Tag Archives: Flood

Map of sea level predictions can assist waterfront owners

A sophisticated analysis of sea-level rise in Puget Sound and along the Washington Coast offers shoreline residents and land-use planners a new map-based tool to assess potential flood hazards for the coming years.

Click on map to access online interactive map
Map: Washington Coastal Hazards Resilience Network

Sea-level rise depends on two factors: how fast the oceans rise and the rate of vertical land shifts. Uplift, such as what occurs along the Washington Coast, slows the rate of sea-level rise relative to waterfront property. Subsidence, which occurs in Central Puget Sound, results in elevated tides sooner than in stable or uplifting areas. One map on this page shows the measured uplift and subsidence and another shows the uncertainty in that measurement.

Ian Miller, a coastal hazards specialist at Washington Sea Grant, has worked on studies that describe sea-level rise in Island County and on the Olympic Peninsula. The new report, titled “Projected Sea Level Rise for Washington State” (PDF 10.4 mb) goes well beyond what he and his colleagues have done before. It takes a more detailed look at where the land is uplifting and subsiding, according to Miller, the lead author on the new report that involves work by scientists at Sea Grant and the University of Washington’s Climate Impacts Group.

The result is a prediction of sea-level rise at 171 locations, covering every shoreline in Washington state — as opposed to more general predictions made in previous studies, including regional and national studies by others.

The goal this time, Ian told me, was to develop an analysis that could be used for predicting future high tides at any shoreline segment in the state. Actual sea-level rise will depend on how much humans can reduce greenhouse gases in the coming years and other factors. Results in the report are given for both high and low scenarios based on climate models, and the findings are presented as probabilities of occurrence.

In Bremerton, for example, the analysis predicts that there is a 90 percent chance that the sea level will rise by 6 inches or more by 2070. At the same time, the probability is 50 percent that the rise will be at least 1 foot by 2070 and 10 percent that it will reach 1.7 feet by that year. That’s under the low greenhouse gas scenario.

Under the high scenario, there is a 90 percent chance that the sea level in Bremerton will reach 7 inches by 2070, a 50 percent chance that it will reach 1.2 feet and a 10 percent change that it will reach 1.9 feet.

In some cases, a rise in the high tide level by just 6 inches can result in serious property damage, especially if winds and waves increase as a result of more intense storms. For Bremerton, there is a 16 percent chance that this level will be reached by 2030, a 50 percent chance it will be reached by 2040 and a 75 percent chance it will be reached by 2050, according to the report.

The new report can help landowners think more clearly when deciding where to locate new buildings on their property, whether to move existing buildings and what to do about failing bulkheads. I covered the issue of planning for sea-level rise for the Encyclopedia of Puget Sound. Check out:

And in Watching Our Water Ways:

Clicking on the map at the top of this page will take you to the online interactive map. Looking at the online map, click on any shoreline location to download the data tables, which may look a little intimidating at first. But don’t worry. Just use the tabs at the bottom to pick a high (RCP 8.5) or low (RCP 4.5) greenhouse gas scenario. You will see two tables for each scenario. In the top table, pick a year (vertical list) and a probability (horizontal list) to get the projected sea level rise (in feet). In the bottom table, pick a year along with sea level rise to get the probability of that level being reached.

Sea-level rise is accelerating as time goes on, as predicted by climate models and supported by recent studies. (See the report on satellite readings in the Proceedings of the National Academy of Sciences.) One hundred years from now, there is a 90 percent chance that sea level will be at least one foot higher in Central Puget Sound and a 50 percent chance that it will be at least two feet higher.

Unlike any previous report in Washington, predictions for changes in vertical land movement in the new report are based on three different sources of information: variations in tide gauges, “leveling surveys” used by highway engineers and data from continuous global positioning satellites. For the satellite data, the analysis of sea-level rise took into account separate assessments of land movement calculated by five different organizations.

By analyzing the sources of data for vertical changes across the landscape, the researchers were able to provide a range of uncertainty for each of their 171 shoreline locations. Knowing the level of confidence for water reaching a given level in a specified amount of time can help people decide whether they are willing to accept the risk or begin planning for the future.

I’ve gone through the map, looking at a variety of waterfront locations in Washington state. In the lists below, I’ve grouped the cities to show how much the sea level is expected to rise by 2050, using a 50 percent probability and a high greenhouse gas scenario.

0.1 foot
Neah Bay

0.3 foot
Sekiu

0.4 foot
Ocean Shores, Ozette

0.5 foot
Aberdeen, Point Roberts, Port Angeles

0.6 foot
Bellingham, La Push, Queets, San Juan Island

0.7 foot
Anacortes, Hoodsport, La Conner, Sequim

0.8 foot
Bremerton-Port Orchard-Silverdale, Everett, Gig Harbor, Hansville, Port Townsend, Poulsbo-Suquamish-Bainbridge, Seattle, Shelton, Tacoma, Vashon Island (most), Whidbey Island

0.9 foot
Ballard, Edmonds, East Vashon-Des Moines, Federal Way, Port Ludlow, Shelton

1.0 foot
Kingston, Olympia

Additional information on this project:

Be alert for tidal flooding and King Tide photos

Some of the highest tides of the year, combined with a strong low-pressure system, could provide “King Tide” observers with ideal conditions tomorrow (Monday) for taking pictures of near-flood conditions or even flooding in some places.

This is the third year the Washington Department of Ecology has put out a call for photos of high-tide conditions.

Photo of Poulsbo waterfront taken during “King Tides” Dec. 28, 2011.
Photo by James Groh, Poulsbo

“Documenting how very high tides affect the natural environment and our coastal infrastructure will help us visualize what sea level rise might look like in the future,” states Ecology’s “Climate Change” blog.

The King Tide photo initiative began in Australia in January 2009. Washington and British Columbia joined in 2010, followed by Oregon and California in 2011.

Tide tables predict that tides in Bremerton and Port Orchard will reach 13.4 feet at 8:28 a.m. tomorrow. Check on other locations and other days in Washington state at Saltwater Tides.

The National Weather Service has issued a coastal flood advisory for Western Washington because of low-pressure conditions, which could add 1.5 feet to the tide table prediction. That would put the Bremerton area at 14.9 feet. Check out the Weather Service advisory and the Kitsap Sun story.

While it looks like we’ll have a very high tide, it probably won’t be a record. I was unable to find historical data for Bremerton, but the record high tide for Seattle is 22.4 feet on Jan. 27, 1983. The tide tables predict that Seattle will reach 12.5 feet tomorrow, or 14 feet with the added 1.5 feet because of the low pressure.

Historical data can be found on NOAA’s “Tides and Currents” webpage after selecting a station.

Shortly after I posted this, Jeff Adams of Washington Sea Grant sent me an email to point out that NOAA’s numbers need to be corrected by subtracting 7.94, because NOAA uses a different baseline than we commonly use in this area. That would place the record in Seattle at 14.5 feet, much closer to what we may see tomorrow. I should have known that something was amiss with that data. For more on this point, check out Jeff’s blog, Sea Life. 

King Tides will continue through this week, declining slightly each day, then will return on Jan. 14.

I’m certainly not hoping for high water levels, but where they occur it would be great to have some photos. Feel free to send them to me at cdunagan, as well as uploading to the Flickr page called “Washington King Tide Photo Initiative.”

Skokomish restoration now focused on ecosystem

Flood control is no longer a primary objective of federal restoration work on the Skokomish River — but improving the ecosystem is likely to reduce flood problems for people who live in the valley.

The Skokomish Watershed Action Team (SWAT) surveys an area where the Skokomish River has wiped out all vegetation and left a massive gravel bar.
Photo by Steve Zugschwerdt

We don’t need to be reminded that the Skokomish is the most frequently flooded river in the state. Although I’m not sure how soon another river might take over that dubious distinction, it’s easy to see that a lot of time and money is being spent to get the river back to a more natural condition.

The Army Corps of Engineers, known for massive projects such as dikes, dams and dredging, won’t be adopting those sorts of projects for the Skokomish River.

Jessie Winkler, Skokomish project manager for the Army Corps of Engineers, explained it this way:

“Clearly, flooding is a problem in the basin. But because of limited residential and commercial activity, it would be very difficult to justify a flood-control project. In order to be justified as a federal project, the economic benefits must be greater than the cost.”

For further explanation, check out my story in Monday’s Kitsap Sun.

The good news is that the Corps has not turned its back on the Skokomish. In fact, the river is considered so important to the Hood Canal region that the agency is considering some large-scale projects focused on environmental restoration — including possibly relocating Skokomish Valley Road.

Other interesting ideas include creating sediment traps to capture gravel in selective locations, relocating existing dikes to create a wider river channel, forming new side channels to relieve flow on the main river and even aeration pumps to boost oxygen levels in Hood Canal.

Many of the projects designed for ecological improvement will also reduce the flooding problems.

A report, scheduled to be released in late spring or early summer, summarizes all information collected so far in the $4.7 million study of the Skokomish River watershed. The report will cover current ecological conditions, future ecological conditions without restoration and a list of potential restoration projects — including preliminary design, estimated costs and ecological benefits, Winkler told me.

Potential projects are only conceptual at this point, though experts have begun to look at locations along the river where different types of efforts may be fruitful. Further study will narrow the list of to a plan to be submitted to Congress for funding.

The upcoming report will begin to explore which of the following actions are most likely to succeed in specific locations:

  • Remove or breach levees/dikes
  • Construct setback levees/dikes
  • Create salmon spawning habitat
  • Reconnect wetlands, side channels, backwater areas, and tributaries
  • Substrate modification
  • Install aeration or oxygenation system in Annas Bay
  • Reconnect dendritic channels in estuary
  • Large woody debris
  • Engineered Log Jams
  • Fish passable weir
  • Channel stabilization
  • Riverbed and wetland vehicle exclusion
  • Enhance vegetation – riparian & estuarine
  • Control invasive species
  • Channel rehabilitation or new channel creation
  • Selective gravel removal on gravel bars
  • Spot-dredge
  • Sediment trap
  • Culverts: a) add; b) remove; c) replace; d) upgrade
  • Road modifications
  • Rehabilitate bank lines
  • Cool water diversion to Annas Bay

‘King tides’ are an invitation to take watery photos

The Washington King Tide Initiative is entering its third year, and state officials would like people to shoot photographs of flooded roads, yards and buildings — if such events occur.

The high tide at the mouth of Gorst Creek comes close to reaching Toys Topless in Gorst. Photo by Meegan M. Reid, Kitsap Sun
In 2010, the high tide at the mouth of Gorst Creek comes close to reaching Toys Topless at the head of Sinclair Inlet in Gorst.
Photo by Meegan M. Reid, Kitsap Sun

High tides are expected to continue for the next few days and return to high levels again in mid-January. Whether flooding occurs at any one place depends on rainfall, winds and atmospheric pressure, as well as tidal levels dictated by the position of the moon and sun. (See NOAA Ocean Service Education.)

Not much flooding occurred during king tides last year, but plenty of photographs were collected in early 2010. That’s when the picture on this page was taken in Gorst between Bremerton and Port Orchard. For additional photos, check out the Flickr page or the video slide show put together by the Washington Department of Ecology.

Taking note of these high tides is one way to gauge how climate change may affect shoreline areas. Over the next 100 years, sea level is expected to rise by at least 2.6 feet, according to the U.S. Fish and Wildlife Service, although previous estimates by the Intergovernmental Panel on Climate Change were in the range of 7 inches to 2 feet.

The King Tide Initiative started in Australia in 2009, according to Ecology’s website on King Tides, but it soon became a project for the West Coast of North America, with Washington and British Columbia joining in 2010 and Oregon and California joining in 2011.

Visit Flickr pages for British Columbia, Oregon and California, which includes regional pages for San Francisco Bay, Santa Monica and San Diego.

For a list of high tides, go to Ecology’s King Tide Schedule page and click on the map. More precise information can be found on NOAA’s page of tide predictions, where you can zoom in to your area of interest.

For past King Tide events, check out my Water Ways entries for Jan. 21, 2011 and Feb. 1, 2010.