Introduction - Hydro-Environmental Analysis: Freshwater Environments - page 3

This text is intended to provide an overview of the factors affecting the quantity and quality of
water (hydro), and considerations for the analysis of that quantity and quality in a variety of environ-
mental systems, including rivers, streams, lakes, and reservoirs. The material covered will include
that in engineering studies of hydrology, hydraulics, groundwater engineering, atmospheric stud-
ies and air pollution, water quality, water resource engineering, and environmental studies. These
studies are generally highly computational in nature. While the text is written from an engineering
perspective, the reader is cautioned that computational aspects will not be emphasized in this topic;
the emphasis will be on more broad and general concepts and factors that may affect the use, or
misuse, of those computations. That structure will make this topic and any courses on which it may
be based dificult for some engineers. However, equations will be sprinkled sparingly throughout
the text so that those engineers do not go into complete withdrawal.
While the topic is organized into a series of sections dealing with rivers and streams, wetlands,
and lakes and reservoirs, this separation and some of the distinctions between these waterbodies are
arbitrary and artiicial. These water systems are inseparable components of the water environment,
thus Hydro-Environmental Analysis is considered an apt title. An organizing principle for hydro-
environmental analysis is presented in Section 1.2.
The artiicial separation of these waterbodies has resulted in considerable confusion in the lit-
erature, such as just trying to deine and distinguish each type of waterbody (river, stream, lake,
reservoir, etc.). A common recurring theme of this topic will also be in pointing out that confusion
where it occurs and in providing a discussion as to how it may impact our methods for analysis and
environmental management. So, let the confusion begin!

1.2 HYDROLOGIC CYCLE
Consider that the earth's total water supply is, for all practical purposes, constant. However, if we
examine each reservoir of that water supply, we ind that it is in a continuous state of lux or motion,
such as between the oceans, atmosphere, land surfaces, and groundwaters. This cycle of water is
referred to as the hydrologic cycle and is the organizing principle upon which much of this topic is
based.
Assuming that the total quantity of water on the planet is essentially ixed, and that mass is
conserved, we should be able to essentially “bookkeep” or quantify the water transfer between
each reservoir and component of the hydrologic cycle (Figure 1.2). The components or processes
include:

• Atmospheric movement of air masses

• Precipitation

• Evaporation

• Transpiration

• Iniltration

• Percolation

• Groundwater low

• Surface runoff

• Streamlow

Figure 1.3 illustrates the relative magnitude of each of these processes in the global water bal-
ance. As would be expected, the greatest luxes are between the atmosphere and the oceans, fol-
lowed by the luxes between the land surface and the atmosphere. As discussed in the following
section, the quantity of water in motion is an extremely small fraction of the earth's water supply.
While small on a global scale, these luxes have enormous impacts on the use and availability of
the water supply.