Council leans to 10-year design for Ammon Road low-water crossings; asks staff to consult landowners

City engineers and consultant STV presented a project update and three design options for two low-water crossings on Ammon Road during a workshop at the Aug. 21 Fair Oaks Ranch City Council meeting.

STV project manager Luba Esquivel and drainage lead Joseph Sosa explained the existing culverts at both crossing locations are 18-inch reinforced concrete pipes and that the current level of service is below a 2-year storm event. The consultant presented options sized to convey 5-year (about 5.5 inches in 24 hours), 10-year (about 6.86 inches in 24 hours) and 25-year (just under 9 inches in 24 hours) storms and showed associated grading, downstream erosion protection (riprap) and estimated costs.

Esquivel said the team recommended the 25-year option as the “safest and most sustainable option for the city and its residents” and said the cost differential for the crossings was “over $200,000” when comparing the options. Council members discussed cost, frequency of overtopping, impacts on neighboring parcels and coordination with the Post Oak development’s planned detention. Developer Ben Bunker (upstream of one culvert) told council the Post Oak project includes planned detention basins: “we're planning to do detention to minimize our impacts,” he said, and that the development agreement requires detention.

Several council members emphasized the trade-off is how often the road would be overtopped versus the additional construction and grading impact to adjacent properties. The engineering team said any grading beyond the existing right-of-way would require property-owner easements; staff said they will reach out one-on-one to potentially affected landowners as design progresses.

After discussion council members instructed staff and the consultant to proceed with the 10-year (option 2) design as the base recommendation to advance the design and cost estimate, with the caveat that staff will present the design to impacted landowners and return to council if significant landowner objections prompt a change to the 25-year design. A city staff member cautioned that switching from a 10-year to 25-year design late in the process likely would require a construction change order and added cost.

Why it matters: Ammon Road is a collector route in the city; selecting a level of service for low-water crossings influences construction cost, grading impact to private parcels, and how often the roadway will be overtopped during major storms. The decision also must coordinate with the Post Oak development’s drainage design and with planned roadway reconstruction paid by a recent road bond.

What’s next: staff will continue design at 30% to refine grades and culvert sizing, notify and meet with affected landowners, and return to council if landowners request the higher (25-year) option or if design refinements require council direction.