APS Survey & Mapping

Owner:

APS

Client:

Corps of Engineers

Scope Of Work

Green River Cross-Sections, Green River, Washington.   APS was selected by the Corps of Engineers to collect thalwegs, cross-sections and crossings (such as bridges and pipelines) along the Green River from mile 37 to mile 60.3 at the Palmer Stream Gage Station in Washington State.   The largest portion of this river survey passed through the Green River Gorge.  This is a very isolated section of the Green River, with cliffs rising in excess of 300 feet from a 70-foot wide riverbed.

 

The flow of the Green River is regulated by Howard A. Hanson Dam, which is artfully managed by the Army Corps of Engineers.  A fraction of the water from the dam is piped from the pristine watershed for Tacoma’s drinking water.  The Corps must maintain the water level while keeping a constant flow to Tacoma in spite of fluctuating natural conditions. This irregular water flow was a constant concern for our surveyors and project requirements.  The range of discharge varied from a low of 135 cfs to 850 cfs during the course of the survey.  850 cubic feet per second in a narrow gorge can be dangerous, especially when trying to take measurements along the riverbed.  Due to the equipment necessary for safety and project completion, the surveyors’ entry to the river was limited to about six launch points from the Kanaskat-Palmer State Park to Flaming Geyser State Park.  These sites were paramount in APS’ overall safety plan.  Phone service in the Gorge floor was at best intermittent and for a five-mile stretch nonexistent.  Five miles through rapids with an injured person would have been life threatening. 

 

During the planning process, APS turned to River Recreation located in Bothell, Washington, a 25-year old river guiding company, for training and support.  All APS Green River Project participants passed a training course tailored specifically to the hazards and issues associated with rafting this river. Big Sky Inflatables of Montana custom built two Grizzly Rafts specifically for this project.  These rafts are lightweight and rated for Class 4 whitewater. Additionally, APS Survey & Mapping elected to have the River Recreation guides with the survey team during the most technical portions of the river. 

The first pass through the river was to layout control.  For the area between Kanaskat-Palmer State Park and Flaming Geyser State Park it was necessary for the team to camp.  Camping became more challenging the further APS ventured into the Gorge; culminating near the Nozzle (a particularly dangerous Class 4 stretch of whitewater).  Here each employee slept on his own semi-flat rock outcrop, roped in at night to avoid rolling into the water. At this point, the team’s goal was to set pairs of intervisible control points at approximately 1500-foot intervals or in spots that provided us with expansive vistas of the River. 

 

Due to the depth of the gorge and 100-foot plus trees on the River’s banks, APS used Trimble R8s to take advantage of the additional satellites in the Glasnost system.  All of the River observations were taken using fast static (45-minute observations periods) with dual occupancy.  The reduction of the fast static gave the team regularly spaced control throughout the project, with relative accuracies better than 0.5 feet (Vertically and Horizontally) at sigma one.  Though the traverses were taken with a one-second Leica TCRP 1201 total station and all angles were doubled (direct and reverse), the GPS Control Network gave the crew the confidence go to the next Thalweg or X-section. Depending on which section of the River the team was on, the Thalweg shots were taken at <50-foot, <100-foot, and <200-foot intervals.  Determining the Thalweg was frequently a difficult task.  Much of the River is strewn with 3-foot to 10-foot boulders.  Changing the location of the shot even by inches can change the elevation by several feet.  When the river discharge was low, the team would walk or float across picking out the deepest point.  When the river was high or muddy from the rains, it required a constant probe of the river bed to establish the Thalweg.  APS tried to use fathometers to track the bed, but they only lasted until the first boulder they smashed into.  In some of the deeper areas they employed lead lines combined with a 12-foot metal rod with a 360 prism.  In those areas where there were extensive rapids or whitewater, they used boats with zip lines to hold a position long enough to get the shot.  The Leica robotic total station has amazing tracking ability, but not when the rod is being thrown from side to side and the undulating water is pitching the prism up and down. 

 

This project taught the APS team patience, problem solving and cooperation.  APS’ task was to hold an 8-foot inflatable raft steady as the rushing water launched the boat over boulders or over a 9-foot straight dropping fall.  Their final approach was to rig a zip line and to control the bow in the line toward the middle, by a third line tied to the boat.  New regulations prohibit using felt soles on Washington’s rivers.  Subsequently, the boots team members were forced to use slipped easily on the rounded boulders.  “During the course of the survey, we destroyed or lost a camera, a prism, a sleeping bag, a pair of sunglasses, a wedding ring, radios, and pocket tapes,” said Scott Edwards, PLS, MBA, APS Vice President.  “Additionally, we broke 7 oar-rings, 3 oars, a prism rod, three fathometer transducers, a set of legs and a Kevlar prism rod.  The crews had definite instructions to protect themselves first, equipment second.” Thanks to the APS safety plan and their training, there were no injuries during this project.

 

For the deliverables, APS provided the Army Corps of Engineers with AutoCAD dwg files and Microstation dgn files, along with paginating Adobe PDF files showing each X-section fully annotated with the bed of the River, water level at the time of taking the X-section, XYZ and Station/Offset for the two control points set near the end of each X-section, any objects crossing overhead, time and date of survey, and discharge rates.  Additionally, the PDF file contains photos looking upstream, across the X-section and downstream.  APS also provided ASCII files of all 8000+ points taken during the course of the survey.