Estuarine salinity recovery from an extreme precipitation event: Hurricane Harvey in Galveston Bay.

With a warming climate and a more humid atmosphere, extreme precipitation events are projected to occur more frequently in future. Understanding how coastal systems respond to and recover from such acute events is of fundamental significance for environmental assessment and management. A hydrodynamic model was used to examine the estuarine responses in Galveston Bay to Hurricane Harvey, an extreme precipitation event with a return period of larger than 1000 years. The enormous freshwater input during Harvey caused long-lasting elevated water level, extraordinarily strong along-channel velocity, sharp decreases in salinity, and huge river plumes, all of which were well reproduced by the model. The salinity recovery time (TR) was estimated as a measure of the system resiliency to stormwater input. Over the entire bay, the TR had a mean of two months, but with great variability ranging from less than 10 days near the bay entrance to over three months in the inner part of Trinity Bay and the middle of East Bay. The spatially varying TR was explained by different contributions of exchange flow and tidal pumping to salt flux. At the bay entrance, tidal pumping facilitated by the shelf current was the dominant mechanism for salt influx, while exchange flow and tidal pumping had a comparable contribution to salt influx to Trinity Bay. The spatial pattern of the TR appears consistent with the changes in the phytoplankton community in the bay. A series of numerical experiments with different amounts of stormwater reveals a non-linear relationship between the bay-wide mean TR and the amount of stormwater, with the rate of increase in TR decreasing when stormwater input increases. The present approach using a hydrodynamic model will be able to provide a quick assessment of the environmental pressure from extreme events.