This study seems to have had trouble finding any measurable economic value of levees, which is interesting.

The value of levee protection to commercial properties

Volume 119, November 2015, Pages 181–188

Levees have historically been a dominant approach to riverine flood control in the United States. Recent investigations have found many levees around the country are in substandard condition, however, and some communities are moving to upgrade and repair their levee systems. Little empirical work has examined how increasing flood protection from levees is valued. We present estimates of the capitalization of upgraded levee protection into commercial property prices in St. Louis County, Missouri. By using controls for surrounding land cover and coarsened exact matching to ensure close distribution between treatment and control on surrounding land cover, we attempt to isolate the price effect of the levee from agglomeration effects that may also be operating. We find that commercial properties protected by a 500-year levee do not have a statistically significant price discount as compared with properties not in a floodplain. We find the selling price of properties with levee protection to be higher (although also insignificant in many specifications) than those in a floodplain without levee protection.