Efficiency, Equity, and Drainage Design

Of the various philosophical concepts considered, those presumably acceptable to a democratic society are utilitarianism and several notions which emphasize equity. Social welfare functions, which map individual preference orderings into a social choice, are examined for certain cases where such functions can be written explicitly. Benefit/cost ratio is one form of utilitarian social welfare function. Consequences to lower owners of upstream drainage developments are investigated, using game‐theoretic techniques and a definition of social power due to Harsanyi. Mathematical analysis indicates that the return period of the design flood and a parameter dependent on land use are “policy variables” requiring determination by a political process if utilitarianism is the social policy. If majority vote is the mechanism of determining social choice, a project design would be based on median value of expected flood damage. Assessment of each acre a uniform amount seems to be justified by application of a theory of games of fair division, while an objective of “equal social power” results in a policy of storm water retention for zero increase in runoff.