ASSESSING NUTRIENT DELIVERY RATIOS AND FLOOD RISKS AMID URBAN GROWTH IN GREENVILLE, NORTH CAROLINA

Abstract

This study examines ecosystem services and tradeoffs linked to land use changes over twenty years (2001–2021) within five sub-watersheds in Greenville, North Carolina. Rapid urbanization in these areas has altered hydrological processes, such as nutrient export, runoff retention, and flood risk mitigation. Using the Natural Capital Project's InVEST ® modeling suite, specifically the Nutrient Delivery Ratio, Urban Stormwater Retention, and Flood Risk Mitigation models, this research evaluates nutrient export, stormwater retention, and flood risk mitigation, providing insight into land use change.

The study addresses two key questions:

(1) How do urban growth and land use change affect nutrient delivery, stormwater runoff, and flood risk within a watershed?

(2) What trends in these metrics emerge as urban expansion occurs?

The NDR model estimates nutrient loads based on land cover types, while the UFRM model evaluates runoff reduction and economic damage from flood and infrastructure data. The USR model assesses runoff retention, stormwater volumes, and avoided nutrient loads, emphasizing the value of retention services compared to infrastructure replacement costs. Data collected includes land use and elevation rasters, building footprints, road vectors, soil characteristics, curve numbers, runoff coefficients, and precipitation records. These data inputs, formatted to fit the models, are analyzed in ArcGIS Pro and Tableau to assess changes over time. The results indicate a loss in stormwater runoff mitigation by increased impervious surfaces such as roads and housing that also increases the potential for flooding, alongside an increase in nutrient export due to the addition of impervious surfaces to the study sites from 2001 to 2021.