TABLE OF CONTENTS 
Hydrology is the scientific study of water, especially in its natural occurrence, detailing its typical characteristics, control, distribution on land, precipitation, storage, runoff, evaporation, and ultimate return to the atmosphere and the ocean. Since a basic understanding of this science is necessary to fully grasp field hydraulics, this section will present a brief overview of hydrology and its related areas in an attempt to set the stage for this manual.
Water is the most common natural substance on this planet. It covers almost three-quarters of the earth's surface, filling the oceans, seas, lakes, rivers, creeks, streams, swamps, and much of the soil. Moisture is in the air we breathe and the clouds in the sky.
Second only to air, water is the single most essential component necessary in nature to sustain life. Without water, life as we know it could not exist. Every living thing, be it plant, animal, or human being, must have water to live. Every living thing consists mostly of water.
It has been estimated that there are about 326 million cubic miles of water on earth. The world's supply of water is dispersed as follows: 97 percent in the oceans and seas, 2 percent in polar ice caps and glaciers, 0.6 percent in groundwater, 0.3 percent in the atmosphere, and 0.1 percent in lakes, inland seas, salt lakes, rivers, streams, and wetlands. Therefore, about 3 percent of the earth's water is fresh.
Water is the only substance naturally present in three different states within...
