Increased Coastal Flooding Can Result from Decreasing Tidal River Discharge Caused by Upstream Overexploitation

We hypothesised that in tidal river segments characterised by a high ratio of tidal amplitude over the total water level, a decrease in river discharge could heighten high tides, resulting in increased flooding of coastal plains. We analysed the response of tidal and sub-tidal components of the water level at high tide to changing discharge in the tidal segment of the Tempisque river in Costa Rica by applying two complementary time series decomposition methods to 15-minute resolution water level data. The comparison of the decomposed signals with the simulated river discharge upstream supports our hypothesis with both methods. We also showed that the increase in flooding volume and duration followed a power relationship with the high tide increase. Our findings warrant further research for the extent and impact of this phenomenon to be better understood and addressed in the Tempisque and tidal rivers worldwide.