Surface and Ground Water Resources

Introduction

Water in our planet is available in the atmosphere, the oceans, on land and within the soil and fractured rock of the earth’s crust Water molecules from one location to another are driven by the solar energy. Moisture circulates from the earth into the atmosphere through evaporation and then back into the earth as precipitation. In going through this process, called the Hydrologic Cycle (Figure 1), water is conserved – that is, it is neither created nor destroyed.

It would perhaps be interesting to note that the knowledge of the hydrologic cycle was known at least by about 1000 BC by the people of the Indian Subcontinent. This is reflected by the fact that one verse of Chhandogya Upanishad (the Philosophical reflections of the Vedas) points to the following:

“The rivers… all discharge their waters into the sea. They lead from sea to sea, the clouds raise them to the sky as vapour and release them in the form of rain…”

The earth’s total water content in the hydrologic cycle is not equally distributed (Figure 2).

The oceans are the largest reservoirs of water, but since it is saline it is not readily usable for requirements of human survival. The freshwater content is just a fraction of the total water available (Figure 3).

Again, the fresh water distribution is highly uneven, with most of the water locked in frozen polar ice caps.

The hydrologic cycle consists of four key components

·         Precipitation

·         Runoff

·         Storage

·         Evapotranspiration

These are described in the next sections.