Page 111 - Biosystems Engineering

92 Cha pte r T h ree

firsthand the effects of soil erosion. Unfortunately, not everyone was
fortunate to witness such dramatic events to recognize the need and
the significance of conservation.
The word “conservation” means preserving or protecting some-
thing from decaying, destruction, or deterioration. In this chapter we
use it under a much wider framework. In addition to its customary
meaning, we also consider mitigation and abatement as a part of con-
servation. In that sense, the word “conservation” will encompass any
efforts trying to protect soil and water resources from deteriorating
from a quality perspective, insufficiency (e.g., drought), or surplus
(e.g., flooding) from a quantity standpoint, as well as any practices in
trying to mitigate these undesirable conditions.
Conservation of water and soil could/should be carried out at two
stages. The first stage is protecting the source, which is protecting the
soil from erosion and water from being becoming polluted. In reality,
even the most virgin lands are prone to erosion and contribute to pol-
lutant loadings to some degree. Therefore, the goal for conservation
cannot be total elimination but does include reducing rates of soil ero-
sion and pollutant loadings. This will not only help alleviate the qual-
ity of downstream receiving water bodies but also preserve or even
increase soil fertility. This first stage is referred to as conservation at the
source or source scale conservation. The second stage involves various
practices or mitigation strategies to improve the water quality of the
water bodies and/or to minimize the potential adverse impacts of
alleviated water quality and quantity problems on humans and the
ecosystem. This stage is referred to as conservation at transport stage or
transport scale conservation. In upcoming sections we will be discussing
both of these stages/scales for soil and water conservation.
To develop and understand effective and efficient conservation
strategies, we must understand the governing physical processes that
take place in soil, water, and at their interfaces. Because soil and water
are in constant interaction, a proficient conservation strategy should
consider their complex interaction. In the following sections, we
describe those processes and present relevant theories and recent
advancements. We start with the hydrologic cycle. After an overall
description of the hydrologic cycle, we delve only in the components
of the hydrologic cycle that are most relevant to soil and water con-
servation. Then we talk about the physics of soil erosion and sedi-
ment transport processes. The last part of this chapter is dedicated to
various best management practices, commonly referred to as BMP,
that are useful at the source and transport scales.

3.2 Hydrological Cycle
Water on the earth and in the atmosphere is in constant movement and
changes its form and its medium. The hydrologic cycle basically describes
this circulation and could be defined as the continuous movement of