Page 190 - Biosystems Engineering

CHAPTER 5

Geographic

Information System-

Based Watershed

Modeling Systems

Puneet Srivastava
Biosystems Engineering
Auburn University, Auburn, Alabama

Latif Kalin
School of Forestry and Wildlife Science
Auburn University, Auburn, Alabama

5.1 Introduction
Agricultural, urban, forest, and mining nonpoint source (NPS) pol-
lutants continues to impact and degrade surface and groundwater
quality. Among the laws that brought NPS pollution to international
attention was the U.S. Clean Water Act (CWA) of 1972 and its amend-
ments of 1987. More specifically, Section 319 of the 1987 CWA amend-
ments authorized planning and limited implementation funds to U.S.
states for the assessment of NPS problems and development and
implementation of programs for their control (Logan 1990). Further-
more, the U.S. Environmental Protection Agency (USEPA), the fed-
eral agency that administers the CWA, required states to develop a
list of high-priority or critical bodies of water [called the 303(d) list]
on a watershed-by-watershed basis to the maximum practicable
extent and to develop total maximum daily loads (TMDLs) for pollut-
ants in these waters. A TMDL is defined as the maximum amount of
pollutant that a body of water can receive and still meet the water

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