The pictures from Houston are horrific, with water, water everywhere and roads flooded in so many places that the only way to evacuate people is with boat. But is it unprecedented? Here are photos of the flood of Dec 1935.
Houston is built on what was once swampland and river delta-land leading into Galveston bay. Houston is now a concrete and asphalt jungle as seen in these photos
There have been many flood disasters in the Houston area, even dating to the mid-1800s when the population was very low. In December of 1935 a massive flood occurred in the downtown area as the water level height measured at Buffalo Bayou in Houston topped out at 54.4 feet.
By way of comparison, as of 6:30 a.m. this (Monday) morning, the water level in the same location is at 38 feet, which is still 16 feet lower than in 1935. But Buffalo Bayou is still rising.
Here is a map of Houston in 1940 and 2017. Green area is undisturbed land, red area is over 50% filled with buildings, asphalt or concrete. In these areas no water is absorbed into the ground.
to a rapid sinking of the Houston area. See map of Harris County of which Houston is a part.
Most of Houston has dropped about 5 feet since 1920, but near the bayou levels has dropped about 10 feet. It is not ocean rising, it is land sinking, since undisturbed land is not sinking.
Vulnerability to flooding will only get worse from now on.