Before, During and After Hurricane Harvey: Performance of an ALERT2 Flood Warning System during a Category 4 Hurricane

Gavin Hewitt, Ken Conner - Campbell Scientific , 15 November, 2018

Harris County, Texas (TX), USA, is home to over four million people and is the third most populous county in the U.S. On August 25, 2017, those four million residents were watching the approach of the first major hurricane since 1970 to make a direct hit on the southern Texas coastline. Hurricane Harvey made landfall as a Category 4 storm with 209 km/h winds, heavy rains, and a massive storm surge. The hurricane was quickly downgraded as it made landfall, and by August 26, it was considered a tropical storm with winds below 80 kp/h. However, as the hurricane lost strength, it also stalled over Harris County. From August 26-30 the storm dropped massive amounts of rain on Harris County, producing catastrophic flash and river flooding. Hurricane Harvey set new records for peak and average rainfall intensity over the duration of the storm.

The average annual rainfall for Harris County, TX is 1,264 mm. The goal of the Harris County Flood Warning System (FWS) is to provide accurate, real-time rainfall and stage data to facilitate crucial decision making before, during, and after flood events. The Harris County FWS relies on 139 gauging stations placed throughout the county bayous and connected tributaries of 22 watersheds.

During Hurricane Harvey, every watershed in the Harris County Flood Control District’s (HCFCD) jurisdiction experienced at least a 100-year rain event and some areas exceeded the 20,000-year rainfall frequency. An average of 860 mm fell across the entirety of Harris County, inundating the region with more than of water—enough to keep Niagara Falls flowing for more than a week. Flooding was catastrophic and Hurricane Harvey became the flood of record for many channels, with nearly 70,000 structures damaged by flooding.

The following paper examines the legacy Automated Local Evaluation in Real Time (ALERT) network and the 2015 upgrade by HCFCD to ALERT2 and includes details on the measurement hardware and communication network.  We will also discuss how the new ALERT2 network preformed during Hurricane Harvey and maintenance that was required after the storm.