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The original item was published from 9/15/2022 9:59:44 AM to 9/15/2022 9:59:49 AM.

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News Flash

Posted on: July 13, 2022

[ARCHIVED] Diving into Water issues with Mayor Pro Tem

Boards on Dam

The City of Llano Council and staff understand that many of you may have questions and concerns about the status of our water situation. Please understand that we have been working in parallel paths to gain needed information, reach out to appropriate resources, evaluate the existing dam structure, and evaluate the flashboards that were used by the City in past years.


During the May 16th city council meeting, a small Water Planning Group was delegated to evaluate the City Dam and flashboard system for installation, look into a bathometric survey of both City Lake and Robinson Park Lake, and gather information to present to council about current and future situations and options. Prior to this May 16th meeting, weather and flow conditions were monitored. May 1st, the average flow rate of the Llano River in town was 66 cfs (cubic feet per second), and by May 15th the flow was already down to an average of 26 cfs. On May 24th, the river reached a low of 9 cfs before coming back up after a few little rains, and by June 1st the average flow was 22 cfs. Flow over the dam was 1-2 cfs around June 20th, and essentially stopped flowing by June 23rd. This streamflow information was gathered from the LCRA Hydromet web site for the Llano River at Llano gage. One should note that the gage reported zero before water quit flowing over the dam. This is due to the physical location of the gaging station downstream and where the water actually flows along the riverbed at very low levels.  


There are only a handful or so days over the last three to almost four months where the wind has not blown at all or when it was below 5-10 mph. The 100-degree days made an early arrival in May and have stuck around with little to no relief. Both of these factors on their own contribute to a certain amount of evaporation but put the two together for an extended period of time, and the evaporation rate is multiplied. There was a little rain at the end of May and then again at the end of June, but not enough to flush the river up.


On May 19th, the Water Planning group met to evaluate the existing anchors on top of City Dam for installation of the flashboards. Upon inspection, the existing stainless steel all-thread anchors were found to be in poor condition. The threads have been worn and abraded from past floods and continuous flow over the anchors. Many anchors were bent or broken from the flashboards being installed in the past and a flood came along. During the inspection, it was determined that new anchors would have to be installed if the existing brackets for the flashboards were going to be used. Robinson Park Dam was also inspected the same day to see if installing flashboards along this dam was an option. Portions of the top of Robinson Park Dam and both end abutment areas would need extensive work to make a flashboard system doable before any anchors could be set.


After the dam inspections, the existing angle iron brackets were inspected and the planning group began to put together a material list/cost estimate for installing the new anchors, utilizing what angle brackets were left, fabricating new brackets, and purchasing the boards. The material cost alone for all new stainless-steel anchor systems was going to be a minimum of about $25,000 for the same type of anchors previously used or a minimum of about $70,000 for imbedded internally threaded anchors. This did not include any boards or any additional steel for brackets that were damaged or lost during the last use. In addition to the cost, installing two rows of new anchors on 5-foot centers across the 755-foot long dam would be very labor intensive and costly.


While continuing to pursue these two options and getting lead times for boards, the team began discussing and evaluating an entirely new design. This design would not use any anchors at all, which would make it safer for those walking the top of the dam, better for the dam structurally down the road, and not to mention, less expensive. This design utilizes the entire length of the tongue and groove boards, instead of wasting two foot of every board and cutting the remainder into 5-foot pieces. It allows for 12-foot panel sections to be built and later fastened to pipe supports. Holes could be cored into the dam on 4-foot centers, that the pipe supports would be dropped into. The overall cost of the materials (boards, pipe, brackets, fasteners) was estimated to be less than $12,000. During the time of evaluating the flashboard options, TCEQ Dam Safety staff was contacted and notified of the plan to install the boards. The new flashboard design was reviewed by TCEQ Dam Safety for structural adequacy of the dam and approved. The design was also vetted thru the city engineers for appropriate loading calculations. At the special called Council Meeting on June 13th, funding was approved to purchase the necessary tools and material to install flashboards. City staff started purchasing the tools and materials, and began installation of the boards on Saturday, June 18th. The flashboard installation was completed on June 23rd.


On a parallel path of the flashboard installation and also stemming from the May 16th council meeting, LCRA was contacted about completing a bathymetric survey of both City Lake and Robinson Park Lake. LCRA had completed the last bathymetric survey in August of 2011. A bathymetric survey tells us the volume of water we have stored in each of the two lakes. With the dredging that occurred before the 2018 flood, the sand that was deposited in the river and lakes during the 2018 flood, and the dredging that occurred in both lakes after the 2018 flood, there was no way to know or calculate how much volume of water is being stored within the two lakes.


One might ask why this is important and why now? The primary reason for completing the bathymetric survey is to know the volume of stored water in order to calculate the estimated days of water we have left once the water quits flowing over the dams. We know the amount of water treated and distributed each day from the water plant. We can divide the total volume of the lakes (acre-foot or gallons of water stored) by the gallons used per day to get the estimate of how many days of water we have left. The more we conserve, the more days of water we should have.


Another reason for the bathymetric survey is to know where we stand with our water rights permits. We are authorized by TCEQ, and therefore the State of Texas, to store 383 acre-feet of water in City Lake and 317 acre-feet in Robinson Park Lake. If we are storing less than our permits allow, then it is justifiable to install the flashboards on the dam, at least to a certain height that brings us to our permitted storage amount. If we are storing more than our allotted amount, it is possible that TCEQ can authorize us to remove the boards. It is also possible to make a request to TCEQ for any additional storage over our permitted amount, which could include any additional storage that the flashboards impound. The 2011 bathymetric survey would give us an estimate of the additional storage provided by the flashboards.


During the Special Called Council Meeting on June 13th, the city council approved an interlocal agreement with LCRA and funding to complete the bathymetric survey for both lakes. LCRA Hydrology Staff started conducting the survey on City Lake on June 15th and completed Robinson Park Lake on June 29th. The final report from LCRA is expected around July 15th. Gathering the field data portion of the survey occurred at an optimum time with the water level just at the top of the dam. Data can be extrapolated or interpolated if the water level was above or below, but this gives us a little more concise data with the heights of the dams and actual storage for this particular point in time.


With the flow of the river decreasing drastically, we could not have waited until the survey was complete to install the flashboards. This is why we chose to work in multiple directions at the same time. We have reached out to TCEQ’s Water Availability staff and notified them that a bathymetric survey is in progress and that we were installing the flashboards on the dam.  Once the bathymetric survey report is received, and upon approval of the City Staff and City Council, a meeting with TCEQ will be set up to discuss our options and where we go from here. We will discuss options for our current situation and how to move forward searching for additional water options.


It was not intentional to wait until water quit flowing over the City Dam to start installing the flashboards. According to the Drought Contingency Plan, this should have come up in late-March/early-April when Stage 1 should have been implemented. The Drought Contingency Plan states that the boards shall be installed after March 1 when the flows fall below 80 cfs. This is the first time this Drought Contingency Plan has been implemented and will need to be revised. Installation of the flashboards with 80 cfs of flow is a safety concern and has logistical issue. Any work to install new anchors or the new flashboard design could not have been accomplished with 80 cfs of flow across the dam.  We have noted other issues with this Drought Contingency Plan and intend on making additional revisions in the near future.


It is important to realize that for any additional water options down the road, we will need to continue to work cooperatively with TCEQ and/or LCRA. From drilling wells to requesting additional water storage by means of the river to wastewater reuse, we will need to involve one or both of these agencies, and possibly others. Please know that these issues are being looked into and we are hoping to provide some additional information in the coming weeks as it relates to our water situation.

From the desk of Mayor Pro Tem Kara Gilliland, Photo courtesy Dust Devil Diver Photography

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