Addicks and Barker Reservoirs are swaths of placid Texas prairie, wetland, and forest straddling I-10 where it hits Highway 6, about 20 miles west of downtown Houston. But that’s not how nature sees them. To nature, those two open spaces are the top of a hydrological basin that drains through the city and into the Houston Ship Channel. Most of the time the reservoirs don’t reserve any water.