ESTIMATES OF FUTURE IMPACTS OF DEGRADING STREAMS IN THE DEEP LOESS SOIL REGION OF WESTERN IOWA ON PRIVATE AND PUBLIC INFRASTRUCTURE COSTS

In the beginning of the 20th century, many streams in western Iowa wer e channelized to reduce flooding and to open swamp land to cultivation . Channel straightening accomplished its goal. However, it resulted in greater streamflow velocities, causing stream channels to degrade. Th is degradation has resulted in significant loss of land and damage to transportation and communications infrastructure in western Iowa and i n several states in the United States. Baumel et al. (1994; Impact of Degrading Western Iowa Streams on Private and Public Infrastructure Co sts. Final Report Iowa DOT HR-352, Stream Stabilization in Western Iow a) estimated the historical cost of this degradation on land loss and damage to transportation and communications infrastructure in western Iowa. The purpose of this paper is to extend the Baumel et al. analysi s to estimate future degradation costs on 141 streams in western Iowa. It also presents two types of degradation cost estimates. One is a ti me neutral cost that does not consider the dates on which the degradat ion costs are incurred. The second is a time value cost which consider s the dates on which the costs are incurred and then discounts these c osts back to 1992 dollars. The time value costs are the more accurate estimates of the cost of future degradation in 1992 dollars and should be used to evaluate stream stabilization project proposals.