The images that I took with my drone can be found at http://briancaustin.wpengine.com/portfolio/flood/
It all started overnight on 4.17 into 4.18. By the time the rain had finished on 4.18 Katy had about 12 inches of rain. On the 18th, quite a lot of roads were closed. I was not able to explore too far away but I was able to get out along George Bush Park off HW6. The Westheimer portion of George Bush Park was completely closed-off. On the 19 and 20th I just ventured out around the Old Katy area. I just happened upon Peek and Stockdick Rds and the intersection was flooded. You could see cars getting flooded as I was flying around, and many more cars were stranded from the day before when flood waters were feet higher.
A little sad note. When I was flying on the 20th, the owner of the horse farm that I was flying over asked if I could spot their lost pony. I flew around until the battery got very low, I unfortunately never spotted the missing animal.