Liberty County gets detailed update on multi‑year master drainage plan; LIDAR, monuments and models to guide projects

William Conlon, senior project manager at LJ Engineering, told the Liberty County Commissioners Court on Oct. 14 that a multi‑year master drainage plan is under way that relies on new 2024 LIDAR, extensive field survey work and multiple hydraulic modelling approaches.

Conlon said most of the past nine to 10 months were spent on data collection and verification, and that the team has consolidated a countywide dataset that includes about 1,300 square miles of delineated drainage areas, roughly 800 subbasins and about 1,700 miles of channel. "We've now constructed about 280 monuments," Conlon said, describing survey rods installed at roughly one‑mile spacing across the county and a web portal that documents each monument's coordinates and elevations.

Why it matters: the combined dataset will feed two model types used by flood practitioners — what Conlon called the applied‑hydrology approach (river‑centric, FEMA‑style mapping) and a higher‑resolution "rain‑on‑mesh" surface approach that simulates runoff across terrain before it reaches channels. That detail is intended to reveal localized urban flood risks, show how culverts and road crossings affect flow, and help the county prioritize repairs and projects eligible for state or federal funding.

Key findings and work completed - LIDAR and terrain: LJ Engineering has incorporated draft 2024 LIDAR from the Harris‑Galveston Area Council and performed peer review to fill gaps in coverage beyond the county line. - Channels and basins: the consultant team mapped about 1,700 miles of channel across some 800 subbasins and redelineated 8–10 primary watersheds affecting Liberty County. - Crossings: the study identified roughly 6,000 road crossings (bridges, culverts). Conlon said about 384 were flagged for full, detailed survey ("category A"), about 1,200 for intermediate field attributes, and roughly 4,500 were located and assigned attributes using aerial and GIS review to be included in the model. - Bathymetry: teams have collected below‑water surveys on many channels and noted about 30% of the planned bathymetric work still remains. - Monuments and portal: about 280 hardened survey monuments were installed countywide; each monument will have a public webpage with coordinate and elevation metadata once the team finalizes data sharing with the Texas General Land Office (GLO) and the USGS.

Modeling approach and schedule Conlon said the team has completed an HMS (HEC‑HMS) flow model that provides peak flows for each subbasin and that they are preparing both the point‑application (FEMA/HEC‑RAS) approach and the rain‑on‑mesh terrain model. He gave an overall schedule: the grant currently runs through March 2026 and the team has asked for two permitted one‑year extensions; Conlon said an "existing condition" working model could be ready for internal review by February 2026, with a more formal existing‑conditions completion by July 2026 and alternative analysis and prioritization by July 2027.

Coordination and next steps Conlon described ongoing coordination with the Texas General Land Office (GLO) — the project is GLO grant funded — and with regional and federal partners for off‑site inflow hydrographs (how flows enter the county from upstream jurisdictions). He said the project team can conduct a pilot deep dive into a single watershed or a specific road/bridge question if the court wants targeted, implementable recommendations sooner. Conlon also said the team will document problem identification and high‑level alternatives so project sponsors can pursue state flood plan project entries and later grant funding.

Questions and public input A participant identified in the transcript as Jim Schneider asked how the work would affect engineers' field work; Conlon described how the models can be used to test alternatives such as adding culvert barrels and to examine upstream/downstream impacts. County leaders asked about timing for "dumbed down" deliverables for public works (timelines cited above) and about coordination for grant writing and project implementation.

What happens next: LJ Engineering will continue data collection, finish remaining bathymetry, reconcile off‑site boundary conditions with GLO/regional partners and deliver interim models for county review. County staff and commissioners discussed using the model output to prioritize state flood‑plan entries and to support grant applications for design and construction work.