Analyzing the Flood Risk of Buried Streams in Wayne County, Michigan

Abstract

Wayne County, Michigan, faces significant urban flooding challenges due to socio-economic disparities, historical urban development, and aging infrastructure. With a population of 1,793,561 (U.S. Census Bureau, 2020) and covering 673 square miles, including 61 square miles of water, the county remains vulnerable to flood hazards. Severe flooding events, such as the 2021 disaster causing over $1 billion in damage and affecting more than 20,000 homes, highlight the need for comprehensive flood risk assessment. This study integrates Social Vulnerability Index (SVI) data, Flood Factor data from the First Street Foundation, and environmental variables such as vegetation cover and proximity to current and historic streams. Using ArcGIS Pro, the study identifies flood-prone areas based on low vegetation (NDVI values), proximity to current and ghost streams digitized from an 1860 map, and Flood Factor scores ≥ 5. A 100-meter buffer around streams captures potential overflow zones. Bivariate mapping and scatter plots analyze the spatial relationship between social vulnerability and flood risk across Wayne County census tracts. The results show that most census tracts fall into the High-Low category, meaning high social vulnerability but low flood risk. Only one tract (5245) shows a Mid-High relationship. Even in areas with moderate or low overall flood risk, buried streams increase local flood vulnerability, as seen in Tracts 5245 and 5133. Scatter plot analyses reveal weak correlations, with R² values of 0.0024 for low flood risk (Flood Factor ≤ 2) and 0.00045 for major flood risk (Flood Factor ≥ 5). These findings suggest that social vulnerability alone does not strongly predict flood risk in Wayne County. Changes in historical stream networks due to urbanization increase surface runoff and reduce groundwater recharge, elevating flood risks. Urban areas with low vegetation, especially in Detroit, face higher flood vulnerability. This study emphasizes the need for more comprehensive analyses, combining environmental, social, and infrastructural factors to improve equitable flood risk mitigation and urban planning strategies.