The relationship between lithology and structure on one hand and the drainage network pattern on the other has long been established [1] - [3] . Several studies in the past have shown that the drainage network pattern and river channel morphology reflect the integration of multiple processes and forces [4] . The litho-structural control on drainage network pattern is strongly evident in an area of complex structure and diverse lithology. Alignment of drainage lines, sharp bends in river courses, obtuse junction angles and breaks in the river profiles are some of the geomorphic features that could be detected visually on maps and images and could be related to joints, fractures, faults, dykes and lithological boundaries. However, in areas of uniform or homogenous lithology, the control of structure is less evident. Therefore, the assessment of the control of lithology and structure in such areas is often subjective and challenging [2] . Dykes are discordant igneous bodies of more or less tabular shape and exhibit a cross-cutting relationship with the country rocks. They occur commonly in the form of group called as swarm. When molten magma flows upward through near-vertical cracks (faults or joints) toward the surface and cools, dykes are formed. Dykes are sheet-like igneous intrusions that cut across any layers in the rock they intrude.

The objective of this paper is to explore the drainage-dyke relationship and to establish the nature and extent of the control of the dykes on the drainage network properties and orientation of streams.

The large mafic dyke swarm around Nandurbar is mapped within basin area of 262 km². The total length of Sivan River is 59.33 km. There are total of 37 dykes exposed ranging from <1 km to 14 km in length. The intruded dykes are of highly weathered basalt flow of compound pahoehoe. Total length of dykes is 201.58 km. with density of 0.76 km per sq. km. Sinuosity index of Shivan River is 1.21, which indicates sinuous river characteristics. The orientation of lower and middle order tributary streams is controlled by the dyke properties formed by genetic streams evolution in the basin. The response of the drainage network to dyke control is inversely related to the stream order network. The dykes have a greater control on lower order stream than the higher order stream attributes. Diversion of streams, bends, insequent, subsequent and resequent streams are developed in the river basin. The dyke ridges play an important role as water divides in the drainage basin, which directs shape and size of drainage basin to some extent.

The present study is significant in understanding the geological setting and the structural deformation caused by lineaments, which would help to understand the influence of lineaments on the alignment of the drainage network. This is also important for improving the understanding of the level of structural control on landscape evolution in general and stream alignment in particular. Such studies also disclose the level of changes that have occurred in the drainage network due to structural deformation caused by dykes [3] .

The area under investigation covers Shivan River basin which forms part of east-west trending Tapi gaint swarm. The area extends from 21˚10'49.3''N to 21˚30'51.3''N latitudes and 74˚05'23.0''E to 74˚16'15.3''E longitudes ( Figure 1 ). It originates on the northern slope of the Sahyadri mountain range at an elevation of 706 M above mean sea level and joins to the Tapi River at 100 M above mean sea level. The Shivan River flows from south-west to north-west for 59.33 KM. It is a left bank tributary of the Tapi River. The basin relief is 606 m. It is crossing through prominent linear dyke ridges. The south eastern boundary of the basin is marked by Western Ghats with steep escarpment towards west.

The southern region of the basin is occupied by plateau extent. North face of the plateau is characterized by valleys of northward flowing streams. Plateaus as well as valleys are intruded by east-west running dyke ridges. The slope of the Shivan basin ranges from >70˚ to ~5˚ from source to the confluence with the Tapi River. The basin relief is generally steep to gentle from south to north.

Climate of the entire basin is controlled by SW monsoon. The basin experiences average annual rainfall from >700 mm in the source region to ~590 mm in the basin [5] .

This study is based on two different datasets. The first set includes the information about the attributes of the dykes and the second dataset consists of the data regarding drainage basin and network parameters.

Analysis of drainage network morphology, or drainage pattern, can provide information about regional slope, underlying structures, and bedrock characteristics [1] [4] - [8] . Shivan river basin shows an indication of superimposed drainage characteristics in the Tapi dyke swarms subset region. E-W oriented dykes is considered here as a main component for the relationship within dykes and drainage pattern and stream orientation. Slope along dyke ridges shows important features to determine stream alignment in genetic form.

Attributes of the dykes, such as length, orientation and density are considered in the context on drainage pattern analysis ( Table 1 ). Dykes’ width is measured during field visits. Width of dykes do not imprint on streams network like as a positive, elevated parallel dyke ridges. Rose diagrams are helpful to compare the dykes and streams orientations relations which prepared in the Rockworks 16 software. Rose diagrams are created from endpoint data in Rockworks software.

Positive outcrops of dykes are more impact on alignment of streams and channel orientation. That strongly guide to drainage networks. The lower part of the Shivan Rver basin clearly represents no appearance of dyke ridges where streams are parallel to slope. This outcome focuses on dyke structures control on drainage networks.

The Rockwork 16 software is used to prepare rose diagrams of dykes orientation and stream directions for each stream order. Rockwork software helps to draw rose diagram by using a line endpoint data and generates a directional diagram that depicts the orientations of the linear features. The dykes’ strikes are mainly orient in E-W direction.

Figure 3 shows conspicuous strike of dykes and streams order wise rose diagrams. The mean value of dykes’ orientation is 83˚N. In each stream order the stream flow direction and the dyke strikes show coinciding directions over certain distances. It is observed that dyke orientation has greatly impacted on first order streams. The streams in each order have east-west orientation which shows an impact of dykes. The streams flow in other direction are insequent streams and

are the indicator of dyke impact within the basin. The dyke orientation impact is greatly observed on initially developed streams along dyke ridges on either slope. Hence, it can be interpreted that, lower the stream order, higher is the impact of dykes on stream orientation. While higher the stream order, lower is the control of dyke on stream orientations.

The investigation of orientation of dykes and stream directions in the Shivan drainage basin throws light on the relationships between them. The alignment of stream flow is oriented to some extent to the respect of geological structure of dykes. Shivan river course has adjusted to some extent to dyke orientation and developed transverse drainage pattern in the alternating parallel ridges of dyke. Linear ridges of dykes have modified main dendritic drainage pattern. The results of the present study revealed that dykes guided the flow of streams with low stream power. This was observed mainly for the streams of the lower order, including the streams of the first and second order, which together accounted for approximately 83% of the total length of the whole drainage network in the study area. The streams of the middle and higher orders were relatively less influenced by dykes. The change in the course of higher-order streams is mainly attributed to the control caused by the dykes and the subsurface lithology. In the present study, the influence of dykes on lower-order streams was observed to have manifested mainly in the form of stream routing or alignment according to the orientation of the dykes. The findings of the present study are important as they revealed the geological setting and its structural deformation caused by dykes, which would, in turn, assist in further exploration of the drainage network and also in water resource management.