Answer: by crowdsourcing information for an interactive map
Marine Weather and Climate and Tailwind Labs have created an interactive map to provide real-time information of flooding resulting from Hurricane Harvey. Called the U-Flood project, the map was created using OpenStreetMap and Mapbox GL JS, and is updated via crowdsourcing.
Citizens simply click on the map for their city or region, and then zoom and click on streets that they know to be inundated or cleared. Areas mapped by U-Flood include Houston, I-45 Corridor, Galveston, Beaumont Region, Lake Charles, Baton Rouge and New Orleans. Since its Tuesday morning launch, more than 1,500 flooded streets have been reported on the map.
Testimonies posted to the website reveal that citizens in Texas and throughout the country have been able to use U-Flood to prepare themselves or warn family and friends of flooding dangers.