19. Geospatial Mapping of River Health Assessment: A Study Case of Spatial and Seasonal Monitoring at Sumbawa Island Watersheds, Indonesia

River water is a vital resource for human use and economic growth, but pollution from anthropogenic activities can significantly diminish its quality. Consequently, regular monitoring is essential for river water conservation. This chapter outlines a river health assessment comprising three stages: (1) developing the Soil and Water Assessment Tool (SWAT) model for the selection of monitoring sites, (2) mapping river health with the Storage and Retrieval (STORET) index using Inverse Distance Weighted (IDW) interpolation, and (3) conducting multivariate analysis to identify pollution sources. The study focused on watersheds in the Bima, Dompu, and Sumbawa districts, on Sumbawa Island (Indonesia). In the initial stage, the SWAT identified observation stations and predicted the conditions of water quality ranged from excellent to moderately polluted. In the subsequent stage, in situ analysis revealed that dissolved nutrient levels in the Bima and Dompu districts exceeded 0.5 mg/L, while total dissolved solids (TDS) in the Sumbawa district surpassed 1,000 mg/L, particularly in downstream areas. Meanwhile, the last stage revealed that excellent river health was found in forest areas on slopes exceeding 25°, whereas decreased health was observed in agricultural and urban areas on gentle slopes, particularly near coastal regions. Analysis of water quality variables indicated that phosphate, TDS, and ammonia concentrations were higher in urban and agricultural watersheds, whereas forested areas showed better river health with higher dissolved oxygen levels. These stages may serve as a comprehensive methodology for riverine monitoring for water resource conservation policies.