November 28, 2014


2013 erosion of gravel road topping at the base of the "High Road", the steepest road onsite. The gravel was blasted of to the side of the road, leaf litter sinuously pushed downhill.

In the August of 2013 we received a big rain event. August and September are the height of the dry season for us, when the parched earth is at its most susceptible to erosion.

In that one event, we experienced significant erosion on many areas of the property. On the steep slopes of the forest we saw a movement of leaf duff, as if someone had sprayed it with a hose downhill. For the most part however, the forest recovered quickly from the rain. Low spots collected the water and slowed it down so that it could sink in.

Erosion on mid-slope of the road where the open top culvert was installed

The greatest erosion was on our roads. With no leaf cover to break the force of the rain, there was Significant movement of gravel road-topping. On un-gavelled roads there was a lot of gullying and movement of the exposed clay subsoil.

I come from Arizona, where torrential monsoon rains come annually. Causing the same sorts of erosion. After working for the South-West Conservation Corps I got to see and construct a variety of hardware on roads and trails designed to mitigate and repair erosion in passive ways.

After the rain event in August 2013 we decided to construct some water features on some of our roads to help preserve the road surface and also to make use of the all the water that is collected on the roads by channelizing it into our forest gardens.

Open Top Culvert

Diagram of open top culvert from Dept of Natural Resources at Cornell University

Summer of this year I constructed an "open top culvert" on one of our heavily used, but still un-graveled roads which runs in downhill, parallel to our zone-1 garden.

An open top culvert is simply a erosion resistant channel (usually constructed of logs, lumber, concrete or steel) which is open at the top. When situated across a road or path, with the top level with the existing grade, runoff drops down into the culvert an is directed out to the side of the road onto a rock lined spillway and to a vegetated “fan” - a wide level or gently sloping piece of vegetated land - where the water can slowly infiltrate without causing further erosion.

construction of the culvert

I built the culvert out of treated 2x4's and 2x6's connected with T25 screws. 1" metal pipe and 3/8" bolts where installed in pairs every 2' to provide structural stability, particularly where car tires will roll over the culvert, and at the staggered joints.

close up of construction. Notice how the vertical and bottom boards were staggered for stablity

Earth excavated from the ditch was place in the gullied out portions of the road both uphill and downhill of the culvert to bring the road grade back up to a uniform height.

Couple of shots of the finished culvert in a rainstorm.

The culvert exits into a rock lined spillway which flows downhill a few feet and exits into a contour swale.

Constructing the swale, and a Muscovy checking out the new digs.

Constructing the swale, here you can see the full length.

The swale has been planted with various perennial plants and seeded this fall with Service Berry.

The finished swale during a light rain this fall.

Road Grade Dip

Diagram of a grade dip, courtesy of the Dept. of Natural Resources at Cornell University

On the opposite side of the zone1 garden, I constructed a quick but rough grade dip. Generally the least expensive and easiest feature to install, it is also one of the least durable to car traffic.

The worn grade dip during a light rain this fall. The flagging in the back marks the contour line where the swale will be constructed.

The grade dip was put in as a temporary feature to make sure we could stop the down grade flow of runoff on the road to the upcoming fall season.

A grade dip involved changing the grade of a sloping road or path so that overland flow of water falls into a slightly lower portion (aka a dip) which is also sloping outward. The water slows down on the road and gently exits the road or path, usually into a spillway and fan as discussed above.

The grade dip has been humming along for more than a year now. While it's been degraded by car travel, it is still diverting water off the road into the lavender patch.

I plan to put in a more permanent open top culvert here at some point in the future, and connect the exit spillway into a contour swale which runs just uphill of the existing lavender patch which will be expanded into a bee forage garden.