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City staff recommends option to keep Old Alliance Road from overtopping in large storms
Summary
Public Works presented five design options — including ponds, culverts and roadway-raising — for drainage and widening of Old Alliance Road. Staff recommended Option 4, which raises the roadway and adds box culverts; the cost estimate is roughly $9.7 million and fits within identified funding of $9.8 million.
Public Works staff presented five design options to the Bryan City Council at a workshop for drainage and widening work on Old Alliance Road and recommended Option 4 — raising the roadway and installing box culverts — as the preferred plan because it prevents the road from overtopping during large storm events while minimizing downstream impacts.
Public Works Director Jason Barfner said the project would extend Old Alliance Road from just east of Austin's Colony Parkway to the city limits and address a recurring problem where the road overtops during major rain events. Barfner summarized five alternatives the city studied: regional ponds (with and without detention for future development), a wet-bottom pond, raising the roadway with culverts and a design that includes a 30-foot bridge span.
Staff provided cost estimates and modeled flood impacts for each option. Option 1 (regional pond without detention for future development) carried a total project cost estimate of about $12.4 million and left the roadway overtopped by about 1 inch in a 100‑year event. Option 2 (regional pond with detention for future development) was estimated at about $11.8 million and showed roughly 10 inches of overtopping in a 100‑year event with larger downstream impacts. Option 3 (wet-bottom pond) was estimated at about $12.4 million and produced about 5 inches of overtopping with no downstream impacts. Option 4, the staff recommendation, would raise the roadway roughly 3 feet, include multiple 12-by-6 box culverts and — in staff modeling — prevented overtopping in a 100‑year event; total project cost was estimated at about $9.7 million. Option 5, a 30-foot span bridge plus partial culverts, had a cost near $9.9 million but allowed about 2 inches of overtopping and increased downstream impacts.
Barfner said the city's identified funding for the project consists of $5.5 million from bond funds and $4.3 million in congressional appropriations, for a total of $9.8 million. He told council, "Our recommendation is to proceed with option 4," citing that option's lower modeled downstream impacts and its ability to meet the project's objective of providing a safe route that does not overtop during large rain events.
Councilmembers asked technical follow-ups about developable acreage and tributary studies for the nearby Harrison Tract. Barfner said about 8 acres in the southeast corner of the tract currently lie outside the mapped floodplain; a small unstudied tributary cutting that corner will need further study and could reduce the developable acreage. Councilmember King and others asked whether the county would participate; staff said the project lies inside the city limits and the improvements extend to the city limit line where county work begins further out.
There was no formal vote at the workshop; councilmembers expressed general support for staff's recommendation and asked staff to proceed with final design and further study of the unstudied tributary and downstream impacts where noted.
