You're reading...
Uncategorized

Chapter 9 Infrastructure Design Manual

          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 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 alreadyhave 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.

•    Reduced Detention and Drainage Capacity

  • Our drainage system is designed for low density 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.

•    Rising Insurance Rates

  • Biggert-Waters Flood Insurance Act of 2012 mandates rates based on actual risk of flooding.
  • Flood maps are being revised to capture true costs of structural flooding.
  • 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.

•    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 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 more than 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 . . .”

Discussion

One Response to “Chapter 9 Infrastructure Design Manual”

  1. The TTI Committee chaired by CM Green will hold the hearing promised by the Mayor over a year ago to review changes in Chapter 9 of the City’s Infrastructure Design Manual. The IDM is not under direct control of City Council, however, the City Code of Ordinances is. Chapter 19 of the Code of Ordinances governs how the City handles floodwater mitigation and is essentially our City’s guarantee to FEMA that we will do everything possible to prevent a 100-year flood. In other words, City Council has an obligation under Chapter 19 to make sure that Chapter 9 of the IDM supports our responsibility to FEMA.

    Houston enjoys a FEMA Community Rating System rating of 5, 4th best in the 872 communities evaluated. One is best and ten is worst. A 1 qualifies for a 45% FEMA insurance discount while a 5 provides a 25% discount. For reference Harris County is rated as an 8 (10%) and the national average is about 7.6.

    Posted by EdB | March 30, 2014, 2:56 pm

Leave a Comment