Lock and Dam: If you’ve ever been to any other big river USACE projects in the U.S., when you come to Wallisville, you’ll notice immediately that our lock and dam does not look like those. Instead of a high concrete structure with a long set of gates closed down to hold the water backed up behind them you’ll find our little four-gate concrete saltwater control structure usually with its gates standing fully opened and above the water line. Instead of a big concrete box with at least one set of gates closed at all times, here we have a wooden structure that doesn’t look like it could hold the water to lift boats upstream or lower them downstream. The navigational lock consists of two sets of paired wood and steel gates. Each gate weighs approximately 83 tons, swings a 45 feet radius, and stands 25 feet tall. The gates are mounted using a pintle type anchor and hinge support. The gates are moved by a combination of Relent electric motors, supplying power to Faulk speed gear reducers.
The motors operate on 480 volts, and produce 1.25 HP at 300 RPM’s at slow speed and 5 HP at 1,200 RPM’s during high speed operation. The gates are operated via control panels inside a control house, at the location of the pair of gates being operated. The area between the two sets of gates makes up the navigational lock chamber. The lock chamber is approximately 1,500 feet long and is 84 feet wide. The navigation channel depth averages approximately 14 feet deep at the low mean tide level. The saltwater barrier dam consists of a concrete structure with four steel tainter gates and their operating equipment sitting on top of the dam structure. The dam, when in operation with the navigational lock, seals the river off completely to prevent saltwater from intruding upstream into fresh water. The entire concrete dam structure, including the bridge, is 224 feet wide in the river and stretches 324 feet long. Each steel tainter gate has a 24 feet radius from the center of the trunion girder to the face of the gate. The trunion girder anchors the gate to the concrete structure. Each gate is 46 feet wide and stands 16 feet tall when sitting on the bottom of the channel. When on the bottom of the channel the gate protrudes four feet above the low mean tide level. The river channel is 12-feet deep at low mean tide level. Each gate is supported by 4- 1 ½” stainless steel cables, two on each side, on the face of the gate. The cables are wound up by parallel shaft gears sitting on the upper structure of the dam 25 feet above the gates where they are operated via control panels. Rueland electric motors are used with 460 volts, to operate the machinery. Each motor produces 3 HP a 900 RPM’s. The motors turn Lufkin gear reducers which have a reduction ratio of 1501:1 in order to turn the parallel shaft connected to the cable.
Open/Closed: There are some major differences between us and other USACE navigation projects. On the big river projects for navigation to work, the locks have to be built so they can use the river’s own water to lift or lower the tow boats, barges, and pleasure boats going through them, because of the natural changes in elevation of the landscape along the river’s course and because of the engineered change in elevation of the water surface created by the dam itself. As Wallisville is a coastal project, there’s not a natural elevation change upstream or downstream of the lock that would require lift and lowering of vessel traffic, nor is there an engineered elevation change because we don’t have a reservoir behind our dam. This allows our lock and dam to stand open most of the time. Closures also have to do with being a coastal project. For closure information, we rely on the U.S. Geological Survey which has sensors on both the up and down stream sides of our dam structure that send data to satellites. This data is updated hourly so it stays current and accurate. The satellite data is transmitted to a website that our hydrologists in the USACE Galveston District Office monitor on a 24/7 basis. When the graphs show salt water at the dam, one of the hydrologists gives us a call with instructions to close including how many feet to lower the gates, when to lower the gates, and when to close the lock. To view the USGS water data site for more information on the Trinity and other Texas rivers. To get to the Wallisville data, on the Predefined Displays dropdown list select TX Streamflow/Lake Table, on the group table by dropdown list select Major River Basin, and on the space to Select Sites by Number or Name, type Trinity. Click GO. This opens a list of all the water sensing sites along the Trinity River. Scroll down to the Wallisville site and select it. To see one or more of the graphs select the ones you want to view on the Available Parameters list. Click in and type how many days you want to view (from 1 – 31), and Click Get Data. The elevation graphs show the effects of tides and river flow, or lack of flow if the gates are closed. Specific conductivity has to do with the ability of water to conduct an electrical current. The specific conductivity graphs are used to compute the salinity graphs. Water temperature is measured in degrees Celsius. Even though the tides drive the water processes there are several reasons for not opening and closing twice daily with the tides. 1. When the environmentalists sued us back in the ‘70’s the review process determined that the Project should operate as closely to normal stream conditions as possible and allow nature to take its course as much as possible before we step in to prevent the salt from going upstream. This keeps us from becoming a reservoir, but it also allows the Trinity estuary to function naturally as nursery habitat for bay fisheries and for river water filtration, retention, and dispersal. 2. Most of the time the tides are not strong enough to push the salt this far upstream. An extremely high tide can push salt up to river mile 47, however, and that’s definitely too far up stream because that would allow the salt go upstream past the freshwater intake structures for at least 3 major freshwater user partners. 3. Drought conditions upstream mean that there’s not enough fresh water flowing down to push the salt back out into the bay and that can cause us to have to close. 4. We’d have to do a lot of costly modification to our electronics to make that work without having 24-hour staffing. Leave the radio buttons set as they are, then on the Region dropdown list select Gulf Coast, click on the get list button and scroll down to Galveston Bay, Round Point, Trinity Bay 4675 and select. Click on search and view today’s tide table. It’s set on 24-hour time, so remember that 1 p.m. is 1300, 2 p.m. is 1400 and so on.