This presentation by ACWADAM on earth sciences in watershed management shows how the occurrence of water within a watershed is governed by the rock types occurring both at the surface and within the subsurface, their sequence and their structure. The presentation deals with the basic components involved in the mapping of a watershed –

• The type of rocks (lithology), and
• The structure (whether these are folded, faulted, fractured, jointed etc.,)

This includes subsurface mapping to understand the nature of rocks and their structure beneath the land surface within the watershed. The geological mapping of watershed characteristics is undertaken for a cross section along the length of the watershed. The maps should represent field observations of changes in rock types, features like regional fractures and dykes and how these are represented in the vertical sense.

Tools like remote sensing can be used during mapping as they help identify geographic and geologic features and make mapping easier. However, groundwater cannot be directly observed on these pictures. The presentation also outlines the scale at which one needs to map, which in turn depends upon whether one needs a regional perspective, a river basin perspective or an understanding of microwatershed/village level issues. Regional information can help ‘kick-start’ the process of systematic planning of groundwater management even in emergencies.

A watershed project can include -

• Mapping and visualisation of subsurface,
• Exploration,
• Water level issues, and
• Conceptualisation of a groundwater problem.

This presentation is part of the training modules on planning, development and management of groundwater with special reference to watershed management programmes by ACWADAM. Please write to ACWADAM at acwadam@vsnl.net for sourcing these presentations.