Briar Branch Creek (W140)

The Issue

MCDDC attended the TIRZ 17 Budget hearing in City Council Chambers on Wednesday, August 10th, 2011,  and presented  our concerns about a planned detention pond.  While MCDDC was pleased that the TIRZ has finally decided to add some much needed detention and we don’t want to seem ungrateful, the detention pond will only be successful if water can reach it.

Remember that water flows west to east in W140.   MCDDC has long complained that the new bridge built by TIRZ 17 is smaller than the old bridge and presents a restriction to water flow, backing up water in W140 and reversing flow in drains at Windhover so that they flood rather than drain the neighborhood.  We argued that the bridge needs to be enlarged as part of the same project as the channel widening and the detention pond, otherwise, water will not be able to access the pond.

Furthermore, we argued that channel improvements must be completed west of Bunker Hill Road prior to beginning any other drainage projects so that increased water from those projects could access the detention pond unrestricted.   The TIRZ’s plan is to: 1) build a 40 acre-foot detention pond on property east of the Costco property; and  2) rebuild W140 between the Bunker Hill bridge east to the detention pond.   Unfortunately, the Bunker Hill Bridge, which restricts water to the detention pond, will only be rebuilt when W140 west of the bridge is rebuilt.  Mike Talbot, Head of HCFCD, says that there are no CIP projects to redo W140 west of the bridge, which we explained to Mayor Parker and City Council.   Since TIRZ 17  Executive Director, Pat Walters, tied bridge construction contingent upon channel widening,  the bridge will not be rebuilt quickly enough to prevent flooding from other scheduled drainage projects.  In spite of our concerns, the TIRZ 17 budget and its list of mobility and drainage projects was unanimously passed by City Council on August 17, 2011.   More background from the Houston Chronicle.

What it Means

TIRZ 17 is floating a 60 million dollar bond and moving forward with various mobility and drainage plans.  The detention pond and W140 channel improvements east of the bridge will be completed in fiscal year 2013 (calendar year 2012), but two other “drainage” projects will be completed only a year later (fiscal year 2014, calendar year 2013).  The two other projects are Gessner Road between Long Point and I-10 (2 phases) and Witte Road between Long Point and I-10 (also 2 phases).

There are only two paths to Buffalo Bayou for water from these projects: 1)W140 (Brair Branch Creek); or 2) under Witte, under I-10, under Memorial City and into W151, which connects to Buffalo Bayou.   Even TxDOT’s I-10 water from Bunker Hill Road to just east of Conrad-Sauer must follow must follow the latter path to W151.  Notice in the picture of the TxDOT drainage system to the right that three 5′ by 8′ rectangular culverts  (cross sectional area = 120 square feet) flow into a single 8′ by 8′ box culvert (cross sectional area = 64 square feet).  What is not clear is how the 8′ by 5′ rectangular culvert under Witte Road ties into the TxDOT system.   The culvert under Memorial City also drains the entire Memorial City Mall  so is often rendered ineffective in a heavy Houston downpour.

Because the underground culverts under Memorial City Mall to W151 are impractical to enlarge,  during heavy rains water floods the I-10 feeder road floods and backs up under Witte to spill into W140 where they are conjoined.  Presently, W140 flows from Gessner Road east to Witte Road in an open ditch, then supposedly enters an 8′ by 5′ rectangular culvert under Witte  across from Pine Lake Drive and continues south in the closed culvert for about 75′ under Witte, whereupon  it exits the culvert into another open ditch east of Witte Road.  Water is going to take the path of least resistance, so if the culverts are full under Memorial City, I-10, and Witte and the I-10  feeder road is flooded, water is not going to flow into the box culvert, it’s going to flow out of it.

Claret Lane and the Drainage Study of Briar Branch Creek

What possible reason would TIRZ 17 have to intentionally make the Briar Branch Creek Bridge at Bunker Hill Road smaller than it previously was?  In order to understand this, we need some historical perspective about Claret Lane and the Brair Branch Creek Drainage Study.

History

One of the first actions of TIRZ 17 when it formed about ten years ago was to gather support for two east/west circulator roads north and south of I-10.  On the north side, the road was called Claret Lane and would have bisected Daniel Industries property, something they were very much against.  Daniel Industries hired people to organize the neighborhood to help fight the road by using two threats: 1) that they would also have to put a north south road across their property, tying into the existing Windhover Road, in order to satisfy federal road spacings along I-10, and, hence, large trucks would pass through the neighborhood; 2) Daniel Industries would sell their property and move; consequently, their gift donations for Woodview Elementary would cease.  The neighborhood organized and attended several Planning Commission Meetings en masse.   Neighborhood solidarity along with objections from  commercial property owners who would be negatively affected by the proposed Claret Lane,  resulted in TIRZ 17 withdrawing their request.

Of course, Daniel Industries had long planned to move and had discussed it at several employee meetings even before TIRZ 17 was formed.  The property was prime retail real estate, so they clearly didn’t want a road bisecting their property that might reduce its value.  Generally, the neighborhood adjacent to Daniel Industries was against Claret Lane, although the local Super Neighborhood (SN 10) had voted to support building the road as a way to reduce cut-through traffic.

Soon after the property owners won their fight against Claret Lane, Daniel Industries, then owned by Emerson Electric, placed a variance sign on their property.   As explained to the SN officers, Daniel wanted the ability to connect  another driveway entrance because they were considering a strip center along Bunker Hill Road.  When the variance made its way to the Planning Commission, the property was changed to be unrestricted commercial property.   The designation change allowed anything to be built without homeowner input.  MCDDC has archival footage of the various Planning Commission Meetings except the one where the property status was changed.  Video of that meeting has been misplaced in the City’s archives.

Shortly after the redesignation, Emerson Electric moved the manufacturing and engineering departments and sold the property to Fidelis.  Fidelis combined several properties and split off the property north of Briar Branch Creek.  Soon thereafter Trammel Crow Residential announced at a SN 10 meeting that they would be building an apartment complex on the part of the old Daniel Industries property that faced Woodview Elementary.  Once again the neighborhood tried to organize, but this time without deep-pocketed support of the commercial property owners.   Since plan approvals had already been signed off and permits granted,  the neighborhood was unlikely to win.  Instead of fighting, they decided to try to convince Trammel Crow to build a small bridge with a back entrance to their parking garage, and asked that Claret Lane be built along the backside of the Fidelis property, so that traffic wouldn’t endanger the kids walking to school.    We had no support from City Council.   Routinely,  people from the neighborhood who came to speak at City Council were scheduled to speak last,  after our Council Member,  Mayor White, and most other Council members were gone.

Prior to one City Council meeting,  a group of neighbors who had come to speak  were told  that Fidelis had agreed to Claret Lane;  however,  at a subsequent TIRZ 17 board meeting, a Claret Lane Feasibility Study was presented with great flourish.   It showed absurdly sweeping curves to move Bunker Hill traffic to Witte Road.   The route that was shown clipped properties on both sides of the existing ROW and would have necessitated removal of the neighborhood pool.    The obvious intent was to upset as many people as possible, from commercial property owners to homeowners, and was clearly a waste of public money.

Drainage Study of Briar Branch Creek

Conduit sizes needed to put Briar Branch Creek under Claret Road

Another later Feasibility Study was sneakier, because it was done under the guise of a drainage study and an effort to extend the Tropical Storm Allison Recovery Project (TSARP) floodplain maps.   It was the Drainage Study of Briar Branch Creek and was essentially done in order to assess the feasibility of enclosing the Creek in culverts so that Claret road could be placed over-top.   Presumably,  it was covertly disguised because Briar Branch Creek is located so close to homeowner’s back doors that the homes would become uninhabitable due to traffic noise.

Page ii of the Executive Summary discloses the purpose: “Improvement alternatives were considered for enclosing Briar Branch channel with storm sewer allowing the future construction of Claret Road over the existing channel alignment. A hydraulic model was used to determine the storm sewer infrastructure required to enclose the channel and provide a 100-year channel level of service without increasing the current risk of flooding. The 100-year event was chosen as the design storm because the existing channel provides a 100-year LOS for much of the study limits. The analysis determined that though it is possible to replace the channel with a storm sewer system, the design process must be careful to allow the sheetflow from the surrounding areas to be collected into the system without adverse impact. The construction cost for the storm sewer infrastructure is estimated to be $11.7 million, not including the cost of the proposed roadway.”

Dual 7′ by 7′ box culverts showing the 12″ steel cased water pipe and the 42″ and 30 ” sewer lines.

While it makes up only a small part of the Executive Summary, enclosing the creek dominates the discussion in Section 5, Preliminary Improvements Alternatives.  In Section 5.2, Enclosing Channel with Box Storm Sewer, Table 2 defines the culvert sizes needed to enclose the Creek and defines the bridge as two 9’ by 7’ RCB’s, although drawings on file show 7′ by 7′ RCB’s were actually used.  Culvert sizes were based upon previously derived TSARP data.

Physical measurements of the culvert show that it is 7′ by 7′ with a 12″ water pipe partially blocking flow.  Entering on the sides of each culvert are 42 inch and 30 inch sewer pipes that will also restrict flow.  It is clear from the design of the bridge that it was built assuming that a it would be possible to enclose W140 entirely in culverts.  The  possibility of  enclosing the Creek inside culverts still exists.

Technically Correct versus Morally Correct; Determining Channel Flow

Engineers call them boundary (or initial) conditions.  They are assumptions made or estimates of the conditions existing at the edges of a model.   In order to calculate flood plane maps east of Blalock Road, engineers established an estimate of the water flow in W140 at Blalock.   As Derek St. Johns discusses in the text, these numbers are an extension of the Tropical Storm Allison Recovery Project (TSARP) flow numbers that were used to redefine the FEMA floodplains for the area east of Blalock Road.  At City Council, MCDDC explained that the TIRZ was within its legal rights to use this numbers.  Morally, they are on shakier ground.   The table in the upper right hand corner for  Exhibit 4 from their Briar Branch Creek Drainage Study shows that LAN calculated the overland sheet flow and found that substantially more water should flow in W140.  Rather than point out to FEMA that their numbers are too low, LAN consciously chose to ignore their own numbers.

LAN claims that W140 begins at Gessner, although HCFCD maps and the City’s GIMS say that it starts near Conrad Sauer.  In any case, W140 is no longer an open ditch west of Gessner, although there is an open drain at Gessner and W140.  Since that area floods frequently, it’s likely that water comes out of the open drain and into Briar Branch Creek. At the City Council hearing, MCDDC presented straight line approximations of the flows in W140 to show the differences in flow under the bridge.  While straight line approximations will not be as accurate as the HEC-RAS modeling used in the Study, to a first order errors will scale.   For City Council, MCDDC presented drawings of three straight lines on the map:

  • a line starting at zero using TSARP numbers (1088cfs) for the endpoint;
  • the sum of the 100-year peak discharge from Exhibit 4, which includes water from west of Gessner, so starts at 1150cfs at Gessner  and ends at 3642cfs at Blalock;
  • and a third line that removes all the water from Region 1 west of Gessner, so goes from zero at Gessner to 2492cfs at Blalock.
Rather than 515cfs at Bunker Hill calculated by LAN using HEC-RAS, a straight line approximation would be about 620 cfs.  Using the second line that assumes nonzero flow at Gessner (1150 cfs), flow under the bridge should be 2670 cfs.   And the third line which assumes zero flow at Gessner,  flow was calculated to be about 1420 cfs.  Any engineer that finds over 4 times difference between the overland sheetflow (2670cfs) and the “TSARP” numbers (620cfs) is both morally and professionally obligated to look  for a cause.  It seems as though the TIRZ engineers calculated the flows based upon what they think the creek will carry rather than the amount of water that the creek should carry.

100 year Floodplain

MCDDC showed City Council the 100-year floodplain from the Briar Branch Creek Drainage Study versus the one from the new TIRZ 17 Regional Drainage Study (RDS) and included a version expanded to make comparison easier.  Please click on each link and look at the areas that the maps show should  flood in a 100-year event.  We knew that the previous maps were incorrect and the RDS dramatically shows just how wrong they were. Literally for years, people in the neighborhood have been showing the TIRZ Board and City Council pictures of flooded areas which the 100-year floodplain map showed should not flood.   Without understanding why, they knew that the Study was wrong, yet the bridge was built undersized anyway.  Later, hydrologist Larry Dunbar explained what had been done.   Had the maps been done correctly, it is likely that the entire Fidelis property would have been in the 100-year flood plain and Fidelis would not have been allowed to raise their property without mitigating one-for-one; for every acre-foot raised, an acre-foot of detention would be required.

Bunker Hill Bridge

A Corvette is a little over 4 feet tall and more than 3 Corvettes would stack under the bridge so the bridge height is over 12 feet.

Especially after a major event has showed that design was flawed, it is relatively easy for a trained hydrologist to look at the report and determine that it is completely in error.  That should have been made clear by testimony before City Council.  In April 2009 we had just had a rain event that is estimated to have been somewhere between a 10-25 year event for the particular neighborhood adjacent to Briar Branch Creek.  Over 200 homes reported flooding, although many more probably were flooded but chose not to report anything.  Yet 100-year floodplain maps generated by LAN in the Drainage Study of Briar Branch Creek show no house should have flooded.   The TIRZ 17 Regional Drainage Study shows the effects of a 100-year event and it is clear that it more accurately models what actually happened.  According to affidavits from people who live along Briar Branch Creek west of the Bunker Hill Bridge, on the morning of April 28th the Creek overflowed its banks.  Hence, the volume of water exceeded what the Bridge was capable of passing.

Okay, so let’s make this clear.  The new Bunker Hill Bridge was incapable of passing the volume of water present on April 28th, which we know was less than a 100-year event.  So the question is why didn’t the TIRZ build the bridge larger?  The clear answer seems to be that increasing the culverts by 3.5 times would dramatically increase the cost and most likely would not fit under the proposed roadway.

 How big was the old bridge

MCDDC has maintained for years that the old bridge was larger than the new bridge, but in order to prove it conclusively, we need to have the original engineering drawings.   Requests for copies of those from PW&E have resulted in “there aren’t any.”  From HCFCD, we found drawings of a bridge that was never there.  When we obtain real engineering drawings, we’ll post them.  In the meantime we used measurements made from a photograph: Briar Branch Creek bridge with measurements.

Another view of the old bridge

Basically, we know that TxDOT requires pedestrian guardrails to be 42″ high so we used that as the basis for measurement.  Because the camera position is closer to one side than the other, the bridge width is probably too large.   For the similar reasons, bridge height is probably too low.   Bridge width is estimated to be 24 feet across by 13 feet high or an opening of 312 square feet.  Sediment and rip-rap have filled in the sides so that the bottom is flat for approximately 6 feet or more.  Very simple area calculations  show that the old bridge was around 3 times larger.  Even with a 50% error in our most conservative bridge measurements, the old bridge would still have been over 1.5 times larger than the new bridge.

The culvert sizes from the drainage study are significantly smaller than the cross sectional area of the open ditch.

Speculation

What is difficult to understand is how tenaciously the TIRZ Board clings to the idea that the two bridges are of equivalent size.  The new Regional Drainage Study shows that most of the area is likely within the 100-year floodplain, yet the 100-year floodplain maps generated from the Briar Branch Creek Study show no homes flooded.   It is irrefutable fact that the homes did flood, and that they did so in something much less than a 100-year event.   This is the same flawed analysis that generated the culvert sizes for the bridge.  Although the Briar Branch Creek Study was flawed, the TC&B Bunker Hill Road Drainage Study was even more so, because its analysis showed an even smaller bridge size culvert was adequate ( dual 9′ by 7′ versus dual 7′ by 7′).   And rather than adding drainage pipes to account for the increased impervious cover of the road and sidewalk, the additional 4.4 acre-feet of water was  “captured” on the roadway surface between the curbs.  HCFCD requested, and obtained, a guarantee that the Bunker Hill Road project would not cause adverse impact up to and including a 100-year event.   Adverse impact has been caused ~ so~

The old bridge prior to reconstruction

Dual 7′ by 7′ culverts under a lowered Bunker Hill Road

Since the bridge was obviously built with the possibility of enclosing the Creek inside culverts and building Claret Road over top, it makes sense to look at the impacts such a structure would have.   Furthermore, Claret Road has recently been brought up again by the TIRZ Board Chairman.  As late as  September 16th, 2011, HCFCD has no projects on their CIP or is aware of drainage work that would increase capacity of W140 before the Witte and Gessner drainage projects are done, yet we have recently been informed that the Bunker Hill Bridge and the Witte Road Bridge will be built concurrently in 2013 and that W140 channel improvements would also be “substantially completed” in 2013.

Paragraph two from 5.3.1 of the Preliminary Regional Drainage Study says:

Existing cross structures at Witte Roads will need to be increased in size from 2-48” RCP’s to 2-5’x5’ RCB’s to compensate for the increased channel conveyance to maximize the benefits of the proposed improvement and to match the lowered channel flowline.

This quadruples the amount of water entering Briar Branch Creek, yet after the August 26th, 2011, TIRZ 17 meeting, TIRZ hydrologist Derek St. John informed the local Chronicle reporter that no additional water would enter the Creek from these projects.  Why would drainage projects be built that will convey no additional water to the detention pond  designed specifically to accept their water?

Enclosing the Creek within culverts would prevent the water from overflowing  into the neighborhood from  back-flowing in existing drainage pipes, but Briar Branch Creek from Gessner to Bunker Hill would also need to be enclosed or water would simply outflow in the open drains west of Witte.   If  W140 were enclosed completely in the culverts  sized as originally proposed in the Drainage Study of Briar Branch Creek, matching the culvert sizing in the Bunker Hill Bridge, then the overall capacity of the Creek would be reduced.   In an extreme event, water cannot flow south to the TxDOT/W151 system, so water would either need to be stored somewhere else or it would back up in the sewer system under Witte, overwhelming the privately owned 15 acre-foot pond north of the Westview and Witte intersection and possibly  flood neighborhoods further north.  If this possible scenario is being considered by LAN for TIRZ 17, then the rapidity and lack of transparency with which these projects are being designed and built will provide very little time for analysis, much less prevention of increased upstream flooding.