Historical Reconstruction of the Clear Creek Watershed

Using the Past to Plan the Future:
Landscape and Land Use Change in the Clear Creek Watershed

Principal investigators: Drew Rayburn, Lisa Schulte, and Laura Merrick, Iowa State University

Issue At Hand Significant opportunities exist to improve the overall health and functioning of agricultural landscapes. To achieve the greatest efficacy, these opportunities should be evaluated at landscape scales and be attentive to where these landscapes have been in the past, as the history of a landscape has enduring effects on its present and future condition. What We Hope to Accomplish In studying landscape history and change, we expect to: • Establish a quantitative baseline for assessing present and future landscape change, • Delineate periods of rapid change, when landscape conditions are dramatically altered, and causes of this change, and • Provide a richer story of the interactions between humans and their environment for the purposes of furthering conservation initiatives.
Study Area We are conducting this work in the Clear Creek watershed of east-central Iowa (~68,000 ac).			Above: The same location in Johnson Co. in 1937 and 2002. Significant landscape changes have taken place in Clear Creek watershed from ~1940 to 2002, illustrated here by the construction of an interstate highway system that has had concomitant effects on the landscape.
Over the past 150 years, the majority of the land within the watershed has been converted from its natural state to row-crops or pasture. The hydrology of the watershed has also been highly modified through construction of drainage systems and the widespread channelization of streams and other waterways. More recently, the area has been experiencing significant urban growth, especially near the cities of Coralville and Iowa City . These and other factors make the region ideal for a study of causes and consequences of landscape change.			What We Expect To Find Our preliminary analyses quantify important ecological and social processes occurring in the watershed, including: • A decline in the diversity of land cover types, with individual land units showing an increase in size and simplification in shape, • A decrease in stream sinuosity over time, as stream flow regimes have been altered, and • An initial decrease in housing density, coinciding with an expansion in farm size, followed by a recent increase as a result of exurban development. These results are already forming the basis for restoration planning by a watershed coalition group local to the Clear Creek watershed.
How We Go About It The primary data source for our analysis is historic aerial photography. We have scanned, georeferenced, and digitized landscape features from the aerial photos of Clear Creek watershed at four time periods (~1940, ~1960, ~1980, and 2002), with 1938 being the earliest date that aerial photos are available for the watershed.
Other sources of historic data are being incorporated to enhance the story of landscape change, including maps from historical state atlases, and vegetation data from the original public land surveys, conducted in the mid-1800s.