GIS
in
Local Watershed Initiatives
Background
Objective
Methods
S Data
Sources
S
Projection of Data
S
Software Environment
Analysis
Future Work
Background
Watershed management has
been actively practiced in the United States for over 100 years. Its origins stretch back to the early 1900’s
with the passage of the Reclamation Act of June 17, 1902. Included in this act was language pursuant
to consideration of basin-wide initiatives (see Appendix A). Though contemporary literature on the subject
indicates that there still exist substantial barriers to a continuous and
integrated approach to watershed management, focus on the ‘watershed as a
planning unit’ can provide the basis for a reasonable approach to dealing with
many water resource issues – erosion, water quality, instream flows and land
use management, to name a few. However,
problems arise and they are primarily due to the following six factors:
-
the scale at
which management initiatives are undertaken;
-
the approach
take towards management goals, whether a “top-down’ or a “bottom-up” process is
employed;
-
the government
agencies involved – federal, state, county, local;
-
the political
boundaries that overlay the natural boundaries of a watershed;
-
the current
social and economic factors at play within, or around, a particular watershed;
and
- the data and science
available for implementation into a project and the extent to which it is
accepted and understood.
A coherent watershed management
and planning schema, to be applied at various levels of scale and government,
may be possible with consideration the above factors. These considerations can also help to decide if indeed a
watershed approach to a given issue is appropriate.
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Objective
The
purpose of this project is to explore the current state of watershed management
initiatives in the United States through literature review and to begin
formulation of a plausible approach to local watershed management. Ideally, the
results will help to define and employ the necessary elements that may best
ensure coherency in data acquisition, data manipulation and dissemination of
results in order to achieve policy objectives.
A case study approach will be taken in order to explore this
objective. The area around El Rito, a
small town in north-central New Mexico will be inventoried and studied (see Appendix B). Appropriate data will be collected, manipulated
and subsequently analyzed with a view towards relating each of the above-stated
factors that tend to inhibit coherent watershed management and planning
initiatives.
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Methods
Data Sources – The data were taken
primarily from the Rio Arriba County Profile data disc that was compiled by the
New Mexico Resource Geographic Information Resource Program (RGIS) and issued
in September 1999. It was necessary for
me, in some instances, to acquire more recent data from the on-line RGIS data
clearinghouse as well as from other sources such as the USGS, The National
Atlas, and the EPA. The data available
from RGIS were offered in two different projections with respective coordinate
systems– State Plane and Decimal Degree.
I opted to use the Decimal Degree coordinate system and from there
re-project each coverage into the Albers Equal Area Projection.
One goal of this project was to use data that would
ultimately comprise a watershed ‘inventory.’
Originally the following data was included:
Additional
tabular was compiled in order that certain socio-economic trends and realities
could be considered and, when necessary, displayed. For a complete listing of the data coverages that were deemed
necessary for this project see the Data Dictionary in Appendix C.
Projection
of Data – All data was projected in the Albers Equal Area Projection. The Albers Equal Area projection is a
secant, conical projection that maintains accurate area measurements of a
region, especially in the central portion of the projected map. By carefully choosing the central meridian
and the two standard parallels, it is possible to attain highly accurate area
measurements. This is important when
dealing with watersheds and any hydrologic modeling that might be performed on
a specific area. It was decided that
the projection properties would be determined by considering the entire
State of New Mexico - not just the study area (see Appendix D). This was done to ensure that comparative
results from other areas of the state would be most accurate.
Software
Environment – The software used for this project was ESRI’s ArcGIS. All three components of this software suite
– ArcCatalog, ArcToolbox and ArcMap – were utilized. It was also necessary in some instances to employ the
command-line driven ArcINFO for certain tasks (for example, ArcINFO can deal
with certain raster/grid functions more efficiently and effectively than
ArcGIS). Also, ArcINFO was used
(extensively) to ‘CLIP’ the coverages used in this study so that the polygonal
area was calculated and/or maintained.
The
data consists primarily of vector-based coverages and shapefiles. Raster-based layers, in particular the DEM
and the shaded relief, were used as well.
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Analysis
The majority of
the analysis will focus on creating a complete database. By ‘complete’ it is meant that all of the
data will:
-
have the same
spatial definition and projection
-
coincide with
the study area
-
form the
foundation for analysis and the framework for a watershed-based
initiative/analysis (if, of course, appropriate to achieve a policy objective).
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Results
The overall results of this project were positive,
in that all of the chosen data was processed according to the aims of the
‘Analysis’ section of this report:
Each
of the data layers was re-projected into the Albers Equal Area projection;
-
The data were
‘clipped’ from the bounds of the Rio Arriba County data to the bounds of the
Rio Chama sub-region and, after other processing on particular data sets, the
data were again ‘clipped’ to that they coincided with the boundaries of the
study area watershed (see
Appendix E).
- Processes were performed
that resulted in data and maps that comprised the foundation of the
analysis. These were location maps,
informational maps (i.e. an elevation map, an ownership map, a soils map, an
aspect map) and, ultimately, a ‘Sensitivity Map’ based on Land Ownership,
Slope, Soils, Aspect, and buffered distance along the river corridor (see Appendix F).
The desired results will
help in determining a useful approach to myriad water resource issues. First, it will help to answer the question
of whether or not a watershed approach is appropriate for a particular
issue. For example, upstream landuses
and ownership affecting a community’s surface water supply might certainly be a
watershed issue. However, the presence
and use of grazing allotment are an issue that might be better considered at a
larger scale because 1) they are managed by federal agencies, and 2) they are
not unique to a particular small-scale watershed. If a watershed approach is appropriate then this methodology will
perhaps be able to aid decision-makers and stakeholders alike in determining
the necessary data and in how to manipulate, analyze, display, and propagate
the (new) data that has been generated.
If it is deemed that a watershed approach is not suitable (for whatever reason),
then this approach can also aid in solving other new or different policy
objectives because the data will still be available for analysis.
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Future Work
There is certainly much opportunity
for further work and analysis within the context of this project. First off, it is imperative to note that
this report was entirely based on literature review and the author’s personal
bias as to how management initiatives and objectives are formed and
pursued. Implicit in this statement is
the need for research into how watershed management is carried out ‘on the
ground,’ i.e. what currently (read: actually) takes place at the respective
levels of government, especially at the local level.
Need
for future work and development, therefore, will necessitate the following:
- Field work that will
facilitate dialogue with federal and local managers, decision-makers and other
involved stakeholders in the El Rito Creek watershed communities;
- Further analysis and
manipulation of tabular data that has been acquired so that it coherently
references and enforces the displayed (map) data. For example, creating appropriate and
accurate (i.e. useful) attribute tables for vegetation, soils, census data,
pesticide and herbicide use, well depth, and water quality and quantity;
- More inclusive and
exhaustive sensitivity analyses relating ownership, landuse, slope, aspect,
erosion and well type, depth and location and how these analyses might better
aid in the interpretation of water resource questions regarding water quality
and quantity;
- Interpreting the application
value of the data sets that have been collected as to their usefulness in this
approach to local watershed-based management initiatives and policy objectives;
- Further literature review
focusing on how local initiatives are instigated in the first place, how
science and GIS are brought into the discussion and how the local
managers, decision-makers and stakeholders react to science and GIS when it
becomes, perhaps, an integral part of the discussion.
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