Boldt explained, "Six months ago, a hunter recovered some human remains in the Tolt River. We have been unable to locate the source-the burial site-despite some exhaustive foot searches. The rest of those remains are important to our investigation, to our possibly identifying the victim and therefore the killer. The man I spoke with offered to set up your computers to help predict where the bones might have dislodged from the bank." "Joe Webster. That's right." He added, "There's a book on this that might interest you," Terkel said. "Fluvial Processes in Geomorphology. River movement. River meandering and material deposits. Sediment actually 'cements' together-if you will-and moves downstream as a whole. Our job is the quantitative determination of water flow. Tracking flows. Predicting the sedimentation process. Erosion, deposition."
Boldt was wondering what language this was. Fluvial Processes in Geomorphology? Nice bedtime reading. Terkel recited like a student, "Material eroded from one bank will deposit on the same bank one to two bars downstream. That's two to four bends," he informed Boldt. "And that's a fact. That's something we can bank on. Pun intended. That's where the HEC computer can help us." Terkel saw Boldt's puzzled face. "HEC-the Hydraulic Engineering Center-runs the modeling computers."
"Maybe we should talk to them," Boldt suggested.
A few minutes later Boldt and Daphne were sitting alongside a Japanese woman, Becky Sumatara, staring at a color screen that offered a menu of choices. Joe Webster, a stocky man in his late forties, towered behind them.
Becky Sumatara said, "When we received your request, we updated our Tolt model for current flow notes, slope, sediment size, distribution, and areas of erosion based on our present data.
That's what took us a couple of days. The updating is a lengthy process."
Boldt apologized, "When it comes to computers, I'm a technopeasant."
The screen changed to a graphics aerial view of a map of King County. "Bodies of water, in all shapes and sizes, are represented by various shades of blue," Becky Sumatara explained, her red fingernail Pointing out the Sound, reservoirs and rivers, "depending on volume. The darker the shade, the more volume. Elliott Bay and Puget Sound are a deep navy, while some of the smaller creeks are almost white. You're interested in the North Fork of the Tolt."
"Yes," Joe Webster answered for Boldt.
She dragged a blinking box to the area in question, bordering the box on Carnation, Monroe, Sultan, Skykomish and Big Snow Mountain. With two clicks of the mouse the screen filled with an enlargement of this area. "During enlargement, color reference is modified. You'll see the Tolt is now navy and its various tributaries are lighter according to volume. Also," she said with another click as the river, streams, and creeks turned various shades of red and pink, "we can view according to rate of flow-how fast the various volumes of water are traveling both Q V in terms of quantity and"-the water all turned -"as regards land speed. All factors shades of green in erosion and flood control."
With the enlargement, a dozen smaller creeks had appeared.
Daphne withdrew the topographic map from Boldt's briefcase. The exact locations where the bones had been discovered were marked. ji Becky Sumatara studied the map with Daphne and then narrowed the computer's target area yet again, creating a corresponding enlargement. "You're up into Snoqualmie National Forest there," she said, stepping the computer through maneuvers. "Rugged country." ' Yes."
"What does this tell us?" he asked. "We have two views of each stream flow," she explained. "Aerial and lateral. This gives us a visualization of lateral erosion as well as a cutaway of stream bed depth, Using the computer, I can increase or decrease volume and rate of flow as well as access any date in the past for visualization. Unfortunately, we've set this up only for the Tolt's stream bed profile, not the tributaries."
"The Tolt's our baby," Joe Webster said. "We have gravel moving one to two bars downstream. We'd like a look at those upper bars. That's all."
"The high-water mark for the Tolt reservoir should give us a fairly reliable benchmark for checking downstream erosion." She put the computer to work. Boldt felt some of the tension leave him. Finally, they were into it! On the left of the screen, she changed a date at the top of a table of numbers. The screen paused before redrawing. "I'm going to ask the computer to compare this projection with one a month prior. it will color-code areas of the most severe erosion, red to black, red being areas of greatest damage." As she described all this, various images appeared and vanished. An arrow raced back and forth across the screen under her direction. "You must keep in mind that this is all speculation. Without field reports we can't be sure of any of this. A fallen tree, a landslide, and we would have to start all over. This modeling is only as accurate as the data it's fed."
"The data is good," Joe Webster said defensively.
Boldt looked on as Becky Sumatara pinpointed some river bends that were bright red. "The computer takes soil composition into consideration," she explained, "which is one of the reasons it's of value to us in a situation like this. You or I could look at a map and circle the tightest switchbacks a river makes, but erosion is dependent on composition, and it's not uncommon for a stream to jump its banks on a straightaway where the soil is soft and relatively uniform. Stream beds generally make turns because the water encounters some form of natural obstacle, whether a rise in elevation, or a rock formation. A barrier.
You could run your search party from turn to turn and never find this grave. My guess is that with flows like this, we're going to see a stream bubble-out well away from the turns. Although Joe may be right about the upstream bars."
"I'd like to see those upstream bars, if we could. I'd like to start there," Joe said. "One thing to keep in mind," Boldt advised, "is road access. Our experience tells us that she would have been buried within a hundred yards of existing roads."
"That's a grisly thought."
Daphne fiddled with the ungainly topographic map. "There are logging roads in this area, even some old homesteads." Joe Webster said, "There were hiking trails until they closed them down. I remember all that a few years back."
Daphne indicated the logging trails, one eye straying to the screen anxiously. "This will help," Sumatara said, referencing the map and comparing it to the screen. She made several small adjustments. The screen redrew itself each time. Boldt caught himself holding his breath again. As if from a descending bird's-eye-view, the screen showed an increasingly magnified area with each new redraw. She pointed convincingly to the screen. "Here are the two upstream bars you're after, Joe." The upper curve of the river was a deep blue; the cutaway of the stream bank showed as a bright-almost neonred, clashing with her nail polish. "It's severely undercut." To Boldt she said, "That's why the search teams missed it." She became distracted then, as the screen seemed to call to her. Again she worked the mouse. Again the screen redrew several times. "You're lucky." "How's that?"
"These most recent rains haven't yet caused the Tolt to reach the high-water level marked last fall, which means there hasn't been any additional undercutting." Now her fingers flew through a volley of commands. Boldt looked over to see both Daphne and Joe Webster glued to the screen. "Uhoh," she added, punching keys furiously. "Becky?" Boldt asked, sensing from her sudden silence that they had problems. "You had better get someone out there quick," she said, pointing once again to the screen. "The projected flow for the Tolt will pass that mark in less than forty-eight hours." Daphne asked, "Would you mark the area for us, please?" But Becky didn't seem to hear, still consumed with working the computer. "And there's something else," she said, the screen changing colors once again. "You're wrong about the depth. About the grave being shallow." She switched to a lateral view that depicted an overhang of brown earth and the animated blue of the river water well below it. "According to this, the undercut is at least six feet below grade-below the surface. Those bones were buried deep."