Applying the Analytical Hierarchy Process to Small Dam Management: A Case Study of the Ames Mill Dam, Northfield,MN

Abstract

As hundreds of small dams across the United States exceed their functional life spans, decision-makers must confront the question of how to manage them. However, due to the multitude of stakeholders and the uncertainty of outcomes, decisions about managing these aging dams are highly complex. For decades, these dams have transformed their surrounding communities and ecosystems. In order to manage aging dams, it is necessary to recognize and predict the social and biophysical impacts of decisions. The Analytical Hierarchy Process (AHP) provides a framework for dividing the impacts and criteria of a complex decision into categories and weighing them against each other relative to an overall goal. We applied the AHP to the a case study of how to best manage the Ames Mill Dam, a small relic mill dam located on the Cannon River in Northfield, Minnesota. To implement the AHP, we determined the potential economic, social, hydrological, and ecological effects of two dam management options, dam retention and dam removal, by distributing surveys to Northfield businesses, conducting community focus groups, and running a hydraulic sediment transport model. We found that removing the dam would provide opportunities for economic growth and that local residents would support restoring the river to a more natural state. Based on model results, we predicted that increased downstream sediment deposition caused by removing the dam could have negative short-term effects on freshwater mussel communities, but would likely increase connectivity between fish populations in the Cannon River. We concluded that although the AHP is better suited for a publically owned dam rather than a privately owned structure, the comprehensive evaluation of decision criteria of the AHP provides decision-makers with the information necessary to select a dam management option that will have an overall positive impact on stakeholders and the watershed ecosystem