Downstream economic benefits of conservation development

This paper evaluates the downstream hydrologic and economic impacts of development strategies that promote greater on-site storage of storm water. This paper applies a methodology to a specific case study that emphasizes flood risk reduction and drainage infrastructure. The estimates are at a first level of approximation. We use widely accepted simulation models and available data to compare alternative development scenarios for the 0.01 annual probability storm event. For a watershed in a rapidly developing area near Chicago, Ill., reduced downstream flooding with the employment of conservation design practices generates from $0 to 19,400/ha ($0-7,800/acre) in downstream property value benefits over all affected areas. For comparison purposes, flood-damage estimation methods generate an average of $16,800-$24,200/ha ($6,700-$9,700/acres present value reduction in damages for the 0.01 probability flood event alone. The two methods yield conservative, but mutually reinforcing estimates. For infrastructure benefits, considering only downstream road culverts, the use of conservation design techniques upstream avoids $3.3 million in costs of culvert replacement or upgrades. The sum of the downstream flood mitigation and infrastructure benefits amounts to $920-1,440/developed hectares ($380-590/developed acres) following conservation design practices.