Application of a SWAT Model for Supporting a Ridge-to-Reef Framework in the Pago Watershed in Guam

Abstract

This study implemented experimental and numerical approaches for supporting the Pago Bay ridge-to-reef management program. Water quality tests for turbidity and inorganic dissolved nitrogen (IDN) were performed using water samples collected from four sites within the Pago Watershed. After conducting a one-way ANOVA test, the result shows significant differences in group means in turbidity levels (F value = 20.4 and p-value 3.29 × 10−7). Application of Tukey’s HSD test identifies one of the sites, the Pago River section, yields more sediment and IDN to the river system and Pago coral reef area. Observation of heavy rainfall, which causes much of the erosion and sediment transport, over the area should be taken into account in order to create best management practices. In addition, this study proposes a SWAT model for the watershed to identify locations of concern. The SWAT model was calibrated using historical streamflow data for the period of 2012–2018 and validated with data for the period of 2019–2020. The NSE and R2 values for the calibration are 0.864 and 0.938, respectively. For the validation period, the NSE value is 0.857, and the value of R2 is 0.937. In terms of sediments and nutrients, sub-basins connected to Pago River comprise the major source areas. Estimation of more sediment loads during the wet-monsoon season implies that heavy rainfall induces more erosion over the region.