New Gabion Fails During First Flash-Flood

Arivaca saw it's summer monsoon season begin at the end of the first week of July with some heavy rains.  My wash is fed from slightly higher elevation hills and terrain with drainage from branching cuts on the land.  So it all funnels down.

Photo below was taken around July 22nd, around two weeks after approximately 4" of rain over that time.  Also notice how much vegetation has grown in less than two weeks (see previous post). 

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The photo below shows the path of the breach at the south end of the Gabion.  I knew I was cutting corners when building the Gabion.  I should have taken the time when constructing it, to ensure the Gabion was properly and securely "keyed" into that south bank of the wash.

The photo below is a closeup of the breach.

Below.  Photo taken downstream, looking upstream with the arrows showing the flow paths.  I was surprised by the large amount of material stripped from the embankment. 

I'm now going to figure out the best repair option for the Gabion and make the repair. 

Second Gabion Added After 10-ears

I recently added a second gabion down-stream about 40-feet from the original gabion built about 10-years ago (see earlier posts in this blog).  

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Q) Why was a second gabion needed?
A)  Because the dry-wash downstream of the first gabion became essentially a 'channel' that directed flash-flood waters from summer monsoon storms rapidly off the property and over time deepened the dry wash channel.

Q) How will this second gabion help?
A) During a flash-flood, the flowing water contains sand, rocks, clay and organic soils that settle once the water slows down.  Over time, the channel upstream of the gabion fills-in with sediment and levels off the land.  This action can be seen in earlier posts in this blog.  

Q) Other benefits of the second gabion?
A) Just like the first gabion, this second downstream gabion will slow the flood flow to allow water to infiltrate the ground.  Also, the gabion acts to spread water out the sides from the channel to saturating the ground around the neighboring Mesquite trees to supply needed water to the Mesquite bosque.

The second gabion was built using rock stripped-off the 'apron' from the first gabion (see earlier posts). The apron attached to the downstream side of the gabion, helps prevent the gabion from essentially being undermined by the flood waters and 'rolling' down the wash.  At this point the apron was not needed because the first gabion was no longer in danger of being swept-away by a flash flood, since sediment has already build-itself-up to the height of the first gabion.  

The gabion in the main channel is simply rocks of various sizes encased in a steel mesh. Both sides of the channel were dug into about a foot to hold the wire-mesh-cage in place.  The rocks on the sides, should also be encased in wire-mesh but time didn't allow that level of detail.  This risks these large loose rock being swept away during a flood, but I'm going to go with my gut feeling that the first gabion will still act to slow and disperse the water sufficiently to maintain the integrity of the second gabion.

The photo above was taken downstream looking upstream.  Notice that there is no apron behind this second gabion.  The reason in part was the time-allowance I gave for the project.  Again, my feeling is that it will hold, but never underestimate the power of water to change the landscape - We'll see.

Next Step?

The gabion seen in the photo below has done its job of maintaining the driveway ground level. 

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Now the problem moves down-steam as the water during flash-floods works around the sides of the dam with high velocity resulting in erosion and begin under-cutting the rock apron as seen in the photo below.

A close-up of the rock apron showing debris from over-flow during flash floods.

Side angle photo of the gabion (left side of photo below), showing the stabilized driveway.

Nice sand build-up after each summer monsoon season (photo below) which I can use as a 'local' resource when mixing cement or other around the property uses.  Downstream of the gabion you can see the eroded wash which acts to remove water off the property too quickly.  Thus additional gabions are required to slow and spread-out the water flow.

The next step is to build a second gabion by the large tree in the top-center of the (above photo).  Over time the sediment will fill in between the gabion here in the foreground and the second gabion to be constructed by the tree.  In the meantime the ponding water between the two gabions will serve to 're-charge' the aquifer and water the surrounding Mesquite Bosque.

For additional details of construction of this gabion, scroll down and view earlier postings.

Early Summer 2012 - Update

The monsoon rains started about a week and a half earlier this year and already the wash has run, so it's time for an update to this blog. Looking at the center of the photo below, you can see fresh sand that was deposited on the driveway as the flood swept left-to-right. The vegetation has responded rapidly to the rains and everything is looking nice and green.

The gabion is doing its intended job for its location, which was originally to keep the flash-floods from creating a deep rut across the driveway.

The second photo (below) was taken standing on the driveway looking at the gabion in the downstream direction. The gabion is almost covered over at this point and that has got me thinking that may need to create a second gabion about 30 feet further down to slow the water again allowing infiltration into the soil to the benefit of vegitation and the mesquite trees which are clustered in this area of the property.

4 -Year Update

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There were a couple of flash floods so far during the 2011 summer monsoon season here in Arivaca. Unfortunately, I wasn't at the property the time of the floods to catch it on film. 

The first picture below shows a buildup of sandy gravel across the driveway.  The rock gabion (now almost covered at left) slowed down the water flow allowing the sand/gravel to deposit on the driveway. 

This is exactly what I wanted as a 'design' goal when I chose the location of the gabion.  If there was no gabion, these fast-moving flash floods would be carving-out 'ruts' in the driveway, resulting in vehicles possibly getting stuck or having the rear of vehicles bottom-out as they crossed.  In addition, I would have to spend time filling-in the rut after each flood.

Another benefit from the deposit of the sand/gravel is that I need to use this sand when mixing cement for the concrete bond-beams that will be supporting and connection the walls and roof on my cob studio I am currently building on the property.

The photo below is a current upstream shot of the gabion looking downstream.

The last photo shows how the gabion looks on the downstream side facing upstream.

1-Year Update

It has been a year since the gabion was first constructed and we've had only two or three"gully-washers" (as the locals like to say), in that year. The organic debris accumulating on the gabion in the photo above suggests that at least one, or more, flash flood events has occurred.

The purpose of a gabion at this location is to build up sediment near and around the upsteam side of the gabion. The location pictured, is where the driveway crosses through the dry wash.

The photo shows that sediment is beginning to build-up at the bottom of the gabion. The surrounding healthy vegetation attests to amble monsoon rain over the past month of so. Less intensite storms this year than last; but more frequent. The ground is getting enough moisture to keep the plants happy. During some monsoons we get a good rain; then 2-weeks goes by before the next rainfall. In that scenerio, the plants start turning brown prematurely and additional rain does little to get the plant to achive its full potential.

Nature Gently Tests Gabion

The video below shows the first 'natural' test of the newly-completed gabion (check dam) featured in this blog, after about 1/2-inch of rain fell in Arivaca on August 15th. This runoff event was a small low velocity flash flood, so there was not much sediment buildup on the upstream side of the gabion. Inspection after the water subsided showed no erosion of sand in wash downstream of the apron.

If there is no video below, please try the following link: 1:24 minute film: Nature Genty Tests Gabion

Day 4: Apron Completed

With large rocks applied to the apron, a top layer of wire mesh was added and then all the ends (top & bottom) were tied together with heavy wire. An analogy would be that of a pita-pocket. All the large stones that make up the apron are now contained with the wire mesh.

The photo above shows the wash upstream and the driveway crossing. Hopefully, during the next big rain, the ensuing flash-flood will carry sand down to the gabion and build-up the level to make crossing the wash with a vehicle easier.

In the future, I hope to add additional gabions upstream to slow the water down, spread it out across my bottom-land to reduce erosion and provide additional water to the mesquite trees that grow along the wash.

In the future, I will be posting photos and short movies to show the impact of flash floods on the gabion, and surrounding bottomland. Repair work and maintenance on the gabion will also be documented.

Let's see what happens from this point forward!

Day 3: Downstream Apron

The reason to construct an 'apron' for the gabion, is to prevent undercutting of soil, immediately on the downstream side of the gabion. Without an apron, water flowing over the top of the gabion would eventually cause the gabion to collapse into the eroded hole and over time, erosion would continue and the gabion, in effect, would appear to roll down the wash and disintegrate.

To construct the apron, wire mesh was first laid-down across the wash and up each side of the wash by a few feet. The wire mesh was then wired to the gabion.

Approximately 12-inches of river rock was applied to the base of the apron. The rationale behind the application of river rock, is to slow the velocity of any water that migrates downward as water flows over the top of the gabion. Note: This approach is experimental: I had river rock left over from other another project.

Day 2: Gabion Spans Wash

On day 2, a second wire cylinder was laid down in the wash and stone was added from the top until filled. The wire mesh was then closed at the top and wired shut. The photo to the left was taken downstream - looking upstream and show the completed 10-foot wide gabion spanning the dry wash.

The next step in the process is to build an apron on the downstream side of the gabion.

Day 1: 6-Tons of Rock

Gabion = Rocks. Lots of them. In the course of the four days it took to build the gabion, I hauled approximately 6-tons of rock from a nearby mountain. Lots of fun :)
I then began to construct the gabion. I dug-down about 6-inches into the wash then across about one foot into each side of the bank. The width of the gabion thus was about 10-feet.

I had a roll of heavy-duty wire mesh left-over from another project and used it to contain the rocks. I created two 3'-diameter cylinder with the mesh (each 5-foot in length), laid them in the trench dug in the wash and filled them with rocks. See photos below showing the first section in place.














This wire mesh can be purchased at a building materials store and comes in rolls. WARNING: The wire wants to stay rolled as you try to unroll it flat. Be careful here. If not secured adequately, the end can spring-back at you and cause serious injury. Wear heavy duty gloves and eye protection.

The need for a Gabion

Here in Arivaca, AZ I had about 12-inches of rain in the past 30-days (July 3-August 3). In Last year during our monsoon season, I had just over 4-inches for the same time period.

My normally dry wash, flash-flooded about three times and removed about 1-foot of sand from the wash. As the picture to the left shows, my entry drive to my property crosses this wash. It's hard to see in the picture, but now my truck dips when crossing the wash.

Earlier in the year I was meaning to build a Gabion (a.k.a. check-dam) just downstream of where my driveway crosses the wash, but I've been busy with other projects like my cob studio.
But with the erosion to date and still a month to 6-weeks of monsoon season left, I decided to tackle the project. the goal for building this gabion is to allow the buildup of sand upstream of the gabion in order to make access across my driveway easier.

Gabions have other other benefits also: 1) They slow water down so it can percolate into the soil and recharge the aquafer. 2) Spread water out in bottomland areas to reduce erosion and soak soil for trees and other vegetation.


The next photo to the left was taken downsteam looking upstream. The truck indicates the crossing and the gabion will be constructed where the clump of grass is in the wash. The width of the wash at this location is about 8-feet.

The photo below shows the wash running following a thunderstorm during last year's monsoon season. The photo was taken looking upstream at the the driveway crossing.