County of Orange Watershed Planning

Orange County, CA


PACE performed a watershed planning analysis and prepared a Watershed Infiltration and Hydromodification Management Plan (WIHMP) for the regional watersheds within the County of Orange, including those within both the Santa Ana and San Diego Regional Water Quality Control Board (RWQCB) areas, to illustrate implementation of new control measure requirements. These measures include low-impact development (LID), hydromodification conditions of concern (HCOC), and tools to support long-term watershed master planning goals. The planning process involved multiple steps of characterizing and analyzing the watershed and sub-surface conditions utilizing sophisticated Geographic Information System (GIS) mapping tools. This information was used to develop watershed plans for each of the 11 regional watersheds in the County to identify opportunities for sub-regional centralized Best Management Practices (BMPs) focusing on integrated water resource benefits.


The project resulted in a dynamic planning tool accessible by County staff and property owners. The planning tool provides watershed-specific support to integrate water quality, hydromodification, water supply, and habitat protection issues when selecting and designing BMPs to meet the requirements of the County’s Model Water Quality Management Plan (WQMP). Specifically, infiltration feasibility and hydromodification susceptibility at the watershed and sub-watershed scale will help inform BMP selection and design for proposed projects. These are fundamental factors in the selection and sizing of BMPs to meet the requirements of the WQMP and Technical Guidance Document (TGD).


Key Features:

  • Inventory of existing drainage facilities
  • GIS based mapping of watershed sub-areas
  • Watershed connectivity for intelligent watershed mapping
  • Automated watershed facility calculation tools
  • Watershed information mapping database characteristics and constraints to assist a site-specific user
  • Technical foundation for site assessment screening using infiltration LID
  • Identification of areas with ability to participate in regional / sub-regional BMP opportunities
  • Sub-watershed plans and strategies planning / process

OC Public Works Stormwater Program

GIS Data Management, GIS Water Resource Applications, Stormwater Management / Flood Control, Watershed Analysis / Planning