The Batavia Dam is located in the town of Batavia, Illinois on the Fox River (river mile 56.26). Aging and inappropriate approach flow patterns developed by an upstream island have resulted in structural failure of the dam. The left extreme of the spillway crest has been breached, and significant flow travels overland around the right abutment and down a natural bedrock cascade. The spillway performance, especially during intense storm events, has been deteriorating. The goal of this study was to propose and test rehabilitation and/or replacement dam structures for the Batavia site.

To this end, a 1:30 physical model based on Froude similarity was constructed. The model was calibrated for the existing condition in terms of stage response and flow split characteristics around the upstream island. Detailed stage, velocity, specific discharge, and flow visualization measurements were taken for five flooding event (2, 10, 50, 10O, and 500 year flows) in order to fully characterize flow conditions. A baseline, or breach repaired structure, was tested in a similar fashion to provide a comparison benchmark.

Phase two of the research involved design and testing of three alternative dams for the Batavia site. Alternative I added a bathtub spillway to a conventional ogee spillway along the same alignment as the existing structure. Alternative II replaced the existing dam with a rock dam. The final alternative provided a modified ogee spillway with two distinct overflow structures to accommodate the flow approaching from left and right sides of the island. For each of these alternatives, stage, velocity, specific discharge, flow visualization, and general response characteristics of the structures were studied.

Alternative I was found to produce improvements in the upstream approach. Flood stage ratings were comparable to those found for the existing condition. Downstream discharge characteristics were slightly improved. Alternative II provided few hydraulic improvements on-site, and the rock dam promoted higher flood stages. Alternative III resulted in excellent approach and downstream discharge characteristics. Flood stages were reduced for all conditions tested. The potential for development of an undesirable submerged roller for Alternative III was noted.

Based on the study, Alternatives I and III are recommended for candidates as replacements for the Batavia Dam structure. Both of these alternatives produced acceptable and improved hydraulic conditions at the site. The two alternatives offered distinct and competing sets of advantages and disadvantages, and the final selection between them will depend on a weighing of economic, community, and technical priorities. Prior to implementation, continued study and optimization of the chosen alternative is strongly recommended.