Collusion or Incompetence–Flooding in West Houston
January 29, 2013: Ed Browne & Cyd Dillahunty met with our attorney Jim Blackburn to discuss the recently published Rebuild Houston Ten-Year Draft Plan. Mr. Blackburn has committed to address our Annual Meeting on Wednesday, March 20th, in the Memorial Middle School Auditorium, on the topic “Collusion or Incompetence: Flooding in West Houston.” His presentation will provide an overview of flooding and drainage concerns in our area.
Before leaving for another meeting, CM Pennington made two notable comments: He said that infrastructure was his number one priority and also said that our area was “in the middle of the pack” on the list of projects on the city’s list. [A visit to www.rebuildhouston.org will show that the area around Springrock south of Westview is a Category 5, the lowest need. Also, the north end of Hollow Lane is a Category 5. This almost guarantees no CIP projects to correct flooding in these two areas.]
CM Bradford stated that it was the city’s view that their job with regard to TIRZ was to approve the budget and to appoint the new board members. Three new board members have been on TIRZ 17 only long enough to attend two meetings. Bradford urged us time to allow the new board members to right the wrongs of the past.
Lois Myers asked repeatedly of the panel why the four contracted detention ponds have not been put into place and why hadn’t the city upheld the contract. Potok said he was unaware of the contract between TIRZ 17 and the COH dated 2003. Lois said she would get him a copy.
John Rickel and Bob Tucker are two of the new TIRZ board members. Both live in the affected areas and formerly were on the other side of this issue so they are well aware of the issues. Bob expressed “great hope” for the future and said the new board is “far more open” to community concerns. NewTIRZ board member Rickel asked LAN engineers for an updated drainage study yesterday (12/12) taking Strey Lane out of the drainage solution and identifying an alternative path for water to flow to Buffalo Bayou.
The TIRZ will focus on drainage and the best use of their monies so the community gets the most drainage in the most cost effective way possible; “more detention is what we want” said Rickel. He added that the Barryknoll east project has been approved and will include a 40 acre detention pond; 30 acre feet is dedicated to flooding, not new construction. This project will be $26 million. However, it is up to the city to provide the channeling to the detention from W140.
COH monies cannot be used in a TIRZ area; only TIRZ money can be used for projects within the boundaries. Rickel brought up the fact that TIRZ 17 is only 800 acres big and all of the outlying areas that are affected by TIRZ projects are under the city and county umbrella. Therefore, coordination and cooperation are needed between the entities to solve the issue.
Bradford said flooding is a regional issue and should be looked at holistically instead of piecemeal as has been done in the past.
It was agreed by many parties that the current Tallowood project, costing $900,000 is a waste of money and will dump more water into W153. Roberta Prazak and Hugh Rawl asked why the Tallowood project was being rebuilt without looking at the RDS. PW&E Menendez did not have good answers why Hugh’s email was not answered.
Keith Brown spoke for the City of Bunker Hill Village. They are opposed to any increase in water down W151. The Strey Lane project is unavailable to the TIRZ. Bunker Hill Village said that the W151 bridge at Memorial Drive will not change in cross sectional area.
John Rickel stated that TIRZ 17 is specifically focused on two things: Mobility and Drainage. He said that they have requested that LAN update the RDS to reflect that Strey Lane is off-the-table. He agrees that TIRZ 17 money is limited so they need to get the most bank for the buck and work in partnership with HCFCD, TxDOT and COH.
Wes Holmes was concerned that there have been a lot of studies, but too little action.
Virginia Gregory repeatedly offered the solution to detention on the north side of I-10 to be constructed under Cross Point Church or in Hayden Park. The current detention on the east side will be rendered useless when Witte is reconstructed. Virginia Gregory shared a letter from Mayor Parker with Daniel Menendez of the PWE that stated the Hayden Park idea was not being looked at because it was deemed unacceptable. Virginia asked for the name of the engineer who gave this information to Mayor Parker; Menendez did not know the answer and was unaware of the issue. At a meeting later, CM Brown said she would reach out to the church to speak with them about the idea.
Ed Browne said that the COH prioritizes projects for thoroughfares first and neighborhoods last, so channeling will not happen. COH doesn’t have money. Menendez refuted these statements and recommended we visit the rebuildhouston.org site for details about upcoming projects which were divided into thoroughfares and drainage lists. Later, CM Bradford corroborated Ed Browne’s assertion that major thoroughfares have priority over neighborhoods. He said that he feels this is wrong because people living in flooding neighborhoods need to be able to get to major thoroughfares to escape.
Ann Givens spoke about her neighborhood’s flooding and hasn’t been given any attention. She said that NSR465 has not been given any priority.
Christina Walsh asked if the TIRZ Board has any possibility to modify the Budget as passed at CC. John Rickel suggests that he will try to modify the budget in order to reflect needs better, specifically projects that do not properly address where to put the water. John also pitches the TIRZ Workshop.
Daniel Menendez says that he doesn’t know anything about the TIRZ contract between the COH, TIRZ 17 and the Memorial City Management District. He commented that the TIRZ never submitted additional CIP projects, necessary to make the drainage projects, work to the City.
TIRZ invited everyone to a “workshop agenda” meeting to be held January 8 in the HCC Theater Building (NE corner of I-10 and Beltway frontage roads) at 5:30 PM. This is an endeavor to have dialogue with the community. Urged we submit our detailed questions for the engineer ahead of time so the dialogue would be improved. The format will be to go waterway by waterway and focus for a length of time on each one.
This meeting will be a chance for the public to ask questions about flooding issues in our area. Although you’re sure to have your own questions, here’s a list compiled from previous meetings and emails that will give you a start.
W140 – Briar Branch Creek
The drainpipe carrying water flowing south under Witte Road, on its way to W151 south of I-10, is conjoined with W140 (Briar Branch Creek) going to the east. When W151 is overburdened, it first backs up at I-10, then begins to overflow into W140. As more water flows down W151, detention under the I-10 feeder roads overflows, causing the feeder road to flood and water to flow out of W151 into W140. Pipes that normally drain the neighborhoods north of Briar Branch Creek begin back-flowing water out of W140, causing the neighborhoods to flood. New TIRZ projects on Gessner and Witte will move more water to W140. There is also a possibility that the W151 will be severed from W140 just south of their conjoining. TIRZ engineers have said that their proposed improvements will provide minimal help for the neighborhood adjacent to the new detention pond.
1) Can the W140 channel be widened and deepened?
2) Can the opening under the bridge at Bunker Hill Road be increased so that water can be conveyed from the neighborhood to the new detention pond?
3) Can the TIRZ look for other possible detention locations along Witte that can be used for detention, either under structures like parking lots (e.g., SBISD bus barn) or open ponds?
4) Can the TIRZ ensure that water from the conjoined W151 and W140 can get to the new detention pond east of Bunker Hill Road?
5) If the TIRZ cannot implement the improvements identified in the Regional Drainage Study to help remove water from the neighborhood, can the City do it?
6) Can the TIRZ use the RDS to rank order the CIP projects necessary to improve the drainage in neighborhoods adjacent to W140?
7) Can check valves be installed to prevent water back-flowing through existing drain pipes into neighborhoods?
8 ) Can new pipes be installed under Pine Lake or other cross streets to bypass the Bunker Hill Bridge and move neighborhood water further downstream?
9) Can we determine why the neighborhood adjacent to the new detention pond may not benefit from it? Are there alternatives that do help?
10) Why didn’t Fidelis, at Bunker Hill and I-10, need to have detention on their property?
11) Why did the COH allow Fidelis to raise their property and where did they expect the water to go?
12) Why was The Room Store at Witte and I-10 allowed to raise their property and why isn’t there any detention there?
13) Does water flow into the drain at Gessner and W140 or flow out?
14) In a heavy rain, can any water in open ditch W140 flow into closed pipe W151 under Witte Road or will water only flow out of W151? How can you tell?
15) There has been some discussion of severing W151 south of W140. This is a 7’ by 7’ box culvert. Can W140 handle the extra water? Where will it go?
16) Has HCFCD agreed to improve W140? If so, will it be concrete lined or enclosed? Will they need extra right of way?
17) Can underground detention be installed at Hayden Park, Crosspoint Church detention pond, under SBISD bus barn parking lot or other properties along Witte?
18) Why is the TIRZ paying for a landscape architect for a detention pond neither visible nor accessible to the public?
19) The provisions of sale for the land used for the detention pond require specific maintenance, no concrete, no straight lines and landscaping. Who in the COH reviewed this contract? Will HCFCD be able to take over maintenance?
W151 – Stoney Creek
General problem –
When W151 south of I-10 and north of Memorial begins to fill with water, the level quickly exceeds the elevation of pipes designed to drain into W151 and water begins to backflow into neighborhoods. W151 gets water from as far north as Neuens Road and TxDot water from Bunker Hill Road on the east to Frostwood/Conrad-Sauer on the West. The 60 acre-feet Conrad-Sauer detention pond is also pumped into the TxDOT I-10 system that drains into W151. The system cannot carry this amount of water.
1) Instead of sending TxDOT I-10 water through pipes under Memorial City Shopping Center, can water be redirected into existing detention ponds (Conrad Sauer “Golden Bathtub”) or can new ponds be built by purchasing vacant land near W156 and the I-10 feeder road?
2) Can the timing of the pumping system for the Conrad-Sauer detention pond be modified to pump water out during a storm only when the water level becomes excessive, fully emptying only after the rain has stopped, in order to minimize street flooding along the I-10 feeder road?
3) Can water from the Conrad Sauer detention pond be redirected to W156 rather than W151?
4) TxDOT has not built three of the detention ponds that were promised in the settlement with the Katy Corridor Coalition to mitigate flooding due to I-10 widening. Can the City and TIRZ ask TxDOT to fix flooding along the I-10 feeder roads west of Bunker Hill Road?
5) Moving water from Frostwood to Kingsride to Barryknoll, bypasses the W151 bottleneck under Memorial City, but increases the amount of water in W151 south of Barryknoll. To avoid increasing downstream water, can local detention can be added under all of these roads during construction?
6) Rather than assume water from Frostwood and Kingsride will be moved down Barryknoll to W151, can TIRZ 17 find alternative paths to Buffalo Bayou (Tallowood, Gessner, Plantation, etc.)?
7) Can a detention pond be added in front of the Great Indoors or Sam’s Club parking lots?
8 ) Why can’t detention be added in Susan Kellner Park and Bunker Hill Elementary’s playground at the northern end of W151?
9) What can’t detention be added underground in the Memorial City Shopping Center parking lot?
10) To provide additional detention, can W151 be reconstructed with large underground box culverts on either side of the main channel?
11) While Gessner is being reconstructed to raise the roadway six inches north of I-10, can culverts be installed under the lanes? Installing 10’by 10’ box culverts under each of the six lanes creates a total detention of between 25/30 acre-feet.
12) Can culvert sizes be maximized for in-line detention on all TIRZ projects?
13) Can we increase the depth and width of the drainage channel north of Memorial Drive, while keeping the flow restricted by the size of the bridge opening at Memorial Drive? Will the bridge over Stoney Creek have the same cross-sectional area?
14) When Witte Road is rebuilt, will the 15 acre-foot Crosspoint detention pond be rendered useless? If so, will it need to be rebuilt? Who would pay to rebuild it? If it is not rebuilt, then the water would need to be redirected to the new detention pond, reducing its capacity.
15) Whenever new buildings are added, can the TIRZ offer to install underground detention under the parking garage or parking lot? Memorial City needs more parking. When the next parking garage is installed, can COH or TIRZ convince the builder to allow detention to be installed underneath? What about detention under the new Metro National building at the NW corner of I-10 and Gessner?
16) HCFCD requires that any new water being added to Buffalo Bayou be mitigated one for one. Does the TIRZ know how much upstream detention will be required for all the projects that it intends to build? When will HCFCD have upstream detention set aside for TIRZ water? Will the COH or TIRZ have to pay for this detention?
17) Knowing all the concerns about flooding within the TIRZ, why has the COH not tried to find ways to force developers to add detention on their property? There have been numerous opportunities along Gaylord that are now gone. Are they unsympathetic to flooding? Won’t flooding hurt property values?
18) How many acre-feet of in-line detention are being added for the new TIRZ projects?
19) Was the RDS used to model drainage down W151 or other channels other than Strey Lane? If not, why did the TIRZ assume Strey Lane as the only option?
20) Can the RDS be updated to account for additional water on Gaylord and other changes within the TIRZ?
21) Drainage from tall buildings builds up a lot of velocity and force so takes precedence over overland sheetflow. Was this considered when designing the drainage systems for the new high rises near Gaylord? Can this be modeled in the RDS?
22) Why were flow patterns within TIRZ 17 not mapped, but flow patterns outside TIRZ boundaries were? Isn’t it important to know how the water flows inside the TIRZ, if for no other reason than to accurately be able to model flows outside the TIRZ?
W153 – Hollow Creek
General problem –
When the Fonn Villas project was constructed, water from as far north as I-10 was redirected into W153 instead of an existing line along Beltway 8. The size of drains and open channels flowing into the creek exceeds the size of pipes under Memorial Drive creating a choke that restricts water from flowing out, so Hollow Creek becomes a classic detention pond. Currently a COH project is being constructed under Tallowood to move water within the W153 watershed, solving nothing. In their Charting the Buffalo study, HCFCD identified several possible detention sites, including 12505 Memorial Drive.
1) Did the COH use the RDS to analyze flow in the W153 while designing the Tallowood project? Since it would have saved $900k, why not? Who authorized and designed this project?
2) Rather than building a pipe to the Bayou, which will require upstream detention, something that may take many years to achieve, why not build a detention pond at 12505 Memorial that can hold between 50 and 60 acre-feet? If underground detention is installed, the land could be dual use.
3) The TIRZ Regional Drainage Study shows an 8’ by 8’ box culvert under Tallowood, which LAN modeled as connecting to Buffalo Bayou through an undefined path. Although this is outside the TIRZ zone, so was Strey Lane, which the TIRZ tried to partner in. Could the TIRZ, the COH and HCFCD collaborate to install the large pipe under Tallowood from at least the W153 bridge southward?
4) Can the COH and TIRZ not construct any more projects that drain into W153 north of Memorial?
5) Can the TIRZ use the computer models that were developed for the TIRZ Regional Drainage Study to identify the most effective drainage solutions, then prioritize TIRZ/COH/HCFCD construction plans to implement those first (applies to W140, W151 and W153)?
W156 – Rummel Creek
1) Given that City Centre and about half of the TIRZ area north of I-10 drain into W156, should it now be added to the RDS?
General flooding solutions for all watersheds
1) End the practice of “Grandfathering” properties. In a semitropical city, anything that increases the floodplain should not be tolerated.
2) Enforce existing drainage ordinances.
3) Do not allow unwarranted variances that would decrease drainage or detention.
4) Scrutinize drainage reports better to prevent “cheating” on required detention.
5) Do not allow properties to be “raised” by adding fill dirt without properly mitigating for the displaced flow.
6) Prior to construction of any drainage project (e.g., Fonn Villas), study the receiving basin to determine that it can accept additional water without flooding concerns.
7) Begin migration of all future projects to two dimensional flow analysis models so that unintended consequences (e.g., flow reversals) are reduced.
8 ) Address all drainage projects on a “Global” level so that unintended consequences are reduced; that is, address impacts on adjacent properties too.
9) Rather than designing in a vacuum, use the Super Neighborhood (SN) program as former Mayor Brown had intended and funnel information from the people who know the flooding patterns best to the engineers trying to solve the problem.
10) Keep the SN’s involved through regular meetings with residents of the affected area.
11) Allow SN’s or their designated representative(s) access to preliminary engineering documents prior to release for bidding so that workable solutions can be worked out prior to homes being flooded.
MCDDC Board Members spoke via telephone with attorneys Jim Blackburn and Mary Conner regarding the status of our lawsuit. Our attorneys have been working on getting the facts absolutely straight and drafting the pleadings for the lawsuit which will utilize a combination of constitutional & state statutory claims. We have decided to delay the filing of our lawsuit until after two upcoming drainage meetings: one will be hosted by District A CM Helena Brown on December 13th (6:00 p.m. at the Sosa Center on Wirt Road) and the second will be organized by the TIRZ 17 Board and is expected to be scheduled in mid January.
Tuesday, November 6, 2012, Public Comments: After a two week delay of the originally scheduled vote, the TIRZ 17 Budget was again on the agenda for vote on Nov. 7th. MCDDC Board Members and other concerned citizens addressed the Mayor and City Council citing specific issues with certain projects that are believed to be poorly designed and will cause problems downstream and/or represent large budget dollars that could be better spent elsewhere with a greater benefit. (Video of City Council meetings including Public Comments can be found on the city’s htv webpage — http://www.houstontx.gov/htv/.)
Tuesday, October 23, 2012, Public Comments: MCDDC Board Members and other concerned citizens addressed the Mayor and City Council regarding the TIRZ 17 Budget for 2013 and CIP 2013-2017 which was on the agenda for approval the following day. Most speakers requested the delay of the vote particularly in light of the recent changes to the TIRZ 17 Board (three new members out of seven, including a new Chair). After Public Comments were concluded, Board Members met with District A CM Helena Brown and her staff. CM Brown prepared a press release (http://www.houstontx.gov/council/a/press/20121023.pdf) supporting delay of the budget vote. Efforts resulted in a two week delay of the vote.
The 7-member TIRZ Board, with a new chair and three new board members*, met before a crowded HEB Community Center to discuss their 2013 Budget and 2013-2017 CIP. Numerous residents expressed concern that the proposed projects would not result in drainage relief and might even make it worse. Rafael Ortega, who is VP of the engineering firm Lockwood Andrews & Newman (LAN) and directs the firms Large Diameter Business Group which performed the engineering for these projects, presented a brief description of the TIRZ projects that are on the front burner — Barryknoll East drainage & road improvements, Briar Branch (W-140) stormwater detention basin, W-140 channel improvements, N. Gessner/N. Witte drainage and roadway improvements and Lumpkin Road drainage and roadway improvements. Based on concerns from residents about some of these projects, it has been suggested that a workshop be organized with representatives from the community, LAN and Harris County Flood Control District in order to talk through some of these concerns.
*New Chair: Ann Givens
New Board Members: Bob Tucker, John Rickel and David Hamilton
Board Members who resigned: Ken Arnold, Chuck Turet (former Chair) and Dan Moody
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.)
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.
Section 9.04 D. Development – The term includes New Development, and In-fill/RedevelopmentDevelopment.
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
(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
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.
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
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.
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 9.05 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).
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.
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.
Tired of worrying about being flooded? Tired of having our constitutional rights taken from us? Too many times after the April, 2009, flood we were told that it was an “act of God” and “Houston floods” as the explanation for flooding. Having testified time and again that missing detention, increased concrete, bad engineering and unenforced ordinances would cause flooding, we knew better. Frustrated, a group of neighbors banded together to hire attorney Jim Blackburn to fight the governmental powers that are doing this to us. We need your donations to stop this illegal seizure of our land. If we don’t act, the situation will only worsen.