New Development Stormwater Requirements
Stormwater Quality Requirements for Development Projects
Water Quality regulations for Priority Projects include Low Impact Design (LID) on-site retention requirements and Hydromodification Management measures which can be significant elements in the site design of your project and therefore it is crucial that they be considered early in the design process.
All development/redevelopment projects, regardless of priority, shall implement the site design and source control principles, where applicable and feasible, to maximize infiltration, provide retention, slow runoff, and reduce pollutants at the sources.
All priority projects shall meet Water Quality Management Plan (WQMP) and Hydromodification Management Plan (HMP) requirements as described in the documents and tools below. The project's WQMP is a plan for minimizing the adverse effects of urbanization on site hydrology, runoff flow rates and pollutant loads. Hydromodification management measures address the changes in the magnitude and frequency of stream flows and associated sediment load due to urbanization or other changes in the watershed land use and hydrology and the resulting impacts on receiving channels, such as erosion, sedimentation and potentially degradation of in-stream habitat.
To determine if your project is a priority project, use the WQMP Checklist Priority Development Project (PDP) Criteria.
Note: The Preliminary WQMP (pWQMP) is required as part of the Project Application. An application will not be deemed complete without a pWQMP. It should be noted that the pWQMP is not a "conceptual" document in the normal sense of the word and requires detailed engineering sizing calculations and location details for selected BMPs.
The following updated documents and tools will assist you in preparing an acceptable Water Quality Management Plan for your project.
Documents and Tools for WQMP/HMP Preparation:
- South Orange County Model WQMP describes the water quality requirements and the process to develop the project's WQMP.
- Technical Guidance Document/Cover Memo for Using the TGD in South Orange County is the technical resources companion to the Model WQMP and the WQMP Template and is the "how" to meet the requirements in the Model WQMP and how to use the WQMP Template to prepare your project's WQMP. The cover memo highlights the key differences associated with applying the TGD in North versus South Orange County, with guidance, either as footnotes or as text insertions, on key topics that relate to South Orange County criteria. It is important to read and understand this as you begin to develop your project's WQMP. This document is bookmarked and internally linked for easy navigation.
- Model WQMP Template is the framework for preparing your project's WQMP. The use of this template is highly encouraged and will facilitate acceptable preparation and City review and approval of your project's WQMP.
- Laguna Niguel O&M Plan Template will help you prepare an acceptable O&M Plan as part of the Final WQMP. Please note that the O&M will be a separate, stand-alone, user-friendly document and includes a BMP site plan.
- Worksheets from the TGD are identical to those contained in the TGD, however they are available in editable MS Word so that they can be created for your project and included in your project's WQMP.
- Hydromodification Management Plan describes the hydromodification requirements and the process to develop the project's hydromodification management measures, when applicable. To download the South Orange County Hydrology Model and Guidance Manual, visit the OC watersheds webpage.
- Watershed Infiltration and Hydromodification Management Plan (WIHMP). The Orange County Georesearch tool may provide information to help develop your project's WQMP and HMP. Data specific to WQMP and HMP preparation is located in the "OC Watersheds" layer. The County will periodically provide trainings regarding use of this tool.