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Comments on the Revised Chapter 9 of the IDM

Update:  The public meeting on Wednesday June 12th has been cancelled.

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 City’s savior by several Houston Mayors, but they are not.  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 640 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, and 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.  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 for the June 12th meeting 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 60000 homes from the 100-year floodplain.  Some of the detention ponds are quite large.  Eldridge Detention Pond is 4500 acre-feet and Arthur Storey Park is 3500 acre-feet, yet Bellaire Boulevard at Beltway 8, very nearby, 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 ponds, flooding in SW Houston occurred along Brays Bayou.

 

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