San Juan Creek Watershed Stream Monitoring Program

Rancho Mission Viejo, CA

PACE provided a Monitoring Plan (Plan) to implement an Adaptive Management Program with respect to stream erosion and sedimentation within San Juan Creek based on field inspection/observations and quantitative monitoring/qualitative assessment for Rancho Mission Viejo Planning Area 1 (PA-1).  The objective of this Plan was to ensure the adjustments within the active floodplain of San Juan Creek are monitored in order to evaluate changes in stability of the streambed and streambanks consistent with CEQA commitments and conditions of approval.  The “active” portions of the floodplain system is the portion of the streambed and banks that experience the dominant discharge and the majority of the fluvial action, such as exposed sand streambed, active thalweg, and stream movement. This includes evaluating performing assessments of recorded stream data in order to evaluate the performance of the channel system, as well as implementing corrective procedures when needed.  An adaptive approach to the monitoring program will be applied which fulfills the following purposes:

  • Identify trends of the creek within and downstream of the project
  • Evaluate the response of the creek system to the development within the watershed
  • Assess long term streambed and streambank stability or instabilities
  • Monitor impacts to public structures within the creek system
  • Application of qualitative and quantitative geomorphic and engineering techniques for evaluation of collected data

The stream monitoring plan provided the technical foundation and guidance associated with the reconnaissance and assessments for evaluation of the channel response.  The stream monitoring data provides the foundation for a broad range of assessments, which included:

  • Monitoring trends in fluvial and geomorphic conditions in time
  • Quantifying impacts
  • Assessing stream and watershed response to different management activities
  • Change in the inventory of stream resources
  • Allowing valid comparisons of the stream system over time