Sustaining the Southwest
Delivering 10 trillion gallons of water to more than 31 million people each year, the U.S. Department of the Interior’s Bureau of Reclamation is the nation’s largest water wholesaler. Reclamation has built dams, powerplants and canals in 17 Western states from the Pacific Ocean to the Great Plains, and these resources provide irrigation water for the 10 million acres of farmland that produce 60 percent of the nation’s vegetables and about 20 percent of its fruit and nut crops. With 58 hydroelectric power plants, Reclamation is also the second largest producer of hydropower in the United States-it produces enough electricity to serve six million homes and generates nearly $1 billion in power revenues. Since its inception in 1902, Reclamation has constructed more than 600 dams and reservoirs, including Hoover Dam on the Colorado River and Grand Coulee Dam on the Columbia River.
Orosco evaluated several vendors and selected Leica Geosystems’ SmartRover RTK GNSS system with SmartWorx software because of the system’s features. “It’s modular, it offers seamless GPS/total station data integration, and you don’t need to have the data collector physically connected to the PC to download data-just the memory card,” Orosco says.
Within just a few days of receiving the hardware and software, the Boulder Canyon Operations Office (BCOO) called Orosco to the field. Supported by Tim Dewey, an inspector with Reclamation’s Engineering Services Office, Orosco was tasked with surveying a remote 11-mile stretch along the Colorado River near Yuma, Ariz.-facing disorienting “junglelike” vegetation, dangerously rough levees, pesky snakes and mosquitoes and 110-degree temperatures-to generate coordinates for a hydrological study.
Prefield IntelligenceDewey was instrumental in planning the team’s field-survey strategy. “[He] had intimate knowledge of the geography of the study area-the back roads, access points, vegetation, levees and bridges,” Orosco says. “He knew which sections would have such thick bamboo that our only orientational guide would be the sun. That was information that I didn’t readily have, and it enabled us to develop a much more effective and efficient field plan.”
BCOO required Orosco’s team to acquire levee-to-levee coordinates and elevation points at half-mile intervals between mile markers 24 and 35-an interesting directive since there are no physical mile markers in the desert or river. To determine a starting point to survey, Orosco acquired an existing GIS file of mile markers from Reclamation’s GIS group and imported it into the standard software used by the bureau’s civil engineers, Autodesk Civil3D, to create end points and mid points for each of the 22 cross sections positioned perpendicular to the flood plain. He then took the Civil3D CAD file and imported it as an ASCII file into the Leica SmartWorx software. Using the SmartWorx line-stakeout feature, Orosco could automatically convert the ASCII file into 22 cross-sectional lines complete with each cross section’s end points as well as end points for each mile marker. He then loaded the file containing the cross-sectional information into the GPS data collector to help navigate these cross sections on the meandering river.
Welcome to the JungleOrosco and Dewey traveled to Yuma in late April 2008 to begin the field-work phase of the hydro study. From their prefield survey analysis, they knew the area provided few access points to cross the river, so they decided to organize their data acquisitions by segments-northern side, water corridor and then southern side.
Using the Leica SmartRover system, they chose locations for strategic control points for the 11-mile stretch, which ended about five miles from the Mexican border, and then established these points using static observations for 24 hours, recording five-second epochs. Starting at the most northerly end, mile marker 35, they worked from sunrise to sunset, navigating to each half-mile survey point to collect coordinate and elevation measurements. Before they even reached their first cross-section end point, they could readily appreciate the precise positioning capabilities of their survey equipment.
“With the thick vegetation of the region, it is really difficult to maintain your direction,” Orosco explains. “Just because you think you’re moving on line doesn’t mean you are. You could take five steps and already be four to six feet off line. But because we could use the line stakeout application of the Leica system, we knew every step of the way whether we were left or right of line or dead center. So we could just stare at the data collector and hope we didn’t trip-or step on a snake.”
Ultimately, reaching each survey point often meant scrambling up riprap (the rock along the shorelines) to reach the top of a levee, fighting through bamboo or marching through boot-sucking charred soil. The lightness and mobility of the Leica SmartRover made it easier for the crew to endure such a physically taxing landscape. “The levees aren’t exactly gentle slopes,” Orosco says. “The riprap is difficult to climb. And in the deep brush, it’s a lot of work just to fight through branches and mosquitoes. Having very light and rugged equipment kept us agile and really efficient.”
At the end of each 12-hour day in the field, the team downloaded all the data collected into the Leica Geo Office software (a program that enables users to view, manage and integrate total station, GPS and level data), analyzed it for completeness and accuracy, and then planned the strategy for the next day.
Fluid DataWhen Orosco and Dewey moved to the water, they again needed to devise a bit of technical ingenuity to acquire the necessary accuracy for the five shots BCOO engineers required: one shot from each bank, one shot at the river’s center line, and one each from the left and right of center.
Because some of the points would take them to shallow parts of the river, the team based their water operations from a jet boat to avoid getting beached on a sandbar or breaking propellers. The three shots in and near the middle of the river also required them to exchange their traditional 2-meter GPS rod for a 20-foot pole. Once they reached a survey position, Orosco would hop into the water, drop the rod and shoot the point. In areas where the water level was deeper than 6 feet, Orosco would drop the pole from the bow of the boat to acquire the shot. Since the Leica SmartRover system uses Bluetooth wireless technology, the team had the option of either attaching the data collector to the pole or leaving it on the boat for Dewey to direct Orosco to the correct position.
“The combination of an extended pole height, wireless technology and a cable-free unit made the water survey possible,” Orosco says. Doing the same job with conventional total station tools would have been more challenging, he says, because the team would have had to traverse down the river from a control point and then stake a point near the cross section. It’s also possible that they would have needed more than one setup to pick up all of their cross section points. Additionally, “you can’t drive stakes in the water,” he says. “With the GPS and the line stakeout, the most laborious part of the process was jumping in and out of the boat.”
The Right Team and the Right ToolsOrosco says the highlight of the project came when they encountered their first bridge. The hydro study included three bridges critical to BCOO’s infrastructure maintenance and water-resource planning: the 80-foot-high Interstate 8, the historic railroad bridge and the one-lane Ocean-to-Ocean Bridge. The team needed to produce a topographic survey of the three structures, including abutments, low- and high-chord positions (the bottom and top of the bridge), and a cross section of the water’s edge directly below each structure.
The Leica SmartRover was capable of acquiring the water’s-edge data, but the bridge structure disrupted the GPS satellite connection, so the crew switched to Leica’s TCRP1201+ robotic total station to collect the topographic survey. According to Orosco, the switch didn’t cause any downtime for the crew because of the seamless data compatibility between the two units. “The Leica SmartRover and TCRP1201+ both use the X-Function standardized interface and common data platform inherent in the systems,” Orosco says. “That means we can use GPS to survey up to a bridge, take the GPS job data memory card and put it in the total station to survey underneath the bridge and, once on the other side, switch the data back into the GPS and continue surveying without ever having to shut down or lose time typing in coordinates.”
In addition to the easy data integration, the Leica TCRP1201+ reflectorless technology afforded the crew the ability to efficiently and safely collect the low- and high-chord measurements from the ground. “Without the Leica reflectorless technology, the only way to collect the low-chord and high-chord measurements would be to hang upside down from a rope and manually hold a prism,” Orosco says. “Setting the total station on the shoreline, I could shoot all of my points-low-chord and high-chord-from a distance of 80 to 500 feet.”
One challenge was that a reliable RTK network wasn’t readily available in Yuma. To verify accuracy on all the points measured in the survey, Orosco and Dewey used their own base radio-a 410 to 430 mHz unit supplied by Pacific Crest-and set up a control point on the I-8 overpass. The two-person team also surveyed and used three additional control points that had been installed recently along the river by Reclamation’s Yuma survey crew for observation purposes. They filtered the raw data into GrafNet software (Waypoint Consulting Inc.) for post processing and then tabulated the solved, adjusted data points into a Word document for a BCOO hydrological engineer to import into the U.S. Army Corps of Engineers’ Hydrologic Engineering Center’s River Analysis System (HEC-RAS), a software package that allows users to study river flow, compute sediment movements and model water temperature. Orosco had created a geoid file of the area in Leica Geo Office before heading out into the field, and he used that model to correct GPS heights to orthometric heights. As additional files were needed, Orosco was able to create them on-the-fly on his laptop.
Completing an 11-mile survey in difficult terrain with a two-person crew and a completely new set of GPS and total station equipment was not exactly what Orosco would have scripted for this survey project, but he says the nature of his crew and the ease of use and reliability of the survey technology, along with its technical support, ensured his success. “Sometimes you are given the wrong tools to do a job, and you have to make it work,” Orosco explains. “This was not the case with this project. I had the right project team, the right hardware and software, and the right technical support. And because of that, I was able to do a four-person job with only two people and create a very efficient, cost-effective and high-quality end product. It was a success in every way.”