Water Resources Engineering

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.
Figure 1. Hydrologic cycle
Hydrologic Cycle would perhaps be interesting to note that the knowledge of
the hydrologic cycle was known at least by about 1000 BC. The earth’s total
water content in the hydrologic cycle is not equally distributed (Figure 2).
Figure 2. Total global water content
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
1. Precipitation
2. Runoff
3. Storage