Bad experiences with Chapter 42 redevelopment inside Loop 610, convinced the Super Neighborhood Alliance (SNA) to mount a sustained effort to improve Chapter 42 of the City Code of Ordinances prior to it’s extension from its current limit of within Loop 610 to encompass the entire City and the extraterritorial jurisdiction (ETJ).  The SNA has been concerned that the increased density will require additional infrastructure, including additional stormwater drainage, so had recommended changes to “grandfathering” clauses in Chapter 9 of the Public Works and Engineering (PW&E) Infrastructure Design Manual.

As a result of the SNA request, the Mayor asked that CM Costello engage the engineering community to suggest revisions to  Chapter 9 regulations associated with “grandfathering” detention; i.e., the regulations that say that if a property is already paved, then no detention is necessary when the property is redeveloped.  One week before the hearing before City Council about the latest Chapter 42 revisions (held on Wednesday, April 10th, 1013), members of the SNA met with CM Stephen Costello to discuss changes that his group had recommended be made.  On Friday, April 5, PW&E released their latest Chapter revisions, which included parts of the requested revisions,  so the SNA called an emergency meeting on Monday, April 8, to try to disseminate the information to as many Super Neighborhoods as possible. CM Costello was asked to be the keynote speaker and graciously accepted.Houston & ETJ

Chapter 42 will have an impact on all of the City of Houston and the extraterritorial jurisdiction (ETJ), not just the area inside Loop 610 that’s arbitrarily defined as urban.   That’s a very large area – much much larger than the area inside Loop 610.  To see just how large, click on the map to the right.  Not all requirements apply to the ETJ, but enough do that the not yet annexed areas should be aware.  From Chapter 42:

Sec. 42-2. Scope.
This chapter shall apply to all development and subdivision of land within the city and its extraterritorial jurisdiction. This chapter establishes the general rules and regulations governing plats, subdivisions and development of land within the city and its extraterritorial jurisdiction to promote the health, safety, morals and general welfare of the city and the safe, orderly and healthful development of the city.

The equations that the engineers have defined may be based upon sound science, but they do precious little to prevent flooding in Houston.  In fact, for “grandfathered” areas of between 1 and 10 acres (100% concrete), developers would only need to add about 4% of the area in acre-feet of detention.  For “grandfathered” areas of between 10 and 50 acres (100% concrete), developers would need to add more, as defined by the equation, up to a maximum of 7.5% of the area in acre-feet of detention. For relative numbers, ground that has never been covered in concrete (and this is a necessary distinction) would need to add 50% of the area in acre-feet of detention.  If the ground has ever been covered in concrete, it is grandfathered, even if the concrete was removed and the land remained dormant for years.  PW&E should remove this onerous definition for several reasons, primarily because it is difficult to verify.  There are numerous examples where PW&E incorrectly claimed 100% impervious cover and allowed a developer to completely pave over the ground without the need to mitigate for any stormwater runoff.  Satellite photographs often tell a different story.

We’ve created a simple Excel spreadsheet that allows you to calculate the amount of detention for a property.  In the orange box, insert the development area in acres.  The percentage of new impervious cover (Aii = new concrete) is in the left column and the percentage of redeveloped impervious cover (Aei = old concrete) is along the top row.  The intersection of the row and column is the amount of detention reREAL 100 year floodplainquired.

Why are we so concerned about detention?  Lots of reasons, but perhaps the most important is that the City is very vulnerable to flooding.  In order to understand why so many people flooded in April, 2009, TIRZ 17 used a two dimension computer model in its Regional Drainage Study to determine stormwater sheetflow in the area around it’s boundary.  The image at the right shows the Study area north of I-10 and the actual 100-year floodplain (there’s a similar map south of I-10).  FEMA defines the 100-year floodplain as water that exits from a bayou or drainage ditch that floods the surrounding area.

What FEMA doesn’t define, and every hydrologist and civil engineer understands this, it that it is the water that cannot get to the ditch or bayou, the overland sheetflow, that causes the most flooding.  That’s the area in green in the picture.  The property that is outlined in yellow is a 46-acre property that failed to install detention and raised the property an average of about 1.5 feet.  Once the lowest property in the area, it’s now the highest, and as a result, many 50-year old homes that had never flooded, flooded in an event that was estimated to be between a 10 and 25-year event.   These are deed-restricted neighborhoods and residents recognized early on the problem and raised the issue with PE&E and the City, but were ignored.

This example is mirrored throughout the City and continues even inside TIRZ 17, despite our efforts to stop it.  Likely it has happened within your neighborhood, or will happen.  CM Costello says that it’s an enforcement issue because the regulations clearly say that sheetflow patterns cannot be interrupted.   If the City is unable to enforce regulations already in place, why should we expect them to enforce regulations when the new regulations are extended to an area many times the size of the existing urban area?  In these budget constrained times, should we expect that the City will multiply its staff many-fold? Probably not.

CM Costello said that the way to solve the flooding is with sub-regional detention ponds – huge detention ponds judiciously spaced throughout the City.  That could work, but there are several problems:

  • They need to be located where they can do the most good and be large enough to handle vast amounts of water – for a 100-year event, say a hurricane, consider something a few inches over a foot deep spread over several square miles.  How deep is defined by where in Houston you reside, but range from 13″ to 19″ in 24 hours.  Consider that the City of Houston encompasses 600 square miles, not including the ETJ, so if one sub-regional detention pond is placed per square mile, then 600 detention ponds would be needed with a capacity of over 640 acre-feet each.  One pond in TIRZ 17 is 44 acre-feet and costs $26 million.  That’s high.  Land cost was about $8 million and most of the rest was because residents weren’t listened to when they warned that the channel and the bridge would have to be rebuilt. Let’s consider a typical cost might be half that.   There are nearly 15 44-acre ponds per 640 acre pond, so one sub-regional pond might cost about $190 million.  One for each square mile would be over $114 billion dollars.
  • All City streets are supposed to be capable of handling a 2-year rain event under the street and a 100-year rain event within the street ROW.  Most cannot handle a 2-year event, much less a 100-year event, yet somehow all this water is supposed to be conveyed to a sub-regional detention pond perhaps a mile away.  For example, Arthur Storey Park surrounds a large HCFCD detention pond near Bellaire Blvd and Beltway 8 along Brays Bayou, yet the intersection routinely floods because the conveyance system cannot move the water the tenth of a mile, or so, to the pond.  Of course that detention pond wasn’t purposed as a sub-regional pond, but it illustrates that building the pond is only part of the cost.

This is back-of-the-napkin math, but the take-away idea is that the cost and time required to build such a system, even scaled to a tenth, would likely prohibit its completion and who would decide which tenth would be protected.  Houston has a history of not keeping its promises and a history of cronyism, so there will always be backroom deals and unwarranted variances.  Keep in mind, too, that the Rebuild Houston Developer’s Fee only provides $1.5 million per year.  At that rate, it would take over 125 years to build one developer-funded sub-regional detention pond.

The infrastructure required for the density proposed is much more than just drainage.  It is also water and sewer service, trash and maintenance, police, fire, power and lighting and the vast majority will be paid for by the taxpayer.  Even if the City is only responsible for those services that occur within the City limits, it still represents a sizable investment, and it’s not likely to keep pace with development.  In the meantime, streets that were designed for suburban use will need to carry more runoff water, and neighborhoods that haven’t flooded in the past will likely flood in the future.



Please follow and like us:

Comments are closed.