When you are paddling outside of a guidebook, one of the key attributes of a stream to ascertain is the gradient. While it won't tell you exactly what you are in for, it can give you a clue, especially if compared to the gradient of similar sized streams in the area.
Iv'e been asked what tools I use to do this more than once, so decided to create a short tutorial for the quickest way I know how. The math is simple and while the whole process can be done with a paper map and a string, I find this method faster.
If you want background knowledge in rise/run and the math, click
here. Kayakers think in elevation lost, so on this page I will use the word "drop" in place of "rise". They are the same, and simply represent the change in elevation.
The simple of it is you want the elevation dropped (in feet) divided by the distance traveled (in miles).
The next step is to find elevation lost and the distance traveled on a stream. Here’s how to do it:
1) I start by going to
Hillmap.com I find it to be a simple and effective tool for this job.
2) I put the program in "terrain mode", using the drop down menu and clicking the terrain option button like shown below. This creates a hillshade effect over-layed with contour lines once zoomed in.
3) I locate the section I am interested in and zoom into it. For this tutorial, I'll be analyzing a section of Cavitt Creek between it's confluence with Plusfour Creek (43.147, -122.9556) and a bridge just under 4 miles downstream (43.1569, -123.0167).
BEFORE CONTINUING, MAKE SURE YOU
UNDERSTAND HOW TO READ A CONTOUR MAP.
4) I find an index line near where I want to start calculating gradient. Then trace the stream using the "path" tool to a contour line down near the end of the section I am interested in. In Hillmap, just click on "Paths" then click on the map and it will start drawing.
- You can see that once the path is traced, the distance of the path shows up in the top center of the screen. 3.67 miles in this case.
- I know the distance between 2 index lines at this scale is 200' (they are written on the index lines themselves) and 5 contour lines are counted before the next index line is reached so I can ascertain that each contour line is 40 feet (200/5=40). Note that if you zoom out enough this changes to 400' between index lines, so be aware of which scale you are at.
- In this case I passed two index lines and two more contour intervals, and the scale was such that the index lines were 200' apart. This means the total elevation dropped was 480'.
- With a drop of 480' and the distance traveled being 3.67 miles, I plug those into the equation as 480'/3.67 miles which rounds to 131'/1 mi or to put it in the form kayakers are used to..........131 fpm
And that's how you calculate the gradient of a stream.
TIP: If you flip the basemap to satellite mode and zoom in, you will be able to trace the stream more accurately, before flipping it back to terrain mode to count the contour lines.
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More
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For kayakers, there is more to it than that. 131 fpm is the overall gradient, yet the most important figure for me to determine on an exploratory run is the maximum gradient. That will answer the question of what is the steepest section of stream we will encounter? Where is the biggest challenge most likely to occur and how big of a challenge might we be talking?
For that, I look for the two closest index lines on the map. When you have done this enough times, that is easy to eyeball. If you are just starting out you might need to guess and check a bit.
For Cavitt Creek, the two closest index lines would be between...
Then I draw the path between those two index lines, and come up with a distance of 0.88 miles.
Since I know those index lines show 200' of elevation difference the calculation is 200/0.88 which equates to 227 fpm. I find this number more important than the overall gradient.
You can get much more in-depth than this, many guidebooks even list gradients mile by mile, but you can make the call about how much information you need. The gradient can be combined with other tools like satellite imagery, flow charts, hiking photos of the stream, fishing forums, scouting trips, rumors from a friend of a friend and anything else you can get a hold of to paint a picture of what you might find on a stream to help you make a decision if its something you want to explore with a kayak.
*Astute observes will notice that when tracing a path in Hillmap, that next to the distance traveled is the ft gained and ft lost. I don't find the
elevation lossed/gained to be represented accurately by Hillmap when
tracing a stream so choose to count the contours myself.
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Story
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The advantages of knowing the gradient on a new stream to explore can be obvious. From 600 fpm, holy cow that's nuts! To 13 fpm, hmm maybe I'll save that one for teaching grandma how to kayak.
A good case study on the usefulness of being able to obtain gradient information was when planning for a southern Oregon tributary to the Illinois River called Lawson Creek. Typically I want to put in as high as possible on a new stream for the first time to see as much of it as I can. Then afterwords can find a put in/take options that gives me the best bang for the buck (if it's even worth repeating the stream in the first place, often it's not).
For Lawson Creek, the stream looked pretty uniform from the satellite imagery, boulder strewn with some tantalizing bedrock at the very top. When I went to calculate gradient, I noted the upper reaches were mostly reasonable, but had some pretty high gradient sections around 300 fpm. Now gradients over 300 fpm can be good fun, but only in rare cases is it not at least class V once you get past the 250 fpm mark in Oregon.
300 fpm and never reaches class V.
Most often though that kind of steepness ends up being extra dangerous and partially to fully unrunnable in the PNW, especially when it is bouldery like was obvious Lawson Creek was from the satellite imagery. Downstream of the 300 fpm section there were a couple more reasonable miles then the gradient soured to over 450 fpm for a short bit. However, I noted that just downstream of that gradient spike, the stream eased off to 100-150 fpm for the last couple miles, which seemed just about right for us to roll the dice on an adventure given the size and style of stream that Lawson is.
The area is rugged, so just bushwacking in below the gradient wasn't a great option, so I looked at a different basemap (CalTopoFS) that includes trails, and found one! I rechecked the gradient starting at the trail going both upstream and downstream, and saw that it was placed in a pretty ideal location just downstream of the last Richter high section of gradient.
This trail ended up having a lower elevation access road than dropping in from the top so snow wouldn't be as large a concern and meant we could do the run as a day trip, and weren't as worried about dealing with long class V and unrunnable sections and could expect more of a IV-IV+ (V) trip which is more our style. You still never know what you will get on those type of runs until you go, but in this case we set ourselves up to have the best chance we could of having a good adventure and it paid off with one of our favorite days of boating that year. On the hike in, we had high visibility both upstream and downstream and could see that we were in fact putting in just below a section of very steep whitewater, and just above what turned out to be a couple miles of fantastic IV-IV+ boulder gardens.
-jacob
A comparison in Gradients
400 fpm and bouldery in Oregon
450 fpm bedrock in Montana
600 fpm polished granite in California
Some known entities in this area and their gradients (rounded).
Rogue.................................................13 fpm
Illinois................................................24 fpm
Clackamas (Three Lynx)....................30 fpm
North Umpqua....................................30 fpm
Wilson................................................35 fpm
Crooked..............................................40 fpm
Bull Run.............................................50 fpm
Breitenbush........................................60 fpm
Grays..................................................65 fpm
White Salmon
Farmlands......................................60 fpm
Truss..............................................130 fpm (174 max)
Middle...........................................50 fpm
Lower............................................30 fpm
Lower Lower.................................50 fpm
Upper Wind........................................90 fpm
Blue....................................................90 fpm
Little North Santiam (Opal Creek).....100 fpm
Quartzville Creek (Upper)..................100 fpm
EF Lewis.............................................110 fpm
Canyon Creek, WA.............................120 fpm
Copper Creek......................................125 fpm
Lower Trout........................................125 fpm
Ohanapecosh.......................................130 fpm
Cispus (Upper, Upper)........................150 fpm
Canyon Creek, OR............................. 90 fpm (200 max)
NF Clackamas....................................200 fpm
Lake Creek Slides..............................200 fpm
Mccoy Creek......................................200 fpm
Brice (Upper).....................................215 fpm
Brice (Lower).....................................60 fpm
SF Coquille (The Gem)......................220 fpm
Clear Fork Cowlitz.............................230 fpm
Miracle Mile.......................................250 fpm
Little White Salmon...........................250 fpm (295 max/Gettin' Busy)
Lostine................................................250 fpm
Hagen.................................................260 fpm
Upper Trout........................................260 fpm
Christy Creek.....................................400 fpm in steepest mile
It's a whole different game in California's High Sierra's, where 300 fpm wouldn't even get you an honorable mention.
