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Critical Areas Ordinance monitoring

Critical Areas Ordinance monitoring

Assessing the land use effects and regulatory effectiveness on streams in rural watersheds of King County, Washington

The Report Explained

This presentation (PDF, 4.6 MB) will walk you through the report. Consider starting here before delving into the full document!

For an explanation of the Hydrologic Condition Index (HCI), please check out this 2014 Salish Sea Conference presentation.
Posted April 29, 2014

The U.S. Environmental Protection Agency provided King County with a grant to perform a long-term assessment of the environmental effectiveness of King County’s land use regulations in rural watersheds. The study began in 2007 and ended in 2012. Six rural watersheds with small, perennial, fish-bearing streams were used for measuring environmental response to development that occurred over that period, with current regulations in place. Change in these watersheds was compared with three forested “reference” watersheds where no development activity took place.

Scientists recorded changes in land cover and environmental variables such as water quality, stream flow levels, insect populations, and habitat complexity as well as permitting and regulatory compliance in each of these watersheds.

The study did not detect a response due to development activity. While this might appear to suggest that existing regulations are protective, the results were inconclusive.  Very little development activity occurred during the study period, perhaps because the timeframe of this detailed study coincided directly with the Great Recession, when overall land development was significantly depressed. 

To put change during project-timeframe in perspective and compensate for the lack of development, scientists compared current conditions with modeled historic (ca 1910, 1936, 1948 and 1965) and future full build-out (nominal “worst-case”) land cover scenarios and a representative urban stream (Juanita Creek). 

The results of the modeling suggested there would be little change in hydrology associated with future development, if conducted with full compliance and with no change in zoning and land use regulations. Modeling also suggested that watersheds in urban areas (outside the rural boundary) may have a significantly more degraded condition than the worst case rural watershed, underscoring the importance of maintaining rural zoning.

Part of the study involved reviewing compliance with regulations. To estimate compliance, changes in land cover were examined to determine whether property owners would likely have needed a permit and, if so, whether they got one.

Though compliance could be improved, no large or ongoing problems were observed over the five years of the study. For example, regulatory compliance was about 63 percent when estimated as the area of land cover change that required and obtained a permit.  But the area of land cover change was very small relative to the area studied; almost 97 percent of the watershed area showed no change in land covers at all during the study period. Furthermore, in regulatory stream buffers, land cover change was even smaller than at the larger watershed scale with over 99 percent of the buffer area remaining unchanged over five years. The fact that very little change occurred in sensitive areas could indicate that regulations are working, by discouraging development that could impact them.

The overall results appear to suggest that King County’s existing regulatory structure will protect watershed hydrological attributes, as future development occurs.  However, the results are preliminary because of the limited development activity observed during the project, and thus the study’s reliance on modeling rather than direct observation. To obtain a more definitive result, more work would be necessary, such as:

  • Studying the impacts of development within study watersheds over a longer time period and after more development activity occurs; and
  • Examining impacts of development on other environmental attributes besides stream hydrology (e.g., wildlife).

This study represents the first known attempt to assess the effectiveness of regulations affecting land use and development in the Puget Sound region. Several innovative tools were developed and applied, including a novel “hydrologic condition index,” which allowed the hydrologic effect of any spatial configuration of land covers and geology to be indexed, providing a precise measure of watershed hydrologic condition for each watershed and scenario, and use of salt tracers to precisely measure change in stream channel complexity using reach-averaged velocity. The project also assessed historic land cover change to assess potential influences of past land uses and to put contemporary change in perspective. 

The study framework will help King County continue to monitor the impacts of development activity and ensure its regulations are effective. The study framework could also be valuable when assessing conditions and effectiveness elsewhere in the Puget Sound Basin. It could be used by other jurisdictions to evaluate their regulatory systems, and potentially to compare regulatory approaches to each other.

Download the report and appendices

Quality assurance project plan for regulatory effectiveness monitoring for developing rural areas

The “Quality Assurance Project Plan for Regulatory Effectiveness Monitoring for Developing Rural Areas” study (QAPP for short) was designed to guide a multi-year study to assess whether the regulations are effective.

Read the full document here: QAPP (PDF, 2MB).

See a map of the study areas here: Watershed map (PDF, 31MB).

County code

King County's updated Critical Areas Ordinance ("CAO"), mandated by the Washington Growth Management Act of 1997 (Chapter 36.70A RCW) went into effect on January 1, 2005. Learn more about critical areas from the Department of Permitting and Environmental Review. 

The CAO has been incorporated into the King County Code. The King County Code is available online at The CAO has been codified as follows:

Critical Areas – KCC Chapter 21A.24 
- King County Basin and Shoreline Conditions Map
- King County Critical Aquifer Recharge Areas Map

Stormwater – KCC Chapters 9.04 and 9.12

Clearing and Grading –  KCC Chapter 16.82

Best Available Science Chapter 7, Aquatic Areas

Additional information

For questions about Critical Areas Ordinance Monitoring, please contact Jennifer Vanderhoof, Senior Ecologist, Watershed and Ecological Assessment Unit.