SonTek/YSI aids Lower Colorado River Authority in assessing water resources
SonTek/YSI has released an Application Note entitled: "Today, Tomorrow and Two Generations Ahead: LRCA data delivers on the spot forecasts and 80-year projections." It discusses how SonTek/YSI equipment such as the Argonaut-SL canal-monitoring gauges, FlowTracker acoustic Doppler velocimeters and RiverSurveyors trimaran-mounted, 3-D river discharge systems make up part of the backbone of LRCA's 237-station Hydromet data acquisition network covering 600 rivers and 1,100 miles of canals...
• SONTEK/YSI APPLICATION NOTE: Today, Tomorrow and Two Generations Ahead -- Lower Colorado River Authority data delivers on-the-spot forecasts and 80-year projections
SAN DIEGO, CA, Feb. 23, 2007 -- Keith Ging, senior hydrologist in the Hydromet Operations group of the Lower Colorado River Authority (LCRA), has a Texas-sized challenge. "Our main purpose is to determine how much water is flowing into streams and canals, how much water is flowing into our lakes and out of our lakes, and to make sure that data gets to the people who can use it in their decision-making," says Ging in LCRA's headquarters in Austin, Tex.
The stakes are high. When thunderclouds build over the state's central Hill Country, discharge data from his team's 60 stream gauges forms a key line of defense in the fight to keep residents of more than 30 counties safe from flash floods, which can swell a 60 cfs stream to 300,000 cfs in a matter of hours. On a day-to-day basis, it's a vital tool for optimizing lake levels and ensuring proper water delivery to the organization's three irrigation systems. And it's part of LCRA's crystal ball as the organization considers whether it can modify its storage and conveyance systems to link with the city of San Antonio while still meeting the needs of its own growing population, its farmers, and the Matagorda Bay ecosystem fed by the lower Colorado.
Capturing the data is no small task. LCRA's 60 stream gauges and eight SonTek/YSI Argonaut®-SL canal-monitoring gauges are the backbone of the organization's 237-station hydrological/meteorological data acquisition network. Called the Hydromet for short, the network is scattered across LCRA's territory of 600 river miles, 18,000 square miles of drainage area, 1,100 miles of canals, and six impoundments called the Highland Lakes. Stage and flow through streams and canals, water levels at LCRA's six dams, and weather data feed into LCRA's headquarters via its own 900 MHz radio system. Eighteen of the 60 stream gauges are maintained by LCRA in cooperation with the U.S. Geological Survey, a close working relationship that has streamlined data collection for both organizations.
The system is slated for expansion -- LCRA is expanding to 270 Hydromet stations over the next two years to improve river and lake forecasting models.
Counting Every Drop
Hard data and solid models are increasingly important to LCRA. "We're trying to count every drop now, more so than we ever have in the past," says Ging. Situated between a $115-million-per-year recreation industry on the lakes, a $234-million annual rice crop and a $63-million-per-year commercial fishing industry on Matagorda Bay, LCRA's water touches a lot of lives and a sizable chunk of the regional economy.
In November 2005, Ging's team conducted a study of groundwater inflows into the LCRA system, part of a feasibility study exploring a proposed connection between LCRA and the city of San Antonio. For fast, accurate flow data at various points along the river channel, the hydrologists used FlowTracker® acoustic Doppler velocimeters mounted on wading rods. Quantifying the water that flows into the river from underground is helping LCRA's Operations team fine-tune its releases to most efficiently maintain in-stream flow requirements and send enough fresh water into Matagorda Bay.
Fine-tuning releases for irrigation is also a big improvement. Ging points out that water allocations to LCRA's irrigation system have historically been based on pump ratings or lift and discharge ratings. But water levels in the river and canals are continuously changing as locks are adjusted and different pumps are engaged or shut down, altering the head values that need to be factored into the ratings equations. In addition, the pumps have been modified since they were installed in the first half of the 20th century.
To remedy the inconsistent flow data under those fluctuating conditions, Ging's team used acoustic Doppler flow meters (which measure both water velocity and stage) to make index velocity ratings to ascertain how much water is really flowing through the system. "By measuring both level and velocity, then indexing that velocity to the mean channel velocity, our discharge data improved dramatically," Ging says. "We are in a variable backwater environment. Flow from pump ratings is just a snapshot in time, but conditions are constantly changing, which requires more advanced technology, measuring velocity directly.
An accurate tab on water in the canals is vital to meet state reporting requirements on diversions. Knowing the difference between the run of the river and stored water also helps LCRA bill appropriately for the water -- each is billed at a different rate. Water diversion data can also be linked with weather data to help determine just how much water to send on its three-to-five-day journey from the lakes to the irrigation systems. Sending a full allocation down the river -- then encountering rain events -- means the volume of the lake releases is lost, flowing to the bay instead of feeding municipal and industrial demands along the river.
He notes that higher lake levels keep LCRA's hydropower systems more efficient. Hydropower is a byproduct of water releases, and it fills an important need during peak demand periods in the summer when the LCRA's coal and gas-fired plants are taxed to the limit. "We're calling on those hydro units more than ever," he says. "Even though it's a small percentage of power that they produce, that little bit is very important during the summer."
Life or Death
Counting every drop takes on special urgency when flash floods blast through LCRA's area. The region, with its thin topsoil over bedrock, is infamous for flash floods, which race toward LCRA's Highland Lakes when storms pound the hills along the horizon, threatening thousands of lives and millions of dollars in property. In fact, Central Texas holds the record for the greatest 18-hour rainfall in the continental U.S., Ging says -- on Sept. 9, 1921, more than 36 inches of rain fell in an 18-hour period near the community of Thrall, about 30 miles northeast of Austin.
In May 1995, 10 cfs Sandy Creek swelled to 100,000 cfs in a few hours. The next year, a stream that normally runs at about 60 cfs directed 200,000 to 300,000 cfs toward the lakes -- and repeated the feat twice the next year. In 2001, Johnson Fork jumped from 10 cfs to 100,000 within four hours, filling its canyon and nearly lapping at the base of the Interstate 10 Bridge.
When clouds gather in the hills, LCRA's staff meteorologist and hydrologists begin assessing weather data, including feeds from the Hydromet system. LCRA's responsibility is to alert residents if lake levels approach dangerous highs, while the National Weather Service (NWS) is responsible for river stage warnings. LCRA data flows directly to the NWS's river forecast models, helping government officials ascertain the threat of stream flooding. Using the same data, LCRA models predict lake levels and downstream flows, which guide decisions on emergency releases from the lakes. "We need to predict how much water is flowing into the lakes -- and not only how high they're going to get, but how quickly that level is going to change," says Ging.
Getting that data isn't easy. Measuring flow during floods is dangerous work, and traditional methods are often inaccurate. Ging describes flow meters with 100-pound weights being pulled nearly horizontal by rushing currents. And when depth can change by four to eight feet per hour, sampling protocols that take an hour or more can yield vastly different readings between start and finish.
LCRA has added three SonTek/YSI RiverSurveyors®, trimaran-mounted, 3-D river discharge systems that use Doppler sonar to take quick, accurate discharge readings as the units transect the channel. "We're able to take measurements in conditions that we really couldn't get into with mechanical flow meters," Ging says. "The RiverSurveyor has allowed us to get some measurements we couldn't have taken in the past because of safety concerns, and others because submerged debris would have interfered with mechanical flow meters. We're looking at the whole vertical column, not just surface velocity. And we can get our measurements in 20 or 30 minutes and we're done. Safety-wise, that's a huge improvement."
The RiverSurveyor's GPS system provides precise geographic references for each reading; where bridges or overhanging trees challenge the GPS system and moving bottom would have confounded the instrument's moving-boat method, the unit's stationary software keeps the process on-track. "The stationary software is simple enough that more hydrologists can quickly understand and use it without the hindrance of a steep learning curve," Ging says. "Its section-by-section method is very intuitive for hydrologists familiar with mechanical current meters. That gives us more flexibility during floods to cover a larger area and more sites that were previously too difficult for conventional methods."
Ging confesses that the trimaran got snagged by a river-borne tree on its first deployment in a 25,000 cfs flow. The hull needed a little banging back into shape, but after a quick diagnostic sequence, the unit was back on the water.
When it comes to flash floods, reliability -- and speed -- are vital. "Accurate data can help save property and lives," notes LCRA spokesperson Krista Umscheid.
The flow data collected by Ging and his team of 16 complements the work of LCRA's Environmental team, headed by senior aquatic scientist John Wedig. With four YSI 600XLM sondes and grab sample kits, the team gathers 30 to 32 pieces of information at each of more than 70 sampling sites around the lower Colorado system. Data is available to the public online at http://waterquality.lcra.org, and drives operational decisions at headquarters and the Hydro Operations Control Center at Buchanan Dam.
Close tracking of temperature and dissolved oxygen (DO) levels deep in the lake behind Mansfield Dam track the thermocline and signal potential problems with hypoxia. If DO falls below safe levels, Wedig can alert Operations, which can engage an aeration system on one of their hydropower turbines. The aeration system can raise DO by 2 mg/L, significantly improving water quality downstream, notes Wedig. He points out that operating the aeration system reduces the efficiency of the hydropower generators by about 10 percent, so knowing when the aeration is really needed can make a difference on the bottom line.
The Environmental team's data also looks into the future. When Wedig picked up signals indicating nutrient enrichment in the Highland Lakes, LCRA began developing a water quality model. "It's the first modeling effort we've ever done for water quality," he says. "We've completed the second year of data collection, and we've collected some highly relevant stormwater runoff data." When complete, the model will be an invaluable tool for guiding decisions on development along the shores of the Highland Lakes; for instance, helping assess regulations such as LCRA's current ban on wastewater discharge.
Big Study, Big Plans
LCRA's most ambitious studies to date will be key to deciding whether to proceed with an ambitious interbasin water sharing plan that would help meet future water needs in the lower Colorado basin and the San Antonio area. The plan was developed during a regional water planning process that occurs statewide in Texas every five years. Regional planning groups for the lower Colorado River basin and the city of San Antonio -- now the seventh-largest city in the U.S. -- both identified future water needs in their regions.
The project would capture and store excess and unused river flows in one to three new holding basins near the Gulf Coast. Intake structures would transport water from the river to the basins. A 160-mile-long water line would deliver the water to San Antonio Water System (SAWS), the city's water utility.
LCRA would deliver up to 150,000 acre-feet of water annually to SAWS for up to 70 years. The amount of water sent to SAWS gradually would decline during the last 10 years of the agreement, after which water supplies would stay in the lower Colorado basin to meet future water needs.
The project, called the LCRA-SAWS Water Project, is under tremendous scrutiny during the six-year study period. Consultants, scientists and technical experts are studying the project's environmental, engineering, conservation, groundwater and socioeconomic impacts. LCRA and SAWS have agreed the project won't proceed if the six-year study period shows that costs are too high, not enough water is available, or the project doesn't meet specific legislative requirements.
San Antonio, which anticipates a 40% shortfall in drinking water by the time its population doubles in 2050, wants the water. Farmers in LCRA's service area want a reliable source of water to help even out weather-related swings in irrigation availability, but they'll have to fine-tune farming tactics and irrigation systems to conserve 118,000 acre feet per year to make the deal work. And environmental groups and fishermen are worried about making sure enough fresh water makes it downstream to Matagorda Bay.
LCRA is halfway through the six-year study period, and early feedback from scientists and regulators indicates that the organization is proceeding with due care and attention to detail. "From the outside perspective, it looks like they haven't gone in with any preconceived notions with what the environmental issues are and the potential effects on the estuary at the mouth of the river," says Barney Austin, Director of the Surface Waters Resources Division of the Texas Water Development Board.
"What's nice to see is that they've been very proactive on two fronts," Austin adds. "One, involving stakeholders -- anyone with an interest in the river and bay ecosystems has been invited to participate throughout the process. There are different kinds of stakeholders out there, from the non-technical to the extremely technical, and each one brings something to the table. LCRA has done a great job of keeping all those stakeholders involved while collecting data in a scientifically rigorous manner. Second, they are also being extremely vigilant in bringing in the scientific peer review process, and on a step-by-step basis ensuring the science is properly vetted."
Years of data have been augmented by laser-sharp focus on key elements of the system. For instance, in an intensive 72-hour component of the study, Wedig's team took salinity, temperature, DO and pH readings at eight sites in a 350-square-mile area of Matagorda Bay. Meanwhile, Ging's team was aboard boats in the river, measuring discharge into its delta, running among six locations to keep the data flowing. Together, the teams built a comprehensive view of flow in and out of the bay -- from both the river and the Gulf of Mexico -- and building a knowledge base on the effect of those flows on salinity and other quality parameters. LCRA's Matt Ables even animated the data using a Flash-driven program, bringing the numbers to life for stakeholders.
LCRA's comprehensive studies of the LCRA-SAWS project won't be completed until 2010 at the earliest. Before then, the lower Colorado and its Highland Lakes will surely face floods and drought. Water skiers will play on the lakes, oystermen will ply the bay, and farmers will flood their rice fields -- and all will benefit from the behind-the-scenes work of Ging, Wedig and their teams at LCRA. So will their children and grandchildren.
"The need to understand and quantify the amount of water we have available -- and to understand the environmental impacts of using the water -- is particularly important, and will become even more so in the future," says Austin. "It's very important to get as much data as we can on our water resources."
Hot Tip for Beating Biofouling
Texas' Matagorda Bay is a very productive ecosystem, which drives thriving finfish and shellfish industries. That presents challenges to aquatic scientists and hydrologists like John Wedig of the Lower Colorado River Authority (LCRA), who rely on sondes to gather hourly readings of salinity, temperature, pH and dissolved oxygen at eight sites in the bay. It takes Wedig's team three days on the water to complete its monthly maintenance of the sondes, so the instruments need to stay clean and operational to deliver the required 90-plus-percent accuracy that Wedig demands.
"Biofouling kicks our booty, man," admits Wedig. He and his team have adopted measures to keep their instruments clean, and he says they gain an invaluable week of service as a result. The YSI 600XLM sondes are deployed in perforated stainless steel pipes, open on the bottom to avoid collecting mud and muck. An irrigation sock over the end keeps organisms from entering from below. Biofouling paint on everything but the sensors discourages barnacles and algae. But the coup de grace is a Texas recipe Wedig learned from colleagues with the state -- a slurry of cayenne pepper and water, brushed on over the biofouling paint to give would-be colonizers the hot foot.
Good Protocols Yield Good Data
The hydrologists and environmental scientists at Texas' Lower Colorado River Authority (LCRA) are among the best teams in the nation at data gathering in a variety of challenging situations. That's a credit to the people behind the organization's extensive network of Hydromet and sampling stations, says John Sloat, Principal Hydrologist for SonTek/YSI in San Diego, Calif., and to their dedication to quality assurance.
"LCRA has been progressive in that they maintain a rigid training program, measurement and maintenance schedule, and reporting program rather than just dropping the instruments in the water and letting them collect data, good and bad. It's a model for a good monitoring program."
Low Flows Demand Careful Measurements
Much of the work along the Lower Colorado River Authority's massive system is done on a large scale -- 237 Hydromet stations; an array of water quality sondes capturing data every 15 minutes, around the clock; three trimaran-mounted Doppler discharge systems ply raging floodwaters. But LCRA also employs SonTek/YSI FlowTracker® acoustic Doppler velocimeters for hand-held flow studies.
Senior hydrologist Keith Ging says FlowTrackers allowed his team to capture flow data quickly and easily at precise locations, including areas too close to the river bank for mechanical equipment. He adds that LCRA's Environmental team uses the FlowTrackers to capture flow data where differences of 0.1 cfs can have a significant bearing on pollutant loads. That's especially important in drought situations, where low flows create demand for load information -- and create extra challenges in measuring flow in tiny tributaries.
Support Clinches the Deal
Hydrologist Keith Ging of the Lower Colorado River Authority (LCRA) has been working with SonTek equipment since the organization deployed its first Argonaut®-SL discharge monitors a decade ago. Other equipment was more expensive, more difficult to deploy and maintain, and not as reliable. "But when it comes down to it, it was customer support that clinched our decision," Ging says. "We've had some problems with the equipment from time to time, and SonTek has always worked with us to fix it. They've been very gracious trying to satisfy our needs -- above and beyond the call of duty, I'd say."
Today, FlowTrackers, RiverSurveyors and Argonauts are the backbone of LCRA's extensive hydrology monitoring and rating system -- the finger on the pulse of the organization's irrigation network and the first line of defense against the flash floods that strike fear across central Texas.
SonTek/YSI (www.sontek.com), founded in 1992 and advancing environmental science in over 100 countries, manufactures affordable, reliable acoustic Doppler instrumentation for water velocity measurement in oceans, rivers, lakes, harbors, estuaries, and laboratories. SonTek/YSI is headquartered in San Diego, California, and is part of YSI Inc., an employee owned company that provides monitoring and data collection instrumentation to global water quality, water quantity, and aquaculture markets.