Object-GAWSER
Object-Oriented Guelph All-Weather Storm-Event Runoff Model
Phase I: Training Manual
Application of Object-Oriented Simulation to Hydrologic Modeling
JOHN A. HINCKLEY, JR.
INTRODUCTION
Object-GAWSER is a temperature index snowmelt model that can be used to demonstrate water-
shed hydrology. Object-GAWSER is best suited for agricultural or forested watersheds, but can be
used to demonstrate the hydrology of other types of watersheds, such as urban or suburban water-
sheds. Because Object-GAWSER is applicable to watersheds with different levels of development, it
can be used to show the effect of development on the hydrology of watersheds. For example, to
observe the hydrologic impact of forest clearing for agriculture, Object-GAWSER can be pro-
grammed to simulate the hydrology of a forested watershed and then reprogrammed to simulate the
hydrology of an agricultural watershed. One can examine the behavior of various hydrologic pro-
cesses such as runoff, infiltration, baseflow, etc., for each watershed. Object-GAWSER was created
using STELLA II, an object-oriented programming language, which allows users to observe the flow
of water on the computer screen via animated objects, graphs, and tables (Richmond and Peterson
1994).
History of Object-GAWSER
In 1977, Hugh Whiteley and S.R. Ghate of the University of Guelph in Ontario, Canada, created
the first version of GAWSER (1.0) for the PLUARG (Pollution and Land Use Activities Reference
Group) Study. Version 1.0 of GAWSER evolved from the HYMO program made by the U.S. Depart-
ment of Agriculture and was created using Fortran IV. GAWSER was revised and updated 15 times
from 1977 to 1989 by several different authors. By 1989, Harold Schroeter developed version 5.4 of
GAWSER and the GAWSER Training Guide and Reference Manual. GAWSER (5.4) was calibrated
for use in southwestern Ontario, Canada (Schroeter 1989).
By 1995, GAWSER (5.4) was recreated in object-oriented format using STELLA II (Richmond
and Peterson 1994). To date, the sections entitled "Snow melt sub-model," "Generation of Runoff,"
"Overland Runoff Routing," "Subsurface and Baseflow Routing," and "Channel Routing" from the
GAWSER Training Guide and Reference Manual have been created in object-oriented format.
Object-GAWSER was developed from the equations and descriptions in the GAWSER Training
Guide and Reference Manual and calibrated to GAWSER (5.4) in three steps. First, Object-
GAWSER was programmed with the same historic data used to calibrate GAWSER (5.4). Second,
numeric outputs from GAWSER (5.4) were compared with the corresponding numeric outputs from
Object-GAWSER. Third, the input parameters of Object-GAWSER were adjusted to correct the
differences between its outputs and those of GAWSER (5.4).
Characterization of the watershed
Object-GAWSER characterizes the watershed as three zones (one impervious zone and two per-
vious zones). The impervious zone (zone 1) is considered to be the area of the watershed that is
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