Connecting Geospatial Research and Community Safety: Assessing Culvert Capacity with GIS-Based Hydrological Modelling

Abstract. Culverts play a critical role in stormwater conveyance, roadway safety, and flood mitigation, particularly within low-lying urban communities vulnerable to extreme rainfall events. In Louisiana, increased rainfall intensity associated with climate variability has placed significant pressure on aging drainage infrastructure. This study assesses the hydraulic adequacy of an existing culvert located along Rafe Mayer Road in the Alsen / St. Irma Lee community of Baton Rouge, Louisiana. An integrated GIS-based hydrological modelling framework was implemented using satellite remote sensing, digital elevation models (DEM), land use/land cover (LULC) data, and rainfall intensity duration frequency (IDF) curves. Catchment delineation was performed using ASTER DEM within a SWAT-based environment. Peak discharge for a 25-year return period was estimated using the Modified Rational Method, while culvert hydraulic performance was evaluated using Manning’s equation and hydraulic principles outlined in the Louisiana Department of Transportation and Development (LADOTD) Hydraulic Design Manual. Results indicate that the existing twin 1200-mm pipe culvert is hydraulically inadequate, discharging only 4.49 m³/s against a computed peak flow of 5.03 m³/s, resulting in overtopping and observed flood depths of 1–2 m. A proposed rehabilitation design involving three 1200mm circular corrugated metal pipes eliminated overtopping and safely conveyed the design discharge. The findings provide evidence-based guidance for infrastructure rehabilitation and demonstrate a replicable methodology for community-scale flood mitigation planning.