Coastal Bluff Erosion:
The $Million Solution vs the $Thousands Solution !!!
I went back to my old hometown last week to attend my Granddaughters 8th grade graduation and my Grandsons graduation to middle school. I also went surfing and checked out Coastal Bluff Erosion.
I always go to Pleasure Point because this was where I grew up - hanging at the beach and surfing at the Hook, . Also, this was my 60th birthday and I needed to get out and surf - just to prove ......
Back to cliff erosion! A couple of years ago my brother asked me to try to stabilize his cliff near Pleasure Point on Opal Cliffs Drive. You may remember that we (myself and Profile Products) did a webinar last year with Civil Engineering News. I think the webinar is still up and archived on the CE News website.
My brothers coastal bluff problem was a timely and perfect opportunity to introduce the Green Armor System. We had stabilized the lower portion of the cliff from wave erosion years ago, so the "biggie" was the rain-splash erosion on the steep, very-difficult to vegetate upper marine terrace deposits. My brother's property also has some subsurface erosion problems - I have corrected all the drainage from gutters, downspouts, patio etc. - no this drainage likely originates miles away and flows along old sedimentary strata referred to as "facies". The really well-anchored Enka Mat was permeable yet strong and could be counted on to resist the "sapping" forces and the of course, the raindrop impact.
So, the common problems associated with coastal bluff erosion in this area is erosion of the underlying Purisima Sandstone by wave erosion, then mass wasting and raindrop erosion of the near vertical upper marine terrace(s) with the common subsurface and localized soil piping.
"Coastal Retreat" has been documented at 0.8 ft per year over the last one hundred years or so. (Gary Griggs and others). This rate was of course localized in certain areas but I remember huge sections of coastal road that have disappeared since I was a young surfer hanging out on the cliffs, watching the waves.
In fact, East Cliff Drive, near Jack Oneil's house, is currently being stabilized by a multi $$ million $$ dollar project involving drilled and grouted slope nails and gunite.
Check out the photos below and then compare with our Opal Cliffs Drive technique using green armor.
We did the Green Armor job two winters ago - January 2009. It has been through two very rainy winters, in fact the cliff received over 6 inches of rain on the week following construction. The Enka Mat and Flexterra are still protecting the cliff face. I put down mycorrhizae and slow release fertilizer with the "native" seed mix. I just wish I had done a more thorough soil test because the grasses are slow establishing and I don't know if pH or salts are the cause. The current photos show the mediocre veg response but also look at the "horsetails" (Equisetum - scouring rush), an invasive that grows near water, at springs and at shores edge! You cant see in photos but we also planted a dozen willow stakes and over half are growing pretty well!
While the East Cliff Drive Stabilization project is really geotechnically appropriate and final concrete slopes have been textured, colored, and sculpted, I can't help but think of a lower technology and more cost-effective alternative utilizing the soil nail launcher and the Green Armor System. Just a thought!! My brothers house has been foreclosed upon so this may be the last monitoring report from Opal Cliffs.
Oh, and here's some pics of me 'not being sixty years old'! :)