I’m not picking on Dickinson, but simply using it to tell why some places flood and others don’t. During Hurricane Harvey, Dickinson flooded causing damage to nearly every building. Texas City on the other hand, had minimal flooding. Why so?
The first thing you hear is elevation. Although elevation can be a benefit, it is no guarantee. Denver, Colorado, has suffered flooding. And, on the other hand, Tiki Island and Bayou Vista, both only a few feet elevation, had no rainfall caused flooding during Harvey.
Before getting technical, lets define the flooding we are concerned with here. It’s rising water due to rainfall. Tidal surge and high tides will be a factor, but the intense rainfall was, in this case, the big problem.
Rainfall flooding is about drainage and not absolute elevation. At any elevation you can suffer flooding if the water is coming down faster than it can drain away. You might not think so, but being very close to Galveston Bay is the best you can do to avoid rainfall flooding; the reason being is that rain water can get to the big pond (Galveston Bay) very quickly and the big pond will not rise from rain water. Not since Noah loaded up the ark has rainfall raised the water in large bays and oceans; they are too vast to be affected by rainfall.
Dickinson flooded because it has an inadequate drainage system (for the Harvey rate of rainfall) and Texas City did not because it does have that good of a drainage system. Other areas, including much higher elevations than Dickinson, flooded too for the same reason. Their drainage systems could not drain the water at the rate it was coming down.
So let’s take a technical look at the Dickinson drainage system. Dickinson being about 10 square miles area has basically only one water highway to the Gulf of Mexico; that being Dickinson Bayou. I did some rough (I mean really rough) calculations and found that Dickinson Bayou cannot even handle a one half inch per hour continuous rainfall from just half the city area. And I have no idea what the other half has as a drainage system.
Drainage systems always work in the long run by raising the upstream elevation of the water enough for it to flow to the big pond. Unfortunately, this rise in water elevation cannot be achieved without the water getting out of the water highway (Dickinson Bayou) so the water gets higher everywhere till it is high enough to make the drainage system work; this of course is the cause of the flooding. When we have a high tide and or a hurricane surge this in-town water elevation must go up an equal amount to keep the elevation difference (that required to get the water to flow as fast as it is coming down) the same.
Texas City of course uses pumps and an intermediate pond (Moses Lake) to artificially force the drainage required. Dickinson solution; increase the width of Dickinson Bayou and add some drainage canals.