rugged terrain with out crops (charnockite & Gneiss) interrupting luxuriant forest. A series of streams, more or less parallel to each other drain this

22

terrain. The valleys are V shaped with steep gradients. Yet the air photos could not reveal the extent of first order streams as they are covered by the canopy.

The reservoir spreads over an area of 6.92 Km2 and the water has filled in three roughly parallel valleys. These filled valleys themselves are inter connected by arms of the reservoir through saddles or lows on the intervening ridges. This has created several island like hills inside the reservoir. Some of these hills are covered by forest where as many others are under plantation crops.

Down stream area of the Dam

The river takes a meandering course in the down stream part of the reservoir. After drawing a sketch of the entire basin area from the photos (photographed in 1979-82), it was compared with the basin map (S.O.I. 1969 toposheet). The river mouth being very dynamic changed faster than the rest of the area. The mouth area photographed in 1979 shows closed mouth (summer bar) and in 1982, connection between sea and river is noticed. Upwards of mouth, the main channel straightened itself in different places like Vellurkonam (W 497584), Puliyamkonam (W 496602), Tiruppuram (W 475619) Neyyattinkara (W 493665) and Manpazhakkara (W 500718). Then measured and compared (the photos 1972-82 and S.O.O. toposheets 1969) there was a reduction of about 5 Km of stream length between river mouth and the reservoir by straightening of bends and loops.

Between Neyyattinkara (W 493665) and Perumkadavila (W 518714) Neyyar follows a trench like channel, cutting a ridge almost at right angles. A gap is noticed in the same ridge on the left bank at Marayamuttom (W 520680). Between Mampazhakkara and Aryankod (W 538752) the channel is very conspicuous and channel walls were covered by grass and brush.

At the time of photography, the reservoir held almost the design storage of water, covering an area of about 6.71 Km2. The base flow was noticed only in the down stream of dam in the main channel.

Eroded slopes

At many places slopes which constitute the basic elements of landforms of the basin are highly eroded by a combination of processes and human activities. The sketch (figure) shows denuded slopes in dark shade. These slopes, due to their barren nature reflect more light and have a grayish white colour in the photos. But slopes which are covered with vegetation absorb more light and are darker than the denuded ones. When filed observation was carried out in the period of April

May 1984, it was noted that these slopes which are denuded were tilled and exposed due to lack of tree cover. Most of the hill slopes are cultivated with seasonal crops viz. Tapioca.

A dissected ridge connecting KIllurkonam (W 485694), Tollukkal (W 502692), Marayamuttom (W 520680) and Tattiyar is identified in the basin. Neyyar cuts this ridge across between Kollurkonam and Tollukkal. This water gap has very steep sides. The north eastern flank of the ridge has a gentle slope which is terraced and protected from soil erosion to cultivate rubber and tapioca, where as the south western flank of the ridge is steep and is an escarpment.

River Terraces

Terraces noticed, one on the left bank at Tirupuram (W 475619) and other on the right bank between Puliyamkonam (W 496602) and Vellurkonam (W 497584) are of unpaired type. The terraces are cultivated with paddy and the steep sides are under mixed vegetation.

Forest

The catchement area upstream of the dam covers highland ( 600m), mid land ( 200 m to 600 m) and a portion of the low land ( 200 m). Thick growth of a variety of trees is present in this region. Rubber and Eucaliptus plantations occupy the isolated hills and slopes surrounding the reservoir. Agarthyamala (5550 feet from KSL) from where the Neyyar originates is situated in the middle of dense mixed reserve forest.

The open patches noticed in the photos suggest that this tropical forest is being exploited. Sectors with rock out crops prevent the lush growth of trees. It was not possible to identify a specific tree type out of the stereopairs due to the dense canopy. About 37.09 Km2 is covered

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by forest which is 7.52% of the total basin area. About 133.14 Km2 of land is under mixed trees which also include rubber and Eucaliptus plantations. Confusion of species and profusion of strand is a typical feature in this tropical forest.

Land use

Land use of Neyyar basin is mainly agricultural. Plantation crops, paddy, Tapioca, and plantation are chiefly cultivated in this basin. In the air

photos, Paddy fields are very easily

recognized even without using a stereoscope as they display a white or grayish white colour and finger like shape. The paddy fields have more or less an even distribution across the basin in the lower order stream valleys. Paddy fields cover an area of 25.4 Km2 which is about 5.16% of the total basin area. Coconut palm is cultivated ubiquitously in the basin and the intensity of cultivation increases toward the down stream in the low land sector. The peculiar geometry of the crown of coconut trees, help their identification in the stereopairs, Coconut plantation extent over a cumulative area of 21.61 Km2 (4.37% of the basin area). Plantain and tapioca are also in paddy fields, but tapioca cultivation is extensively noticed on hill slopes. Though it is difficult to demarcate tapioca from plantain (may be due to intercropping) the reflection of light from plantain leaf and tapioca leaf can be discerned by a sharp eye and a hand lens.

Rubber plantations in the downstream of dam are mainly situated on hills and slopes. In the stereopairs,plantations manifest as continuos stretched of single strand. An area of 13.25 km2 is under plantation, which accounts for 2.69% of the basin.

CULTURAL FEATURES

Aerial photos of the basin depict a rural landscape. Agriculture is the main occupation of the people in theist basin, but there are some stations, like Neyyattinkara, perumkadavila, vellarada etc. falling under urban category. Besides agriculture, sand borrowing, brick making and stone quarrying are the main activities reflected by the photos. Major brick making units located in the photos one near valavilakom (U497584) and second at viranakavu are considerably large aand are clearly documented in photos of 1;25,000 scale. At ongummudu (U475746) a large quarry (charnockite) is noticwed. Borrow pits of mud can be seen on sides of the main channel as bring white strios especially at tributary confluences.

Discussion

The land use pattern of Meyer Basin is fast changing and very dynamic. It is interesting to note that land previously under paddy, is later being utilized for tapioca and plantain, and those hill slopes previously under tapioca or under mixed crops are giving place to rubber plantations.

Exploitation of mud and sand may result in the reduction of stream length by straightening of bends and toops.

CHAPTER V

SLOPE STUDIES IN NEYYAR BASIN

Introduction

While, making a study of any river basin, the geomorphology is examined using morph metric analysis. For many investigators, geomorphology meant morph metric analysis. However, when geologists and geographers realized that any landform is composed of an assembling of slopes of various types and steep nesses; and evolution and relation of slopes to climate, relief, and litho logy would tell eloquently the spatial variation of the landform and development of drainage net; slope studies received legitimate attention. With the onset of organized agriculture and acceptance of Agriculture as an industry in the western world, land management and land sue studies and practices increasingly depended on measurement, description and analysis of slopes and dynamics of slopes. Further, it was soon realized that

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the mass wasting and erosion phenomenon largely depended on the nature of cover material on the slopes, on the slope hydrology, and on the stability of slope materials.

Early studies slopes endeavored in the identification description, measurement and analysis of slopes of varying types and the relation of slopes to litho logy, relief, climate and the variation of slopes in the same climatic and lithotomic environments. The agricultural engineers were interested in the soil loss from slopes, habilitation of denuded, wasted, slopes and failed slopes. Further climate and litho logy being the same, the length and steepness of slope happened to be accepted as crucial factors in determining the extent and degree of erosion of slopes and sill loss, as reflected by the various soil loss or soil erosion formulae.

In the Meyer basin, in addition to the analysis of river net to working out the optometry of the basin, research time was devoted for the study of slopes, distribution of slopes of various categories with in the basin, for the study and measurement of slopes at several locations in the various sub-basins, one to four slope profiles in different directions were surveyed on selected hills. The direction of measurement of slope profiles on each hill was selected along the direction maximum steepness. Such measurements were made to select a sample of sub-basins where soil loss or soil transport along specific profiles could be monitored with a bedstead type erosion meter, fabricated in the Instrumentation facility of the Karalla University.

Slope distribution analysis from Toposheets

In order to look into the pattern of distribution of slopes of varying steepnesses within the entire Neyyar basin, the survey of India topographic sheets of 1: 63360 scale were used. Use of topographic maps for such general studies have been recommended by several investigators and pioneering efforts in this direction of study were put in by researchers like Wentworth ( ). Though the accuracy of slope maps generated out of topographic sheets are limited by the scale of the maps themselves, these maps are considered to be value by several workers. Such maps on slope provide reliable information on the overall steepness distribution with in the basin, show variation of steepness from locality to locality and hence is of extreme value to the planner and developer at the primary stage of planning for development.

In the Neyyar basin a study of slope was undertaken to facilitate the realization of objectives, like the general overall distribution of slopes within the basin, investigation of slopes in specific sub-basins within the Neyyar basin to understand the distribution and variation of slopes within the midland and loweland regions, and to select specific slope sites for monitoring of soil loss at selected locations.

Slope distribution in the basin

It is essential that a knowledge of distribution of slopes in any basin is at hand, as it provides a picture of various slope categories and their distribution within the basin. Such information is a basic requirement from the point of view of the planner, the developer and land form analyst. It tells one about the distribution of steeper slopes and gentler slopes in space. However, such map data is only a first step in that it only helps to identify specific area for detailed field studies prior to the siting of suitable spots for any developmental activity. For the Neyyar basin, a slope distribution map was prepared to asses the distribution of various categories of slopes. The basin was identified in the toposheets (S.O.I. 1914, of 1:63360 scale). This map had an advantage in that it showed the grid reference cells. With in each cell, the maximum and minimum contour values were identified to asses the relif with in each cell, out of which the maximum distance separating the specific contour lines was precisely estimated: By following this scheme, the steepness of slope in degrees of angle within each cell was calculated, and enterede in each cell. When ever it was not possible to identify two contour lines of differing values in a cell, it was ignored , and dreped. Fuirther, along the boundary of the basin, whatever cell did not contain within it the basin, to least half of the cell area, that cell was dropped. The slope angles were then classed into several groups (see Table II) and the frequency percentages were estimated (see Fig. ). Noreover, with different patterns, the basin falling under various classes of slopes were marked(see Fig ).

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Discussion

The slope map in figure giving the division between lowland (below 200 m )

Midland (between 200-600 m) abd highland (more than 600 m ) is of certain interest. It is seen that a major portion of the terrain classifies itself under lowland (86.56% or 425.8 km2) where as the shares of midland (11.17% or 54.96km2) and highland (2.27% or 11.17 km2) are considerably lower.

A histogram of slope frequency of the Neyyar basin is given as figure . In the histogram the modal slope class falls between 10-20 covering an area of about 209.85 km2. An area of 134.96 km2 falls under the next steeper slope category i.e., between 20-30. But under the gentler slope class of 1-10 only 56.98 km2 is represented. The histogram referred to above does not show the spatial relation or spatial distribution of different slope classes. Instead only the summary picture alone is suggested.

On the contrary, the slope map referred to earlier does show the distribution of the parcels of land failing under different slope classes. At a glance this map does not over-whelmingly show any patern. On a careful scrutiny, it is revealed that the downstream area of the basin is dominated by terrain having slope classes of 0-10 and 10-20. The right bank side of the Neyyar basin, which constitutes about 1/3 of the total basin, shows large parcels of land with low slope values, viz., less than 20. The left bank on the other hand with a variety of slope classes and abundances has a rugged terrain. The northeastern part of the basin does posses land of steeper slopes, i.e. steeper than 20. 30-40 slope classe occurs scattered over most of the basin, but a higher incidence of such terrain is the rule in the upper reaches of the loweland, (i.e., towards the midland sector). In order to select certain specific slope categories for measurement of degradation of slope by soil erosion, several slope profiles were measured in many of the tributary basins.

FREQUENCY DISTRIBUTION OF SLOPE DATA NEYYAR BASIN

Class interval in degrees

Number Frequency

Frequency percentage

Area Km2

0-10 62 10.38 56.98

11-20 249 43.68 209.85

21-30 158 27.72 134.99

31-40 79 13.86 69.96

41-50 17 2.98 15.98

51-60 2 0.35 1.68

Slope not determined

3 53 2.55

570 100.00 491.99

Slope studies from field surveys

Further by measuring profiles of slopes distribution and variation in the attitude of slopes were investigated in selected subbasins of Neyyar. In 16 subbasins falling on either banks of the stream and downstream of the dam site at Kallikkad, slope Profile surveys were carried out in selected hills. At eah location one to four slope profiles (from the summit to the foot) were measured in different azimuthal directions. The surveying equipments included a quick set level or theodolite, engineers staff and tape to measure the distances. The direction of measured slope was determined by a Brunton compass.

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The data on slopes were plotted as profiles and the distribution of angles of slope were

analysed to determine the mean and standard deviation. Further the cover material along the line of traverse was also documented.

The slope investigations with such details were carried out for several reasons. It was essential to describe the slopes within the selected subbasins. The distribution of steepness of slopes from one basin to another bad to be known. Further within the subbasins, mean angle of slope had to be estimated for selecting suitable areas for monitoring the transport of soil material down the slope. The degree of cultivation of slopes is indeed a measure of the degree of human intervention.

Though the type of agricultural landuse is not reflected in the profiles nor the type of landmanagement, the data capture scheme provide an opportunity for collection first hand information on the landuse and land management. During profiling, a total number of 484 instrument stations were occupied and a cumulative profile length of 5271.70 meter was covered in all the sub-basins. The details of the profiles are presented in the appendix.

Cover material on the profiles

As all the profiles fall in the lowland region, the profiles do show a soil cover of varying degradation or denudation. It has been noticed that the soil over along the profiles is either interitic (an ubiquitous weathering product of cryistalline rocks in the tropical environment) or derived from laterite of modified subsequently by erosion and transportation and redeposition. There are very few sites in the profiled locations where one could identify a humus layer. (Perhaps the humus was easily oxidized. In the profiles a typical catena would show the following type of cover material from summit to the toe, and in the midslope.

In a catena the summit will show a cover material of the following description. In uncultivated sum it areas, the soil will occur as a hard crust of fine particles with embedded grains of granule and gravel. The medium sized particles would have been easily removed by sheet and splash erosion. On top of this hardened layer, one would notice a layer of free (coarse) gravel without any matrix material or cement. This is true when the soil is barren, the slope in this sector is very gentle say of the order of 5 to 3 or 10 degrees, or sometimes even gentler than this.

This mid-portion of the profile (catena) will show a variety of cover material whose nature is mainly a function of the slope. The slope in this sector is certainly more than 10 degrees and rarely exceeds 20 degrees. The soil movement is quite high across such a slope especially in a region like Kerala which enjoys two monsoons every year. The rills and incipient gullies that occupy such portions of the slope vouch for the above. The splash erosion and sheet erosion that dominated the summit gives way to rill erosion and concentrated channelised flow. Most of the finer soil particles have been removed from the soil by the above processes, enriching the soil with coarser gravel and sand sized material. This sector would form a typical example of a denuded soil. The A horizon of the soil profile will be invariably absent or if present will be extremely thin. The B horizon will show up on the ground here and there. The surface will be covered with a lag gravel or boulder deposit. Humus is conspicuously absent in the such sites. Truncated profile is the rule here.

On the other hand at the toe of the slope (catena) the cover amterial is embodied by mostly transported soil and the B and C horizons are at considerable depths. All the evidences for transportation and redeposition of the soil are explicitly noticed, like stratification, segregation of similar sized particles etc. Indication of humus is also not uncommon. The soil may be of the loamy or gravelly loan category.

Land management

The efficiency of landmangement, varies form very efficient to very poor. In fact a medium managed category can also be identified in the Neyyar basin.

Type of management Degree of efficiency

Well built rubble walls High

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compacted soil and stone

walls Poorly laidout soil walls

Medium

Poor

Well built rubble walls

Rubble walls, made of properly packed boulder size rubble along contours belong to this category. The width of terraced land bounded by such walls varies from point to point in the slope mainly guided by the steepness. Besides, the steepness seems to be a factor in siting the location of wall. Such terraced and walled hills-are a frequent sight in the areas planted with rubber. Such land management loss of soil. The run-off from each torrace is contained with in the same terrace and the water percolates through the wall and through the soil as seepage.

Such terracing has helped to reduce the length of the slopes, and the steepness of slopes within the terraces. Then, it is natural that the erosional loss is minimal on such slopes.

Compacted soil and stone walls

Instead of rubble walls made of compacted soil and stone are emplaced for reducing the length of the slopes and terracing the slopes. The worth of such walls are indeterminable. The frequency of failure of such walls are rather high as run off from the terrace, on seepage through the walls lead to their failure. This results in soil loss and rill erosion, and will lead to cascading failure of the walls downslope. However, such walls have been identified only on slopes of lower steepness. As in the former case the trap efficiency of such walls are good as long as these are not over helmed.

Soil Walls

Such partitions are common the tappiocca farms. Though the wall is formed with a pile of loose soil, with very low relief, following the contour, these do not survive rains and surface flow successfully nor de they have excellent trap efficiency. Extensive failure of such walls are a common sight after rains and the slopes are scarred by rill and sheet eroision. Naturally the loss of soil is phenomenal and it could be a reason for absence of a horizon of the soil profile in tappiocca cultivated slopes. Besides such slopes are outstanding examples of denuded and depleted soil profiles. However, in the following season the rilled surface will be tilled to reverse the rills any way.

Quality of landmanagement vs. type of crop

The slopes studies have led the to suggestion of a correlation between the quality of land management and crop type. It is seen that wherever, slopes are planted with rubber or similar cash crops terracing and walling have been efficiently carries out. Such modification of slopes largely helps to reduce and even avoid loss of soil and assures excellent trap efficiency.

On the other hand, when annual crops like tapioca are planted very poor attention is paid to the proper management of slopes, and this leads to soil loss.

Generally speaking may of the slopes in the Neyyar basin shows a cover of lag gravel on top of the soil profile. Such lag deposits could have formed by the splash erosion of soil particles and its removal down slope. Below the layer of gravel, the soil tends to be very fine grained and has the consistency of mud. On drying it forms a hard crust. Such transformation of top layers of soils is taken as an indication of denuded soil profiles. Humus layer is practically unseen in any of the soil profiles on the slopes. Only exceptions are in highlands where humus is restricted to low lying areas depressions and gentle slopes.

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CHAPTER VI

VALLEY FILL DEPOSITS IN NEYYAR BASIN

Valley fill deposits are ubiquitously observed in parts of the Neyyar basin in association with the paddy fields. The paddy fields are in fact vast rectilinear expanses of valley fill sediments, mainly in the form of clayey silt or silty clay. The design and development of paddy fields in such valley fills are human actions which are generally ignored by many investigators. The shift from pastoral to sedentary type of cultivation coincided with the conversion of valley fills into terraced paddy fields.

From the point of view of the process geomorphologist, the valley fills are sediment reserves which accumulated in valleys by a combination slope processes and stream deposition. Perhaps, the local sediment sinks in the valleys have reached an extended threshold beyond the normal threshold limit of accumulation of sediment in them. It is argued that the extended threshold is the direct result of human action, viz., the conversion of valley fills into paddy fields.

Distribution

All the major tributary valleys in the midland and the lowland demonstrate large scale conversion of valley fills into paddy fields. The high land area on the other hand neither shows extensive development of valley fills not conversion of these into paddy fields. The high gradient of the valley bottoms, the narrow disposition of the valley s themselves, and steeper gradient of the opposing slopes with very little soil or grass cover, would have jointly prevented formation of valley fills. Further it is likely, that the fill material that had collected in there would be composed of course clastics which did not attract the attention of the early settlers as suitable substrata for paddy cultivation. Valley fill is also noticed on the banks of the master stream mainly in the form of overbank deposits. In this discussion attention is devoted to the fills that have formed in the tributary valleys of the Neyyar basin.

Description of the valley fills

As note earlier, valley fills of considerable extent occur only in the tributary valleys occurring in the midland and low land sections of the basin. The width of fill varies considerably from few tens of feet at the head of the valley to few hundreds of feet at the distal end. The length of the valley is of the order of several kilometers. The gradient of the fill shows considerable variation say from 10 feet to a mile to 20 feet to a mile. The gradient steepens towards the head of the valley as well as in the valleys of the upper midland and lower highland.

The valley fill material is of clayey silt or silty clay composition. Sediment of this nature is ideal for wet-farming due to the minima percolation loss. Wherever, deep channels are cut by streams in the fill material an opportunity exists to examine the vertical and lateral variation of the texture of and structure the fill. However, deep cuts in the fill exists in few locations only. It has been noted in such places that the fill material is composed of clayey silt of silty clay for most of the exposure. Towards the bottom there is an increase in the sand content, and the sediment can be classed as sandy-silty-clay or sandy-clayay-silt. Indications of paleochannels or cut and fill though may exist in the valley fill, but were not identified in sections. Along places with proximity to the slopes, with washed and eroded laterite substrata is noticed. At several places the exposures of unaltered or partially altered basement of crystalline rocks are noticed.

It is only logical then to assume that along points in the deepest portion of the valley, one would expect law deposits of gravelly or bouldery material.

Stock ponds of varying sizes are also noticed in many of the filled valleys, mostly at the head or upper reaches of the valleys. Such ponds serve as water-storage reservoirs for irrigation of the paddy fields after the off set of mainy season. It is common place that such ponds get reasonably quickly filled with sediment of muddy nature, needing frequent maintenance, to restore their storativity. The stock ponds also play a minor role in trapping the fine sediment along with water during the monsoons. This diversion results in reduced supply of fine sediment and water into the tributary streams.

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Formation of the valley fills

The processes leading to the formation of valley fills are rather obvious, than the time span required for formation of the valley fills, or variation in the rate of accumulation of the valley fills. Further appreciation of human role in hastening or otherwise, of fill formation processes, the conversion of the fill into paddy fields and the consequences arising out of this act etc. is of significance in the study. In the following these aspects are examined.

As the tributary occupying the valley is part of the major stream net in the basin, one has to agree that sediment fill is partly derived from the fluvial deposition. What is not certain, is the extent of the fluvial action in making the valley fill. Further, slope processes also would have been considerably instrumental in the formation of fill material, as the valley itself is bounded on either sides and at its head by various categories and types of slopes, with variable cover material and varying types of processes. Generally the processes leading to the production of fine sediment are weathering of the rocks leading to laterite and or soil and masswasting process like creep, rain splash erosion sheet erosion rill and gulley erosion of the slope material.

Hydrology of the filled valleys

In the Neyyar basin, the tributary valleys filled with sediment vis-a vis the master stream and for that matter the entire river basin enjoys a tropical climate with alternating spells of dry and wet seasons. In the Kerala region, at least there are 198 days every year showing some record of precipitation. This does not mean that for al those 198 days the streams are flood. It can easily be seen from the record of stream gauge data that bankful discharge exists only for 10 to 20 of the wet (rainy) days. The rest of the time the stream net conveys only the base flow or rising and falling stages.

Due to the dominance of the base flow in the discharge, for most of the time, the channel forming, modifying processes and the maintaining processes and associated with the bankful and flood flows which occur only during portions of the year mainly in two seasons.

From in the streams occupying the valley fills, at times of rain, a major share of discharge is funneled into the paddy fields resulting in a reduction of the height of the flood crest in the channel. The terraced fields function as basins to retain the flood water. The paddy fields due to their horizontally terraced nature reduces the velocity of flow allowing the settling of a major fraction of the wash load. Due to deposition from flood waters into the fields, there exists a potential for very slow but steady rise in the elevation of terraced beds. The stock ponds also serve to subtract a portion of the sediment and water draining through the valley fill. At times of unusual rains, however the flood waters will overwhelm the fields and cause erosion of the dikes separating the terraced fields.

At times of dry spell, on the other hand the streams occupying the valley fill go dry and the topsoil of the valley fill develops polygonal mud cracks. The stock ponds also go dry during the same season.

Relation of the valley fill with the master stream

A point that needs elucidation is the relation of valley fill and master stream. Theorectically the sediment that accumulates at the bottom of any tributary stream should ultimately reach the master stream for further down stream transport. This can happen only if the stream draining the valley in question, has the required capacity to do that job. Truly, the streams should have the required capacity to remove most of the sediment that accumulated in the valley bottom, except for over sized clast and coasrser clasts supplied to valley. However as suggested earlier, in valleys sediment accumulates not only by stream activity, but a large proportion of the sediment is contributed by the adjacent slopes, by mass wasting, by geological erosion or accelerated erosion. Therefore a good deal is sediment is bound to be trapped in the valley bed raising the valley bed by aggradation. This shall lead to reduction in gradient of the stream draining the valley and will result in further reduction of the capacity of the stream. However, toward the distal and of the valley, the lower order stream draining the valley fill endeavours to join the master stream at the same level as the bed of master stream. This may lead to development of deep stream channel (say gulley) at least within the lower reaches of the tributary.

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At the same time, the over bank deposition of sediment on the channel banks at flood stage will promote sedimentation into the tributary valley mouth. In fact there seems to be competition between the master stream and the tributary joining it; the master stream trying to build a bank in the cove like mouth of the tributary valley, and the tributary stream trying to maintain its own right of way at the confluence. Further due to the reduced discharge from the tributary due to diversion of water into the stock ponds and by temporary storage of water in the terraced valley fill, the master stream will successfully build a bank, and would force the tributary stream to maintain a channel suited its capacity.

Human action

Possibly actions, like conversion of forest land into dry agricultural lands and terracing of the fill into fields for cultivation of paddy, are the main categories of human intervention. Continued cultivation of slopes without proper land management practices, should promote accelerated erosion initiated by the initial clearing of tree cover by the (pioneer) settlers.

The consequences of such actions are nothing new to the researchers. But what is not sure is, the status of accelerated erosion, the degree of degradation of soil profile and the extent and rate of depletion of forest cover. Further how such actions influenced and controlled the formation of valley fill needs investigation.

However, it is agreed that conversion of forest into agricultural land hastened supply of clastic sediment from the upper parts of the slopes and from there into the streams or directly into the valley itself. In such a context, the sediment supplied to the valley should excedd the capacity of stream to transfer it into the master stream. As a consequence of this the valley fill should have enlarged itself in volume. The terracing of the fill material, to transform, it to paddy fields, further promoted the accumulation of fine sediment with in the terraced fields, by their settling out of the water that seasonally floods the fields. Indirectly the fills in the tributary valleys continue to remain in a mode of vertical growth, by functioning as a sediment trap. In other words, the sediment output from the tributary valleys through the streams that drain them, into the master stream, laws very much behind the input into the valley. The causality of such action is the deprivation of the master stream from its due share of sediment from the tributary, and accumulation of detritus in the valley.

What if no human action

Well, it is interesting to examine the consequences of no human intervention to convert the fill into terraced fields for paddy or other cultivation. First of all, there will be a limit upto which the sediment can be stored in the tributary valley, i.e., there is threshold for the sediment storage. The stream process should respond to the crossing of the threshold by the valley fill. Due to the homogeneous nature and monitonous texture of the most of the fill material, and due to the need for conveying the sediment and the water that is supplied to the filled valley, against what is seen to day with only a single stream occupying the valley, a river net with several tributaries of a dendritic network should emerge in the fill material. However, the climate being congenial for the establishment of vegetation, one should expect vegetation cover gradually establishing in the fill material. However, before the spread of vegetation, the gulleys would have developed. Further extension of this net, any way, will be retarded by the vegetation. The typical box like cross actions with steep walls and flat bottoms should develop in the gulleys as long as the channels are cut with in the fill. Headward such gulleys, will join with the rills or gulleys on the foot of the slopes or end abruptly with in the valley fill.

Summary

The valley fills form due to the inability of the streams, to transport all the sediment that is supplied to the valley by hill slope processes and fluvial action by head ward erosion and extension of streams. Thus main sources of sediment into the valley are from slope processes and fluvial supply.

The terracing of the fill material reduces the over all length of the slopes and allows flood waters, to be trapped in them, resulting in a gradual increase in the elevation of the valley fill by settling of sediment in wash load.

Had the fill material been left alone undisturbed by homo sapiens, a phase of gulley erosion will set in and continue to erode the fill until such time when the fill gets sufficient protection against erosion from the vegetation cover that will establish on it. Some of the gulleys may

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even transgress the foot slope or to the upper parts of the slope, while others may cease along the boundary between the fill and the grass that covers the lower parts of the slope.

Though the terracing action tantamounts to reduction in sediment supply to the main stream, such human actions like conversion of the fills into paddy fields stand as lone examples of a positive human action.

CHAPTER VII

HYDROCHEMICAL AND HYDROLOGIC STUDIES

Introduction

The investigation of water chemistry (TDS estmation) and of suspended load (TSE estimation) of river waters is rather new to our country. However, the engineers engaged in stream gauging, have been assessing the suspended load at the gauging stations along with discharge data. Elsewhere in the world several examples exist of studies relating to the TSS and TDS to change in landuse, fertilizer application, waste disposal etc. It has also been possible to relate the variation in suspended load to changing climate in the last century like in the case of arroyos of S.W United States.

The TDS & TSS load estimates are considered important in the study of process geomorphology because such data assist in the estimation of load flux from rivers into the ocean. Further variations of such load flux are taken to indicate changes in the climate and tectonic regiment of the fluvial system or to modifications of the system by a variety of human actions. Additionally this type of study helps to assess the water quality status of the system. Then an added bonous from such analysis is the revelation of prevence of man introduced pollutant in solid or liquid form, or their total absence. The TDS and TSS data also helps in the estimation of the average rate of dunudation in a basin.

Objectives of Present Study

In the present investigations on the Neyyar basin it was decided to assess the temporal and spatial variations of suspended load and dissolved load in the various tributaries and the master stream at several points. It is hoped that the analytical results of water samples for TSS & TDS will tell us:

i. The rate of load flux into the adjoining ocean.

ii. The rate of denudation of the hinterland and

iii The concentration of various chemical ions in the water and their variation from place to place and from time to time.

Ideally the present day load flux estimates shouls be compared with that of earlier period or periods to decipher the rates of variation and identification of the causes for such variation, say due to intervention by man in the system. However, in the context of the Neyyar network or for that matter of any other stream in Kerala such comparisons and prediction of the causes for variations in load flux is out of question due to the lack of earlier estimates or base line data. However, there is a point of pride in the present attempt to estima to the TDS & TSS in the Neyyar network as it could very well form a set of base line data.

Method of sampling

As per the research proposal, point samples of water were collected from the tributaries at points upstream of their confluence with the main stream, and from the stream at points below the confluence of the tributaries. In either case sampling points coincided with the cross sections selected for discharge estimation.

Approximately 2.5 lit of water was collected at each sampling point, at mid-depth of the stream. It was always made sure that water samples were collected from points of maximum mixing in the flow. This was observed to ensure the homogeneisation of suspended load in the water. The samples were properly labeled and were soon shifted to the laboratory for

32

determination of electrical conductivity and hydrogen ion concentration. The water temperature was determined in the filed itself.

Estimation of suspended load

The total suspended load of water samples were estimated by vacuum filtration using a sartorius filtration unit and sartorius filters of 0.45 u, and 47 mm diameter. The suspended load was weighed after drying the filtrate at 60 c, in a hot air even, using a Sartorius Electronic Balance. The weight of the filtrate is estimated for a unit volume of one liter.

Though the plan was to estimate the mineralogy of the suspended load, it could not be determined as the facility at RRL, Trivandrum has not been commissioned yet.

Estimation of dissolved load

Titration (HCO z3, Ca++, Mg++, SO-

4, C-l-) flame photometery (K+ and Na+) and calorimetry (spectrophotometry

Fe+++, Si++++, Mn2+, NO3) were used in the analysis of water samples. The total dissolved load in each sample was estimated by cumulating the per liter concentration of the various ions. The results of the analysis along with the TDS and TSS are given in Table.

Summary

The results of the analysis reported in the foregoing relate to the water samples collected in months of Nov., 1984 and Feb., 1985. As per the program bimonthly samples and discharge of water will be captured. Any meaningful contribution or opinion can be made elicited out of the study water samples only after the completion of the analysis of the data for a period of at least one year converting the monsoons and the base flow periods.

Hydrologic studies in the Neyyar Basin

As part of the major programme in the Neyyar Basin, the hydrology of the basin has been taken up for investigation. Study of hydrology is considered essential in this programme, as there has been reports published elsewhere, demonstrating the relation of water discharge and the load carried by the streams. The load factor of the streams has also been found to depend on the landuse of the drainage basin. In fact actions like conversion of large parcels of forest land to agricultural land or something else should lead to enhanced liberation of load from the land area of the basin into streams. Further, the construction of the dam at kallikkad and creation of a reservoir have conceivably curtailed the through transfer of load and water in the channel beyond the point of the dam.

Therefore the discharge of water through 16 cross sections sited below the confluence of a left bank or right bank tributary with the main stream, was monitored. Though the programme was to measure the discharge at least once in two months the schedule could not be adhered to, during certain months due to exhaustion of funds. However, it has been possible to carryout the monitoring of discharge in the months of Feb. 84, May 84, Nov.84 and Feb. 85. The discharge data for the last three monitoring sessions are given in Table. Field procedure in stream discharge monitoring is discussed in an earlier technical report.

Summary

It is proposed to collect hydrologic data for over a period of at least two years convering four monsoons. Only such extended data coverage can lead us to any meaningful suggestions and predictions on the influence of human action on altering the natural behaviour of the physical system of the Neyyar basin.

Collection of Rain fall data

As part of the project on River metamorphosis due to Human intervention, the soil erosion rate from different categories of slopes are to be determined. Data on rain fall has to be collected for the various parts of the basin, for this purpose. Unfortunately, it was reported that the only rain guage located bear the dam site, in the basin is presently defunct.

Therefore, for the purpose of this study we established a set of FBP rain gauges in the basin, three each on either banks in selected subbasins. The FRP rain gauges were supplied by the Lawrence & Myyo (p) Ltd. and conformed to the ISI 5225. The measuring cylinders were

33

graduated to measure a minimum of 0.2 to 20.0 mm rain fall. The gauges were installed on open flat roofs a top houses and the measuring was carried out regularly at 0800 hrs by a trained volunteer member of the same house hold. The operation started from the October, 1984.

Further, once in mouth of two months our field party compiled the rain fall data from all the six locations, and the data are given in Table.

34

CHAPTER VIII

BED-STEAD TYPE EROSION FRANE

One co ponent of study included in the project on River Metamorphosis due to Human Intervention is the monitoring of rates of erosion or deposition of soil on slopes of various attitudes and different crop and soil covers. Though a variety of monitoring techniques for estimating soil movement on slopes are known to soil conservationsits and agricultural engineers, and lately to geomorphologists, in the present study it has been decided to use a Bed-stead type erosion frame, originally devised by snow from season to season.

The Bed-stead type erosion frame is a simple device light in weight and can easily be fabricated in any work shop with some effort. This device was fabricated in the central Instrumentation Laboratory of the University of Kerala. This device has a toughened aluminium frame made of squares and a set of measuring pins made of aluminium tubes. The frame will cover an unit of area of one square meter. Four legs of 25 cm. length are attached to the terminal ends of the square sections falling on opposite sides where the sections themselves extend outward for about 25 cm. each. The one meter square area or the unit area is further divided at 25 cm, apart by fitting one meter long aluminium squares to the frame. This arrangement facilitates the division of the unit area into cells of 25cm sides. Further holes are drilled at the nodes of 25 cm. sided cells. The holes will carry the measuring pins vertically. Once the frame is placed on the ground supported by its legs, and the rods are in position, the top ends of the rods will project outward above the frame (a function of the shape of the ground below). Then the relative heights of the rods from the frame are measured with the help of depth guage and the results are plotted in a map to scale, with the spot heights at the proper locations, a scatter diagram of the ground elevation in a unit area is the result. The analyst can then contour the spot heights to create a topomap.

By periodic monitoring of the surface configuration through time the erosion or accumulation of soil in that unit area can be easily estimated. If such monitoring can be done in several locations within the basin, then we are bestowed with a simple technique and procedure, for estimation of soil loss or gain, due to natural or accelerated processes. The results of the proposed study will be reported in the third technical report.

35

TABLE SLOPE DATA, NEYYAR BASIN

Station Name & Pfofile No. Location Mean Standard

deviation No. of observations

Profile Length height Direction of the profile

1 2 3 4 5 6 7 8

Valathankara 1 LB1 13.96 6.6 14 16.75 38.49 S.E

2 Ponvila 13 4.80 10 82.95 21.085 N.W

Pazyayakade RBII

1 8.75 5.99 8 111.97 15.95 N.W

2 6.07 3.50 7 182.32 19.94 N.E

Amaravila LBIII

1 22.5 7.07 8 86.96 24.38 N

2 20.67 4.72 6 56.00 19.5 N.W

3

Manchavilakom

17.0 3.39 10 101.40 27.90 S.E

Clathanni RB IV

1 Olathanni 8.5 3.75 163.35 22.4 S.E

Aruvipuram N

LB V

1 12.5 4.81 10 112.94 23.38 S.E

2 11.03 5.66 12 136.29 25.005 N.E

3 11.67 4.93 12 176.94 31.600 S.E

4

Aruvipuram

12.50 6.45 12 147.24 31.290 N.E

36

1 2 3 4 5 6 7 8

Aruvipuram 3

1 R.B. VI 19.58 5.88 12 125.29 37.65

2 20.00 15.81 7 98.66 17.72

3 10.96 3.03 13 202.65 37.58

4

Mampazhakkara

10.0 1.58 5 57.80 9.935

Perumkadavil LB VII

1 14.17 2.35 9 115.5 29.7

2 Perumkadavila

17.50 3.02 11 126.5 37.655

Aruvikkara RB VIII

1 21.65 6.12 15 100.73 40.565 N.E

2 16.88 8.05 16 115.09 34.345 S.E

3 11.79 3.74 14 124.29 27.505 N

4

Aruvikkara

10.83 4.71 6 59.90 11.72 S.W

Kizharoor LB IX

1 22.03 8.35 16 124.80 40.28 N.E

2 5.71 7.43 7 70.15 12.72 NW

3 11.79 4.16 7 65.25 12.995 S.E

4 14.64 4.89 14 130.29 34.06 N.E

Parachal RB X

1 23.13 6.69 16 105.53 39.655 N-NE

2 Pulimuttom

21.92 12.02 13 123.57 37.68 S.E

Aryankod 1 LB XI 27.71 6.81 21 130.42 62.86

2 Mylachal 20.96 4.106 13 125.73 44.55 N-NE

37

3 20.96 4.106 13 125.73 44.55 N-NE

Kuttiyanikkadu RB XII

1 10.0 3.23 12 155.96 24.435 S.E

2 12.5 2.83 5 43.56 8.78 N.E

3

Kuttiyanikkadu

6 2.29 10 167.96 13.56 S.W

Ottasekharamangalam

LB XIII

1 31.41 8.75 11 50.34 27.86 S.W

2 Valiyod 15.63 4.46 8 98.60 22.26 N.E

3 10.28 5.24 9 95.70 19.15 N.E

Mandapathinkadavu RB XIV

1 15.35 5.98 7 70.06 16.79 N-NE

2 16.0 9.0 10 75.68 18.36 S.SE

3

Amachal

11.97 5.10 19 185.77 33.37

Puzhanadu LB XV

1 15 15.63 9 90.07 18.83 A.N

2 11.5 2.00 5 67.83 13.225 A.W

3 10.33 4.7 6 87.61 14.685 A.S.E

4

Puzhanadu

21.43 15.51 7 52.86 12.830 A.E

Kallikkadu RB XVI

1 27.07 6.83 14 85.04 41.935 A.N.E

2 Kallikkadu

4 2.29 10 143.25 10.45 A.S.W.

38

TABLE : HYDROLOGIC DATA FOR MASTER STREAM, MAY, 1984

Sl.No.

Station

Urainage Area Km2

Channel Capacity

m2

Actual width W.m.

Effective width Wm

Depth D.m

Mean velocity m Sec 1

Discharge m3 Sec 1

Bankful capacity

m2

1 2 3 4 5 6 7 8 9 10

1 Valathankara 434.85 21.20 37 28 0.67 0.40 7.53 199.6

2 Pazhayakada 407.02 15.30 23.5 21.5 0.69 0.26 3.78 128.80

3 Olathanni 395.67 25.31 26.0 24 0.94 0.15 3.89 118.40

4 Amaravila 369.15 11.60 18 18 0.6 0.99 11.48 153.40

5 Aruvippuram (S) 349.65 18.30 23 22 0.83 0.25 4.63 173.60

6 Aruvippuram (N) 336.72 10.60 33 26 0.38 0.98 8.73 172.60

7 Pernkadavila 287.22 52.80 42 40 1.32 0.09 5.25 160.40

8 Aruvikkara 272.75 13.18 48.8 22.8 5.75 0.96 5.75 195.00

9 Parachal 270.32 28.64 19 18 1.59 0.99 28.55 161.00

10 Kizharoor (N) 257.87 14.17 18 16 0.85 0.41 5.82 170.00

11 Kuttiyanikad 255.80 15.87 22 20 0.76 0.18 2.78 143.00

12 Ariyankod 253.32 10.40 23 24 0.37 0.68 6.00 184.00

13 Ottasekharamangalam 248.62 13.30 14 12 0.89 0.27 2.84 170.80

14 Mandapthinkadavu 241.40 6.90 20 12 0.41 0.45 2.20 79.00

15 Puzhanad 214.65 8.0 15 8 0.73 0.52 3.00 164.00

16 Viranakavu 210.75 8.50 16 10 0.70 0.67 4.69 206.00

39

TABLE : HYDROLOGIC DATA FOR MASTER STREAM, FEBRUARY, 1985

Sl.No.

Station

Urainage Area Km2

Channel Capacity

m2

Actual width W.m.

Effective width Wm

Depth D.m

Mean velocity m Sec 1

Discharge m3 Sec 1

Bankful capacity

m2

1 2 3 4 5 6 7 8 9 10

1 Valathankara 434.85 29.67 33 31 0.89 0.25 8.22 199.6

2 Pazhayakada 407.02 28.20 28 24 1.16 0.88 21.64 128.80

3 Olathanni 395.67 34.30 28 22 1.48 1.36 46.29 118.40

4 Amaravila 369.15 16.10 20 20 0.80 0.60 9.93 153.40

5 Aruvippuram (S) 349.65 18.10 24 22 0.82 2.83 46.13 173.60

6 Aruvippuram (N) 336.72 38.50 36 36 0.07 0.18 6.86 172.60

7 Pernkadavila 287.22 42.70 36 34 1.28 0.06 3.00 160.40

8 Aruvikkara 272.75 31.07 44 44 0.71 0.59 18.27 195.00

9 Parachal 270.32 33.60 21 21 1.60 1.35 45.33 161.00

10 Kizharoor (N) 257.87 13.6 18 18 0.76 0.20 2.68 170.00

11 Kuttiyanikad 255.80 8.8 20 20 0.44 1.24 7.13 143.00

12 Ariyankod 253.32 9.16 29 25 0.35 0.79 6.03 184.00

13 Ottasekharamangalam 248.62 12.41 20 20 0.62 0.31 3.06 170.80

14 Mandapthinkadavu 241.40 2.05 11 11 0.19 1.15 2.61 79.00

15 Puzhanad 214.65 3.60 12 12 0.30 1.32 0.75 164.00

16 Viranakavu 210.75 8.20 13 10 0.71 0.21 1.51 206.00

40

TABLE : HYDROLOGIC DATA FOR MASTER STREAM, FEBRUARY, 1985

Sl.No.

Station Urainage

Area Km2

Channel Capacity

m2

Actual width W.m.

Effective width Wm

Depth D.m

Mean velocity m Sec 1

Discharge m3 Sec 1

Bankful capacity

m2

1 2 3 4 5 6 7 8 9 10

1 Valathankara 434.85 10.35 21 17 0.61 0.61 5.01 199.6

2 Pazhayakada 407.02 11.90 23 20 0.58 0.31 4.02 128.80

3 Olathanni 395.67 22.4 26 18 1.02 0.12 2.18 118.40

4 Amaravila 369.15 10.16 20 20 0.48 0.15 1.84 153.40

5 Aruvippuram (S) 349.65 14.06 22 18 0.72 0.10 1.53 173.60

6 Aruvippuram (N) 336.72 35.73 34 34 1.05 0.20 7.22 172.60

7 Pernkadavila 287.22 34.14 36 36 0.95 0.18 6.11 160.40

8 Aruvikkara 272.75 47.4 41 .. .. .. .. 195.00

9 Parachal 270.32 2.24 8 8 0.28 0.31 0.85 161.00

10 Kizharoor (N) 257.87 12.48 16 14 0.85 0.04 0.51 170.00

11 Kuttiyanikad 255.80 6.09 20 16 0.34 0.13 0.77 143.00

12 Ariyankod 253.32 4.96 18 6 0.75 0.86 1.52 184.00

13 Ottasekharamangalam 248.62 8.57 17 5 1.46 0.08 0.67 170.80

14 Mandapthinkadavu 241.40 1.36 12 6 0.16 0.48 0.69 79.00

15 Puzhanad 214.65 0.84 5 8 0.15 0.52 0.67 164.00

16 Viranakavu 210.75 0.60 5 4 0.14 0.71 0.43 206.00

41

TABLE : WATER CHEMISTRY OF MASTER STREAM, NOVEMBER, 1984

Sl.No.

Station HCO3

Cl

NO3

SO4

Na+ K+ Ca++ Mg++ Fe++ SiO2 TDS in mg/lit

Total suspended gm/lit solids

Total load gm/lit

1 Valathankara 17 21 0.1 0. 4.5 1. 6. 4. 0. 3.8 57.4 0.0692 0.1266

2 Pazhayakada 16 22 0.1 0. 2.5 0. 3. 6. 0.7 3. 53.3 0.0920 0.1453

3 Olathanni 21 25 0.2 0. 3.5 0. 4. 4. 0.5 2.6 60.8 0.0792 0.1400

4 Amaravila 18 23 0. 0. 4.5 1. 3. 6. 0. 5.3 60.8 0.0678 0.1286

5 Aruvippuram (S) 18 22 0. 0. 5.5 1. 5. 6. 0. 6. 63.5 0.0216 0.0851

6 Aruvippuram (N) 19 25 0. 13 5.5 1. 3. 13 0. 3.5 73. 0.0135 0.0865

7 Pernkadavila 25 22 0.3 0. 4.5 1. 4. 5. 0. 6. 67.3 0.0230 0.0908

8 Aruvikkara 11 17 0.5 11 2.5 1. 4. 5. 0. 3. 55. n.d. ..

9 Parachal 15 23 0. 15. 4.5 1. 3. 14 0. 3.6 79.1 0.0430 0.1221

10 Kizharoor (N) 21 16 0.2 0. 6.5 1. 3. 5. 0. 4.6 57.3 0.0231 0.0804

11 Kuttiyanikad 19 22 0.3 0. 4.5 1. 5. 3. 0. 3. 57.3 0.0273 0.0851

12 Ariyankod 16 22 0.4 0. 4.5 1. 2. 6. 0. 4.5 56.4 0.0850 0.1414

13 Ottasekharamangalam 14 15 0.2 1. 3.5 1. 3. 6. 0. 5.8 49.5 0.0424 0.0919

14 Mandapthinkadavu 16 18 0.2 2. 4.5 1. 5. 5. 0. 3.5 55.2 0.0188 0.0740

15 Puzhanad 15 8 0.1 4. 1. 0. 3. 4. 0.7 3. 38.8 0.0210 0.0598

16 Viranakavu 17 14 0.1 0.48 1. 1. 4. 3. 0. 3.5 44.1 0.0180 0.0621

42

TABLE : WATER CHEMISTRY OF MASTER STREAM, NOVEMBER, 1984

Sl.No.

Station HCO3

Cl

NO3

SO4

Na++ K+ Ca++ Mg++ Fe++ SiO2

TDS in mg/lit

Total suspended gm/lit solids

Total load gm/lit

1 Valathankara 15 25 0.2 0 1.5 1 4 4 0 4.5 55.2 0.0418 0.0970

2 Pazhayakada 16 18 0.3 0 3.5 1 4 6 0 3.8 52.6 0.0918 0.1444

3 Olathanni 16 24 0.3 0 1.5 1 3 5 0 4 54.8 n.d n.d

4 Amaravila 14 19 0 8 1.5 1 7 6 0 4.9 61.4 0.0206 0.0820

5 Aruvippuram (S) 17 20 0.1 5 2.5 1 4 4 0 4.5 57.5 0.0312 0.0887

6 Aruvippuram (N) 17 21 0.2 0 1.5 1 6 4 0.7 4.1 55.5 0.0240 0.0795

7 Pernkadavila 16 22 0.2 12 3.5 1 5 4 0 4.5 75.2 0.0267 0.1019

8 Aruvikkara 13 13 0.3 0 1.5 1 4 4 0 3.7 40.5 0.1611 0.2016

9 Parachal 12 14 0.2 0 3.5 1 5 2 0 3.8 41.5 0.1907 0.2322

10 Kizharoor (N) 16 17 0.1 0 3.5 1 5 4 0 5.1 51.7 0.0302 0.0819

11 Kuttiyanikad 17 13 0.1 8 3.5 1 5 3 0 4.9 60.5 0.0242 0.0847

12 Ariyankod 16 13 0.2 0 2.5 1 6 3 0 4.5 51.2 0.0519 0.1031

13 Ottasekharamangalam 17 23 0.2 0 3.5

1 6 3 0 5.1 58.8 0.0547 0.1135

14 Mandapthinkadavu 17 13 0.1 0 2.5 1 4 4 0 4.7 46.3 0.013 0.0597

15 Puzhanad 15 13 0 18 1.5 1 4 11 0 6.3 54.8 0.0167 0.0715

16 Viranakavu 14 16 0.1 0 2.5 1 3 5 0 5.6 47.2 0.00875 0.0559

43

TABLE : WATER CHEMISTRY OF MASTER STREAM, FEBRUARY, 1985

Sl.No.

Station HCO3

Cl

SO4

- Na+ K+ Ca++ Mg++ SiO2 TDS in mg/lit

Total suspended gm/lit solids

Total load gm/lit

1 Valathankara 14 20 0 7 2 4 7 5 59 0.0049 0.0639

2 Pazhayakada 14 19 5 6 2 9 5 5 65 0.0133 0.0783

3 Olathanni 14 18 2 6 2 9 5 5 61 0.0137 0.0747

4 Amaravila 14 21 0 7 2 10 3 3 60 0.0099 0.0699

5 Aruvippuram (S) 13 23 11 7 2 10 4 3 73 0.0094 0.0824

6 Aruvippuram (N) 13 21 0 7 2 10 2 3 58 0.0160 0.0740

7 Pernkadavila 13 17 0 7 2 10 3 4 56 0.0278 0.0848

8 Aruvikkara 13 21 0 5 2 7 5 3 56 0.0363 0.0923

9 Parachal 14 16 0 7 2 7 5 5 56 0.0152 0.0712

10 Kizharoor (N) 14 16 2 5 2 8 5 3 55 0.0139 0.0689

11 Kuttiyanikad 13 18 7 5 2 7 5 4 61 0.0145 0.0755

12 Ariyankod 14 19 6 5 2 8 4 4 62 0.0273 0.893

13 Ottasekharamangalam 14 11 3 5 2 7 6 5 53 0.0460 0.0990

14 Mandapthinkadavu 13 18 13 5 2 7 7 4 69 0.0090 0.0780

15 Puzhanad 13 10 0 5 2 7 6 3 46 0.0058 0.0518

16 Viranakavu 14 11 0 5 2 7 4 4 47 0.0084 0.0554

44

TABLE : RAINFALL DATA FOR NEYYAR BASIN (IN MM) OCT. 1984 FEB. 1985

October 84

Vlathankara subbasin (LB-I)

station No.1

Olathani Subbasin (RB-

IV) Station No.2

Perumkadavila subbasin

(LB-VII) Station No.3

Parachal subbasin

(RB.X) Station No.4

Ottasekharamangalam

subbasin (LB. XIII) Station

No.5

Kallikad subbasin (RB.

XVI) Station No.6

1 2 3 4 5 6 7

1 .. .. .. .. .. ..

2 .. 98 .. .. .. ..

3 89 .. .. 85 .. ..

4 39 20 .. 13 23.4 23

5 14.8 .. .. 10.8 17.05 13.8

6 15.6 19 .. 14.8 21.4 28.8

7 1.4 1.2 .. 1.2 3.3 2.2

8 4.6 2 .. .. 0.5 0.4

9 0.3 .. .. .. .. ..

10 .. .. .. .. .. ..

11 0.2 .. .. 3.8 7.1 11.4

12 3 3 .. 7.9 7.0 5.6

13 2.4 28 .. 5.4 2.2 2.4

14 to 24 Nil Nil Nil Nil Nil Nil

25 .. 4.8 3. .. 35.5 14.2

26 .. 2 4.9 10.0 35.5 25.4

27 .. 3 1.6 15.0 12.0 71.8

28 22.8 5 22.6 41.2 19.2 53.0

45

29 3.6 2 .. .. 19.0 2.0

30 3.6 .. .. .. 23.75 46.0

31 .. .. .. .. .2 ..

November 1984

1 .. .. .. .. 8.2 0.6

2 .. .. .. .. 8.2 ..

3 .. .. .. .. 8.2 1.0

4 .. 5.2 32 32 8.2 25.4

5 .. 2.2 .. .. 8.2 ..

6 .2 .. 8 8 4.8 2.4

7 to 8 Nil Nil Nil Nil Nil Nil

9 .. .. .. .. .. 2.0

10 9.6 7.2 10 10 13.5 11.0

11 .. 21 37.8 37.8 1.5 0.2

12 to 13 Nil Nil Nil Nil Nil Nil

14 4.85

15 4.85

16 24.0

17 2.3

18 69.2 25.6 24.2 12.2 11.0 1.8

19 2.9 14.6 5.25 26 5.2 9.4

20 7.5 6 5.25 14.8 15.4 4.2

21 1.2 5.0 16.2

22 11.1 18.0 68.20 0.2

46

23 34.2 10.2 23.0 26.6 3.0

24 43.8

25 4.2

26 36.5 9.2 7.1 6.8 12.40 11.4

27th Nov. to 4th Dec. 84

Nil Nil Nil Nil Nil Nil

5 9.6 1.2 12.6 16.6 6.0

6 to 27 ... .. .. .. .. ..

28 .. .. .. ... .. 2.6

29 .. 14.6 8.9 .. .. ..

30 .. .. .. .. .. ..

31 .. .. .. .. .. ..

January 85

1 67.3 46 100.18 78.4 72.5 67

2 21.2 1.4 .. .. .. 5.6

3 .. 10.2 .. .. .. 64.4

4 5.4 11 51.5 13.0 28 64.4

5 28 0.6

6 8.8 11.5

7 4.2 13.42

8 10.0 17.2

9 to 16 Nil Nil Nil Nil Nil Nil

17 1.0

Feb. 1985

1

47

2 9.6 6.6 7.0

3 7

4 6.2

LOCATION OF RAINGAGUES, NEYYAR

Station No.

Name of Station Tributary Basin Subbasin area,

Km2 Location

1 Mariapuram Vlathankara (SB) LB-1 22.10 At Mariapuram on LB of RB tributary joining at Vlathankara

2 Thalayil Olathanni (SB) RB-IV 20.60 At Thalayil near Balaramapuram on RB

of RB tributary joining at Olathanni -

3 Permkadavila Perumkadavila (SB) LB- VII 7.55 At Perumkadavila on LB-of RB tributary joining at ampazhakara

4 Thungampara Parachal (SB) RB-X 9.9 At Thungampara on RB between two

branches of the tributary joining at parachal

5 Vazhichal Ottasekharamangalam (SB) 49.2 At Vazhichal on LB of RB of feeder

stream of Chit Ar joining at Ottasekharamangalam

6 Kallikad Kallikad (SB) RB-XVI 4.90 At Kallikad on RB of RB tributary joining at Viranakavu

48

49

Distribution List

1. Director Cemtre for Earth Science Studies, P.P. 2235, Trivandrum Pin: 695010

2. Director, Geological Survey of India, Kerala Circle, Thampanoor, Trivandrum.

3. Libraian, Legislature Library, Secretariat, Trivandrum

4. Director, Centre for water Resources Development & Management Kunnamangalam, Kozhikode

5. Director Kerala Engineering Research Institute, Peechi.

6. Prof. Stanely Schumm Colorado State University, Fort Collins. Colorado 80523

7. Prof. Ian Douglas School of Geography University of Manchester Manchester, U.K. M13 9PL

8. Dr. Chris Park Department of Geography Lancaster University Railrigg, Lancastor U.K. LAI 4YR

9. Prof K.J. Gregory Professor of Geography University of Southampton U.K.. S09 5NH.

10. Prof. S.M. Casshyap Department of Geology Aligarh Muslim University Aligarh, 2 UP.

11. Prof. Ramesh Prof. of Geography Madras University Presidency College Madras

12. Prof. Madhav Gadgil Centre for Environmental Information System Indian Institute of Science Bangalore 560012 India

13. Prof.k Vaidvanthan Dept. of Geography Andhra University Waltair

14. Prof. V.K. Varma Department of Geology Delhi University New Delhi

15. Dean, School of Environmental Sciences Jawaharlal University New Delhi

16. Prof. B.K. Sahu Department of Geology IIT. Powai, Bombay 400 076

17. Prof. Dipankar Nivogi Department of Geology IIT. Kharagpur

18. Dr. S.K. Chanda Department of Geology Jadavour University Calcutta

19. Head of the Dept. of Geology Banares Hindu University, Banares

20. Head of the Dept. of Geography, Madura Kamaraj University Madurai

21. Librarian Central Library Geological Survey of India Calcutta 700 016

22. Librarian Kerala University Library Trivandrum

23. Dr. Indra Bir Singh Dept. of Geology Lucknow. University Lucknow

24. Officer in Charge Data Processing Centre GSI. Hydrebad Pin 500 001