A: Why did parts of Sienna flood?
B. Why did some portions of Sienna retain standing water and fail to drain when other sections of Sienna did not have the same problem?
Flooding in Sienna was caused by 34 inches of rain over four days. The system is designed to handle 8.5 inches over that period. The lakes, channels, and pumps were simply overwhelmed by the amount of rain. But nothing failed, everything worked as designed. This was just an event so far beyond anything that we had modelled or designed.
The areas that had the most water were those located near channels that flow to the South Outfall Station. Initially, the rainwater that falls fills the channels and lakes, so rain falling in a neighborhood on Friday and Saturday would have flowed into the Channels with no problems. What happed on Sunday and Monday was a result of the channels filling up and then getting out of their banks. The rain was falling faster than the pumps could pump it out, and with the channels already full, the additional rain had nowhere to go. There is about a 6-9 foot drop in elevation from NE to the SW in Sienna. As the water tried to drain out of the system and could not get out fast enough, it ultimately pooled at the lower natural elevations within the system. Note that Sunday and Monday rainfalls were not “light” with rainfall totals of 7-9 inches. Once the water gets out of the channel banks, it spreads out over a large area. The pumps were continuously pumping out the water. Because the area covered is so large and spread out, pumping down the first few inches takes the longest time. No one has ever modeled an event with this much rainwater in the system.
A. Did the pumps fail or were they stopped at any point during the storm? Everyone was saying that the levee and the pumps failed. Is that true?
B. If the pumps didn’t fail, why did it take so long for the water to go away? Are we going to get more pumps.
A. The pumps did not stop or fail during the event. There are 6 very large pumps in the south pump station that are capable of pumping 260,000 gallons per minute and 8 pumps in the north pump station capable of pumping 286,000 gallons per minute. We had people watching the pumps 24-7. They never failed. The social media reports of a local electrician fixing the pumps were false. He repaired pumps in another district.
B. When water gets out of the banks of a lake or channel, it spreads over a large area. You can think of it as an inverted triangle. As you pump that water out, the first inch takes the longest. As the water gets lower, it goes down faster. That why it appeared to be going down so slowly at first, but, in reality, it was going down at a constant rate…the rate of the pumps. As for more pumps, that will be part of the Event Analysis Report. Ultimately, options for any additional enhancements to the system above the design criteria will be presented to the Board.
How will SPLID handle the additional development planned for Sienna?
SPLID’s current capital improvement plan accounts for additional improvements to serve future development. The current plan calls for improvements to the channels, plus additional regional detention storage on part of the undeveloped land. In addition to the currently planned capital improvements, our Event Analysis will contain recommendations for enhancements to the system to reduce the risk of flooding for both existing and future development.
Why was I told I didn’t need flood insurance if I’m in a flood plain?
Unfortunately, there is a lot of confusion between when flood insurance is mandatory and when it is not, as well as when it might be a good idea, even if it is not mandatory. Flood insurance is currently only mandatory if you have an FHA loan on your house and you are in an area that has 1% chance or greater of flooding (100-year flood zone). Our levee system reduces the risk of flooding to less than 1% so no one in Sienna is in the 100-year flood zone. Therefore, no one is required to have flood insurance, but flood insurance is available at the lowest rate ($450/year).
Even if you are not required to have flood insurance, you should strongly consider having it. No flood protection system is failsafe. Flooding can still occur in these areas as a result of system failures or simply being overwhelmed. For example, if the Brazos River were to crest at an elevation higher than the levees (which are 4 feet higher than the 100-year event) flooding in homes would occur. While that is a very unlikely event, flood insurance is the ultimate safety net in case the unlikely occurs.
Why were supplemental pumps only brought in after the storm had passed? Why weren’t they brought in sooner?
No one has ever modeled a rain event of this magnitude. We simply did not know how much rain the system could handle. Our standard operating procedure does not account for ordering supplement pumps when all the pumps are working. The supplemental pumps were brought in to speed up getting water out of the system, and to handle the next event, not the one we had. At the time they were brought in, additional rain was forecast for the remainder of the week and there was a 20% chance of another tropical depression developing in the gulf. The supplemental pumps that are deployed in Waters Lake will remain there until November 1, when hurricane season ends. As part of our Event Analysis we will evaluate additional permanent pumps as well as having additional portable pumps available that can be moved around the system as needed.
Who is on the levee board and how are those positions filled? When do the current board members terms expire?
The Board of Directors is composed of three directors who are appointed by Fort Bend Commissioners Court. All three directors are residents of the District. Their terms expire in 2019. These positions are essentially a volunteer/civic duty position. The positions are not paid, except for a small per diem ($150-300/mo.). If you are interested in serving please contact the County. It’s a thankless task, as I’m sure you can imagine.
Kendall Beckman, President
(Term Expires 2019; Has served since May 1999.)
John P. “Bucky” Richardson, Vice President
(Term Expires 2019; Has served since August 2007.)
Temika B. Jones, Secretary and Assistant Vice President
(Term Expires 2019; Has served since July 2017.)
We received two questions on the evacuation order. 1st question: Why was the mandatory evacuation order not made sooner? 2nd question: The water in my street was only a foot and a half deep, why was a mandatory evacuation ordered?
First, SPLID cannot order evacuations or lift them for that matter. Only the County Judge can do that. We can, however, make requests to the Judge. During Harvey, SPLID requested the Judge order a mandatory evacuation of Sienna on the morning of August 28th. The request for the evacuation order was based in part on the water levels in the streets at that point, although we did not know what the internal water level would ultimately be. The mandatory evacuation was primarily based on the National Weather Service’s projection that the Brazos River would crest at 59 feet, which is 3.5 feet above the level the system is designed for. In addition, every road leading into and out of Sienna is impassible at that river level. That threat presented a significant risk of widespread flooding in Sienna, with no way into or out of the community. That is why the mandatory evacuation order was requested.
The Brazos River was projected to crest at 59 feet at the Richmond Gauge. My house is at elevation 63 feet, so why should I be concerned?
The Brazos River gauge in Richmond measures the depth not elevation. The bottom of the river is 27 feet above MSL, so if the river depth is 59 feet. The river elevation above sea level is 86 feet. That river elevation falls as it gets closer to the gulf. Without getting into detailed hydrology, if the Brazos River is at 59 at the Richmond Gauge, that level is almost to the top of our levees. It is also 6 to 12 feet above the slab elevations of houses in Sienna.
Where can homeowners who had damage from flood waters go for financial assistance?
There are two public resources that people can use to obtain financial assistance:
Unfortunately, the Texas law prohibits SPLID from spending tax dollars on grants or financial assistance to homeowners who had water damage from the flood. However, SPLID can request the central appraisal district do a reevaluation of the values of homes damaged by the storm (both tornado and flood victims are eligible for this tax break.) If your home was damaged, you must contact the CAD to get your home on the reevaluation list.
Should the foundations in the Sienna be poured at a higher elevation? How are pad elevations determined?
It’s not likely that it will be required for slabs to be poured at a higher elevation since the current elevations are sufficient for a 100-year event. Pad elevations are determined based on City/County plat requirements at 1 foot higher than the 100-year flood elevations in the section and adjacent channels being developed and minimum elevations above natural ground.
Will flood plain maps be re-drawn for the area and will our area be considered a “flood zone?” Who determines this and when could we expect it?
We don’t expect flood plain elevations to be redrawn, but that is a function of FEMA. Floodplain maps show areas with a 1% chance of flooding (100-year event) and a .2% chance of flooding (500-year event). The event was .125% to .1% chance (an 800-1000 year event.)
Specifically, what changes and improvements will be made to prevent flooding from occurring again? What is the timeline for this and who is paying for these improvements and any future maintenance?
SPLID has asked its engineers and operator to prepare an Event Analysis Report that will contain verified information related to Harvey and how the system functioned during that event. The report will also contain recommendations for enhancements to the system. There is no way to guarantee with 100% certainty that homes will never be flooded again. SPLID’s long-term Capital Improvements Plan currently calls for improvements to be made to 4 of the 5 major channels and an additional detention capacity in Sienna South as build-out continues. In addition, the engineers will analyze the data from this event and make recommendations to the Board for any enhancements to the system that might reduce the risk of home flooding from the type of rain event experienced with Hurricane Harvey. Any significant additional capital expenditures will likely require a bond election in May 2018 at the earliest. So ultimately, it will be up to our community to decide how “overbuilt” the system should be.
How will homeowners be able to monitor progress on these improvements, as well as any quality control measures and safe guards that are put in place? How often will we receive transparent and up-to-date communication regarding these issues and through what method of communication?
SiennaLID.org in now online to provide a vehicle for communications. The best way to monitor our progress will be to sign up for alerts on the website. In addition, the Board meets twice a month in a meeting open to the public. All of the plans and specifications are public records and may be requested at any time thru the website.
How will this flood impact the value of our homes moving forward?
In the short term, the Board will ask for a re-appraisal of damaged properties, which will provide some relief on property taxes for the effected homeowners. We can’t speculate on the long-term values, but we believe how our system performed in Harvey should give most people comfort in the effectiveness of the system.
How are you planning to create positive publicity for the Plaza, despite its new reputation as an area at risk for flooding?
SPLID has engaged a public relations consultant to help correct the misinformation reported in the traditional media.
Will SPLID consider hiring a 3rd party engineering company outside the LID engineers/LID district to assess ways to improve the efficiency of the drainage in the Plaza, Sawmill and future Sienna Plantation villages?
The Event Analysis Report will be peer-reviewed by a third-party firm who will review both the engineering and operational aspects of the system. The Report will be available to the public once it is complete.
There were reports that the levee failed, is that true?
No that is false. All 41 miles of the levee were inspected daily by drone, four wheeler, or helicopter. The levees performed as designed, and at no point did the levees fail or were they at risk of failing. One very small area had superficial top soil erosion that was discovered during the inspections. After our engineers consulted with the Corps of Engineers, that area was reinforced with sandbags as a precaution during the event. That area has already been permanently repaired and recompacted.
Why did the north portions of Sienna see less street flooding than the southern portions? Why does the north pump station have more pumping capacity than the south pump station?
Generally, the answer is because of different topographical features, and a fortuitous turn of events. The area of Sienna within the north levee outfall to Flat Bank Creek which is natural channel that happens be very deep compared to the surrounding land. That allows more water to get into that channel and out to the river faster. The north pump station has more pumps for two reasons: first, the water table in the north is very high, so water is constantly flowing into the system. The pumps have to account for that ground water infiltration, so they are slightly bigger than if there were no ground water. Second, the north pump station initially had half the number of pumps, but had a large detention pond. In 2001, the City of Missouri City purchased that land for its water treatment plant. As part of that project, the detention pond was replaced with additional pumps.