Development of hydrological based physical model for nutrients transport simulation: case study of Makkah city, Saudi Arabia

Urban flooding poses significant risks to water quality and public health due to inadequate drainage systems, leading to the dispersion of harmful pollutants in the neighborhoods. This study investigates the transport of nutrients during the flood events in Makkah (Saudi Arabia), underlining the city’s vulnerability to such environmental challenges as a pressing concern. The research aims to quantify the impact of non-point source (NPS) pollutant loads resulting from urban floods, emphasizing the need for improved flood control and pollution mitigation strategies. Employing the Gridded Surface/Subsurface Hydrologic Analysis (GSSHA) model, this research simulates the transport and fate of nutrients for variable percentages of manhole overflow (5%, 10%, 15%, and 20%), addressing the challenge of direct measurement and data scarcity in urban environments. This approach allows for the examination of NPS pollution from sewer systems, considering the mixing of contaminants with floodwaters on urban surfaces. To analyze the effects of rainfall intensity on the temporal and spatial distribution of nutrients, the methodology includes the simulation of storm events with 2- and 10-year return periods. This study facilitates the prediction of contaminants’ dispersion, accumulation sites, and potential impacts on groundwater quality, highlighting the model’s utility in urban flood risk management. The findings indicate that while nutrient concentrations from storms with less than a 10-year return period remain within acceptable limits, the infiltration and subsequent potential for groundwater contamination during more severe events pose significant environmental risks. The study reveals critical insights into the dynamics of contaminant distribution and accumulation, especially during the less frequent but more intense flood events. In essence, this paper highlights how the GSSHA model can simulate the intricate relationships between urban drainage systems and floodwaters, providing a strong framework for evaluating the risks of pollution caused by flooding when specific data is lacking. The study presents an innovative approach to managing urban water quality, which aids in the development of efficient flood response plans and pollution control measures. By highlighting the importance of integrating hydrological models in urban planning, the study provides valuable information for enhancing resilience against flood-related public health and environmental hazards.