final project boise valley land use analysis 1939 to 2000 ... use analysis.pdffinal project boise...
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Final Project
Boise Valley Land Use Analysis
1939 to 2000
NR402 – GIS Applications in Natural Resources
November 11, 2007
Table of Contents BACKGROUND AND OBJECTIVES ........................................................................................................ 1 DESCRIPTION OF DATA LAYERS (SOURCE, SCALE, AND ACCURACY) ...................................................... 1 GIS ANALYSIS METHODS (DETAILED) ................................................................................................. 1 RESULTS AND DISCUSSION ................................................................................................................. 3 ACCURACY AND LIMITATIONS OF ANALYSIS ........................................................................................ 3 CONCLUSION .................................................................................................................................... 4 REFERENCES (LITERATURE REFERENCES AND GIS DATA LAYERS USED) ............................................... 5 Table 1: Reclassification of 2000 Land Use Data (IDWR). ........................................................... 2 Table 2: Results of Land Use Analysis in Boise Valley. ................................................................ 3 APPENDIX A – MAPS ......................................................................................................................... 6 Figure 1: Extent of Land Use Analysis. .......................................................................................... 1 Figure 2: 1939 Land Use in the Boise Area. ................................................................................... 2 Figure 3: 2000 Land Use in the Boise Area. ................................................................................... 3 Figure 4: Comparison of 1939 and 2000 Land within 1000 Meters of the Boise River. ................ 4
BACKGROUND AND OBJECTIVES The Boise area has experienced unprecedented growth in the recent past. Since the early
1940s, population in the Boise area has grown from an estimated 26,130 to almost 185,800
residents (http://www.boisechamber.org/area_demo/growth.htm). Historically, farming was the
primary use of land, but as population increased, more farms that were used for agriculture have
been converted to residential and other uses.
This purpose of this analysis is to identify the area of irrigated crop land (ICL) that has
been converted to other uses in the Boise area. In addition, an analysis of ICL adjacent to the
Boise River converted to other uses was performed. The extent of the analysis included most of
the Boise City area west to Middleton, Idaho as shown in Figure 1 in Appendix A.
DESCRIPTION OF DATA LAYERS (SOURCE, SCALE, AND ACCURACY) Information for use in this analysis was downloaded from several internet sites; the Idaho
Department of Natural Resources, Inside Idaho, and the United States Geologic Survey. Most
map scales were at 1:24,000 with the exception of the hydrography layers (i.e., major rivers and
lakes), which were at 1:100,000. This broad scale data was easily accessible on line and while a
finer resolution would have aided in the analysis, the available data provided sufficient detail to
indicate trends in the Boise Valley. Additional details about the information source, scale, and
coordinate system are provided in the References section.
GIS ANALYSIS METHODS (DETAILED) Land use data from the 2000 dataset were provided by both Land Use Code and
Description. The dataset from the 1939 was only numerically classified so a “Use” description
field was added and classified by the descriptions found in the metadata. The 1939 data was
either classified as “Irrigated pasture and cropland” or “Other” (opened Editor, used Xtools,
Land Use Analysis Page 2 Select by Attributes for the Land Use Code, and replaced blank fields with land use code
description).
For additional analysis, the two datasets were converted from feature to raster sets with a
cell size of 30. Because the 1939 dataset contained only “other” and “Irrigated Cropland and
Pasture” the 2000 dataset was reclassified using “Irrigated Cropland and Pasture” and “Other
Agriculture” among others so that more accurate comparisons could be made of agricultural land
that had been converted to residential. Data from 2000 were reclassified according to the
following breaks:
Table 1: Reclassification of 2000 Land Use Data (IDWR). Reclassified Numbering
Dataset Title Uses included in that reclassification
0 Irrigated Cropland and pasture
Irrigated Cropland and Pasture
1 Other Agriculture Agriculture, feedlot/stockyard, other ag land, rangeland, barren land, residential farmsted, abandoned ag, and
dairy 2 Residential Residential, new subdivision, old urban/high density
Land in transition farmland to urban 3 Idle land Idle land and unclassified data 4 Commercial Commercial/Industrial, Public, sewage treatment,
petroleum tanks, junkyard 5 Riparian Riparian, perennial, water, canal, recreation
The spatial analyst extension was used for the balance of the analysis. To confine the
analysis, a polygon shapefile was created in ArcCatalog that extended from the east end of Boise
westward to Middleton. An analysis mask was then generated using the polygon as the extent
(options tool under spatial analyst) and is provided on each figure in Appendix A for reference.
The raster calculator was used to perform all of the calculations to determine various
changes of ICL in the 1939 and the 2000 layers. To evaluate the potential impact of increased
flows in the Boise River, a distance of 1000 meters was measured from the Boise River feature
Land Use Analysis Page 3 line and an analysis of land converted to any other uses other than ICL was performed (spatial
analyst, distance, straight line).
RESULTS AND DISCUSSION This analysis shows that between 1939 and 2000, the Boise Valley area experienced a
92% decline in ICL in the analysis area. Of the nearly 468,002 hectares present in 1939 (Figure
2), less than 40,000 hectares were present 60 years later (Figure 3). Of the ICP in 1939 that was
converted to other uses, almost 90% was converted to residential use (Table 2).
This conversion of land use from agriculture to other uses such as residential decreases
permeability of the soils and in turn, increases the flow in neighboring rivers. In 1939, almost
56,200 hectares of ICL could be found within 1000 meters of the Boise River in the analysis
area. In 2000, only less than 38,500 hectares remained, which is a decline of 32%. The most
significant reductions were observed in the Boise vicinity (Figure 4).
Table 2: Results of Land Use Analysis in Boise Valley. 1939 2000 Hectares Acres Hectares Acres Delta
Irrigated Cropland (ICP) 468002 1155964 36941 91244 92%
Land in 2000 that was ICP in 1939 and is now zoned
Residential 308367 761666 90%
Irrigated Cropland 1000 meters from Boise River 56174 138751 38448 94967 32%
ACCURACY AND LIMITATIONS OF ANALYSIS The dataset from 1939 was delineated by only two descriptions whereas land use codes
present in 2000 consisted of over 20 descriptions. It’s unclear if the definition for ICL for the
1939 data was the same as that in 2000. The metadata was not specific about the 1939
description as it was in 2000. This may have resulted in minor differences in the information
Land Use Analysis Page 4 extracted between the two datasets, but the results still indicate the expected decrease of the ICP
land use throughout the analysis extent in close proximity to the Boise River. Some of these
lands may have been zoned as an area under the “Other Agriculture” description in Table 1. The
inability to capture these land use area changes because of the absence of that descriptor in the
1939 dataset may have altered the results.
Another source of error is the use of the pixel cell size of 30 meters. For the larger extent
analysis (ICP converted to residential), the error may not have been as significant. However, for
the proximity of residential land use within 300 meters of the river, some errors are likely.
CONCLUSION The results indicate that land use in the Boise vicinity has changed significantly from
cropland to other uses. Those changes are amplified within 1000 meters of the Boise River,
which is within the floodplain of that river system. Flooding in the Boise Valley has occurred
throughout its history (Stacey 1992) and will continue even though the river is now regulated. In
2006, flooding caused significant damages around the Eagle area because of the residential
development that has been allowed to take place. Because changes in land use within the Boise
River floodplain is not expected to change in the near future, flood damages can only be
expected to increase over the coming years. Because continued growth and conversion of land
from agriculture to residential is expected, increases in the results shown in this document will
also be expected.
Land Use Analysis Page 5
REFERENCES (LITERATURE REFERENCES AND GIS DATA LAYERS USED) Stacy, Susan M. 1993. When the River Rises. Flood Control on the Boise River 1943-1985. Program on Environment and Behavior Special Publication No. 27. Institute of Behavioral Science, Natural Hazards Research and Applications Information Center, University of Colorado. Websites (all data obtained in October/November 2007 by T. Turner): Idaho Department of Labor; http://www.boisechamber.org/area_demo/growth.htm Idaho Department of Water Resources; http://www.idwr.state.id.us/gisdata/default.htm Inside Idaho; http://inside.uidaho.edu/geodata/other.htm USGS; http://www.usgs.gov/pubprod/ GIS Data Layers Used (and additional details)
Major Rivers o Source: Idaho Department of Water Resources o Scale: 1:100,000 o Projected coordinate system: IDTM83 o Geographic Coordinate System: GCS_North_American_1983
Major Lakes o Source: Idaho Department of Water Resources o Scale: 1:100,000 o Projected coordinate system: IDTM83 o Geographic Coordinate System: GCS_North_American_1983
Boise Valley 1939 Land Cover o Source: Idaho Department of Water Resources o Scale: 1:24,000 o Projected coordinate system: Custom – IDTM83 o Geographic Coordinate System: GCS_North_American_1983
Boise Valley 2000 Land Cover o Source: Idaho Department of Water Resources o Scale: 1:24,000 o Projected coordinate system: Custom – IDTM83 o Geographic Coordinate System: GCS_North_American_1983
Digital Raster 24,000K sid o Source: USGS o Scale: 1:24,000 o Projected coordinate system: Transverse Mercator o Geographic Coordinate System: GCS_North_American_1983
APPENDIX A – MAPS
Appendix A – Maps Page 1
Figure 1: Extent of Land Use Analysis.
Appendix A – Maps Page 2
Figure 2: 1939 Land Use in the Boise Area.
Appendix A – Maps Page 3
Figure 3: 2000 Land Use in the Boise Area.
Appendix A – Maps Page 4
Figure 4: Comparison of 1939 and 2000 Land within 1000 Meters of the Boise River.