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Critical Areas: The Importance (and Difficulty) of Knowing Where They Are


July 18, 2017 by Greg Wessel
Category: Critical Areas

Critical Areas: The Importance (and Difficulty) of Knowing Where They Are

For roughly 30 years, development near critical areas (also known as sensitive areas) in Washington State has been governed by the Growth Management Act. Enacted in 1990, the act requires local governments to manage growth in part by identifying and protecting critical areas. Following the Oso landslide in 2014, interest in critical areas, and especially landslide hazards, peaked as many cities, counties, and even states discovered that they didn’t know as much about these areas as they should.  

What are critical areas?

Regulated critical areas vary from place to place but those that are most common include wetlands, streams, lakes, the marine shoreline, steep slopes, and erosion hazards. Landslide hazard areas, seismic hazards (soils prone to liquefaction), and flooding hazards are common as well. Volcanic hazards associated with our Cascade volcanoes are also regulated and some jurisdictions host hazards resulting from past coal mining. 

In other parts of the country, regulated hazards include natural concentrations of hazardous materials, such as asbestos, that occur naturally in some soils. Soil contamination from human activities (think of the ASARCO smelter contamination in Tacoma) may be regulated but is typically not classified as a critical area.

Development regulations are strict when it comes to many critical areas. In some, new construction is not allowed. For others, proper characterization of the hazard present defines the mitigation that might be required to prevent loss of life and minimize environmental damage. For this reason, regulatory agencies have a huge interest in knowing where critical areas are located.

How can I know where critical areas may be located in my jurisdiction?

In most parts of Washington, the regulation of critical areas preceded in-depth knowledge of their actual locations. The importance of critical areas was recognized even though we lacked the tools to adequately map and survey them. Because of that, most building/zoning codes require critical areas to be delineated prior to the issuance of permits. 

To assist planning and development, some cities and counties have mounted efforts to map selected critical areas on a landscape scale. For the most part, these maps are not recent and some have been made obsolete with the recent availability of LiDAR data.  

Short for Light Detection And Ranging, LiDAR is an airborne scanner that measures surface elevation using a pulsed laser. It is capable of providing detailed topographic information that can be used to map many things, including some critical areas. For example, King, Pierce, Skamania and Klickitat counties all have acquired new landslide hazard maps for portions of their territories using LiDAR data. Mapping critical areas in this fashion is not trivial, but depending on the local geology and the size of the area, acquiring good information may be easier than you might think.

The value of accurate critical areas data

A good example of the value of updating critical areas mapping can be seen in a comparison of landslide hazards taken from King County’s Sensitive Areas Folio of 1990, which was used for 26 years to screen permit applications, alongside landslide hazard mapping that was completed in 2016 using LiDAR data. 

The area depicted below is a portion of Vashon Island, roughly .5 mile square, as shown on two different landslide hazard maps. The one on the left is from 1990 and the one on the right is from 2016. Between the two maps is LiDAR shaded-relief topography of that same .5 mile area on Vashon Island. 

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The map on the left shows what was considered a landslide hazard area (green diagonals) in 1990. Using data provided in the LiDAR shaded-relief topography image, the map on the right (2016) provides more detailed information, such as steep slope critical areas (dark green) and potential landslide hazards (purple), giving a much clearer picture of the dangers present. 

The problems that might arise from relying upon out-of-date or inaccurate mapping of critical areas should be obvious. In the best case, confusion can lead to extra cost and delay; in the worst case, hazards might go unrecognized.

Consider the case where a permit applicant might apply to build his home in that same .5 mile square of Vashon Island as the maps depict,  but on a lot located within the left corner. Depending on which map the permit office uses, the decision to approve or not approve the permit might be quite different. In the 1990 version, the upper left corner seems entirely free of hazards while the 2016 version paints a very different story. There can be significant liability in relying on inaccurate data.  

What should I do in my jurisdiction?

If you are wondering whether the critical areas in your jurisdiction have been adequately identified, inquire first with staff in the building or with your planning department. Many have ecologists on staff and some have geologists as well.  If the information they rely upon is not recent, or if no one is sure, the next step might be to have a consultant assess the situation. The consultant should have knowledge of the regulatory use of critical areas data and should be experienced in construction and land use. An assessment can be completed quickly with the proper consultant.

If new critical areas mapping is needed you may need to assemble qualified staff or consultants. Few people have experience mapping hazards and critical areas but outside resources can be tapped. For example, geologists at the Washington Geological Survey (WA-DNR) are engaged in a program of mapping landslide hazards for some portions of the state. If you are in one of those areas, your problem may have been solved. There are also opportunities to improve the collection of critical areas data simply by revising your permit review process or by relying upon help from interns or students at nearby universities. 

Critical areas data should be assessed on an ongoing basis with updates scheduled at regular intervals, perhaps every 5-10 years. A small investment now can save a lot of headaches in the future.  

Questions? Comments?

If you have questions about this topic or other local government issues, please use our Ask MRSC form or call us at (206) 625-1300 or (800) 933-6772. If you have questions or comments about this blog post, please email Greg Wessel

About Greg Wessel

Gregory R. Wessel, PhD, LG holds degrees in Geology from Colorado School of Mines (PhD) and the University of Missouri-Rolla (BSc and MSc; now called the Missouri University of Science and Technology). Dr. Wessel is licensed in the State of Washington as an Engineering Geologist and has over 35 years of experience in metals and industrial minerals exploration, geologic hazard abatement and environmental restoration, geotechnical applications and mapping of geologic hazards, the development of agricultural minerals (sulfur and potash) in Texas, Poland, Ukraine, and Russia, and the recovery of magnesium salts (for metal production) in Russia.

He has specialized in geologic mapping and structural evaluations, and has mapped large areas of the southwestern United States and the Altiplano of Bolivia, using aerial photography and extensive field work.

Dr. Wessel has authored or co-authored over 20 articles and abstracts, including a number of maps available from the Washington Geological Survey, the Texas Bureau of Economic Geology, and a widely used educational chart available from the Geological Society of America entitled The Geology of Plate Tectonics. Dr. Wessel also serves on the Mapping Advisory Committee for the Washington Geological Survey and sits on the State’s Geologist Licensing Board.

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