THE USE OF AN L-THIA BASED MODIFIED CURVE NUMBER RUNOFF MODEL FOR FLOOD HAZARD MAPPING IN CHARLESTON, SOUTH CAROLINA

Conrad, Casey

THE USE OF AN L-THIA BASED MODIFIED CURVE NUMBER RUNOFF MODEL FOR FLOOD HAZARD MAPPING IN CHARLESTON, SOUTH CAROLINA

Authors

Conrad, Casey

Abstract

Since 2015, the Charleston region has experienced high intensity rainfall events, subjecting the peninsula and surrounding area to severe flooding, and causing massive damage to both property and infrastructure. Such meteorological events are likely to increase in both frequency and scale under widely accepted current climate change scenarios. Risk of flood damage from these events is exacerbated by rapid urbanization due to unprecedented increases in population of the Charleston area and the resulting explosion in development. Allen and Lu (2003) predict a nearly 247% growth in Charleston’s urban area square mileage between 1994 and 2030 Understanding how precipitation affects flooding in urbanized and urbanizing settings is critical to proper watershed management, and identification and delineation of areas susceptible to runoff based-flooding was the ultimate objective of this project. We employed a GIS-based implementation of the Long-Term Hydrologic Impact Assessment (L-THIA), modified to incorporate accurate impervious surface cover into the Curve Number runoff model. We also used rainfall in inches over a 24-hour period rather than long-term averages, as these are becoming increasingly unreliable in our ever-changing climate. This modified L-THIA model was used to create flood inundation maps for each of our rainfall scenarios in Peninsula and West Ashley study areas, and in the former, these were used to assess parcel and building level risk.