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.