Friendswood consultants outline master drainage plan, prioritize 15 projects to reduce flood risk

Consultants from HAP Associates presented the draft Comprehensive Master Drainage Plan to the Friendswood City Council during a work session, walking through the metrics and alternatives the firm used to prioritize roughly 15 projects across the city.

"There were 3 metrics that we looked at as part of this project. They are flooded structure counts, inundated roadway miles, and inundated area," said Jason Becker, the project manager and water-resources team leader for HAP Associates (speaker 15), as he summarized the quantitative framework the team used to compare alternatives.

Becker and his colleague Kyle Alton (speaker 2) said the analysis used local storm-sewer inventories, lidar-derived terrain and existing detention-basin plans to build a new baseline model of Friendswood's drainage system. The team emphasized a design focus at the five-year level of service while showing impacts for 10-year and 100-year storms as bookends for comparison.

"We also developed cost estimates," Becker said, noting the team used recent TxDOT and Harris County bid tabs as a basis and explicitly included right-of-way acquisition, mitigation, 15% engineering cost and a 30% contingency in the order-of-magnitude estimates. In one area the consultants identified a pond that could provide roughly 300 acre-feet of mitigation; initial excavation-cost estimates for similarly sized detention projects were given in the $15 million to $20 million range.

Council members probed technical assumptions: how "inundated roadway" is defined (the consultants said the screening threshold is roughly 3 inches of ponding), how mitigation would be secured to avoid moving flood risk downstream, and how phasing might make large projects feasible. Staff and consultants emphasized that in alternatives where a proposed improvement increases inundation elsewhere, the added impacts would have to be mitigated before the city moved forward.

The presentation mapped targeted, neighborhood-level pipe-upsizing and surface-detention options in areas such as Upper Clear Creek, Dunbar Estates and Chigger Creek, and it also included larger channel-improvement concepts for Coward and Chigger creeks that would require multi-agency coordination and likely federal involvement.

Next steps: the consultants said they will finalize benefit-cost ratios, prepare one-page project summaries for each recommended project and complete an implementation plan that describes funding pathways and phasing. Becker told council the team anticipates delivering the draft report and supporting materials in the next one to two months.

Council members said they welcomed the detailed modeling and asked staff to prioritize needs for any near-term funding decisions. The work session concluded with staff committing to include asset-management and storm-sewer maintenance recommendations in the final MDP report.

The consultants presented key slides and maps to support the analysis; council members asked for additional data (e.g., starting/ending inundated-acre totals) that the final report will include.