Res 2021-064/approving Substantial Amendment No. 10 to the Community Development Block Grant-Disaster Recovery (CDBG-DR) Action Plan

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IDinbron LJCfiUn The City of San Marcos, Texas (hereafter referred to as "the City') was inundated with historic flash and river flooding in Hays County on two separate occasions within six months of each other in 2015. The first event, now called the "Memorial Day Floods", occurred overnight on May 23rd and early May 24th. May 2015 has been documented by the National Weather Service as the wettest month in Texas History, with well above -normal rainfall during the first two to three weeks of the month. A persistent area of low pressure over the western United States brought multiple rain events throughout the month of May that saturated soil throughout south-central Texas. By the time Memorial Day weekend arrived, much of the region was at least 2-4 inches (100- 300%) above normal. These wet antecedent conditions meant that any new rain, and especially heavy rain, would become rapid run-off directly into rivers, streams, and flash flood prone areas. This "worst-case" scenario came to pass Memorial Day weekend. A thunderstorm cluster organized west of Hays County on Saturday afternoon and produced upwards of 12 inches of rain in less than 6 hours. The majority of this rain fell in the upper reaches of the Blanco River watershed at rates that exceeded 4 inches per hour as thunderstorms merged and regenerated for hours over southern Blanco and eastern Kendall Counties. Most of the rain fell from Saturday afternoon into the overnight hours of early Sunday morning, leading to a rapid rise in the Blanco and San Marcos Rivers. The Blanco River at Wimberley rose from near 5 feet at 9 p.m. on May 23rd to near 41 feet by lam on May 24th. The Blanco River rose 5 feet every 15 minutes just before midnight, equating to a 20 -foot rise along the river within a one-hour time frame. Numerous high-water rescues occurred throughout the late evening and morning hours along the banks of the Blanco River and eventually the San Marcos River. The resulting flash flooding caused a tragic loss of life and extreme property damage. Rescue and recovery efforts stalled on May 25th as another round of severe weather struck the neighboring counties of Williamson, Travis, Bastrop and Caldwell. Large areas of these counties experienced flash flooding and tornados. Another catastrophic flood event took the area on October 30, 2015, referred to as the "All Saints Flood", where water caused portions of Interstate 35 to be closed for a second time that year. The impacts of this event were widespread, leading to the closing of Austin -Bergstrom International Airport, approximately 30 miles away. The National Weather Service reported "nearly 6 inches of rain ... within an hour... flooding the ground floor of the Austin Air Traffic Control Tower and Terminal Radar Approach Control facility." Elsewhere in Texas, some areas received more than 10 inches of rain with heavy rains washing away RVs, boats and trailers along the Guadalupe River in New Braunfels, Texas. The powerful waters of the All Saints Flood struck Cypress Creek in Wimberley, the Blanco River, and the San Marcos River, causing additional property damage and delaying recovery efforts from the previous flood. However, the community's heightened sense of awareness and improved reaction to alerts translated to no loss of life during the All Saints Flood. Both events were considered historical flood events for Central Texas, but for different reasons. The Memorial Day Flood was noted for its extreme water velocities, analogous to the velocities of Niagara Falls. The All Saints Flood was noted for the extreme volume of precipitation in such a short period of time in various locations around Hays County quickly inundating the rivers, ditches and ephemeral streams. Last Updated 3/03/20 Page 9 of 63