Compound flooding in Houston-Galveston Bay during Hurricane Harvey.

Hurricane Harvey reached Category 4 when it made landfall on the coast of Texas in late August 2017. Harvey not only affected the coastal region with wind speeds that peaked near 50 m/s, it also dumped ~7.6 × 10 m of rain over 3 days. This rainfall was equivalent to the discharge of the Amazon River over the same period and made Harvey the wettest tropical cyclone to affect the United States. Winds and rainfall interacted to produce atypical storm surges along the coast and estuaries of Texas and compound flooding in the Houston region. Data from the NOAA's Center for Operational Oceanographic Products and Services provided information on water levels in this region. The highest water levels, 3 m above predicted, occurred from August 27th to 29th at Buffalo Bayou in the uppermost reaches of the Galveston-Trinity-Tabbs-Burnet Bay system. The peak surge occurred on Aug 29th because of the triple punch of a) the ocean wind stress and corresponding surge, plus the rainfall-related land-derived discharge from b) Buffalo Bayou and then from c) the San Jacinto River. Winds from the ocean persisted during that 3-day period and drove onshore water transport. This transport, together with anomalously high mean sea levels and the coastline modifications in the upper bay system, delayed the seaward motion of the land-derived discharge. Numerical model simulations that turned forcings on and off, highlighted the importance of the two river pulses in causing the widespread flooding. Simulations also underscored the influence of the interaction between land-derived discharge and ocean-derived surge along different parts of the Houston-Galveston Bay system.