Mapping Housing near Yellowstone River to Protect Property and River Health

By Patty Gude, Project Manager, Headwaters Economics

The Yellowstone River stretches for more than 670 miles and is the longest free-flowing river in the lower 48 states. Originating in Yellowstone National Park, it runs through Montana, draining 70,000 square miles of land before it joins the Missouri River in North Dakota.

View from the Yellowstone River.

Record-setting snowfall across Montana in 1996 and 1997 contributed to flood conditions in many parts of the state. In those consecutive years, the Yellowstone River experienced "100-year flood events" that damaged homes, infrastructure, and other property and caused channel changes and large-scale erosion.

In response, more than 100 permit applications were subsequently filed to armor or otherwise stabilize and modify the riverbanks. Environmental groups contested some permits, and the controversy led to the authorization of a comprehensive cumulative effects study on the entire river. The federal study was led by the US Army Corps of Engineers with the Yellowstone River Conservation District Council as the local partner. The goal was to acquire a working knowledge of the dynamics of the Yellowstone River and its associated riparian area to predict effects from natural processes and humans and develop best management practices.

Trends in Home Construction

Documenting trends in home construction along the Yellowstone River was an important part of the cumulative effects study. The lack of information on existing housing patterns and potential for future growth made it more difficult to manage the river to balance human uses with objectives for fish and wildlife. Therefore, as part of the cumulative effects study, Headwaters Economics, an independent, nonprofit research group, used ArcGIS for Desktop to produce an online resource called the Yellowstone River Atlas. The staff at Headwaters Economics, Bozeman, Montana, had long been familiar with ArcGIS and used it to document the economic and demographic conditions of counties bordering the Yellowstone River and display maps showing past, current, and forecast residential development along the river.

Maps of the recent distribution of housing show that growth has occurred along much of the length of the Yellowstone River.

To map trends in housing along the Yellowstone River, Headwaters Economics used the GIS to join tabular data published by the Montana Department of Revenue with a Public Land Survey System (PLSS) shapefile published by the US Bureau of Land Management (BLM). The dataset, maintained and made available to the public by the Montana Department of Revenue, describes many characteristics of taxable properties, including the locations of homes in PLSS units (township, range, section, and quarter section) and the year of construction. Once this data was joined to the BLM shapefile, the resultant GIS layer described both the location and year of construction for all homes in 18 counties of southwest Montana through which the Yellowstone River runs. Headwaters Economics used ArcGIS software's Select By Location tools to identify those quarter sections (roughly 160-acre tracts of land) that intersected the Yellowstone River's 100-year floodplain and summarized several spatial and historical trends in housing within the floodplain, including existing numbers of homes, average lot sizes, and the area of land developed for housing over time.

The GIS layer was also used to produce a series of maps showing growth in housing over time. Since the counts of homes per quarter section were stored in a polygon shapefile, the software's dot density symbology was used to display one point per home, randomly placed within the quarter section. When viewed at the scale of southwest Montana, this representation worked extremely well to show the cumulative growth in housing per decade. The series of 12 maps, showing the locations of homes by decade from 1900 to 2000, along with 2008, were made available via an online slide show at headwaterseconomics.org/Yellowstone-River-Slideshow.

Next, Headwaters Economics and Western EcoSystems Technology, Inc., Cheyenne, Wyoming, teamed up to produce a model that identified landscape characteristics correlated with new home construction and estimated the location and amount of future housing. The majority of variables used to develop the forecasting model were generated using the ArcGIS Spatial Analyst extension and included such factors as (1) the mean Euclidean distance per quarter section to the nearest major water body, (2) the mean road density within 1 mile of each quarter section, (3) the mean number of mountain peaks per square mile within 10 miles of each quarter section, and (4) the mean travel time in minutes to the nearest town from each quarter section. Details describing the statistical methods are at headwaterseconomics.org/Yellowstone-River-Methods.

Maps of the recent distribution of housing show that growth has occurred along much of the length of the Yellowstone River.

The online atlas featuring maps of past and future housing along the Yellowstone River continues to be used as a resource by the public and scientists studying plant and animal communities and water quality issues along the length of the river.

The website also received some unexpected attention during the July 2011 oil spill into the Yellowstone River. In the days following the 42,000-gallon spill of crude oil from a ruptured Exxon Mobil pipeline into the river, many local residents and cleanup workers utilized the maps to assess the impact of the spill to property along the Yellowstone.

About the Author

Patty Gude specializes in research on land use, land management, and ecosystems, and she is the Headwaters Economics project manager of software development for exploring socioeconomic and geographic relationships.

For more information, contact Patty Gude, project manager, Headwaters Economics (e-mail: patty@headwaterseconomics.org).

The Yellowstone River Atlas is located at headwaterseconomics.org/Yellowstone-River-Atlas.