Moccasin dam response

NAA response to the Moccasin dam emergency
March 2018, updated May 13 2018

Moccasin dam aerial orthomosaic and down stream conditions
2018: 2017 all over again.
Massive amounts of rain in a watershed causing evacuations downstream, what to do next time.

All of Northern California is acutely aware of water. Recent history dictates there is not enough of this liquid gold as we continue to endure a decade long drought. Add in a pineapple express and/or the ‘March Miracle’ two years in a row and we end up with more water than systems can handle in a short period of time. Reasons for this? The experts will continue this debate in politics and think tanks for years to come as water is the lifeblood of California.

Local news coverage from Groveland as the event unfolded.

Hwy 49 washed out in the foreground, high water marks on the power station, labs and the incoming penstock to the power station. Image credit: – stitched pano of eight images

Upon hearing of the news flash, we called one of our clients in this area, in a different watershed. I was a bit surprised to get the hydro manager on his cell. To my surprise he had not heard about any news and since I got him at his desk as he was coming in from the field, I suggested that he open up the website for water flow records. As we chatted a bit, he started with a ‘wow’, then a ‘whoa’ followed by: …” I got to go right now and make some calls. I will be back in touch. Thanks bye…” click.

NAA readied our pilots, six different drones, safety equipment, air space (no TFRs!) / ground planning, filled up the F-150 4×4. We left at at first light for the three hour drive to Moccasin, CA. No contract, no client, no expectations except having the ability to help in a productive way. Once on site we quickly made contact with the IC from the SF water agency and a representative from DWR. Presented our business cards and credentials with a near by dam inspection and a desire to help. We were accepted as professionals and asked why we there? Simple answer: because we care and we can. As you can see the day was amazing with little to no clouds and light winds, not what they had lived through in the last 24 hours for sure. We suggested that we set up away from the emergency work and out of the way of the coordinated operations and would be happy to share whatever we found at the end of the day. Everyone exchanged business cards and went our separate ways.

Close up of the crews working the banks and the snags. Entire new ‘beaches’ formed in hours. Image credit: – stitched pano of three images

This is where all of our preparation, practice and patience bears fruit. My lead pilot got to work, I oversaw the safety aspect and our VO was ever aware of capturing ground images when we did not have aerial ops in action. With our prep we had everything we needed to be successful in the field. In short order we had flown four missions. The mission in the first ortho of the dam and the downstream condition contained seventeen and half acres and took eight minutes to fly. We did a quick process using Pix4D on our field laptop and had results in under a half hour. The amount of damage was hard at times to get your head around. Highways washed out, trees snapped in half like toothpicks, sand bars causing the river to be rerouted, snags now all over the infrastructure and constant reminders on just how high the water did rise. We made highly accurate 4K aerial orthomosaic images (sub 2 cm per pixel) of many different areas. The rest of the missions we processed later that night back in our office with our dedicated workstation again using Pix4D. Patience was needed as we shared the airspace with a CHP helicopter as they completed their job right at the estimated four hundred foot ceiling we had in class Gulf airspace. Our site operation checklist clearly makes co-hab airspace a safe reality following the FAA Part 107 regulations.

Twenty four hours with no rain was all that was needed for the infrastructure to recover. Thanks to the professional response, labor from the local prison and a ton of equipment, Moccasin is mostly recovered as this post finishes editing. Feel free to explore the after ground images, some of these are clear examples of what the full power of water is capable of.

What happens next? Lots of time reviewing images from the past, overlaid with the current orthos. Plans of every kind from staging of equipment, supplies, material and people. The dam came within two feet of over topping, yes down stream lake Don Pedro could easily contain this even in the worse case and no lives were lost, but how can we learn from this for the next rain ‘event’?

Full DSM dam demonstrating multiple processes on the same image