Feature: Rockin' on the River
Professional Surveyor Magazine - January 2011
Conducting a hydrographic survey on Wisconsin’s historic Rock River in winter proves treacherous at times.
by Patrick Fuhrman, PLS
Dating back more than two centuries, the Rock River has seen its share of historic events that typify the struggles of the American Indians as white settlers made their way west, staking their claims to land in our new country. Today, the Rock River is home to many private homes and small commercial boat rental businesses. Recreation is plentiful, including snowmobiling and ice fishing in winter and boating and waterskiing in summer. But in carrying out an extensive survey of the river, we experienced our own set of dangers that come with taking hydrographic measurements while dealing with swift currents, ice, and snow.
The Wisconsin Department of Natural Resources
(WDNR) contracted K. Singh and Associates of Elm Grove, Wisconsin to conduct a primarily hydrographic survey of the Rock River. The WDNR needed to know the volume of water the Rock River currently holds and what potential the river has to hold maximum water level without overflowing its banks and creating a flood disaster. This data would provide for flood control and management, and it had to be formatted and coded to enable entry into FEMA
databases for emergency management coordination in the event of a flood.
We needed to have uniform control throughout the project, so we went to the website of the Wisconsin state cartographer’s office and found NGS
monumentation along the Rock River and on nearby roads and highways. Each monument had a data sheet that gives you history, physical location, latitude/longitude NAD83 and NAVD88 coordinates, and elevation along with other useful information.
The project was to be submitted in meters, NAVD 88, so we contemplated making that conversion. We set everything up in U.S. survey feet and made the conversion to meters after all the data had been gathered, processed, and finalized. We felt this would eliminate any errors made in the field by confusing the two units, especially likely under the many adverse conditions on the river.
The effort in the first stages of the project was far less physically demanding compared to the difficulty posed by getting to the designated cross sections. The WDNR supplied us with coordinates of various locations for channel surveys to be conducted along with aerial panels showing the approximate locations. I chose to do a static run using the Topcon
GPS with a Hiper GD Rover along with the Trimble
(TDS) NOMAD data collector, and I used Survey Pro software that included the advanced GPS package.
Driving among bridge structures, base stations, and NGS monuments, we performed the control survey. Depending on the number of structures, we achieved a distance of three to five miles a day in setting and establishing control using GPS; I could sometimes get up to six miles between base stations. Except for one week when I worked with Paul Kubicek, PLS, I did the entire control survey alone because most of the surveying came only a short distance from the truck, allowing me to walk to the points I shot or set and visit each point for only 60 to 90 seconds.
Because we were representing the WDNR, we needed to maintain a certain demeanor with the public. Since many of the channel survey coordinates fell in areas where private land needed to be accessed, friendly public contact was very important. Most of the people we came in contact with were friendly and understanding of what we were doing. For the many people who wanted to know what I was surveying, just replying “the Rock River” would usually satisfy even the most curious. Few people needed to know the details, thankfully.
One of the most curious was the Edgerton Police Department
. An NGS control monument had been set in a city park back in the 1950s. This monument was not GPS friendly, and it was impossible to get a signal from anywhere in town, so it ended up not being suitable for occupying with the rover or base station. With my continual movement in the park, I apparently drew suspicion, and I noticed that at the end of my one-way exit, two squad cars were parked observing me. At that point I decided it was time to give up trying to get a signal on this monument, so I left and smiled and waved on the way out, but I didn’t get a response from them. I decided I didn’t want to give up on shooting this monument, so I went back to the area about a block from the park to at least try to get a good signal for a base station, when a van approached me. It was one of the officers I waved to earlier, now in civilian clothes. He told me he was a landowner and wondered what I was doing. When I told him I was surveying the Rock River, he seemed relieved. I wasn’t sure if he had just gotten off duty or actually went undercover to find out what I was doing.
After finalizing the control, Paul and I analyzed the horizontal and vertical accuracy, and we were thrilled that many miles of flat stretches along the river proved to have a vertical accuracy of .04 feet and a horizontal accuracy of .3 feet in 25 miles. The other areas a gradual rising of the terrain accompanied elevations between base stations ranging from 15 to 80 feet, which caused a separation issue in my ellipsoid heights versus sea level heights. Our elevations were deviating from my published datum, and it seemed likely it was causing a surplus in our horizontal distances. By the time I got to Edgerton, I had an accumulated error in our northing of 3.8 feet farther north in 42 miles. Thankfully, I picked up only .30 feet vertical error. Because I had two other NGS monuments near two of our structures, I used them to adjust back into the NGS system.
I then re-localized with a new file so I could tie into the Jefferson County network and overlap the two counties. I carried this control to Watertown, where I adjusted and re-localized, creating a third control file using three primary monuments. Our final stretch to Horicon revealed that I had a vertical error of only .05 feet carried from Jefferson County to Dodge County and .20 feet horizontally. This gave us comfort knowing we had quality in our control data. Paul had made further control checks throughout the project with the VRS (virtual reference system) and revealed minimal error in hundredths of a foot throughout the entire project.
After completing the control network, the project consisted of three control files tied into the NGS network, covering a distance of 83 miles. All three files were tied in to each other with overlapping data, and then the data was compared and adjusted as “final control” and created in a separate file. Next, we loaded all the channel survey coordinates into the same file and created a working control file. This file was used to upload our controllers and data collectors through ActiveSync. Any crew could now go out to any town or bridge on the project and collect data on the same system and tie into the same control network as a crew 80 miles away.
This proved especially useful when two crews were out doing channel surveys, often 30 or more miles apart. The crews can access everything on the entire project. When using these files with the Trimble VRS and Trimble Survey Controller, the speed and versatility proved useful when covering 10 to 15 miles a day in a boat without having to keep moving a base station to maintain geodetic position. The crew could quickly arrive at their stakeout point and start doing a channel survey immediately. We could usually get about 20 cross-sections done in one day with the VRS.
After control was finalized, we had to quickly advance into the next phase, structure surveys, to include complete and accurate hand sketches and pictures of each bridge. We chose the Trimble Robotic S-3 total station with Trimble Survey Controller and TDS software for this phase, especially since it could shoot in the reflectorless mode and locate all bridge piers underneath without a person holding a prism while steadying a boat under the bridges. I used the Topcon Total Station 600AF with the NOMAD data collector using established control points on the bridge decks from our control survey. The older equipment I used was slower than the Trimble S-3 and required the need to have a survey assistant.
As we completed the last of the structures, the weather began to deteriorate rapidly, and we knew the late fall season would not bring warmth and sunshine back. We started the final phase of channel surveys when November winds began reminding us that winter was not far away. These channel positions were rarely in accessible locations. The easiest way to reach the channel positions was by boat, but by now the river had begun to freeze over, and we were left with picking areas of open water where we could launch the boat, complete the channel surveys, and return safely without the ice jamming our launch site while we were downstream working.
Cold Weather Hits
As we worked the first week in December, temperatures reached the 20s for daytime highs, and the wind chill dropped it to around 9 degrees. We had hoped to get eight channel surveys completed four miles north of the boat landing by day’s end. As we stood on the pier shielding our faces from the bitter wind, we watched a steady parade of ice floes drift downstream. As we looked south, we could see that the ice had totally jammed, and there would be no chance of getting a boat downstream from the boat landing, but we knew we still had a chance upstream.
As we headed out in our three-man crew with a 12-foot boat and five-horsepower motor, two 25-foot icebreakers headed towards us with five men each. As they approached us, they warned of the danger of the ice jams upstream and that it wouldn’t be safe. Instead of heeding their warnings, we followed the path they created by breaking the ice and “GPS-tracked” our destination.
We reached a railroad trestle and still had another 1,000 feet north to get to our farthest cross-section area. As we approached the trestle, we experienced heavy turbulence and larger chunks of ice moving faster towards us. Our boat operator had to be vigilant to keep the boat from getting hit by an ice chunk or caught in the turbulence.
We struggled with nearly every channel survey. Between breaking ice to reach the shoreline and trying to keep the boat on course against a strong current, we decided to abandon three of the eight surveys and wait until the ice would freeze over so we could walk to the remaining ones. Some of the cross-sections had a sheet of ice extending 200 feet into the river where it met open water. The ones that we did complete were the result of luck and careful boat maneuvering.
The last area free of ice for the season extended from the Wisconsin/Illinois state line to the Black Hawk Dam in Beloit, Wisconsin. It snowed heavily that day, dumping wet snow that made getting in or out of the boat a challenge, and it became more of a controlled fall just to get in. Our clothes and equipment became wet well before noon. As we motored upstream, the current was so swift it would make you nearly seasick if you didn’t focus on something on land.
More treacherous tasks consisted of surveying the face of dams, where undercurrents pulled the boat towards the dam and violently tossed it in different directions. Spillways and scour pools had to be measured from the boat using VRS and a depth finder while maintaining position with the boat.
The boat crew now formed two ice surveying crews, each with four persons carrying a hand ice auger, 25-foot level rod or depth finder, tether rope, rover, and data collector.
We stayed aware that the ice could be thick enough to walk on in one spot and dangerously thin 10 feet away. So we tethered out at 50-foot intervals and drilled holes with a hand auger to check the ice thickness and measure the depth for each riverbed shot.
Our safety procedure proved valid when we tethered to the shoreline and my assistant made it to shore successfully. I had failed to follow my own procedure when I drifted off the chosen path by a few feet and broke through the ice with my left leg, managing to escape with only a wet foot as I tumbled away from the soft area to thicker ice.
The ice along bridge structures is especially hazardous because of current around the piers. It was common to find large cracks under a bridge along with areas that have opened up and refrozen. Walking in these areas sometimes would buckle the ice from the added weight and cause loud, large fractures in it. Walking along the face of structures had become unnerving because of huge cracks that existed. A couple of times when we approached a bridge pier, the ice let out a loud pop from one end of the bridge to the other, and we saw a new crack that traveled within 10 feet of us.
Praying for a Signal
For two weeks, Bryant Polzin and I walked three to four miles a day through flooded swampland, channels and creeks, deep snow through ravines, and dense underbrush to reach the remote areas between Ixonia, Watertown, and Johnson Creek. We had to pray we still had a GPS signal when we got there. Thankfully, we had surprisingly good signal in most areas. Sometimes we had to move our channel survey 50 feet up or downstream to get a signal through the dense brush along the river.
Completing the channel surveys at the trestles proved challenging because the ice at these structures was many times more treacherous than the regular channels due to water turbulence under the ice. This showed at the surface, where we could see discolored ice, buckled ice, and open spots that had re-frozen and become a thinner ice layer. Most of these trestles had to wait until ice-out before we could do them because they weren’t safe to walk near.
My crew and Paul’s crew would take channel depths from the bridge decks when we encountered open water. We tied a 200-foot cloth tape on a 200-foot long rope with duct tape, then taped on a 2-inch-diameter rebar at the end so it would withstand the turbulence, and then dropped it down and got a measurement from the river bottom to the bridge deck. We would then change the rod height in the data collector to represent the bottom of the river and shoot the deck with the GPS rover. We got much better at this technique as we practiced with the many structures we had to survey.
As late winter turned to early spring, we finally completed the survey of the Rock River, as the ice had slowly turned to open water on the southern half. We still had difficulty in the northern end near Hustisford and Horicon, where we used the boat as an icebreaker. We jumped on and rocked the boat in a successful effort to keep the boat moving while plowing through two inches of ice at bends in the river, and it helped to have strong guys on the crew to portage the boat through the woods to get around at least six areas of fallen trees that extended over the water.
When we completed the survey, we had set more than 20 base stations, set nearly 240 bridge structure benchmarks and control points, surveyed more than 80 structures, and conducted more than 250 channel surveys spanning a distance of 83 miles.
The experience was memorable for all of us who participated. I will always hold a special place in my heart for the Rock River after experiencing the abundance of wildlife—wild turkeys, osprey, bald eagles, and deer—and learning the history of the river. Stories from landowners about past floods and the measures they took to protect their lives and property add to the lore. The river holds an abundance of natural beauty and an element of danger that commands respect from anyone who journeys onto it or lives in its path.
Based in West Bend, Patrick Fuhrman, PLS
is a surveyor with K. Singh and Associates of Elm Grove, Wisconsin.
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