Ex post evaluation of flood control investments: A case study in North Dakota

Ex post estimates of a flood control project in North Dakota are compared with the U.S. Army Corps of Engineers ex ante estimates. Ninety‐two percent of the ex ante benefits were suppose to come from water supply and 8% from flood control. Ex post estimates found zero water supply benefits and flood control 37 times higher than ex ante estimates. These added flood control benefits were enough to make up for all the lost water supply benefits. Still the ex post analysis shows that the ex ante estimates were based on inadequate information and did not include commerical fishing and recreation benefits which accounted for 28% of the ex post benefits.