“The water isn’t sinking in anywhere in southeast Texas; it’s all running off and drowning…
Victor Eijkhout

Good question. I’m not a hydrologist, but I know enough to say that land cover changes due to urbanization are a factor here… especially in the sprawling Houston metro area. However, once you dump a foot of rain on an area, none of the water would go into the soil anyway. I will check on this and try to provide an answer regarding the first foot. The other consideration is prior conditions; it’s my understanding that SE Texas had been unusually wet already. That reduced the ability of the soil to absorb water from Harvey, regardless of urbanization.