Where Did the Water Go? Interbasin Water Transfer from the Extreme Flooding During Hurricane Harvey (102)

Derek Giardino, National Weather Service West Gulf River Forecast Center, Fort Worth, Texas

Katie Landry-Guyton, National Weather Service Houston/Galveston Forecast Office

Kris Lander, National Weather Service West Gulf River Forecast Center



In late August of 2017, Hurricane Harvey impacted Texas with a 30-inch rainfall footprint that covered 11,492 square miles, or over 10 times the areas of Chicago, New York City, and Los Angeles combined. These rainfall amounts over the coastal region set new records for flooding in many areas, creating conditions that had never before been experienced. One such condition was the volume of water in sections of some rivers was so immense that water left the watershed entirely and started to flow into other river systems. This interbasin water transfer is an extremely rare condition occurring only in extreme flooding in some regions, so the determination of when it is happening and how it impacts forecasting is vital in severe flooding operations. A case study will be presented on the tools and techniques used to identify interbasin transfer and modify the river forecasts issued for Colorado River at Wharton and San Bernard River at Boling during Hurricane Harvey.

Naturally occurring interbasin transfer is a rare phenomena and requires an extreme hydrologic event to force flows to cross watershed boundaries. The first method employed to detect these events is the use of the CONUS scale GOES-16 Satellite imagery to animate the breakout flows. Another method is an analysis of the gauge network along both river systems, and combined with model runs to develop an estimate of volume transferred due to the interbasin flow.

Lastly, further investigation will be conducted utilizing other resources such as post-event site visits, aerial photography, topography, and high water mark to reconstruct the interbasin flow transferred during Harvey. The impact of this recalculated flow will be compared to the actual NWS forecasts and warnings to determine any potential recommendations to improve operational workflows when interbasin flows occur.