Abstract:
ABSTRACT In recent years numerous site-specific water quality and quantity
studies have been conducted. However none of these addressed questions on the
national/regional scale concerning policy decision options for water quality
and quantity. The HUMUS (Hydrologic Unit Model for the United States) project
improves on existing technologies for making national and regional water
resource assessment
... considering both current and projected management
conditions. The major components of the HUMUS project are: 1) a basin scale
Soil and Water Assessment Tool (SWAT) to model the surface and sub-surface
water quality and quantity, 2) a Geographic Information Systems (GIS) to
collect, manage, analyze and display the spatial and temporal inputs and
outputs, and 3) relational databases needed to manage the non-spatial data and
drive the models. The HUMUS project will simulate and validate approximately
350 6-digit hydrologic unit areas that have been delineated by the USGS for the
18 major river basins in the U.S. The emphasis of this paper will be on the
formulation of the HUMUS project and a sample application to one of the 8-digit
hydrologic units located in the Texas Gulf river basin.
INTRODUCTION
Water quality and quantity are ever-increasing environmental concerns
throughout the world. Damage from soil erosion alone, which does not include
nutrient and pesticide contamination, is estimated at several tens of billion
dollars in the United States (Committee on Conservation Needs and
Opportunities, 1986). The distributed nature of spatial and temporal processes
involved often limit identification and assessment of water quality and
quantity. Once the water quality problems are identified, there are several
techniques of controlling and regulating the polluting activities. Models are
often used to evaluate the best available alternative control measures. Type,
scale, and level of application of these models depend on the kind of questions
to be answered. General rules or solutions infeasible since water quality
problems are primarily site-specific.
HUMUS SYSTEM
The Resources Conservation Act of 1977 as amended (RCA), requires the
Department of Agriculture to appraise the status, condition, and trends in the
uses and conservation of non-federal soil and water related natural resources.
The HUMUS project has been designed to provide the technical basis for
conducting the appraisal of water resources for the 1997 RCA Appraisal Report.
It is intended to provide better information than has ever been obtained before
about the uses of water on irrigated and non-irrigated agricultural lands and
of the physical and economic effects of changing agricultural practices and
cropping patterns on future water needs and supplies.
Recent advancements in computer-based natural resource simulation technologies
give opportunity to do comprehensive regional and national water resources
assessments. The integrated HUMUS system components are shown in Figure 1. The
components include: 1) Simulation Models, 2) Spatial Database System (GIS) and
3) Relational Database System. The HUMUS system is expected to be a prototype
for similar uses of the models for other national natural resources policy
development forums and for uses of the technology at the regional level by
various agencies involved in natural resources concerns. For approximately
2,150 watershed areas (the 8-digit hydrologic accounting units delineated by
the Water Resources Council in the Second National Assessment), this project
would include information about local weather, soil properties, topography,
natural vegetation, cropped areas, runoff, erosion, groundwater, irrigation,
and agricultural practices. Water flows would be routed from the 2,150
watershed areas through the 18 major river basins. The system would be
calibrated by comparing simulated water outflows with actual stream flows
derived from gaging records at the 350 (the 6-digit hydrologic unit areas)
locations. Details of the tools, model, and database involved were discussed in
detail in the following section, followed by an application of the HUMUS system
to a 8-digit watershed area located in south-central part of Texas.
Please contact Dr. Raghavan ("Srini") Srinivasan for more information 
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