Hydraulic Culvert Design
Hydraulic analysis and capacity calculations for a county drainage system serving a small watershed. The existing culvert was undersized and showed signs of headwater overtopping during 25-year events.
Rural infrastructure quietly carries a lot of weight, and this culvert had been failing for years before anyone noticed. I took it on because I wanted to learn what a real watershed analysis felt like outside of class — and because somebody's road keeps washing out every spring.
Flow modeling, headwater depth analysis, and retrofit recommendations for aging infrastructure on a rural county road.
Lead analyst — hydraulic calculations, drawings, and the recommendations memo.
- 01Quantify capacity of the existing 36" CMP culvert under 10/25/100-year storms.
- 02Recommend a retrofit that fits the existing footprint and budget.
- 03Produce a clean memo a non-engineer county supervisor could read.
Process & progress
- Phase 01· Mar 2024Site walk
Walked the inlet/outlet, photographed scour, measured the channel cross-section by hand.
Milestone — Site walk + survey
- Phase 02· Apr 2024Hydrology
Pulled NOAA precipitation data, ran TR-55 for the contributing area.
Milestone — Hydrologic modeling complete
- Phase 03· May 2024Hydraulics
Modeled inlet/outlet control in HY-8. Cross-checked with hand calcs.
Milestone — Three retrofit options drafted
- Phase 04· Jun 2024Recommendation
Compared three retrofit options on cost, capacity, and constructability.
Milestone — Final memo delivered
Documentation
- 01Field measurements catch what GIS layers miss — the channel had migrated 4 ft since the last as-built.
- 02Hand calcs first, software second. It's the only way to know when the model is wrong.
- 03A short memo with one good figure beats a long memo with five.
County selected the box-culvert retrofit option. Design picked up by a regional firm for final stamping; construction scheduled for 2026.