In the present atlas, the drainage maps of Survey of India (SOI) on 1 : 250,000 scale have been used as base map for the delineation of basin, sub-basin and Watersheds. Administrative boundaries have been obtained from administrative maps of Survey of India / National Informatics Center (NIC), New Delhi. Major drainages and drainage names are derived from drainage map of SOI. Locations of major towns along with attributes were obtained from NIC.

STAGE OF DELINEATION AND TERMINOLOGY

A hierarchical approach is essential in delineating watersheds in a river system. An appropriate terminology to clearly indicate each sub-division is also equally important. The watershed boundaries have been demarcated based on the drainage and elevation contour maps on 1:250, 000 scale from SOI. The demarcated maps so prepared have been digitized through National Informatics Center, New Delhi. After different stages of quality checks, the attribute table has been attached to the digital map data to bring into GIS format. Further, keeping in view the utility and easy handling of the Atlas, the maps have been printed basin wise on 1:2 million scale on a convenient paper size giving sub-basin and watershed boundaries along with the watershed codes, major rivers, towns and state boundaries. Entire map data have been created in ESRI platform using Arc GIS 9.0 software. The data are available with CGWB in Geo-database format.

Stage I : Basin Delineation

The entire country have been divided into a total of 34 Basins more or less coinciding with the basins as delineated in Watershed Atlas of India, 1990 by AISLUS (1: 1 million scale) which has a total of 35 basins except Brahmputra whein left and right bank has been merged together. While delineating the river basins, the groundwater flow and its linkages / interactions with river flow system has also been considered.

Stage II: Sub-basins Delineation

The basins have been further divided into a number of sub basins. Sub basins consists of an independent tributary streams. For examples, Godavari basin has 8 sub basins. Sub basins have been delineated from down stream to upstream. Keeping in view the groundwater flow and its linkages / interactions with river flow system the concept of left bank and right bank has not been followed while delineating the sub-basins.

Stage III: Watershed Delineation

Each sub basin is divided into a number of watersheds. Watersheds are the smallest hydrological unit that can be delineated cartographically on base map of 1 : 250,000 scale. Watersheds are delineated from upstream to downstream.
The entire country has been divided into 34 basins, 94 sub-basins and 3448 watersheds. The names of the basins, sub-basins along with their ID and numbers of watersheds are given in the table.

Basinwise

Watershed

Codes