Note: sheet flooding is flooding from sheet flow; which is the main type of flow that causes street flooding.
With the upcoming flood bond election later this month, and a vote on the language regarding the rain tax in November, this is a good time to take another look at the flooding issue.
In Harris County we have three different types of flooding – river, sheet, and storm surge. The upcoming elections will only directly address river and sheet flooding, but depending on how the river flooding is addressed could have an impact on storm surge flooding in Harris County.
Much of the current focus/discussion has centered on river flooding. That’s what the election this month is slated to address. While devastating to those impacted, river flooding (and storm surge) only impacts a small segment of the county. Sheet flooding, which is supposed to be addressed by the rain tax, has far greater general disruption to the county. Voting in favor of the flood control bonds later this month seems like a wise course of action. Voting in support of the rain tax in November is a much more open question.
Climatological Rainfall Data – increased precipitation is not causing the floods
For starters, it’s a good idea to look at climatological data to see if increased precipitation or increased urbanization is causing the flooding issues. Much of the data being presented in the aftermath of Harvey focused on Bush airport. However, looking at Hobby rather than Bush paints a significantly different picture.
The National Weather Service has readily accessible climatological information from 2000 to the present. Bush and Hobby have some noteworthy differences over this time span. In general Hobby receives more total precipitation which is to be expected given the difference in proximity to the Gulf and sea breeze effects. More noteworthy, while Bush had 9 years of rainfall above the 30 year average and 9 years below the 30 year average, Hobby had 6 years above the 30 year average and 12 years below the 30 year average.
This is more remarkable when you consider both Allison and Harvey are within the time period. Leaving these two storms out, Hobby would have been 14 years below normal precipitation versus 4 years above normal. This suggests that, overall, total rainfall rate is not increasing at Hobby, and that any increased rainfall totals are because of named tropical systems rather than because of generally increasing precipitation amounts.
The precipitation deviation at Bush is more in line with what would be expected, with half the years above normal and half below normal. However, once again Allison and Harvey skew these results. Plotting a trend line from 2000 to the present gives a formula of y = 0.0099x + b. This flat trend line is artificially raised by Allison and Harvey. If not for these two systems the trend line at Bush would be negative.
With this in mind, the conclusion is that overall precipitation increase isn’t the reason we are experiencing greater flooding problems. That leaves increased urbanization as the culprit for the increased flooding.
The rain tax is supposed to address drainage issues
After this month’s election the flooding election turns to November when a vote on the language for the rain tax is back on the ballot. One of the biggest issues with the rain tax is the question on where has the revenue been spent. The City, so far, hasn’t given a good explanation as to where the collected funds were spent. However, insofar as the future is concerned, what are the plans for future expenditures is the critical question.
In 2016 I wrote atechnical piece explaining how drainage woes lead to worsening river flooding and offered a shell of a plan on how to combat the issue. The City needs to do more in the way of sheet flood control with the rain tax if continued taxation is going to be beneficial. The two ways to reduce sheet flooding are keeping water off the streets and better drainage of water that makes it to the streets. Both of these areas are, from an engineering standpoint, very simple. Both of these areas are what the rain tax is supposed to fund.
The increased urbanization is what’s leading to the more recent drainage issues. Combating the effects of increased urbanization is simple. As was suggested earlier, a simple philosophical tweak to roadwork would go a significant way to increasing drainage. Simply installing grates in the road when roadwork is ongoing would go a significant way towards reducing the flooding.
Right now we have a situation where neighborhoods are dry, but all paths out of the neighborhood are flooded. Take Fondrin and Bellaire and Fonderin and Harwin as an example. You could get out of the neighborhood, but can’t get past either light in a flood. Essentially, the residents (myself included) are safe, but trapped in our neighborhood. Adding extra drainage at these intersections makes them passable and allows for exit from the neighborhood. Once you can exit the neighborhood then the economic impact of the floods lessens. If you can get out of the neighborhood you can get to work.
Lessening water flow onto the roads is the second piece of the puzzle to stopping drainage issues. The previously mentioned beautification plans would help lessen the impact. However, the City also has the capability to help with this task outside of business participation. Permeable concrete doesn’t work too well for roadwork since traffic speeds need to be below 35 mph in order for the permeable concrete to maintain integrity. However, this isn’t a concern for sidewalk repairs. This also could be used where driveways meet the roadways. Even a simple strip the width of the sidewalk where parking lots and the roads meet will have a significant reduction in the amount of water that flows onto the streets.
Something needs to be done to combat flooding. That’s why a vote in favor of the bonds this month is a palatable expenditure. However, the current flooding issues establish that the rain tax is not working. Unless and until the City can articulate some specific plans on how the rain tax is going to be used differently in the future a vote against the rain tax in November is the wiser course of action.