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County engineering firm presents near-complete countywide drainage study, urges adoption of maps for permitting and grant applications
Summary
LJ Engineering told commissioners it has completed existing-condition drainage models at about 90% and proposed publishing interactive 10- and 100-year maps to support permitting, grant applications and a consistent watershed naming scheme; consultants recommended calibration with May 2024 high-water marks and a public web portal within months.
William Conland of LJ Engineering told the Liberty County Commissioners Court the firm has completed its existing-condition drainage modeling for the county and estimated the dataset is about "90% perfect." The presentation described two complementary approaches: a rain-on-mesh model for urban sheet-flow and nuisance flooding, and applied hydrology models for riverine channel behavior and FEMA-style mapping.
"We've completed the modeling of existing condition and I'm going to declare it about 90% perfect," Conland said, noting the team supplemented the latest H-GAC lidar with drone surveys to capture recent channel meanders. Senior modeler Luke Villoeva showed zoomed-in examples of modeled extents, velocities and flow paths and highlighted differences between the rain-on-mesh results (which reveal additional nuisance inundation) and the riverine results intended for formal flood mapping.
Consultants said the next steps are calibration against high-water marks from the May 2024 storm and additional model tuning of surface roughness and soil-infiltration parameters. "We have high water marks from the May of '24 storm," Villoeva said, and added the team will run that event through the models to check whether simulated water-surface elevations match field measurements.
Conland recommended the county adopt the models as "best available data" for permitting and impact analysis once calibration is complete, build a consistent watershed naming convention for GIS, and deploy a public-facing web portal with time-slider visualization so non-engineers can view inundation timing and engineers can access flow outputs. He estimated a public, usable dataset in a few months and a multi-year horizon for full program use, including grant-ready project identification.
Melinda (county grants/permits staff) and other commissioners asked about how the models would be used in plan review. Conland said engineers would still need to run pre/post development scenarios for specific projects, but the county model would provide a common foundation and reduce the need to recreate expensive baseline models for each submittal.
The commissioners accepted the report and directed staff to make the modeling files and maps available for review and to coordinate next steps for calibration and broader distribution.
The consultant presentation began in SEG 0636; the court accepted the report later in the meeting.
Next steps: calibration with May 2024 high-water marks, development of a watershed naming standard, web-hosting draft maps for public review, and use of the dataset in grant and permit reviews.
