The $165 Million Waller Creek tunnel is the City of Austin’s largest flood control project to date. Located in Downtown Austin, the mile-long, concrete lined 26.5’ (average diameter), 70-foot deep inverted siphon began accepting flood waters in May 2015. The tunnel as designed and built diverts almost all (~90%) of the upland flows in to the tunnel. A new creek bypass that can convey smaller storm intensity flows around the existing dam being built as part of Waterloo Park improvements will be presented. The bypass will route flows from low intensity storm events that currently account for about 50 % of the flow volume that enters the tunnel in a given year away from the tunnel and to the creek, thereby creating a much-needed sediment transport system and flow diversity to the lower reaches of Waller Creek. In addition to significant improvement to the safety of OM personnel performing subsurface confined space work, added benefits include improved ecological function and reduced long term sediment removal costs. Key components of the project include an ecological weir structure with natural stream riffle beds and an intentionally placed aquatic organism habitat.