GPS Keyline Accuracy?

Hi, this question might be a simple yes/no kind of deal-- in my experience (older Garmin 60Csx backpacking GPS) the accuracy of a waypoint or track is usually +/-30ft from the actual location you are at. If you want a more accurate waypoint, you have to stand there for several minutes while the GPS runs the numbers and averages out a better reading.. to about +/-5ft. Given all the inaccuracy and waiting involved, I would prefer to flag out my contours with a laser transit or even a homemade a-frame or bunyip. Is my Garmin just blown out of the water by newer GPS technology? Thanks.

The low-end Ag GPS are +/- 6 inches or so. The higher end are sub inch. They are insanely good.

The cheapest receiver I have found with low GPS drift is $900.. that gets you near a +/- 1ft or so in the best conditions. Any advice on a specific model or is that what I should expect? Thanks.

Daniel Bowman wrote:Hi, this question might be a simple yes/no kind of deal-- in my experience (older Garmin 60Csx backpacking GPS) the accuracy of a waypoint or track is usually +/-30ft from the actual location you are at. If you want a more accurate waypoint, you have to stand there for several minutes while the GPS runs the numbers and averages out a better reading.. to about +/-5ft. Given all the inaccuracy and waiting involved, I would prefer to flag out my contours with a laser transit or even a homemade a-frame or bunyip. Is my Garmin just blown out of the water by newer GPS technology? Thanks.

Current GPS technology is freaky-cheap and scary-accurate. Within inches. The tech we've pioneered uses an on-site survey of lots of points (we rent engineer-grade tools, cost- ~$10/acre) This gets tied to local waypoints which boosts accuracy even further. (If a missile can go down a ventilation tube into a bunker, we can use same tech to create better livelihoods)

After two years of research, we distilled a solid understanding of GPS Keyline technology into a 2-day workshop, someone can attend that and get everything done within inches of accuracy. Laser levels and flags are fine for a single swale on a site 2-acres or less. Those that want to have multiple swales, use a Yeomans or similar for subsoiling, or have 2+ acre sites (1,000 acres anyone?) are time and money ahead using a GPS Keyline methodology.

http://www.versaland.com/workshops/gps-keyline-design/

R Scott, I'm looking forward to your reply about GPS models and costs. That kind of accuracy would be useful as we will be doing keyline design this summer on a small property.

More info or advice on where to find engineer-grade tools for rent in my area would be greatly appreciated. I am working about 4 acres of sloped pasture, 2 acres of flat-ish bottomland and 18 acres of steep woodland.. kind of borderline overkill for the high-tech route and dodgy for running heavy equipment on these slopes. I prefer a small diesel BCS 2-wheel tractor for terrace and swale building. I wonder if there is a quicker solution for flagging contours to rip keylines (one at a time!) with a walk-behind tractor, though.

Jerry McIntire wrote:R Scott, I'm looking forward to your reply about GPS models and costs. That kind of accuracy would be useful as we will be doing keyline design this summer on a small property.

I was referring to the guidance systems for tractors--well above affordable costs to buy for us small timers. But they are pretty much standard even on "small" family farm tractors these days.

Daniel Bowman wrote:More info or advice on where to find engineer-grade tools for rent in my area would be greatly appreciated. I am working about 4 acres of sloped pasture, 2 acres of flat-ish bottomland and 18 acres of steep woodland.. kind of borderline overkill for the high-tech route and dodgy for running heavy equipment on these slopes. I prefer a small diesel BCS 2-wheel tractor for terrace and swale building. I wonder if there is a quicker solution for flagging contours to rip keylines (one at a time!) with a walk-behind tractor, though.

If you're in heavy timber, fastest way to lay out a single swale is use a handheld sight level on end of a 5' long 1" diam PVC pipe. Aim it at a friend holding a 6' PVC pipe with 5' mark clearly marked with red/black tape. Works well in heavy cover, super-fast to deploy.

I'd then do some timber stand management and selectively drop undesirable trees/brush on contour (against 1-2' TALL STUMPS as an in-place stake). High slope keyline, voila!

Love that idea, Grant! We have Oak-Hickory woods (with a lot of Tuliptree) up to the top of our ridge and are beginning to replant and diversify the understory (currently overgrown with multiflora rose). Thinning on contour is a great way to begin building trail switchbacks. The log berm can be further staked out and stabilized with mushroom logs. I am planning on ripping into the pasture this spring and running some alley tree crops. The slope is too much for a full-sized tractor, so it will be slow-going.. but worth it.

Daniel Bowman wrote:Love that idea, Grant! We have Oak-Hickory woods (with a lot of Tuliptree) up to the top of our ridge and are beginning to replant and diversify the understory (currently overgrown with multiflora rose). Thinning on contour is a great way to begin building trail switchbacks. The log berm can be further staked out and stabilized with mushroom logs. I am planning on ripping into the pasture this spring and running some alley tree crops. The slope is too much for a full-sized tractor, so it will be slow-going.. but worth it.

Here's a great use for steep timber:

Mushrooms, shade-loving adaptogens (ginseng, etc) and understory fruit. We have a lot of native gooseberries. Give them a little sun and they fruit like mad!

Oh yeah, 'sangin is a big deal here! You have to camp out near your patch to fend off poachers during hunting season. Love the photo.

I wanted to do swales on a 1% grade. I assume the same idea of a 5' pvc pipe with a handheld sight level would work, but use a 7' pvc pipe with black and red tape at 6'. Step out 100' and line up the level on the 6' high mark and I should have your 1% drop. I am curious on pros/cons of on-contour vs. moving water with a 1% or 2% drop? Also for steep slopes does 2% make more sense than 1%, both making switchbacks easier and moving water a little more quickly to prevent washouts? I have a 32 degree slope (200' rise over a 330' run) with very little top soil under my sage and coyote brush. I don't think I can get a subsoiler to get in pulled by a BCS or otherwise, but the idea of dropping small tree along the path may work. Any other ideas on my 20 acres would be appreciated.

Patrick Freeburger wrote:I wanted to do swales on a 1% grade. I assume the same idea of a 5' pvc pipe with a handheld sight level would work, but use a 7' pvc pipe with black and red tape at 6'. Step out 100' and line up the level on the 6' high mark and I should have your 1% drop. I am curious on pros/cons of on-contour vs. moving water with a 1% or 2% drop? Also for steep slopes does 2% make more sense than 1%, both making switchbacks easier and moving water a little more quickly to prevent washouts? I have a 32 degree slope (200' rise over a 330' run) with very little top soil under my sage and coyote brush. I don't think I can get a subsoiler to get in pulled by a BCS or otherwise, but the idea of dropping small tree along the path may work. Any other ideas on my 20 acres would be appreciated.

Patrick, it's clear you have a firm grasp on Keyline methodology - congrats you're way ahead of most. If you have your swales at proper spacing (able to hand any likely rain event), water isn't really migrating laterally(along the swale) very far. 1% vs 2% won't make any difference in preventing washouts (rain clouds cover all you land, not just the valleys/gulleys).

re: switchbacks - you'll have those at end of swale anyway, don't think you'd gain any lateral height, can just turn vehicle or trail sooner. The goal of Keyline is to bank water towards ridges, which are typically bilateral convergences. You want lots of flat V's headed upslope, not alternating.

e.g.
{{{{{{ <- slope

not
\ / \ / \ / <- slope (this is how I envisioned your idea of switchbacks, picture this turned 90º)

In my understanding of keyline, one of the rare times you would want to design your swales off-contour is if you are trying to distribute water from the valley to the ridges (by going "downhill to the ridge", which is a little counter-intuitive until you get that the ridge slopes downhill from the keypoint of the valley). The other most common reason for going off-contour is probably to stack functions of a swale as a pond spillway or to deliver the water to some concentrated use point.

Edit-- oops yeah what Grant said.

I'm an advocate for always being 1-2% off contour, directing water to driest areas based on needs. (soil types, topography[ridges], and water features[sometimes a pond needs a little help to fill])

Thanks. I owe my understanding of keyline to Mark Shepard and Peter Allen's PC Course with Savanna Gardens and the permies forum. You're right, I did want to have alternating contours against the slope /\/\/\ as you described, but I have never seen Yeomen or anyone else describe doing it that way so it may not be a good idea. I have a seasonal creek that gets water from my neighbors run-off on my Northern boundary. It seems like pushing water around may be difficult on my land with all of my mini ridges, but it still seems useful to make some mini ponds in the valleys and push water to the ridges. This is what I'm thinking, but going straight on contour seems a lot easier to setup. I assume to spacing, having more contoured swales vs less reduces the chance of washouts and if possible putting keyline plow lines between would catch a lot of water. Thanks again, Grant.

Looks like you're making great strides. I'd start your installation from the high ground and work your way down. This will give you maximum initial benefit, without the risk of pushing a young swale beyond capacity. For broadacre installations of 2+ acres, GPS Keyline Design can make installation so inexpensive that it makes sense to design and install a complete Keyline system in one swoop.

Hello everybody

What mapping system are you using to generate those contour charts! I recently purchased 18 acres to homestead. I am working with a local designer to layout what I want. I recognize the need to plot the contours but I'm not sure how to get the elevations. A contour chart of my area would be a big help.

Any suggestions?

Are you wanting any 'ol topo map? Depending where you are in the country, a USGS survey may be available. LIDAR maps are often available to 2ft elevations. County assessor or FSA office may also have something. So many options.

You might try http://www.mytopo.com/search.cfm
or http://www.mytopo.com/states/index.cfm