Project Description
I need a complete hydraulic study carried out in HEC-RAS to demonstrate that my proposed development site actually sits in Flood Zone 3a rather than 3b, as required for a UK planning submission to Surrey Heath Borough Council. Once the model verifies the 3a classification I also need you to prepare the associated NPPF Exception Test and map a safe dry-access route to public highway standard.
Here is where things stand:
• Preferred software: HEC-RAS (feel free to couple with GIS tools such as QGIS/ArcGIS if that speeds up mapping).
• Existing data: I don’t currently hold topographic, rainfall or river-flow data, so you will need to source Environment Agency datasets or advise me on any additional surveys we should commission.
• Site extent: exact boundary to be confirmed with you, but the developable envelope is small (single residential building); please allow for refining the model domain once we firm up limits.
What I expect from you
1. A well-calibrated 1D or 1D/2D HEC-RAS model with input files, boundary condition rationale and sensitivity checks.
2. Flood outlines for relevant return periods, clearly illustrating the site in Zone 3a.
3. Written Exception Test referencing Surrey Heath and NPPF guidance, showing wider sustainability benefits and manageable residual risk.
4. Plan and section drawings (GIS layout) proving a safe pedestrian evacuation route in the design + climate-change scenarios.
5. A concise but planning-ready report that explains the methodology, data sources, model build, results and conclusions, finished in Word/PDF.
Please outline the data you will access, your proposed modelling approach, and the timeframe you need once all inputs are available. I’m happy to answer follow-up questions quickly so you can get started.