Shifting dehydrating, degrading ephemeral water channels to better-vegetated, rehydrating, agrading channels with Bill Zeedyk-directed efforts in Altar Valley, Arizona
By Brad Lancaster with gratitude to Bill Zeedyk for his edits, feedback, and mentoring www.HarvestingRainwater.com
Starting January 2012, Bill Zeedyk and Steve Carson directed the largely volunteer-installed on-the-ground work in a collaborative conservation/restoration project in the Altar Valley in southern Arizona, aiming to reverse the erosive down cutting of water channels/arroyos and dirt roads at the Elkhorn/Las Delicias Watershed Restoration Demonstration Project site by using three primary strategies:
• induced meandering within the water channel with one-rock-high baffles and one-rock dams seeded with native restoration seed mixes;
• treating a 3.25-mile stretch of dirt road with 54 rolling dips that drain stormwater off the roads and passively irrigate roadside vegetation, and 14 road crossing stabilization structures stabilizing road crossings of streams;
• upland restoration with one-rock high rock media lunas and one-rock dams upstream of the main water channel
The project and its effects were and are extensively monitored.
As Bill Zeedyk says, the intent of the project was to reverse the trend by shifting from erosion of soil to deposition of soil.
It has done that.
In addition, moisture now lingers longer in the watershed, enabling more vegetation to grow, better capture sediment, and hold and build soil. All this also reducing flooding and erosion downstream.
I just attended the 10th anniversary tour of the project, and wanted to share photos and videos taken over the years at the project, plus links to data from the project’s extensive monitoring, so you can see some of the positive results.
Work within one of the main water channels/arroyos
Media luna structures above the water channel (scroll down for photos) are also helping heal this part of the channel. The media lunas have helped slow, spread out, and infiltrate sheet flow in upper reaches of this water channel’s watershed to re-wet and re-vegetate about 2 acres of previously bare draining and eroding land.
By reducing the volume, depth, and speed of peak flow of stormwater (by spreading out the flow) within and above the water channel, the force and ability of the flowing water to carry sediment is also reduced. So, you then see more smaller particles of sediment compared to the larger particles seen before restoration work.
As the water flow is spread out and slowed down, more water saturates the soil, and prolongs the length of the time the water flows and lingers in the landscape, enhancing the growth of more water-slowing and -spreading vegetation.
As more vegetation grows, the roots increase the permeability of the soil, which then increase the volume of water that infiltrates the soil — especially within the site’s otherwise hard, exposed subsoil. Vegetation continues to grow, and sets is roots deeper and deeper as it also grows a thicker and more absorptive sponge of organic matter above the soil’s surface; more water is slowed and infiltrated, and more vegetation grows—a beneficial feedback loop.
The topography, in the four photos immediately above, is typical of what the valley floor looked like before headcut erosion and resulting gullies arrived and drained the valley.
The erosion was due to severe overgrazing, which removed much of the vegetative cover of the land, which then sped up the flow, depth, and force of the water draining off the land. Other practices that similarly drained and dehydrated the land were irrigation diversions and railroad embankments that channelized sheet flow; dirt roads that diverted, captured, and channelized sheet flow; and fire suppression.
The main channel of the Altar Valley Wash (downstream from these photos) then erosively down cut, and all tributaries draining into the down cut Altar Valley Wash then also down cut—starting at headcuts formed where water flow from the tributaries dropped over a newly steepened drop into the recently down-cut Altar Wash. The whole Altar Wash and its tributaries throughout the Altar Wash watershed down cut and head cut up valley.
So, the four photos above, show a relic of what the landscape would’ve looked like without gullies. Though it would’ve been better vegetated.
Erosion caused by wagon roads is what really caused the whole system to originally degrade, plus there was an irrigation dam upstream in the Altar Wash that blew out in the early 1900s. When it blew out, flows got caught in the wagon wheel ruts that were paralleling the water channel. Ruts were straighter than the meandering channel so the paths of the ruts were steeper, water flowed faster within them, and easily carried away the fine clay soils. This started the whole unravelling.
It was made worse by the irrigated pastures on the ranch that is now the Buenos Aires Wildlife Refuge.
Due to erosion from road and irrigation ditches, head cutting and down cutting started (due to main channel being incised) and this head cutting and down cutting continues to this day.
It is hard to prioritize where to do grade control work in the watershed, since there is such a large need throughout.
So, at least encourage restoration work wherever it is welcomed by the land owner, manager, volunteers, etc. Such work could be on the refuge or any of the ranches where channel incision is still occurring. For as Bill says, “You can lead people, but you can’t push a rope.”