Use of the SWAT model for estimating reservoir volume in the Upper Navet watershed in Trinidad

Abstract

In tropical small islands the application of hydrological modelling is challenged by the scarcity of input data. Using in situ and statistically estimated data, a hydrological model was calibrated and validated for the Upper Navet watershed in Trinidad, a small Caribbean island. The model was built using the soil water assessment tool (SWAT). The sensitivity analysis, calibration and validation were performed in SWAT calibration and uncertainty program (SWAT-CUP) using sequential uncertainty ftting (SUFI-2). The results revealed that for the estimated volume of water fowing into the res ervoir (Flow_In) there were six sensitive parameters. To estimate the reservoir volume (Res_Vol), a modifcation of only the efective hydraulic conductivity was required. The model’s performance for the Flow_In validation showed accept able values (R2=0.91 and NSE=0.81). The uncertainty analysis indicated lower than recommended values for both the R-factor (0.46) and P-factor (0.31). For Res_Vol, the model’s validation performance indicated acceptable values (R2=0.72 and NSE=0.70) and the P- and R-factors were 0.80 and 0.64, respectively. Based on the statistical metrics, the uncertainty for the Res_Vol was regarded as reasonable. However, care must be taken with the model’s use in the dry season, as the simulated Flow_In was generally over-predicted. A second validation of the model was performed for the reservoir under diferent negative (removal) and positive (addition) water amounts which confrmed the model’s ability to estimate the Res_Vol. The hydrological model established can therefore serve as a useful tool for water managers for the estimation of the Res_Vol at the Navet reservoir.