A lot of nonsense has been written about the causes of flooding in Houston. Anti-immigration people blame immigration. Anti-development people blame development. Anti-Trump people blame Republicans.
The truth, however, is that Houston has flooded regularly since it was founded. Moreover, unlike Katrina, the flood systems have mostly worked as they are supposed to–diverting water to the highways, for example. The problem has been that there is just a lot of water.
In a superb post, Phil Magness has the details. From here on in this is Magness. I won’t indent.
We’ve seen a flurry of commentators in the past few days attributing Houston’s flooding to a litany of pet political causes. Aside from the normal carping about “climate change”… several pundits and journalists have opportunistically seized upon Houston’s famously lax zoning and land use regulations to blame Harvey’s destruction on “sprawl” and call for “SmartGrowth” policies that restrict and heavily regulate future construction in the city.
According to this argument, Harvey’s floods are a byproduct of unrestricted suburban development in the north and west of the city at the expense of prairies that would supposedly absorb rainwater at sufficient rates to prevent natural disasters and that supposedly served this purpose “naturally” in the past.
There are multiple problems with this line of argument that suggest it is rooted in naked political opportunism rather than actual concern for Houston’s flooding problems.
First, as we’ve established in the preceding history lesson, flooding has been a regular feature of Houston’s landscape since the beginning of recorded history in the region. And catastrophic flooding – including multiple storms in the 19th century and the well-documented flood of December 1935 – predates any of the “sprawl” that has provoked these armchair urban designers’ ire.
Second, the flooding we saw in Harvey is largely a result of creeks and bayous backlogging and spilling over their banks as more water rushes in from upstream. While parking lot and roadway runoff from “sprawl” certainly makes its way into these streams, it is hardly the source of the problem. The slow-moving and windy Brazos river reached record levels as a result of Harvey and spilled over its banks, despite being nowhere near the city’s “sprawl.” The mostly-rural prairie along Interstate 10 to the extreme west of the city recorded some of the worst flooding in terms of water volume due to the Brazos overflow, although fortunately property damage here will be much lower due to being rural.
Third, the very notion that Houston is a giant concrete-laden water retention pond is itself a pernicious myth peddled by unscrupulous urban planning activists and media outlets. In total acres, Houston has more parkland and green space than any other large city in America and ranks third overall to San Diego in park acreage per capita.*
But even more telling is a 2011 study by the Houston-Galveston Area Council that actually measured the ratio of impervious-to-pervious land cover within the city limits (basically the amount of water-blocking concrete vs. water-absorbing green land). The study used an index scale to measure water-absorption land uses. A low score (defined as less than 2.0 on the scale) indicates a high presence of green relative to concrete. A high score (defined as greater than 5.0) indicates high concrete and low levels of greenery and other water-absorbing cover. The result are in the map below, showing the city limits. Gray corresponds to high levels of pervious surfaces (or greenery). Black corresponds to high impervious surface use (basically either concrete or lakes that collect runoff). As the map shows, over 90% of the land in the city limits is gray, indicating more greenery and higher water absorption. Although they did not measure unincorporated Harris County, it also tends to be substantially less dense than the city itself.
Does this mean that impervious land uses are not a problem and do not contribute to floods in any way? No. But to cite them as a principle cause of the destruction witnessed in Harvey is purely a political move aimed at generating support for a long list of intrusive regulatory policies.
Houston’s flood problems are a distinctive feature of its topography and geography, and they long predate any “sprawl.” While steps have been taken over the years to mitigate them and reduce the severity of flooding, a rare but catastrophic event will unavoidably overwhelm even the most sophisticated flood control systems. Harvey was one such event – certainly the highest floodwater event to hit Houston in over 80 years, and possibly the worst deluge in its recorded history. But it is entirely consistent with almost 2 centuries of recorded historical patterns. In the grander scheme of causes for Harvey’s flooding, “sprawl” does not even meaningfully register.
Read the whole thing for more historical background.
* Earlier version said second which was a typo as source reports third; other sources can differ depending on year and what exactly is counted.