Channel Morphology, Plant Association Groups and Habitat Diversity of River Kanand (Maharashtra)

Vegetation is an important factor of a drainage basin, especially the river channel. Since 1967, although considerable interest has been created in fluvial geomorphological aspects of drainage basins, the significance of vegetation has not been considered in an integrated way. It appears from the recently published accounts of channel forms and processes that there is now a general agreement over the significance of vegetation in the management of a river channel. The precise way in which this factor affects the river behaviour is however, still not very clear. The study focuses on the influence of a variety of channel variables on the bed vegetation in down-stream direction and across the channel. The associations and correlations between these factors and the bed vegetation do reveal the complexity of environmental interactions. The methodology adopted was based on specific lithological, hydrological and vegetational aspects of the river channel. The primary focus of this work is to ascertain the linkages between geomorphological, hydrological and ecological processes and the bed vegetation which are a part of phytogeomorphology and ecology of the river basin.


Introduction
Terrestrial ecosystems include river ecosystems which have many significant points. Detailed understanding of a river ecosystem would not be possible without the knowledge of fluvial geomorphology. The study of any fluvial system includes the study of different variables of river morphology such as channel depth, width, discharge, slope and the river veg-etation. The vegetation asepct however, has not been considered in an integrated way till recently (Gregory and Gurnell1988).
The fluvial systems are normally very complex. The main streams can be classified as lowland streams, upland streams and mountain streams (Haslam 1978). To understand these complex ecosystems, it is necessary to study the phytogeomorphological aspects like river vegetation and river morphology. This paper is devoted to such aspects of fluvial ecosystems. In this study the relations between river morphology, plant association groups, habitats and substrate types are examined in a gravel bed of a stream named Kanand river, a tributary of the major river Nira.

The Study Area: Location and Geomorphic Environment
The study area is the channel of the river Kanand a tributary of the river Nira. It drains the major part of Velhe tahasil of Pune district. The river basin covers an area between 730 32' E to 730 45' E longitudes and 180 15' to 180 20' N latitudes.
The river originates in the high rainfall zone of Western Ghats and flows over trappean landscape represented by Basalt. The drainage of the river is governed by the regional slope of upland Maharashtra. It is considered as representative of upper reaches of most of the rivers originating in the Western Ghat region of Maharashtra.
The river rises at an altitude of 1205 m and meets the river Gunjavani at 670.5 m ASL. The basin is bounded by Rajgad and Torna forts to the south, attaining a height of 1402 m and 1411.2 m ASL respectively. The source region of the river Kanand is characterised by exposed, basaltic lava flows, capped 29 10.54081/JES.010/11 JOURNAL OF ECOLOGICAL SOCIETY by laterite at some places. The drainage network and hydrogeomorphic environment (Fig. 18) of this stream is a result of specific hydrogeomorphic conditions (Table 1). These conditions have in turn affected the vegetation in the channel. The bankful width of the channel is 51 m., whereas the low flow width is nearly half of it which is around 27 m. The channel bed slope has a gradient of 2.18%. The valley floor of the river has also a gradient of 2.J5%. The total length of the river course under study is 25 km between its source and confluence with the river Gunjavani.

Materials and Methods
The channel vegetation along the river Kanand was studied in pre-and post-monsoon seasons, at least for seven years, from 1988 to 1994. The study was exclusively based on field observations and field measurements in the said river n~ach. The detailed study was carried out for the iden ification of bed plants, their habitats, substrates and "1lantassociation groups along channel cross sections.
Bed sediment samr :~s were collected for different plant species. The flLwers, twigs, leaves and roots were collected from t1.e field and species were identified. The area of veget. -tion patches was measured and the total plants in tha area were counted and classified into different h. .bitats.

The Plant Habitats
The plants in the Kanand river were classified into following broad hal-itats (Gole 1983) : 1) The plants of tl,e marshy places: The plants such as Asteracalltha IOllg~folia and Homolloia riparia found in marshy, stagnant \\ iter and in the shallow pools on the river bed were ound grouped in this habitat.
2) The partly submerged plants: These are aquatic plants and the 10-. fer portion of their shoot was found partly submerge,: in water. Cyperus rotlmdus and Crillumsp were !ne plants found in this habitat.
3) Plants of rock crevices: The species like CYllodoll dactyloll and Phyllallthus lliruri were invariably found to grow on the joints and crevices of .rocks on the bed.
4) The sand and gravel bars: The most common habitat in the river was the sand and gravel bar. The point bar and the mid stream bars were the ideal locations. Lalltalla camara and Eugenia heyllealla were the species found growing luxuriantly on these bars.

The Channel Morphology
The morphology of a river changes from its source to mouth. The change in morphology is the result: of a change in gradient width, depth and discharge. There are marked variations in most of these parameters as a result of lithology, topography and human interferences in downstream direction. All these changes are reflected in the variation in the pattern of vegetation across and along the channel (Fig. 3).
The study of hydro&e0morphic parameters ( Table  1) clearly indicates that the river basin is not mature and has maintained a steep gradient. The valley floor slope and channel slope ratio is considered to be a variable, of stability (Kale and Rajguru 1988). For the river Kanand it is 0.99, indicating a less stable channel, leading to observed non-existence of bed plants to a distance of 11 km from the source. Therefore, one can consider the channel stability as an important aspect of river vegetation. The Kanand basin is less circular in shape and has pronounced elongation ( Fig. 1). In this respect, the drainage basin is comparable with the rivers of Konkan (Dikshit 1981, Karlekar 1981. The other geomorphic parameters like relief, width and depth show that the channel of the river Kanand is in incision phase. This is confirmed by the presence of knicks and inflection points at a few places in the river. Such points occur at 14 to 16 km from source and between 550 to 700 m ASL (Fig. IB). Gorges and pot holes are the characteristics of river Kanand. The stream of Kanand exhibits a valley asymmetry as well as channel asymmetry.

Plant Association Groups and Habitat Diversity
Plant association refers to a group of plant species sharing similar environmental conditions. The environmental conditions for plant growth in the channel are governed by substrate and supply of water. Each association group in the river Kanand has distinctive and dominant plant species (Fig. 4). In the river, plant association shows a downstream variation from source to the confluence.
To study the association of plant species in the river Kanand, the river stretch was divided into five major sectors (Fig. 4) each with a length of five km thalweg distance. It was found that the channel upto a distance of 11 km from the source does not show significant growth of plants, except some algal growth. This stretch of the river bed has a steep gradient and is mainly a channel cut into the rock.
The channel upto a distance of 11 km from the source is devoid of vegetation. Downstream, the dominant associations could be identified upto the confluence. The major species upto 16 km are Tamarix ericoides, Eugenia heYllealla, Cyperus rotll1zdus and CYlladolldactyloll. Acacia arabica was also found associated but rarely with the gravel and sand bar habitat. The Crinum sp. (Nadi Kanda) waS' also seen in this section, in partly sumberged habitat. The species mentioned above also belong to the bank vegetation. Since they are growing in the bed of the stream, they suggest drastic fluctuations in the flow of the stream.
The river reach between 16 km to 21 km from the source, shows slight variation in association of the species. Hereafter, Cynodon dactylon becomes dominant rather than Tamarix ericoides. The frequency of occurrence of Tamarix ericoides decreases significantly. The new species Homonoia riparia and Crinum are reported from the sand bar and partly submerged habitat. Downstream of 21 km, Cynodoll dactylon' shows its dominance in association but the frequency ci Homonoia riparia decreases, which is replaced by another species, Argemone mexicana ard Acacia in bushes. These associations are dependent on the flow regimes.
This definite variation in association of plant species is due to changes in the habitat. Existence of preferred habitat favours the growth of a specific plant species and dictates its dominance in the association. The channel to a distance of 11 km from the source is rocky and cannot provide the favourable substratum and habitat to the species, therefore it is devoid of vegetation. The channel between 11 km and 14 km from the source has gravel bar and marshy habitats. Downstream of this, gravel bar habitat is replaced by the sand bar habitat and partly submerged habitat which are sometimes accompanied by habitats of rock crevices and marshy environment.

Conclusion
Thus channel morphology directly affects the plant association groups (Fig. 3 and 4). The pattern of habitats discussed here is the result of morphological changes in the river channel. Field observations and detailed studies of vegetation in the river Kanand also suggest that bars covered with vegetation are more stable. The luxuriant growth of different species or that of one single species leads to impoundment of water. The vegetation makes for flow training and acts as an obstacle to bed material. Table 2 gives the section wise account of morphology of the Kanand river channel, plant associations and habitat diversity including the substrate preferred by association groups of plants and habitats.
A wide range of variation (Fig. 3) in the vegetation pattern in the river Kanand is due to the rapid changes in the gradient and the flow pattern. The vegetation pattern seen in upper reaches ( Fig. 3/1, 2 and 3) is significantly different from the one observed in lower reaches ( Fig. 3/16, 17 and 18). These changes are also due to heterogeneity of sedimentary environments within the stream.
On the bed of the river Kanand, in fact, several substrate types occur at one site. This results in the association of specific plants at a particular site. The Tamarix ericoides and Homonoia riparia association is associated with gravelly substrate. The Eugenia heyneana and Cipadessafruticosa association was found to grow in a substrate comprised of coarse and medium sand. Phyllanthus niruri prefers sandy silty substrate. In general the changes in particle size from gravel to coarse sand to clay and the development of soil affect the species composition in the bed of the river channel.
An important obervation in the study area is that the recent growth of vegetation is found to be associated with sand bars and the old growth on the terraces.
The emphasis, thoughout the study, was on the longitudinal and transverse variations in river bed vegetation in terms of its frequency of occurrence and habitat diversity. Since the study was conducted in the stream channel from the hilly terrain, there were rapid changes in the gradient, which assured some variation in the plant species. The study area lies upstream of sediment control structures like dams and bunds in the lower reaches. Moreover, human intereference in the system is not significant. In the course of this study it was also noted that the channel is undergoing metamorphosis due to a decrease in relative proportion of vegetation. The silting of the bed is on the increase and the terraces on the sides, are being destroyed at a rapid rate.
Although there is insignificant human interference in the river system as a whole, relatively more disturbance is observed on the bank of channel in the form of agricultural practices. These have induced the erosion of bank and destruction of channel walls leading to the silting of river bed.