Assessment of stormwater quality across land-use types in a rapidly urbanizing South African town: Guideline compliance, multivariate patterns, and exceedance mapping

Stormwater runoff is a significant non-point source of pollution in rapidly urbanising regions. This study assessed physicochemical parameters, trace metals, and major anions in stormwater collected from 33 sites representing different land-use categories in Thohoyandou, South Africa. Guideline compliance was evaluated using South African Water Quality Guidelines, while principal component analysis (PCA), hierarchical cluster analysis (HCA), and exceedance mapping were used to identify pollution patterns. Turbidity (800–1100 NTU) exceeded domestic guideline thresholds at all sites, while nitrate concentrations ranged from 109.89 to 829.33 mg/L and exceeded domestic and irrigation limits at most locations. Aluminium (0.44–7.63 mg/L) and iron frequently exceeded domestic guideline values, whereas Cu, Zn, and Mn generally remained within acceptable limits. PCA explained 58.5% of the total variance and identified dissolved ionic enrichment and particulate-associated contamination as dominant pollution gradients. Traffic-intensive land uses showed the greatest pollutant enrichment. These findings indicate that untreated stormwater is unsuitable for direct domestic reuse and requires treatment before irrigation reuse. The study provides evidence-based guidance for stormwater management in rapidly urbanising secondary towns in South Africa. Overall, effective stormwater management strategies are needed in rapidly urbanising areas, particularly in traffic-intensive regions, as shown by PCA and cluster analysis.