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.
What is missing is removal of “Grandfathering” (see below) and a significant decrease in detention requirements for lots 15000 square feet or less, which represents the vast majority of residential properties. 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.
- 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 . . .”