More on 22 January...

We've recently had the opportunity to recover two cameras set up to record time-lapse photos of the Elwha River delta, both of which were recording during the 22 January high-water event that I've written about previously. In this post I'm simply going to post some of the information from those cameras as well as document some of the impacts of that high-water event on the delta.

Again, the event on 22 January had a few characteristics. First, there was a perigean high tide that day, with an additional "non-tidal residual" of about two feet:






That non-tidal residual was probably driven primarily by low sea-level pressure. Here are the air pressure data (the second panel from the top) from the Port Angeles airport from Jan 22 (from Weather Underground):









The peak low air pressure corresponded almost exactly with the peak high tide. The other interesting part of this event was the relatively strong east wind associated with it, which pushed

The first camera is sited on the west side of the river mouth on private property overlooking the river mouth. The higher berm on that side of the river mouth, combined with the relative protection from east waves afforded by the delta itself, seems to have held off most of the sea's energy. This photo was taken right at high water, and in it you can see that the lagoons formed by sediment movement right at the river mouth are full and the berms surrounding them are probably over-topping them. To the left in the image though the high berm fronting the beach doesn't appear to be over-topped anywhere.










Another camera placed on an old communications tower on the east side of the delta did record some of the berm overwash that was evident after the storm. This beach profile, collected just to the east of Charles road on the east side of the delta gives you a sense of what I am talking about. Between 4 January and 27 January the top of the beach set back at least 5m, while the lower foreshore (below about 2m on the profile) shows little sign of change over the same time period:








And the view from the tower at 1:15pm on 22 January looked like this:









You have to sort of know the delta to see where the over-topping is happening in this photo. It might help if you have something to compare it to. This photo is from the following day at the same time.









The combination of high water and strong east wind and waves are driving water over the berm (which is only about 3.5 m above MLLW along much of this shore)along pretty much the entire stretch between the two clumps of trees on the left and right sides of the photo. Our observations suggest that this wide scale overtopping was associated with lots of erosion on the upper part of the beach, and it appears that much of that sediment was pushed back over the berm in to back beach areas:








and finally, to see the whole storm in action check out the entire timelapse video collected from the tower between December 2011 and February 2012:

Moving to Higher Ground

In this era of climate change and an increasing understanding of our tsunami-risk the coastal communities of Washington have to come to terms with the concept of retreat. One of the only reliable adaptation measures available to us is to move up and out of the way of an encroaching ocean. Some are showing us how to do this. The Quileute tribe, in recognition of the tsunami-risk that they face, came a step closer today to moving infrastructure off of the low-lying Quillayute River delta with a vote by the U.S. House of Representatives.

I am a supporter of Olympic National Park, and guess that there was some concern about the park losing ground. Given its history and how hard-won every acre of the park is, this is understandable. By the same token, I am a supporter of the Quileute and their right to live with a modicum of security. Their present circumstances are perilous, to say the least. Furthermore, over the next century there are going to be more and more cases of coastal communities moving to decrease their coastal hazard risk. Overall I support that trend - its expensive, but in the long run I feel that its the right thing to do. Its impressive to see the Quileute, a small tribe and small community, leading that national movement.

The new tool...ground-based LiDAR

Over the last few years a new tool has been applied to the problem of measuring topographic change of the Elwha watershed and floodplain. LiDAR (Light Detection and Ranging) uses a focused light source to develop precise measurements of range to an object. With its extraordinary high sampling rate it can be used to develop comprehensive digital terrain models at very high resolutions. Repeat surveys can efficiently identify topographic changes. Amy Draut and Josh Logan of the USGS recently put together this LiDAR derived view of the lower Elwha River and floodplain, which is pretty cool:



I am part of a team that was recently funded to start collecting LiDAR derived data on the morphology of coastal bluffs on the Strait of Juan de Fuca. Once we get a few repeat surveys we are going to be able to start calculating erosion rates that are going to be far better than anything we've developed before...

looking forward to it...

The Convergence

We had a really interesting and rare set of processes that combined yesterday to bring some potentially destructive sea conditions to the North Olympic Peninsula. I haven't heard any confirmation of serious damage, though initial reports from La Push suggested the possibility of some damage to their harbor. In Port Angeles where I was three factors came together. First, we were at the tail end of the the last of a series of "king tides" for this winter. These exceptionally high tides occur when the sun, the moon and the earth are in alignment AND the moon is relatively close to the earth in it elliptical orbit. The gravitational forces combine to give us what are generally the highest tides of the year.

Additionally, a low pressure system passed over that coincided exactly with the predicted high tide, which elevates sea levels a bit due to the "inverse baramoter" effect (nicely explained by Cliff Mass here). And, because low pressure is often associated with wind, the strong southerly winds on the outer coast probably also acted to elevate water levels in the Strait of Juan de Fuca. In Port Angeles, local water levels were elevated by about 2 feet ABOVE the predicted high tide:




and the part of it that made yesterday's event interesting was that the peak in that water level residual corresponded almost exactly with the predicted high tide. In sum, the measured water level reached 9.3 feet above MLLW, only about a foot shy of the highest water level on record (from Jan 2 2003). Part of that is due to the fact that yesterdays convergence was at the tail end of the king tide series, and the predicted high was about 6 inches less than the high predicted from two days before. As I've said before, coastal flooding is a game of probabilities.

The final piece of yesterday's puzzle that made it potentially dangerous was the waves. Waves almost always approach from the west here, which typically turns out okay for Port Angeles since the western approach is protected by Ediz Hook. But every once in a while we get strong east winds that can generate waves in the eastern Strait of Juan de Fuca and push them straight into Port Angeles harbor. I am jealous that some even had the chance to surf in the harbor (and it wasn't me...photo from the Sequim Gazette)



My visual estimates suggested wave heights of about 4 feet, with a 5 second period. Our closest real-time wave measurements are made just south of the San Juan Island, where significant wave heights were about 2.5 feet with periods of about 5 seconds. Waves, of course, deliver the energy that often does the most damage during high water events. In this case the combination of very high water levels and large waves send water up and over the Olympic Discovery Trail (photos below also courtesy of the Sequim Gazette) and on to the public wharf.





Again, coastal flooding is a game of probability. When the processes converge is when we can see the ocean starting to influence us in ways that don't necessarily work to our advantage. The final part of the equation not considered here is sea level rise, and how the probability of damaging events changes with time as the mean level of the sea rises. More on that in future posts...

What Sea Level Rise Looks Like

I've been doing a lot of reading of late, dredging up all of the peer-reviewed scientific literature on coastal climate change relevant to the outer coast of the Olympic Peninsula. There's not a lot, but there is some. People that spend there time thinking about and planning for climate change locally make much of tectonic uplift trends around here, which thus far have out-paced sea level rise on parts of the Olympic Peninsula (Neah Bay in particular). As a results, Neah Bay has a relative sea level rise pattern that looks like this:



Local sea level is effectively falling in Neah Bay, largely because the current sea level rise rate, estimated to be about 2mm/yr, is easily outpaced by uplift, estimated at about 4mm/year at Neah Bay. By contrast check out Seattle's relative sea level trend:



Uplift in Seattle is thought to be minimal, and the trend in local sea level measured there has been tentatively attributed almost entirely to rise in the true sea level due primarily to warming ocean water (the "thermosteric" component) and the melting of land-based ice.

The outer coast of the Olympic Peninsula is not entirely off the hook though, for a variety of reasons. First, many models of sea level rise suggest an acceleration in the true sea level rise rate during the coming century. My analysis of the available literature suggests to me that true regional sea level rise on the order of 1 m is quite likely by 2100, whereas extrapolation of the current estimated sea level rise rate to 2100 would suggest a rise of only about 20cm. Also, there is some evidence (though the literature isn't fully in agreement on this point) that waves, and particularly the storm-generated extreme waves, in the North Pacific are getting larger. The larger the wave, the higher the "run-up" pushed up on the beach, and the greater the likelihood of flooding. Finally, there is general agreement that storm tracks in the North Pacific will change over time (and there is some evidence that this is already happening), which could potentially alter our seasonal pattern of sea level driven by local winds and sea level pressure. All three of these processes could conspire to bring the influence of sea level rise to us much quicker than is suggested just by extrapolating the current relative sea level curves into the future. And the key point? The evidence suggests that we can't rely on relatively rapid tectonic uplift to save us, even in Neah Bay where the uplift rate is greatest.

Today's Peninsula Daily News ran a picture of beach at La Push today, and said that the school in La Push was closed yesterday and other actions were taken due to the threat of coastal flooding. This is what sea level rise looks like here. Its not inundation - its an increased risk of coastal flooding. Fortunately in this case there was no reported flooding.

The recipe in this case was two-part. First, a dose of parigean high tides ("king" tides) generated by the combination of the monthly high "spring" tides (when the moon is closest to the earth in its orbit) and the full moon (when the moon, sun and Earth are all in alignment). This special combination happens two times a year - once in the winter and again in summer. The second component was large waves. Here are the wave measurements made by a buoy off-shore of Aberdeen, WA:




Yesterday's 3 to 3.5 m significant wave heights are big. Here is the web cam shot from right now, with offshore wave heights on the order of 3m:



In this image waves are breaking a good distance offshore, but they still aren't really that big for La Push in the winter. You can see that on Friday significant wave heights crested 6m offshore- about 20 feet. Probably the biggest fortunate turn of events is that the "non-tidal residual" (the difference between the actual water level and the water level predicted from astronomical forcing alone) has been effectively zero at La Push over the last few days. Note the green line in these water level data collected in La Push:




You can make a case that this is unusual for the winter on the coast. Usually water levels are elevated above what would be predicted due to astronomical tidal forcing due to winds that pile water up against the coast and low sea level pressure. Together they can raise the local water level by 1 meter or more - and that may have been plenty to send water over the beach berm in La Push yesterday. Its a game of probability - bringing all of these different processes together. Sea level rise just slowly raises the probability that everything will line up and send water over the berm.

Ediz Hook getting a new dose of gravel

Just wanted to add a few views of the most recent gravel nourishment on Ediz Hook. The Army Corps contracted with Bruch & Bruch construction (a local P.A. based construction firm), agreeing to pay them $626,000 to dump and spread 50,000 tons (about 40,000 cubic meters - probably somewhere, in a sorta kinda way- around what the Elwha spits out during a big flood) of mostly gravel (with some sand mixed in) in the intertidal zone. For the two short (~500') hook segments over which the gravel is spread the hook gets about 20' wider. But its obvious that this material is quickly transported along shore (and, I am guessing a lot of it is transported off-shore), spreading out along the hook, due to the oblique wave angle. It would be pretty cool to tag some of these...

Its amazing to see the slopes maintained by the seaward edge of this gravel pile. Unlike most of our beaches, which are mixed, the "beach" formed by this temporary sediment pile is a true gravel beach, of the sort studied in the UK. Waves interacting with this beach crash impressively on the steep beach face, and standing on top of the pile you feel like you are going to get washed away by the run-up. But then, the whole wave just dies as the energy is dissipated into the void in the rocks. As a result, even though the beach is so steep, there is very little apparent reflection.

Where do they get this stuff from?

Today's Peninsula Daily News ran a front page story on the most recent gravel nourishment project on Ediz Hook. Now let me first be clear that I love my local paper. I am a loyal subscriber to the PDN, and proudly read it every morning. But for this article I feel that I know too much. So let me ask the question, "Where do they get this stuff from?". It appears from the Army Corps of Engineers, who should know better.

The story that we are told is that the dams and the placement of rip rap have reduced sediment supply to Ediz Hook and that, as a result, Ediz Hook would go away without the engineering solutions provided by the ACOE. I want to examine an alternative hypothesis though - that Ediz Hook is, by its very nature, a mobile feature, a pile of sediment moving in response to a complex interaction between sediment supply, waves and sea level. The "erosion" observed on Ediz Hook MIGHT have less to do with these relatively small changes to sediment supply (I will discuss this assertion later) and more to do with the simple fact that Ediz Hook is heavily developed. It simply can't be allowed to move. Let me say in advance that this alternative hypothesis doesn't suggest that the engineering on Ediz Hook is the wrong approach. Regardless, Ediz Hook is important and there is a strong case to be made that it needs to be kept in place. I just think that the story backing it up should be right.

Let me start with the mythology that permeates this story: "Wave erosion and a lack of new sediment feeding the spit caused bank failure". In their 1971 "Report on Survey of Ediz Hook for Beach Erosion and Related Purposes" on page 13 the Army Corps forward the idea that, I think, persists to this day: "the system was able to maintain equilibrium". The idea is that the damming of the Elwha River combined with the placement of rip-rap to the west of Port Angeles under tall bluffs restricted the alongshore transport of sediment enough to create a severe deficit, "upsetting the balance" of sediment supply and loss on Ediz Hook. Erosion was the result. Interestingly, this story contradicts the geomorphic model of Ediz Hook published in Appendix B of the same report (and subsequently republished by John Downing in his 1983 book and again by Galster and schwartz in a 1990 Journal of Coastal Research manuscript, and shown here) which suggests that Ediz Hook has evolved and moved landward continuously since about 5000 years ago. The notion of equilibrium in such an extraordinarily dynamic environment - marked by changes in sea level, punctuated sediment supply and variable wave climate, is a difficult one for me to stomach.

The second question is, "How much has sediment supply been reduced?". The PDN quotes a figure suggesting that the removal of the dams will increase sediment supply by 35%. This figure comes from the National Parks Draft Environmental Impact Assessment for dam removal, published in 1996. This estimate was sourced to personal communication and was subsequently struck from the final EIS (though it appears in ACOE documents published as recently as June of 2011). Interestingly, this figure contradicts the Army Corps own estimates of how much sediment supply has been reduced by dam emplacement. In the same 1971 report mentioned above, a post-dam reduction of sediment delivery to the coastal zone exceeding 90% is stated. This would imply that after dams are removed that sediment delivery should increase 9-fold from its present delivery. What actually made it into the final environmental impact statement for the dam removal project (from 2005) was a nearly complete (98%) reduction in sediment delivery to the coastal zone, from an estimated 280,000 cy/yr to about 5000 cy/yr - figures that are cited to a 1993 Federal Energy Regulatory Commission Report. My own research suggests that the dams have probably reduced the supply of coarse sediment to the coastal zone by, on average, about 50 to 90%. But it is important to note that this supply is extraordinarily variable and seems to be related primarily to the magnitude of winter floods.

The key thing though, is to move away from percentages. A good estimate for the annual average historic (i.e pre-dam) coarse sediment supply is probably about 100,000 m3/year (based on what has accumulated in the reservoirs). Some of my work suggests that the river is delivering, on average, between 15,000 and 45,000 m3/yr. so the volumetric deficit would be on the order of 55,000 to 85,000 m3/yr. This then begs the question - how does this fit in to the whole sediment budget for the drift cell. And that question, well, nobody knows...my guess is that, relative to the budget for Ediz Hook, that that volume reduction is relatively insignificant.

Finally, I want to consider another key argument made first by the Army Corps of Engineers in their 1971 report, that erosion from the bluffs to the west of Ediz Hook has been significantly arrested by rip-rap at their base. I am no fan of this rip-rap, lets be clear, but I have noted that the bluffs give every sign of being active (steep, unvegetated) and that the base of the bluffs is now, on average, about 70 feet from the rip-rap. Photos taken at the time of the placement of the rip rap (1929) suggest that the water line and protection structures were placed right at the base of the cliff. Bluff erosion is on-going. Doing the math in a rough fashion suggests that, at a linear erosion rate of about 1 foot/year the bluffs deliver on the order of 25,000 cy/yr of sediment to the coastal zone. This equates roughly with what the ACOE estimated in their 1971 report as the contemporary (i.e. post-rip-rap) supply rate. But has it decreased over time? Figures published by the ACOE in 1971 suggest that the answer is yes, but they provide none of their methodology and no estimation of uncertainty in their measurements. Based on my rough calculation using their erosion figures, the bluffs would have been eroding at a mean annual rate of about 2.5 meters, or about 8 feet, per year to deliver the estimated volumes. Given that the Dungeness bluffs seem to erode at a mean annual average rate of around 1 foot year I view the high estimate as suspect. This is an area that is well worth additional research - finding the old surveys used by the ACOE, revisiting them, working out their uncertainties, etc.

There is more to cover here. Notably I haven't even delved yet into observations published by the ACOE that they used to "show" that the hook was shrinking. Maybe my next post. In conclusion, though, it should be clear that I am not yet sold on the story of Ediz Hook's erosion. Its worth noting again, though, that this doesn't mean that I am, by default, opposed to the engineering done on the hook. Even if its not about a sediment deficit and more about migration, the fact of the matter is that a strong case can be made that Ediz Hook needs to be kept in place - I just want the story to be right.