Empowering Decision-Making for Watershed Management – Launch of the Los Angeles County Watershed Management Modeling System (WMMS)

Date / Time:
Tuesday, Sep 15 3:05pm to 3:35pm
Track / Session:
Track: Data Management, GIS / GIS Tools, and Modeling / Session 3

In Summer 2020, the LA County Flood Control District (LACFCD) will formally release the new version of the Watershed Management Modeling System (WMMS 2.0), the highly anticipated modeling system that will support updates to Reasonable Assurance Analyses (RAAs) supporting Watershed Management Programs (WMPs) and address requirements of the LA Region MS4 Permit. WMMS was originally developed in 2009 to support watershed water quality and BMP implementation planning, and represented a major achievement in regional scale modeling and cost-optimization of BMPs. The original WMMS has also been used to support analysis of climate change impacts, BMP project designs, academic research, and assessment of local water resources and opportunities for capture and use. The new WMMS 2.0 includes significant improvements for simulation of pollutant sources and transport, but also provides groundbreaking, web-based access to model utilities and functionality to promote transparency and easy access to model input assumptions and outputs that can inform the development of cost-effective BMP implementation plans. This presentation will provide a tour of the WMMS 2.0 platform, and a demonstration of the system’s application to support RAAs.


WMMS 2.0 utilizes EPA’s Loading Simulation Program C++ (LSPC) as the basis for modeling watershed hydrology and pollutant transport. The LACFCD performed updates to the LSPC software to improve functionality and provide a web-based user interface that is tailored to County watersheds. The LSPC model was configured based on the best available data to best characterize land attributes and meteorological conditions that drive hydrologic processes. This resulted in significant improvements for representing land use, the amount and type of impervious surfaces (e.g., roof tops, roads), slope, soil types, and other aspects that drive hydrology and pollutant transport or inform BMP placement. The model also includes major improvements to meteorological boundary conditions that provide high resolution spatial and temporal representation of hourly rainfall over decades. The modeling system was calibrated and validated for hydrology and water quality (i.e., sediment, metals, nutrients) based on all available monitoring data compiled for watersheds throughout the county. The resulting LSPC model represents the state-of-the-practice for representing hydrologic processes and pollutant transport within each watershed, and will serve as an essential tool for performing future water quality investigations.


The BMP model and cost-optimization tool within WMMS 2.0 is based on EPA’s SUSTAIN. The LACFCD performed significant advancements in the application of SUSTAIN to support large-scale, watershed-wide optimization of the thousands of BMPs (and millions of combinations) often represented in an individual RAA. The LACFCD also strived to develop a system that provides improved transparency of BMP modeling assumptions, and user access to parameters that represent BMP processes and design assumptions. WMMS 2.0 includes new web-based user interfaces that allow users to enter information on identified BMP opportunities, setup a scenario for performing optimization to select cost-effective BMP implementation plans to meet water quality goals, and visualize and access results in graphics and tables that can be incorporated within WMPs.


WMMS 2.0 represents new technical advancements that have set a new bar for modeling tools to inform stormwater management. Once released, WMMS 2.0 will available in the public domain, including web-based access for model download and application. The presentation will provide a step-by-step overview on the use of WMMS 2.0, and help inform municipalities on new visions for modeling that avoids a “black box,” and promotes greater understanding of model functions, input, and outputs that can inform decision-making for responsible and cost-effective watershed management.

Primary Speaker:
TJ Moon, Los Angeles County

TJ Moon is a Senior Civil Engineer with the Los Angeles County Public Works and has been actively working to address stormwater quality issues for the County for the past 16 years.  Mr. Moon seeks to develop innovative and multi-benefit solutions to address stormwater issues.

Supporting Speaker 1:
John Riverson, Paradigm Environmental
John Riverson is an engineer and principal at Paradigm Environmental with 21 years of experience in water modeling, stormwater management, data analytics, and systems design and application.