Update 11/6/14: Chapter 9 released

The Public Works and Engineering Department has released the long awaited Chapter 9 revisions of the Infrastructure Design Manual.  Most of our requests were ignored, although the City did add back text stating, “The combined system is intended to prevent Structural Flooding from extreme events up to a 100-year storm.” This was necessary to maintain Houston’s extraordinarily good FEMA rating and discounted flood insurance rate.  

PW&E didn’t remove “Grandfathering” (see below) and significantly decreased detention requirements for lots 15,000 square feet or less, which represents the vast majority of residential properties (94%).  Detention requirements for these properties have been reduced to 7% from 10% proposed earlier this year.  Compare this to 50% detention required to develop on virgin properties over 2 acres.

The new Chapter is still not harmonized with Chapter 42 of the City’s Code of Ordinances, which designates the entire incorporated City as urban.  For example, runoff coefficients still reflect suburban densities, meaning that new road construction need only assume 55% runoff rates in areas with residential lots of less than 1/4 acre (10,890 square feet).  Given that Chapter 42  allows up to 90% concrete coverage on properties this size and that Chapter 9 only mitigates for 7% of the runoff, this discrepancy will produce street and structure flooding in the extreme event.  There is clearly a disconnect between the claim of preventing structural flooding up to a 100-year event and its Chapter 9 implementation.

Super Neighborhood Alliance (SNA) Chapter 9 Comments

•  What’s at Stake?

  • Increased Risk of Flooding
  • Reduced Detention and Drainage Capacity
  • Rising Insurance Rates
  • Decreasing Economic Competitiveness

•   What Needs to Change?

•     Chapter 9 should be revised to insure consistent and transparent enforcement and eliminate unwarranted variances (§ 9.02.A.2).

  • Chapter 9′s standards for evaluating the storm water impacts should be revised to reflect both increased amounts of impervious cover and time of concentration.
  • Raise and reduce number of run-off coefficients (§ 9.05.B.3)
  • Protect existing development from increased risk of flooding (§ 9.05.D.5)
  • Specify more than two Manning numbers for roadside ditch design (§ 9.05.F.2.d)

•     Chapter 9 should be revised to eliminate “grandfathering” and require full mitigation for the storm water impacts of all types of new development

  • “What is Grandfathering?”
  • Off-Site Mitigation (§9.05.H.3.b)
  • On-Site Mitigation (§9.05.H.3.d-e)

 •    Chapter 9 should be reorganized or harmonized with City Code of Ordinances.

  • Chapter 19
  • Chapter 42

•     Chapter 9 should be revised to improve city records by require maintenance of public records showing the location and capacity of detention on private property so that capacity is not lost during redevelopment (§ 9.07).

•     What Should City Council Do?

  • Provide resources needed to enforce standards consistently and transparently
  • Demand compliance with Chapter 19 of the City Code
  • Educate and inform
    • Schedule presentations
    • Call special meetings
    • Summon witnesses


What’s at Stake?

•    Increased Risk of Flooding

  • Amendments to Chapter 42 of the City Code of Ordinances passed in 2013 expanded “urban” standards for residential development from the Inner Loop to the entire city.
  • The amendments to Chapter 42 increased allowable density of single family housing outside Loop 610 from roughly 8 to 27 units per acre without requiring corresponding increases in supporting infrastructure or full mitigation for storm water impacts.
  • Local watersheds already have tens of thousands of properties in existing floodplains. Unless Chapter 9 is amended to require full mitigation for storm water impacts of new development, more properties than ever will be at risk of flooding.
  • Harris County Flood Control has recently changed its mitigation requirements from 1/2 acre-foot per acre of increased impervious cover to 1/3 acre-foot per acre.

•    Reduced Detention and Drainage Capacity

  • Most of our drainage system is designed for low density suburban development with low discharge flows.
  • Unless Chapter 9 is amended to require the calculation of detention and drainage needs using coefficients that assume high density development with higher peak discharge flows than currently exist, city engineers will continue to evaluate detention and drainage needs using calculations that incorrectly assume low density development with low discharge flows.
  • Calculations that incorrectly assume low density development with low discharge flows where density and discharge flow is increasing will reduce detention and drainage capacity.
  • High density development increases demand for street and parking capacity that is often satisfied by filling-in roadside ditches that further reduces detention and drainage capacity.
  • New roads need to be constructed assuming full urban density since it is impossible to know where very dense development will occur.  Likewise, roads reconstructed under Rebuild Houston should also have drainage systems assuming runoff from fully developed urban density.

•    Rising Insurance Rates

  • Biggert-Waters Flood Insurance Act of 2012 mandates rates based on actual risk of flooding.  Even though the Affordable Homeowner Flood Insurance Affordability Act of 2014 rolled back or slowed many rate increases for homeowners, businesses are still impacted fully.  All rental and vacation homes will all have a yearly $250 surcharge to help subsidize at risk homes.
  • Flood maps are being revised to capture true costs of structural flooding.  55% of homes flooded in Houston are not in a FEMA floodplain compared to 33% nationwide.  A 100-year rain event occurs on-average about every 5 years, and a 500-year rain even occurs about every 8 years.  Under Biggert-Waters, FEMA will need to capture these anomalies.  As a result, the floodplains will continue to grow.
  • Revisions to flood maps are increasing the size of the city’s 100-year flood plains and the number of structures at risk of flooding.
  • PW&E is removing references to meeting a 100-year Level of Service (LOS) from Chapter 9.  FEMA has publicly stated that without this verbiage, Houston will loose its extraordinarily good FEMA Community Rating System (CRS) rating of 5.  For each point lost, Houstonian’s flood insurance premium will increase 5%.  For reference, the national average is 7.6 and Harris County is an 8.  Only 4 communities of 872 are better than Houston’s CRS rating .

•    Decreasing Economic Competitiveness

  • Reduced drainage and detention capacity, increased risk of flooding, and rising insurance rates will threaten economic competitiveness.


What Needs to Change?


  • Chapter 9 needs to retain references to meeting a 100-year level of service and rather than giving up on achieving it, PW&E needs to rework Chapter 9 in order to achieve it and stop worrying about hurting development.
  • Chapter 9 should be revised to insure consistent and transparent enforcement and eliminate unwarranted variances (§ 9.02.A.2). Section 9.02.A.2 allows the city engineer to grant site-specific variances that result in annual increases to 100-year flood plain. Site specific plans should be considered openly and have stringent requirements
  • Chapter 9′s standards for evaluating the storm water impacts should be revised to reflect both increased amounts of impervious cover and time of concentration
    • Raise and Reduce Number of Run-Off Coefficients (§9.05.B.3): Chapter 9 should be revised to reflect higher run off coefficients because drainage from all types of new development will have higher flow than from existing development. And now that high density development can occur throughout the city, the number of run-off coefficients should be reduced to two, e.g., (e.g., 75% for residential development and 100% for roadways).
  • Protect Existing Development from increased risk of flooding (§9.05.D.5): Roadways are designed to capture water in excess of two-year events up to 100-year events, but emergency routes are not allowed to flood even in 100- year events. Absent full mitigation for all types of new development, existing neighborhoods are wrongfully forced to serve as de facto detention ponds.
  • Specify two Manning numbers for roadside ditch design (§9.05.F.2.d): Using a large Manning number (e.g., 0.045) when replacing an earthen ditch with a concrete conduit will result in a channel that does not have as much conveyance capacity as the original ditch and thus increased flooding.
  • Chapter 9 should be revised to eliminate “grandfathering” and require full mitigation for all new development
    • “What is Grandfathering?” Chapter 9 allows property that either has impervious cover or had impervious cover in the past to be fully redeveloped without any on-site mitigation for storm water impact. Exemptions and/or reductions in detention and drainage requirements for redevelopment on such  properties is referred to as “grandfathering.” “Grandfathering” needs to end because it shifts the cost of flood damage and reduction from developers to neighboring landowners, public agencies, and taxpayers.
  • Off-Site Mitigation (§9.05.H.3.b): When drainage from new development is directed to public right of way (ROW), Chapter 9 should require infrastructure to receive and convey water into storm sewer system and not redirect water to neighboring properties as occurs when roadside ditches are filled-in or curb and gutters don’t work properly. SNA has proposed that developers be allowed to install underground detention for lots smaller than 15,000 sq.ft. in the ROW to allow for maximum development and adequate detention.
  • On-Site Mitigation (§9.05.H.3.d-e): Chapter 9 requires detention as a % of existing impervious cover as follows: up to a maximum or 4% of the property size for lots of 1-10 acres, and up to a maximum of 7.5% for lots of 10-50 acres. Use of equations to determine the amount of detention are difficult and expensive to police. The best action is to eliminate the equations and require 0.5 acre-feet per acre for all types of new development.
  • Chapter 9 should be reorganized and harmonized with relevant chapters of the City Code of Ordinances.
    • Chapter 19: Chapter 19 of the City Code governing floodplains embodies a “No Adverse Impact” policy that should require full mitigation for all impacts of new development.
  • Chapter 42: Standards for storm water detention and drainage on private property should be moved out of Chapter 9 of the Infrastructure Design Manual and into Chapter 42 of the City Code of Ordinances to insure that  (1)  development standards are approved by City Council; (2) variance requests will be considered and approved the in open meetings, e.g., by the Planning Commission; and (3) variance requests will be subject to public comment.
  • Chapter 9 should be revised to require maintenance of public records showing the location and capacity of detention on private property so that capacity is not lost during redevelopment (§9.07). Parking lots can be used for detention, but such does not need to be recorded. Because analysis for new development assumes no detention, such properties are treated as “grandfathered,” and as a result run off increases.


What Should City Council Do?

•    Provide resources needed to enforce standards consistently and transparently

Recent amendments to Chapter 42 of the City Code of Ordinances and proposed revisions to Chapter 9 of the Infrastructure Design Manual necessitate additional inspectors and engineers. Failure to provide adequate staffing to support these changes further exposes the city risk of flooding.  Clarifying the standards will simplify the enforcement.


•    Demand compliance with Chapter 19 of the City Code.

  • Sec. 19-1.b states: “The provisions of this chapter shall take precedence over any less restrictive conflicting laws, ordinances, codes, or official determinations.”
  • Chapter 19 also states in several places that the city engineer must use the strictest interpretation regarding conflicting provisions when interpreting provisions relating to flood control. Among these is the express obligation of the city engineer regarding the use of data provided in Sec. 19-4.b.1: “To the extent of any inconsistencies between the study data and the effective FIRM, the more restrictive base flood elevations and special flood hazard areas shall be controlling.”
  • Sec. 19-11 provides that no permit, plat, or variance in the affected areas shall be granted unless it is shown to comply with this chapter.
  • Educate and inform
    • Schedule presentations: Chapter 2, Sec. 2-2 of the City Code of Ordinances, rules of procedure for meetings and proceedings of the city council, Rule 2.a.3 governing presentations to the city council by persons, groups, or organizations allow presentations to be scheduled by council members through the office of the mayor pro tem. Presentations on the issue of flooding and drainage could be scheduled to educate council and the public on these issues.
  • Call a special meetings: Article VII of the City Charter, Sec. 3 titled “Meetings” provides: “Special meetings shall be called by the City Secretary upon the written request of the Mayor or three Council Members.”
  • Summon witnesses: Article VII of the City Charter, Sec. 5 titled “City Council May Summon Witnesses” provides: The City Council shall have power to summon and compel the attendance of witnesses and the production of books and papers before it whenever it may be necessary for the more effective discharge of its duties, and shall have the power to punish for contempt . . .”

Since May, the Super Neighborhood Alliance and the City of Houston were supposed to be discussing changes to Chapter 9 of the City’s  Infrastructure Design Manual.  We haven’t been.

Instead, we have been discussing one small part, a “fee in lieu of detention” for development and redevelopment of properties less than 15,000 square feet.  For reference, that’s approximately a third of an acre and detention is already required by Chapter 9, so a change in this requirement can affect 94% of single family residences.  As an elevation challenged city, Houston needs all the detention that it can get, and it needs to be where the new density is occurring, but land to build large regional detention ponds where needed for  maximum benefit is often unavailable.

We have proposed an alternative,  a single paragraph to the existing wording that permits a fee to be used for under sidewalk detention of up to 15 cubic feet per linear foot of sidewalk.  The fee would be paid to the City who would subcontract one of several companies who do this sort of thing.  A phone call to the company at the top of a search list resulted in an estimated cost of $5.50-$6.75 per cubic foot of detention.  The proposed “fee in lieu of detention” was to have been $7.50 per cubic foot of required detention as calculated by a formula in the City’s Infrastructure Design Manual and didn’t include the cost of a sidewalk.  The maximum fee for “under sidewalk detention” would be $5000 for a 15,000 square foot lot.  For the City’s average lot of 5,000 square feet, the cost would be $1667.

Under the sidewalk detention provides an immediate solution to rainwater runoff when construction occurs, rather than delaying to gather enough funds to build a regional detention pond.  Distributed detention can provide surprising large amounts of detention and it’s located where the detention is needed, so doesn’t need to be piped to the lowest cost land when, and if, it becomes available.  And the open bottom system drains water into the aquifer, rather than letting mosquitoes breed as they do in regular storm sewers.

If you think “under sidewalk detention”  is a more reasonable alternative than a “fee in lieu of detention” for single family residential properties under 15,000 square feet, please contact your City Councilmember.


Update (3/29/14) CM Larry Green has put Chapter 9 on his Agenda for the TTI Committee meeting on Tuesday April 1st, 2014 in City Council Chambers at 9:00AM.

Update (10/8/13): The City has refused to release Chapter 9 of the Infrastructure Design Manual to the public or to the TTI Committee Chair for review.  As a result, TTI Chair Melissa Noriega is not calling a Public Meeting.

Update (9/25/13):  Our meeting with CM Costello regarding “fee in lieu of detention” was a waste of time.  His position was that either we agree to a fee in lieu of detention or he would march across the street and have the Mayor sign it anyway.  He refused to consider our proposal for under sidewalk retention at all. 

Update (7/10/2013): The  5-year look-back has been tabled.  Now they are exploring no look-back, but instead using the current drainage fee area as the existing impervious cover for new construction; i.e., if no fee is paid now, the land is permeable so detention is required.  I asked that in addition to this, the clause adding some detention for existing impervious cover also be kept.  In the future, sites that have been fallow for a long time can no longer use grandfathering to eliminate detention requirements; for example, under these rules the Heights Walmart would have required detention.

Update (7/9/2013):  The TTI Committee meeting on Chapter 9 will be delayed once again by approximately 60 days, now meeting sometime in September.  The delay is to allow CM Costello and Andy Icken to advocate for a fee in lieu of detention for smaller lots and to address the look-back time for the “grandfathering” clause added by CM Costello that requires a small amount of detention for preexisting concrete.

Update:  The public meeting on Wednesday, June 12th was cancelled.   It has been rescheduled for July 17th at 5:00PM.  Although the City promised final revisions by July 1st, they are only required  to make them available 1 week prior to the meeting.  Consequently, revisions will be available July 9th at 5:00PM.

The public comment period for revisions to Chapter 9 of the City of Houston Infrastructure Design Manual closes on May 24, 2013.  Comments must be submitted to standardsreviewcommittee@houstontx.gov no later than that date.  The draft of the revisions for Chapter 9  was released prior to the final City Council vote on Chapter 42 (which deals with urban development) of the municipal Code of Ordinances.  Please note that these two manuals, the municipal Code of Ordinances and the Public Works and Engineering (PW&E) Infrastructure Design Manual (IDM), are distinct but different.  The Code of Ordinances are voted upon by City Council after public hearings, while the IDM is approved by a PW&E Standards Committee not subject to a vote or hearings.

Here’s a link to our comments on proposed revisions to our red-lined copy of Chapter 9.

There are several points that are particularly important to note:

  • This sentence was removed in the new version of Chapter 9: “Drainage criteria administered by the City of Houston and complemented by Harris County and the Harris County Flood Control District (HCFCD) for newly designed areas provides protection from Structural Flooding from a 100-year storm event.”   We hope that the City doesn’t quit trying to provide protection from a 100-year storm event and that FEMA and commercial insurers don’t abandoned Houston to our floods.  Removing a sentence does not remove the City’s responsibility to protect its citizens from preventable disasters. (see Section 9.02.A.1)


  • Chapter 9 is not harmonized with Chapter 42.  Recent Chapter 42 changes include increasing development density for single family residences  dramatically (from 7 to 27 homes per acre) and designating all of incorporated Houston as urban.  Urban density means more concrete and more concrete means more water runs off of properties.  The stormwater runoff coefficient, C, that percentage of a property that is impermeable, needs to be changed in Chapter 9 to reflect an all urban City.  Any roadways being reconstructed by Rebuild Houston need to assume stormwater runoff of 90% or higher. (see 9.05.B.3.a.1)


  • Chapter 9 allows fees in-lieu-of detention (see Section 9.05.H.2.a.).  Section 9.02.J. says that payments in-lieu-of detention will be allowed only if deficit drainage systems are improved to sufficient capacity to convey new and existing runoff.  If conveyance systems are being asked to carry all the runoff, then they need to have been designed using urban stormwater runoff  (C>90%)  that assumes all the water will be carried by the roadway conveyance and have capacity in excess of this.  If Rebuild Houston intends to install sub-regional detention ponds, then all conveyance routes must be designed and built to handle more than the 100-year event; i.e., C >100%.   Any fee paid in-lieu-of providing detention needs to go to a Rebuild Houston fund earmarked to build subregional detention in the subregion where the fee was paid.  It should not go towards the General Fund, nor to be used on any road project anywhere within the City.


  • Attempts by the City to deal with “Grandfathering” will cause more confusion than anything.  Inspectors will be unable to discern the small amount of new detention added when redeveloping properties with existing impervious cover (concrete).  Enforcement would be virtually impossible.  Our suggestion is that all development or redevelopment install the same amount of detention.  Inspectors could very easily tell whether detention was installed or not and requiring everyone to install the same detention would reduce, if not eliminate, creative ways to avoid detention.  We also recommend that elevating properties would require mitigating for 100% of runoff due to the elevation. (see Section 9.05.H.3.)


  • Sub-regional (huge) detention ponds have been touted as the means to save us from flooding by several Houston Mayors, but that’s misleading.  It will be years (if ever) before Rebuild Houston funding begins to accumulate enough funds for these detention ponds.  Back-of-the-napkin math suggests that we would need approximately 600 sub-regional detention ponds, each of about 320 acre-feet (huge), if we want to do away with requiring local detention.  This would cost tens of billions and land available for purchase may not be optimally placed for detention; moreover, land will become scarcer as Chapter 42 is implemented.  Clearly, we’ll need to build some anyway, even if local detention is used, because we’re only mitigating for half the runoff produced.  A more subtle problem is our insistence that our roadways are designed to convey excess water in heavy rains, so the roadways will need to carry the water to the sub-regional detention ponds.  Trouble is, major thoroughfares that need to carry emergency vehicles, or provide an evacuation route, must not flood even in an extreme event.  Theoretically, all neighborhoods will have access to emergency and evacuation routes, so the question becomes, “How will the need to convey water to sub-regional detention ponds and the need for safe passage be reconciled?”  The answer is that they cannot unless major thoroughfares are designed with much larger drainage systems than currently used, and that costs even more money and adds more delay.  Chapter 42 densification will not wait for Rebuild Houston money to accumulate, so we strongly advocate for local on-site detention with no in-lieu-of payments. (See section 9.05.D.5)

Please refer to our other pages for more information about the relationships between Chapter 42 and Chapter 9.  Use whatever comments you wish to get your own talking points or to send comments to the City (standardsreviewcommittee@houstontx.gov).

Previous Chapter 9 comments were written to show what would be necessary if Houston wants to improve flood protection to a 100-year level of service.  Those comments are at Can We Stop Houston Flooding?

Interspersed in the last bullet are pictures of detention ponds being installed along Brays Bayou by HCFCD as part of Project Brays, which will remove about 60,000 homes from the 100-year floodplain.  Some of the detention ponds are quite large, for example, Eldridge Detention Pond is 4500 acre-feet and Arthur Storey Park detention pond is 3500 acre-feet, yet Bellaire Boulevard at Beltway 8, very nearby to Arthur Storey Park, floods during relatively small rain events.   If the water cannot get to the pond, it doesn’t matter how large it is.  In spite of the numerous detention ponds (picture – Brays at 610 Loop), home flooding in SW Houston occurred along Brays Bayou  for a bad but not unusual event.  This should be some indication of how bad the situation really is.

Comments of Bob Schwartz, President of Brays Bayou Association

Comments of Carol Caul, Attorney, Advocacy Chair of Citizen’s Transportation Coalition

Chapter 42 was passed

April 24, 2013

Chapter 42 of the City of Houston, Code of Ordinances passed as proposed by the Mayor’s administration with minor amendments at the April 24, 2013, Houston City Council with only three votes against: CM Andrew Burks, CM Helena Brown, and CM Jerry Davis.  It is now the law.  As a consequence, our Chapter 42 discussions have been removed.  If you have linked to them, please let me know and we’ll work something out.

CM Laster’s two amendments passed as well. CM Laster’s amendment to reduce from 60% to 55% the level of support needed to complete an application for minimum lot size protection passed with only one vote against (Bradford), and his amendment to allow development on less than an acre of land outside of existing neighborhoods had unanimous support.  CM Brown’s two amendments (1) to keep most of District A “suburban” and, alternatively, (2) to refer Chapter 42 back to the administration, both failed.

Houston & ETJChapter 42 extends the “urban” density formerly found only inside Loop 610 to all of incorporated Houston; i.e., inside the City limits.  Suburban density now only applies to the extraterritorial jurisdiction (ETJ).

What should homeowners do?  You should begin scheduling somebody from COH Planning to come explain how to adopt minimum lot size criteria for those neighborhoods that don’t have provisions in your deed restrictions.  If you haven’t started already, you should also begin the process of modifying deed restrictions to add protection verbiage.  You cannot start too soon.

Also, plats not associated with any neighborhood are eligible for redevelopment instantly, so drive through your area to see if you can identify any that don’t seem to be a part of any subdivision; for example, abandoned utility ROW or abandoned drainage ROW.   Likely it’s too late to do anything about these, since developers have had 6 years to identify these odd parcels, but it may not be too late to begin planning for denser development.

If you are building a new home or rebuilding on an existing site, consider pier and beam construction.  Construction costs may be slightly higher, but ultimately the serviceability and flexibility offered over the life of the home will make up any difference.  If water shows signs of rising in the neighborhood, it’s relatively simple to raise the house higher and install more porch steps.  Despite the fact that Rebuild Houston doesn’t credit pier and beam as being permeable, it does allow water to flow under the house and provides less surface area to flowing water.  Piping is accessible and less prone to stress cracking as the ground shifts during Houston’s periods of torrent and drought.

Finally, Chapters 9 and 13 of the City of Houston Infrastructure Design Manual that deal with Stormwater are up for revision.   With the increased density that Chapter 42 will provide will come increased stormwater runoff.  This is particularly problematic in areas where flooding is already prevalent and may migrate to areas that are marginal.  Chapter 9 deals with the “grandfathering” of existing permeable surfaces.  Currently, if a property has existing concrete, mitigation of on-site detention need only be done for increased imperviousness, but only at 50% of the impact rate for properties above 1 acre in size.  Smaller properties are mitigated at 20% with properties below 15000 square feet only requiring 10% of increase impervious cover.

Because of objections by homeowners, minor changes to these requirements have been made already, but these are insufficient to prevent an increase in flooding.  Instead, we recommend complete elimination of any special provisions for already developed areas because many were originally installed without adhering to detention requirements, so should not be grandfathered. Arguments that it is unfair to burden new developers with the transgressions of the past don’t seem logical.  We think that it is unfair to developers of virgin properties to have to mitigate stormwater runoff while those of older properties are allowed to remove existing concrete to elevate their property without any mitigation.  It is also unfair to adjacent property owners.

Please help us protect Houston from future flooding.  Please join us to get these provisions updated.

Can We Stop Houston Flooding?

September 27, 2012

Overview – Chapter 9 of the City of Houston Infrastructure Design Manual, Stormwater Design Requirements, is up for comments. We have reviewed Chapter 9 and recommend that the following changes be made in order to prevent future flooding. Our central concern is the yearly rise in Base Flood Elevations and the increase in the size of the 100-year floodplain, which we believe is largely caused by the practice known as “Grandfathering.”

Our issues with Grandfathering are: unwarranted variances have been granted to builders, such as elevating property with no consideration of sheet flow obstruction or compensating detention; proper detention simply wasn’t installed; the land was developed prior to annexation by the City; or, for any number of other reasons, adequate detention and/or site drainage wasn’t installed. Once built, these properties are forever Grandfathered and new ones are added every year, so that the floodplain will continue growing until Grandfathering is removed from City Design Manuals.

Each year that the 100-year floodplain grows, Houston’s viability as a good location for new businesses is diminished. Moreover, the cost to residents increases in the form of diminishing home values, increased insurance rates, or actual flood damage to property. Our practice of using streets as drainage channels and neighborhoods as detention areas routinely brings the City to a standstill with untold property damage and work hours lost.

While water flow in roadways is certainly preferable to flooded homes, going forward with Rebuild Houston, we need to design to a higher level of service using realistic numbers. Progress has been made over the years; new subdivisions do a much better job at protecting structures than older neighborhoods, but developers and City engineers need to be cognizant that most people live in older homes that still need to be protected.

Temporarily waiving Rebuild Houston’s presently unimplemented Developer’s Fee can be used as a positive incentive for, for instance, adding more detention than necessary or building using low-impact design criteria. (editor’s note: the developer’s fee was passed by City Council Spring 2013 and will only add approximately $1.5M to Rebuild Houston.  Final deadline for comments on the revisions is May 24. It is located here.)


  • Change Section 9.02 F. to add the lines in italics. The most interesting comment about disallowing development in areas that have deficient drainage systems is that it would “bring development to a standstill.” Nothing could have proven the point better because that’s equivalent to saying, “Houston is knowingly developing in areas that negatively impacts flooding in adjacent properties and neighborhoods. If we continue to insist upon following this path, then it needs to be done in a more responsible way. A development so located must completely mitigate the effects of their project in-situ to a particular level of service (TBD). To incentivize Development despite the additional costs, the Rebuild Houston Developer’s Fee could be waived for a finite period.

Section 9.02 F. Development or Redevelopment in Areas that have Deficient Drainage Systems: Development or Redevelopment will not be allowed in areas that have deficient drainage systems until existing drainage infrastructure is improved to sufficient capacity to convey all existing and new run-off. Payment in-lieu of detention (Section 9.05 H.2.a.) is only possible if drainage infrastructure capacity is improved to carry all area run-off and runoff from the Development. Alternatively, Development may continue if project impacts are completely mitigated on-site. The City will consider joint project funding with a private entity for construction of drainage systems that improve existing drainage infrastructure. The City’s first priority will be to fund those projects included in the Capital Improvement Plan (CIP). Where feasible, City funding will be leveraged with other funding sources including private entities, civic organizations, and other public agencies (Harris County, HCFCD, Corps of Engineers, Housing and Community Development, and other funding sources). For drainage systems that have been identified as deficient and are not scheduled to receive funding in the current CIP, the City will consider authorizing improvements performed by the private entity that comply with the City’s objectives.


  • Amend Section 9.04.D to combine the definitions of “in-fill” and “redevelopment” to provide for two, instead of three types of development; i.e., development that is either (1) “new” because the storm drain infrastructure has not been constructed, or (2) “in-fill”/“redevelopment” because the storm drain infrastructure is already in place and takes advantage of the existing infrastructure in place as a drainage outlet. The only reason to bother to make the distinction is because redevelopment might take advantage of Grandfathering clauses and in-fill would not. Removing Grandfathering obviates this need.

Section 9.04 D. Development – The term includes New Development, and In-fill/RedevelopmentDevelopment.

  1. In-fill/Redevelopment Development – Development of open tracts of land in areas where the storm drainage infrastructure is already in place and takes advantage of the existing infrastructure as a drainage outlet.
  2. New Development – Development of open tracts of land in areas where the storm drainage infrastructure has not been constructed and a drainage outlet must be extended to a channel under the jurisdiction of the HCFCD.


  • Find a more realistic way of defining rainfall events in Section 9.04 K.

In my relatively short time in Houston (35 years), my area has suffered no less than six 100-year events – something that is statistically improbable:

A rate of 6 events in 35 years is the same as 17 events in 100 years so:

Assuming independent stationary random events

PT= (PA)(PB)(PC)…(PN)

(PA) = (PB) = (PC) = (PN) = 0.01

PT ~1 in 1034

This very large number strongly indicates that hypothetical water level tables used by the City when defining the frequency of rainfall events (2-year, 10-year, 50-year, 100-year, etc.) are grossly inaccurate. Even if only six events occurred in one hundred years, the probability of such an occurrence would be one in a trillion – still indicating the tables are wrong. Given improved record keeping and technological improvements that can permit near real-time water-level monitoring, the Houston Metropolitan area needs to begin creating better definitions by analyzing actual long-term rainfall history.

Judging from the following comment, HCFCD’s grasp of probability is not much better. “In fact, about half of all flooding events in Harris County occur outside a mapped 1 percent (100-year) floodplain.” If there’s a 50/50 chance of getting flooded outside or inside of the 100-year floodplain, then the distinction is moot – we are all in the 100-year floodplain.

Section 9.04 K. Rainfall Frequency – Probability of a rainfall event of defined characteristics occurring in any given year at a given location. Information on Rainfall Frequency is published by the National Weather Service. For the purpose of storm drainage design, the following frequencies are applicable: (insert mathematically correct numbers here)



  • Section 9.05 B.1.a Rainfall Durations specified render the runoff coefficients in the Rational Method useless.

Section 9.05 B.1.a Rainfall Durations

  1. For design purposes, the rainfall duration for drainage areas less than 200 acres will be no less than 3 hours in duration.
  2. For design purposes, the rainfall duration for drainage areas more than 200 acres will be no less than 6 hours in duration.


  • Remove all calculations in Section 9.05 B.3.a.(1) for the runoff Coefficient for the rational method, particularly for areas designated as “urban.” Runoff coefficients are determined based upon the amount of impermeable cover, but it may be assumed that with increasing density, 100% impermeable cover will eventually occur.  Certainly everything designed for use inside the urban zone needs to assume that it will see maximum runoff, and hence, should use the maximum runoff coefficient. 
  • Why is the maximum runoff coefficient only 0.8? The rational Formula fails to account for storm duration and can provide low estimates of actual runoff.  If, for example, the intense duration of the storm exceeds the time that it takes water to flow to the watershed outlet from the most remote part of the awtershed, then the facto, C, should be 1.0.

  • TxDOT defines maximum runoff coefficients for downtown areas as 0.95. Using 0.95 for the runoff coefficient in urban areas would skew calculations toward more underground capacity. Clearly, application of 0.18 for the runoff coefficient for all parks ignores the dramatic permeability differences between pedestrian trampled parks like Hermann versus wooded portions of Memorial Park. I n reality runoff will also be dramatically different.
  • If we are truly interested in reducing the 100-year floodplain, then all development and redevelopment should be returned to runoffs equivalent to a pre-Columbian condition; i.e., prior to development, and every property would mitigate their runoff on-site. Adoption of better methods to compute runoff rates would likely improve drainage efficacy. There are valid arguments for defining all drainage requirements in terms of runoff volumes and peaks rather than impervious cover.

Section 9.05 B.3.a.(1) Determination of runoff

Use 0.95 for the runoff coefficient C values in urban areas when using the rational method formula.



  • If Houston wants to stop increasing the 100-year floodplain, runoff from New Development must be mitigated on-site, otherwise downstream areas will be subjected to greater runoff than experienced before the New Development. Change Section 9.05 C. 1.a. and Section 9.05 C. 1.b. to add the lines in italics. This is one of the Grandfathering clauses that need to be changed.

Section 9.05 C. 1.Design Frequencies

a. New Development: The Design Storm Event for sizing storm sewers in newly developed areas will be a 2-year rainfall. In addition, on-site detention must be installed for 100% mitigation of New Development runoff.

b. Redevelopment or In-fill Development: The existing storm drain (sewer, ditch) will be evaluated using a 2-year design storm, assuming no development takes place. The storm drain will then be evaluated for the 2-year design event with the Development in place.

(1) If the proposed Redevelopment has a lower or equal impervious cover, and the existing storm drain (sewer, ditch) meets 2-year level of service, then no modifications to the existing storm drain are required; otherwise, the property will need to be brought up to this code.

(2) If the proposed Development results in the hydraulic gradient of the existing storm drain below the gutter line, no improvements to the existing storm drain are required. Detention shall comply with Paragraph 9.05.H. Flow discharged to the storm drain shall be in compliance with Paragraph 9.05.H.4.b.

(3) If the analysis of the existing conditions finds that the existing storm drain is deficient (i.e. the hydraulic grade line is above the gutter line), the applicant should check with the City to see if a CIP project is proposed that will require a capital contribution. If a CIP project is not proposed for the subject system, then on-site detention will be required in accordance with Paragraph 9.05.H. Flow discharged to the storm



  • The City has long touted Regional Detention Basins as the answer to regional flooding, but the obvious problem with this approach is that drainage systems under Houston’s roadways were only designed to carry water from a 2-year event. They were not designed to also carry all the water from a large Development. Doing so clearly exacerbates regional flooding. If drainage capacity from the new Development to the Regional Detention Basin is insufficient, then the Development should not be allowed to forego on-site detention. This entire section needs to be rewritten, but the salient points are there.

Section 9.05 H.2.a.

The use of on-site detention is required for all Developments within the City and for new or expanding utility districts within the City’s ETJ. Detention will not be required if the City has developed detention capacity for a drainage watershed, and/or infrastructure improvements, to serve the drainage watershed in compliance with the requirements of this Chapter. Drainage capacity from the Development to the City’s detention capacity must be capable of carrying not only the water from the Development, but it must also do so while maintaining 2-year level of service for all neighborhoods and Developments already located in the drainage watershed. If these criteria cannot be met, on-site detention must be installed. In lieu of this, either the City or Development may elect to improve area drainage capacity to insure 2-year level of service. Under these conditions, the City will consider a funding contribution in lieu of on-site detention volume constructed by the owner.


  • We recommend that Section 9.05 H.2.d be replaced. This is the primary Grandfathering clause responsible for much of Houston’s increasingly bad floods. First, the old verbiage, then recommended changes.

Section 9.05 H.2.d.If Redevelopment occurs without increasing the overall impervious character of the site, then no detention will be required by the City.

Section 9.05 H.2.d. Redevelopment of preexisting sites must be brought up to current code for detention requirements. If the site cannot easily be altered and there are adequate existing storm sewers to convey site runoff, detention may be installed within 0.5mile of the site. If adequate storm sewers do not exist, developer may petition PW&E for upgrades.

  • Section 9.05H.2.e.1. needs to be modified to make it clear that the conveyance channels must be large enough between the Development and the regional facilities to not increase the risk of flooding to adjacent regions.

Section 9.05 H.2.e.1.

Development is located in an area determined by the City to not need detention due to the geographic location in the watershed, the Development’s proximity to regional facilities, or the capacity of the receiving outfall facilities and there are adequate existing storm sewers to convey site runoff while maintaining a 2-year level of service for all neighborhoods and Developments already located in the drainage watershed. Such conclusion by the City shall be supported by submittal of a Hydraulic Report as described in Paragraph 9.05.H.2.e(2).


  • Neighborhoods have requested that the Hydraulic Report in Section 9.05 H.2.e.(2) be accessible on-line. Too often totally fabricated analyses have been permitted, which have resulted in neighborhoods being flooded. City Permitters and the Professional Engineer who signs his name on the report would know that their work can be seen and reviewed. While there may still be honest mistakes made, fraud would be dramatically reduced. Transparency is miraculous for preventing corruption.

Section 9.05 H.2.e.(2) Hydraulic Report: Submit a hydraulic analysis prepared, signed, and sealed by a professional engineer, registered in the state of Texas, to demonstrate compliance with the conditions stated in this Chapter. The hydraulic analysis shall consider (1) the current developed condition of the watershed of the stormwater conveyance system, and (2) the fully developed condition of the watershed. The probable land use for the fully developed condition will be determined by the design engineer for review and approval by the City. The hydraulic analysis shall demonstrate no negative impact to upstream or downstream conditions and shall demonstrate that a positive impact will be achieved (reduced flood crest due to the exemption. The City of Houston will post Hydraulic Reports in a public database indexed by actual property address.


  • Once again, if Houston wants to stop increasing the 100-year floodplain, runoff from Development must be mitigated on-site, otherwise downstream areas will be subjected to greater runoff than experienced before the New Development. Section 9.05.H. 3. should be modified accordingly.

Section 9.05H. 3. Calculation of Detention Volume

a. Detention volume for Development areas is calculated on the basis of the amount of area of increased impervious cover. Impervious cover includes all structures, driveways, patios, sidewalks, etc.

b. Single family residential (SFR) lots of 15,000 square feet in area or less: If an adequate area stormwater conveyance system is available that meets 2-year minimum criteria, then SFR Lots are exempt from detention if proposed impervious cover is less than or equal to 75.0 %. Detention volume of 0.20 acre feet per acre required for impervious cover over 75%.

Existing SFR lots of 15,000 square feet or less may be further subdivided and exempt from detention provided the proposed impervious cover remains less than or equal to 75.0%. If an adequate area stormwater conveyance system is not available that meets 2-year minimum criteria, then 100% of runoff must be mitigated on-site.

c. Areas less than 1 acre: If an adequate area stormwater conveyance system is available that meets 2-year minimum criteria, detention will be required at a rate of 0.20 acre feet per acre of increased impervious cover. The subdividing of larger tracts into smaller tracts of 1.0 acre and less will require the detention volume of 0.5 acre-feet per acre of increased impervious cover. If an adequate area stormwater conveyance system is not available that meets 2-year minimum criteria, then 100% of runoff must be mitigated on-site.

d. Areas between 1 acre and 50 acres: 100% of runoff must be mitigated on-site.


  • Missing piece 1: Drainage systems that were designed years ago had different requirements than those existing today and often slab foundation’s base elevations are lower than those required now. As a result, these older neighborhoods are more prone to flooding. Yet, when redevelopment begins in a region, City code has no provision to check surrounding locales to make sure that increased flooding does not occur. This common-sense check should be mandatory. Tools exist to study the cumulative local, nearby, and downstream impacts – impacts that should be mitigated whenever possible and disclosed when not. This impact review should be part of the initial platting review process and should not wait until after a plat has been approved.


  • Missing piece 2: Public and private detention ponds can be breeding grounds for mosquitos. Either these ponds must be graded so that water drains toward the exit channel, reducing the possibility of standing water, or redesigned as permanent wet-bottomed detention ponds containing mosquito fish (Gambusia).


On Wednesday April 24, 2013, the Houston City Council will vote on Chapter 42.  Citizens will have one last opportunity to raise their concerns at the pop-off session before City Council on Tuesday afternoon.

I think that I can speak for the Super Neighborhood Alliance (SNA), when I say that everyone agrees that the City needs to grow and densify, but there are good ways to grow and bad ways.  Tomaro Bell, President of the SNA, and Jane Cahill West, its Vice President, have experienced the negative aspects of Chapter 42 inside Loop 610 where it has been the law for over 10 years.   They and others inside the Loop decided that the rules need to be cleaned up before subjecting the entire City to them.  SN 22, along the Washington Avenue corridor, has been a test case for a lot of these issues.  Jane gave a tour for City Council members and SN leaders in her area of problems created by Chapter 42 and although many have been addressed by the City, some of the more important ones still need attention.

We had been told by the Mayor and developers that the main thrust for Chapter 42 was to redevelop run-down apartments and strip centers, but no sooner had the SNA removed its objections, then the Mayor started backpedaling – offering to reduce the wait time for neighborhoods to establish minimum lot sizes and setbacks from 2 years for lots under an acre to 1 year for lots under 1/2 acre.  Small lots like this are not run-down apartment complexes.  They are neighborhoods like yours.  Fortunately, with help from CM Costello, SNA leaders were able stop these changes from going forward.

Underground street infrastructure for most of Houston is old and antiquated, so we want to be sure that high density building does not occur where the streets have inadequate storm sewers, water lines, and sanitation sewers. When the toilet flushes next door, will you get scalded?   But Jane pointed out that high density also makes every detail more important.  Where are trash cans stored? Where are mailboxes? Air conditioners?  With a requirement of one guest parking spot for every 6 homes, where do guests (and homeowners) really park?  In Cottage Grove, emergency vehicles cannot access many homes because too many vehicles are parked on narrow streets.  Ladder trucks needed for the 3 or 4 story homes need a place for support pads so they don’t topple over.  These were Fire Marshall concerns, too, not just Jane’s.

Average lot size can be as low as 1400 square feet, but there is no minimum lot size.  Permeable ground can be no less than 150 square feet on a 3500 square foot lot – tiny.  Chapter 42 and Chapter 9 are not harmonized; i.e., they contradict one another.  Chapter 42 requires green space which increases as the lot sizes reduce until at 1400 square feet 600 square feet of green space is required, but there is no minimum lot size .   More about that later.

Very dense development makes sense in areas that have good mass transit because then people can do without a car.  People who fondly remember brownstones in Chicago or New York forget that both cities have excellent mass transit and until recently, neither had the flooding concerns that Houston does.   Multiple small shared driveway developments scattered throughout a neighborhood creates a parking mess, increases traffic, and would probably remove the trees and shade that define the neighborhood’s character.  That doesn’t matter to somebody who only wants to make money, but it does matter to people who’ve searched for the perfect house for their family and have committed to a multi-year mortgage to realize it.

From the drainage perspective, neighborhoods in my area have been dealing with redevelopment of commercial tracts that have not adhered to City ordinances for detention or were granted unwarranted variances to do without.  We approached CC well before these properties were completed seeking help, but found none.  In a meeting on April3, 2013, CM Costello told SNA representatives that homeowners in my area were victims of a lack of enforcement. Had it been one instance, I would agree, but it was worse that – it was multiple occurrences of systematically ignoring ordinances that continues even now.  So unless we want recurrences of what happened in my area, before Chapter 42 is passed, we need legislation setting up oversight committees, clearly written enforcement criteria, and personnel dedicated to enforcement.  Keep in mind, though, that the area to service increases by 8.4 times that inside Loop 610, so this is not a small requirement.  All present politicians will be gone when this experiment is in full swing, so all uncodified promises are meaningless.

City Council has been told by Mayor Parker that the City needs density to generate funds, but it may be false economy.  Presently, growth is primarily in the extraterritorial jurisdiction (ETJ) around new activity centers of The Woodlands, Sugarland, Katy, the Energy Corridor, etc.,  so I expect that much of the new development will continue to be near these centers.  Chapter 42 affects the ETJ as well.  The further away infrastructure is, the more it costs.  Our water comes from Lake Houston.  Pumping that water across the entire City while maintaining flow and pressure is expensive. And if a development explosion occurs in a previously undeveloped area, providing the infrastructure may consume most of, or more than, the increased revenues generated.

Section 42-182 clearly shows that minimum lot sizes in the ETJ can also be reduced to 1400 square feet, although each lot of that size must have 720 square feet of compensating green space versus the 600 square feet required in the urban zone.  Compensating green space can be replaced by a recreational center, so clearly this is not to prevent flooding.  Normal lot size in the urban area without requiring green space is 3500 square feet and is 5000 square feet in the ETJ.  Plats in the urban area can be less than 1400 square feet as long as the average is 1400, yet under no circumstance can ETJ plats be below 1400 square feet.   The upshot of this is that if the City’s reason for doing Chapter 42 is to increase density inside the City limits in order to generate new revenue, then why are they increasing density outside the City to almost the same levels?  It makes no sense.

All this may not stem the migration to the suburbs either.  That’s being driven by jobs (Exxon, Noble Drilling, etc) moving to the ETJ and the construction of the Grand Parkway and its induced development.  Better schools, more property at a lower cost, newer construction, lower taxes, lower insurance, less traffic, etc., also affect the transition, not to mention that the size of the ETJ is more than double the existing City limits.  Why is it a surprise that there’s explosive growth?

High density developments in Jane’s area started as high-end properties drawing empty nesters looking to simplify their lives.  The aforementioned issues became apparent – parking, noise, traffic, etc.- so they soon became rental properties and the values began to slide.  It should not come as a surprise that many are inhabited by multiple singles splitting the rent, nor should it surprise that Jane’s neighborhood is the test bed for new parking ordinances, noise ordinances and who knows what’s next.

Common sense says that Chapter 42 should not be sprung on all 4 million people at once with most not understanding what it’s all about, particularly since so many people are unaware of its ramifications.  Just three days before the CC vote the Houston Chronicle wrote an OpEd about Chapter 42, but said that it applies to the area inside Beltway 8.  That’s wrong.  If the Chronicle Editorial Board doesn’t know what’s going on, why would City Council expect the rest of the City’s citizens to be any better informed?  At least give the Chronicle time to catch up.  Common sense says implement the changes inside Loop 610 immediately, test the results, then plan a staged roll-out into areas that have been identified as being served by adequate infrastructure or where infrastructure has newly been added in anticipation of densification.  Stage it with expansion of mass transit and commercial revitalization, improved drainage and detention.  But common sense does not seem to hold sway.

Chapter 42 and Growth

April 17, 2013

This is part of a continuation of a series of articles about Chapter 42 and its effects on the city of Houston.

After the City Council hearing on Chapter 42 on April 10th, 2013, it became clear that removal of the Super Neighborhood Alliance’s objections had paved the way for its passage.  Unfortunately, concerns about flooding were not abated and I’m not sure if the well-meaning City Council members understand that Chapter 42 will likely increase flooding and not stem the disparity between growth in the City and its extraterritorial jurisdiction(ETJ).  Depending upon which expert is cited, growth in the ETJ is somewhere between 5 and 10 times the growth in the City.  Developers used this argument to convince Mayor Parker to change the City from and urban/suburban City to a completely urban City – the largest urban-only City in the country; i.e., uncharted waters.  Herein we’ll attempt to shine a penlight into the murky waters.

The growth in the ETJ has been driven by many factors: lower housing costs, jobs, lower insurance rates, planned communities, less risk of flooding, less density, and better schools.  Historically, what prevented moving to the ETJ was the bad commute to downtown jobs, but jobs are leaving the City to relocate in the ETJ so the disincentive is now an incentive.   It should be no surprise.  No matter how big a slab of concrete was poured, within 5 years or so it was almost as clogged as it had been before with  the SW Freeway and I-10 being good examples.  Had Houston pursued commuter rail to give an alternative to the frustrating freeway delays, perhaps the situation would be different.  In the meantime the Grand Parkway (GP or NAFTA Highway, as insiders know it) is being built in the ETJ to service the increasing number of residents.  The GP has already induced growth along it’s planned route as new housing developments spring up to service the new jobs.

Can Chapter 42 bring the jobs back to Houston?  Maybe some, but the Mayor needs to find a way to sweeten the medicine.  Her “because I say so” approach is doing little, except helping her political opponents.  The issues raised by the SNA are real issues that deserve better answers.  Everyone knows that the drainage is defined in a different manual, and parking is in a different chapter, and noise is still undefined, but the reality is that they are all related to increased density, so all need to be addressed before moving forward.

It’s difficult to believe that the City spent 6 years on this one chapter and never considered the need to deal with related issues.  Now we are.  Chapter 42 and Chapter 9 need to be harmonized – right now they don’t agree.  It shouldn’t take six years, but it certainly should be given more than two weeks.


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.



Memorial Examiner article about Jim Blackburn’s presentation.

“A combination of actions by governmental entities and developers have exacerbated flooding problems in Memorial City and West Houston, environmental attorney Jim Blackburn said Wednesday.

Blackburn addressed the Memorial City District Drainage Coalition’s annual meeting on March 20, to a crowd of about 100 residents, including several Houston city council members and candidates for council positions, and representatives from Super Neighborhoods.

Blackburn said the flooding and drainage problems in West Houston aren’t isolated, that similar situations exist across the region.

But MCDDC is a unique group, he said. Blackburn used a presentation put together by members of MCDDC.

“This is one of the neatest collaborations I’ve worked with, and I’ve worked with a lot,” said Blackburn, who, besides being a partner in the law firm Blackburn and Carter also teaches at Rice University and is co-director of the SSPEED Center at Rice. “These citizens put together most of this information.”

This is the link to Jim Blackburn’s PowerPoint presentation from the MCDDC Annual Meeting on March 20th.  Several new slides were added (marked) to help tell the story.

What can I do?

March 27, 2013

During our meeting people began to realize that the increased density called for in Chapter 42 would worsen flooding.  They asked what they might do.  Below is my quickly written reply.  The hearing for Chapter 42 is April 10th, 2013, so we need to educate people quickly about what we can do and what we need to ask for.

Thanks for getting involved.  There are several things that you can do:

1) call and email politicians to let them know your concerns.  That includes your council member and all 5 at large members
2) talk with friends and neighbors to educate them about Chapter 42 and your concerns about it.
3) alert your civic association and super neighborhood about your concerns and your suggestions for a solution.
4) make plans to attend the April 10th hearing and sign up to speak.
5) contact your County Commissioner to ask for more detention in our area and ask the County to be more restrictive when they know the City is doing things that will cause more flooding.  While we may be in the incorporated area, what happens in the City affects the County and vice-versa.

Talking points are:
1) Suburban roadways were built assuming suburban densities so storm sewers are inadequate above 45% impervious cover. Chapter 42 allows up to 96% impervious cover for residential building so we should increase the City standard for runoff coefficient to 100% for urban areas and don’t assume that parks have a runoff coefficient of 18%, particularly for urban parks that are well packed from foot and bike traffic.
2) Too many variances have been allowed on new builds so there is too much concrete and not enough detention; i.e., do not grant more unwarranted variances.
3) Enforce existing ordinances.  Grandfathering wouldn’t as big be a problem if the ordinances had been enforced to begin with.  Once detention for a property is incorrectly calculated, under current rules it is grandfathered forever.
4) End grandfathering completely.  As you saw from the slides, the actual 100-year floodplains are dramatically bigger than FEMA indicates when runoff water is considered.  We live in a very flat subtropical area near a large body of water where heavy rain is always possible.  If runoff water cannot get to the drainage system, then flooding occurs.  The maps showed that in the majority of the area modelled, drainage is inadequate and structural flooding is likely to occur in a major rain event.
5) The Manning number used by the City (0.04) for open ditches assumes a nearly worse case for the ditch and optimal case for enclosed pipe, so it allows a large ditch to be replaced by a much smaller pipe, effectively reducing drainage capacity.   This was used in our area to dramatically reduce the capacity of the Bunker Hill Bridge, causing water to back up pipes and flood roads and homes.  It’s at least partially responsible for the severe flooding along I-10 feeder roads where the large ditches along the MKT rail line were replaced with much lower capacity underground drainage.  Choosing a smaller Manning number would require a larger pipe size, so for a City beset with drainage issues, assuming the same Manning number as concrete, for instance, would automatically add drainage capacity when a roadway is rebuilt with underground drainage.
6) Use low impact design practices.  This might be as simple as using permeable concrete for parking lots.  Other ideas are using cisterns (a water “retention” system) to capture rainwater for watering, rooftop gardens that reduce runoff, plant trees for shade and to absorb water.

We have years of bad building practices to overcome with diminishing opportunities to buy land to install the necessary large detention facilities.  After 3 hours of rain, land becomes water saturated and we have 100% runoff, therefore, even without grandfathering, we only mitigate for 50% of the covered ground used for development.  We should incentivize detention by providing breaks from the Rebuild Houston fee to those who add extra detention on their properties.

In “Drainage Attainment Districts” (DAD’s), my term, we can use a percentage of tax money from local homeowners and businesses to pay developers to store more water than is required on their property.  DAD’s would be set up much like a TIRZ, but would specifically require that area detention be installed; i.e, no grandfathering.  After the area’s detention needs are met and the cost of the facilities paid for, the tax would end, however exemptions from Rebuild Houston fees might extend for the developers as long as the detention remains in place.

I’m sure that there are many other ideas that you will uncover when your start talking to people.

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