I developed a technique last year during the Keyline Design Course at Tuscon, Arizona for making a contour map using cheap available materials. One of our students didn't have the cash to get a surveyor to do the job on his 40 acres, so I came up with this solution on the whiteboard and have since tested it on the ground quite a few times now.
1. Using a Bunyip/Water Level, A Frame, Laser Level or Dumpy/Automatic Level mark out a contour line using stakes or pin markers.
2. Using a Bunyip/Water Level, Laser Level or Dumpy/Automatic Level go down or up the desired elevation (eg: 1 foot or 0.5m).
3. Repeat in sequence steps 1 & 2.
4. Using a consumable GPS (I have a Garmin Etrex VistaC - about $200 worth) record waypoints at each of the stakes. Be sure to wait for the GPS to 'settle down' reducing its error. Hold the GPS out in front of you over the stake and then take the waypoint.
5. Using a measuring wheel (or paces if you're good!) take some 'ground truthing' measurements across the site. This will be useful later when you want to rough out the 'coefficient of error' from the GPS as there will always be with a consumable model. It's good enough for a bush job though!
6. Then load the GPS data onto com-puter. Most GPS units come with a basic mapping programmes or you can (as I do) use a programme like Map-Info, other GIS or CAD programmes.
The waypoints will come up marking the pattern of the contours. You can then join the dots and, hey presto, you have your contour map. You can also record the boundary fences and other features of the site using the GPS to give you your contoured feature plan. I have just done one of these yesterday, the results of which can be found at: http://picasaweb.google.com/permaculture.biz/Dalpura/ photo#5234877346927198562. For this job I only needed a few contours. The accuracy came in at between 1-3m which over 20 acres is fine...
Coming to the UK summer/autumn 2011!
Darren Doherty is teaching an 8 day Advanced Design Course in Regenerative Agriculture including holistic management, keyline design, permaculture, biofertilisers & polymarketing
Plus a 3 day practical farming course - surveying, project management, agroforestry, earthmoving, soil development and carbon farming.
For more detsial email [email protected]