Culvert Sizing for County Permit

I need an engineer to calculate the appropriate culvert size for a driveway (passing over a drainage easement) proposed for custom home based on the drainage area to satisfy a county engineer in order to be granted a county permit. County requires document that shows drainage calculations. Drainage area is expected to be less than 10 acres. Available: Site plan in CAD/dwg indicating driveway crossing location. LIDAR DEM file is available from recent USGS survey.

Requirements:
- Use provided topographic map and soil type information
- Consider peak flow rate and any other factors county engineers typically consider
- Residential land use

Ideal Skills and Experience:
- Civil engineering background; PE Texas needed
- Experience with drainage design
- Familiarity with county permitting processes