Highway Hydrology Metric Version

Hydrology is often defined as the science that deals with the physical properties, occurrence, and
movement of water in the atmosphere, on the surface of, and in the outer crust of the earth. This
is an all-inclusive and somewhat controversial definition for there are individual bodies of science
dedicated to the study of various elements contained within this definition. Meteorology,
oceanography, geohydrology, among others, are typical. For the highway designer, the primary
focus is with the water that moves on the earth's surface and in particular that part which
ultimately crosses transportation arterials, i.e., highway stream crossings. A secondary interest is
to provide interior drainage for roadways, median areas, and interchanges.
Hydrologists have been studying the flow or runoff of water over land for many decades, and
some rather sophisticated theories have been proposed to describe the process. Unfortunately,
most of these attempts have been only partially successful not only because of the complexity of
the process and the many interactive factors involved, but also because of the stochastic nature
of rainfall, snowmelt, and other sources of water. Most of the factors and parameters that
influence surface runoff have been defined, but for many, complete functional descriptions of
their individual effects exist only in empirical form. Extensive field data, empirically determined
coefficients, and sound judgment and experience are required for their quantitative analysis.
By application of the principles and methods of modern hydrology, it is possible to obtain
solutions that are functionally acceptable and form the basis for the design of highway drainage
structures. It is the purpose of this manual to present some of these principles and techniques
and to explain their uses by illustrative examples. First, however, it is desirable to discuss some
of the basic hydrologic concepts that will be utilized throughout the manual and to discuss
hydrologic analysis as it relates to the highway stream crossing problem.
Download File