Los Angeles Basin Study Summary Report

U.S. Bureau of Reclamation (USBR) | November 1st, 2016

Changing demographics, climate change, and competing interests for available water supplies all present long-term risks to the stability and reliability of the region’s

Changing demographics, climate change, and competing interests for available water supplies all present long-term risks to the stability and reliability of the region’s imported water.  The region recognizes that today’s challenges require an integrated water resources management approach. For decades, this region has operated and maintained one of the most effective flood control systems in the world that protects millions of people from the impacts of flooding in the region. This system sends much of the stormwater runoff into the ocean, water that historically recharged local groundwater basins, making this region even more dependent on imported water supplies. As regulatory pressure to clean up polluted stormwater runoff continues and imported water resources diminish, this local source of water supply is becoming more and more attractive (GLAC IRWMP 2014). Many of the region’s water management agencies have studied and planned for increasing use of local recycled and graywater supplies, ocean and brackish desalination, developing more groundwater, and implementing improved water conservation initiatives to extend existing supplies. Additionally, social trends and concerns also drive the emphasis on the use of local water supplies. However, the one major local resource that has not been studied in-depth is stormwater and its opportunities to optimize the reliability of local supplies. To enhance the capabilities of the existing stormwater conservation infrastructure within the Los Angeles Basin, the LACFCD began to investigate long-term projected needs and future climate conditions within the region. Given that local groundwater plays such a vital role in the region’s water supply portfolio, detailed scientific, engineering, and economic analyses were conducted to identify strategies for enhancing stormwater capture for groundwater recharge. The LA Basin Study examined the region’s water supplies and demand, and impacts from projected population growth and changing climate in the watersheds of the Los Angeles region. The objectives of the study were to: • Use state-of-the-art climate change analysis to develop projections of future water supply and demands in the Basin. • Analyze how the Basin’s existing water infrastructure and its operations will perform in the face of changing water realities. • Develop and highlight opportunities to adapt to current and future water demands. • Conduct a trade-off analysis of identified opportunities. Concepts ranged from enhancing the existing stormwater capture system and modifying existing facilities (including those capturing runoff for groundwater recharge), to developing new structural and nonstructural concepts that could help resolve future water supply and flood risk issues. This Summary Report presents highlights of the critical tasks associated with this Basin Study and the results and findings produced throughout this collaborative study effort. Full study chapters and appendices: Plan of Study Fact Sheet Task 2: Water Supply and Demand Task 3: Climate Change Analysis Task 3.1: Development of Climate-Adjusted Hydrologic Model Inputs Task 3.1:  Climate Change and Hydrologic Projections Appendices Task 3.2:  Hydrologic Modeling Report Task 3.2: Annual Hydrologic Results Workbook Task 4: Existing Infrastructure Response & Operations Guidelines Analysis Final Report Task 5: Task 5 - Infrastructure & Operations Concept Analysis Final Report Task 6: Trade-off Analysis Final Report Click here for Reclamation's full index  including public outreach and webinars

Los Angeles Basin Study The Future of Stormwater Conservation: Task 6 – Trade-Off Analysis & Opportunities

U.S. Bureau of Reclamation (USBR) | January 5th, 2016

The Los Angeles Basin Study (LA Basin Study) is a collaborative partnership between the Los Angeles County Flood Control District (LACFCD) and the U.S. Department of the

The Los Angeles Basin Study (LA Basin Study) is a collaborative partnership between the Los Angeles County Flood Control District (LACFCD) and the U.S. Department of the Interior, Bureau of Reclamation (Reclamation). The purpose of the LA Basin Study is to investigate long-range water conservation and flood risk impacts caused by projected changes in climate and population in the Los Angeles region. The LA Basin Study highlights opportunities for potential modifications and changes to both the existing regional stormwater capture system as well as for the development of new facilities and practices, which could help to resolve future water supply and flood risk issues. The stormwater capture concepts and alternatives developed in the Task 5 – Infrastructure & Operations Concepts report are evaluated in the trade-off analysis and opportunities highlighted in this report.  The primary purpose of Task 6 – Trade-Off Analysis & Opportunities is to evaluate the quantifiable and non-quantifiable benefits and costs of the stormwater concepts identified in the Task 5 report and to provide an analysis of the trade-offs among concepts. In most cases, various project concepts would generate benefits for some impact categories but not others, and would also impose various types of costs. The trade-off analysis provides a methodology for comparing different types of benefits and costs that cannot all be quantified in monetary terms. These trade-offs include economic, financial, environmental, and social effects. Economic effects include the benefits associated with different types of goods and services supported by the concepts, the costs of the different concepts, the impacts of the different concepts on the regional economy through changes in the amount and type of spending, and the cost effectiveness of different project concepts. Financial effects reflect the impacts of paying for a project, such as paying off capital debt and covering operation and maintenance expenses. Environmental effects reflect the type and quality of environmental and natural resources that would be potentially influenced by a concept. Environmental effects include items such as water quality, energy consumption, impacts on habitat, and ecosystem function. Social effects reflect how the concepts may alter the social characteristics of a community or region such as impacts to education, environmental justice, and quality of life.  Benefits are quantified for three categories of resource impacts. The first category is additional stormwater conserved or stored, which is measured in terms of acre-feet per year. The second is recreation, which is measured in miles of new trails. The third is increased habitat acreage and additional acquisition of right-of-way acreage that would provide habitat benefits. Stormwater conservation benefits are valued as improved water supply reliability, recreation is valued as a type of general recreation activity similar to outdoor activities at a local park, and habitat acreage is evaluated as an ecosystem improvement. In the case of the Regional Impact Programs concept, right-of-way acreage also produces some ecosystem benefits. Quantified benefits and costs as well as categories of qualitative benefits are summarized in Table ES-1. All benefits and costs are present valued over a 50-year planning period using the current Fiscal Year 2016 federal water project planning rate of 3.125%.  The economic analysis of quantified benefits can be used to evaluate the magnitude of potential benefits of each project group, recognizing that many additional benefits may exist that are not accounted for in a traditional benefit and cost analysis. It is important to note that quantified benefits could only be developed for a subset of the total beneficial effects associated with the concepts identified in the Task 5 report. There are many potential benefits associated with environmental and social improvements, flood risk mitigation, environmental justice, and other effects that could be large but cannot be evaluated quantitatively for this level of analysis. These unquantified benefits may be larger than quantified benefits in some cases and smaller in other cases. The intent of the qualitative assessment is to provide an indication of the potential magnitude of unquantified benefits. 

Los Angeles County Department of Public Works Hydrology Manual

Los Angeles County Department of Public Works (LACDPW) | January 30th, 2006

This manual establishes the Los Angeles County Department of Public Works' hydrologic design procedures and serves as a reference and training guide. This manual contains

This manual establishes the Los Angeles County Department of Public Works' hydrologic design procedures and serves as a reference and training guide. This manual contains charts, graphs, and tables necessary to conduct a hydrologic study within the County of Los Angeles. Examples provide guidance on using the hydrologic methods.

Los Angeles County’s Climate Cost Challenge

Center for Climate Integrity | April 2nd, 2024

Within the first two months of 2024, the City of Los Angeles had already exceeded its average annual rainfall, receiving nearly 15 inches of rain in back-to-back deluges.

Within the first two months of 2024, the City of Los Angeles had already exceeded its average annual rainfall, receiving nearly 15 inches of rain in back-to-back deluges.1 The storms flooded roads, brought massive wind gusts, ripped down trees, and killed nine people.2 The year prior was the hottest year ever recorded, including unseasonably hot weather into the fall months in Southern California. In October 2023, a wildfire ripped through rural lands southeast of the City of Los Angeles, destroying multiple buildings and forcing approximately 4,000 people to evacuate. With climate-driven disasters in Southern California growing more intense every year, it’s more important than ever for communities to invest in a growing range of climate adaptation and resilience projects. This study is the first-ever attempt to calculate the costs of preparing for and adapting to 14 different climate impacts on municipal, county, state, and federal governments in Los Angeles County.

Managing Floods in California

Legislative Analyst's Office (LAO) | March 22nd, 2017

This report is intended to provide basic information about floods and flood management in California. (Whereas previous generations referred to “flood control” or “

This report is intended to provide basic information about floods and flood management in California. (Whereas previous generations referred to “flood control” or “flood prevention” activities, experts now prefer the term “flood management” in acknowledgement that floodwaters are recurring and inevitable.) We begin by summarizing the history, causes, and risk of floods across the state. We then describe flood management agencies, infrastructure, and strategies, as well as how governmental agencies typically respond when floods occur. Next, we describe the spending levels and funding sources currently supporting flood management efforts, as well as estimates for how much additional funding may be needed to improve those efforts. We conclude by highlighting some key challenges confronting the state in contemplating how best to manage floods in California.

Managing for Future Risks of Fire, Extreme Precipitation, and Post-fire Flooding

U.S. Bureau of Reclamation (USBR) | September 30th, 2016

On September 22–23, 2014, 23 scientists, resource managers, and urban planners convened in Las Vegas, Nevada, to discuss research and management needs related to seve

On September 22–23, 2014, 23 scientists, resource managers, and urban planners convened in Las Vegas, Nevada, to discuss research and management needs related to severe fires and post-fire flooding in the Intermountain West. The workshop was motivated by the concerns of water management agencies about the potential for a changing climate to exacerbate fire impacts through: 1) projected increases in acres burned; 2) potential changes in the intensity of future extreme precipitation; and 3) the frequency of extreme events, which the National Climate Assessment projects to at least double across the region. The workshop was convened by the University of Arizona with funding provided by the U.S. Bureau of Reclamation.

Memorandum Report on the Floods of January and February 1969 in the Southern District of the Department of Water Resources

California Department of Water Resources (DWR) | February 27th, 1970

Merced River Watershed Flood-MAR Reconnaissance Study

California Department of Water Resources (DWR) | November 15th, 2023

DWR, in partnership with the Merced Irrigation District (MID), is conducting a preliminary study using flood waters for managed aquifer recharge that can reduce flood ris

DWR, in partnership with the Merced Irrigation District (MID), is conducting a preliminary study using flood waters for managed aquifer recharge that can reduce flood risk, increase surface and groundwater supply reliability, and enhance ecosystems in the Merced River Basin. This Merced River Reconnaissance Study (study) is exploring the potential, feasibility, and effectiveness of Flood-MAR concepts, testing theories, and assessing strategies in overcoming barriers and challenges to project planning and implementation. The study will assess current conditions of the Merced River watershed and the vulnerability of these watershed management characteristics to a range of potential climate change futures. The study will also describe the public and private benefits that may be achieved through Flood-MAR strategies and quantify a range of benefits that Flood-MAR could provide in or adjacent to the Merced River watershed.

Meteorological and geographical factors associated with dry lightning in central and northern California

Environmental Research: Climate (IOP) | August 8th, 2022

Lightning occurring with less than 2.5 mm of rainfall—typically referred to as ‘dry lightning’—is a major source of wildfire ignition in central and northern Cali

Lightning occurring with less than 2.5 mm of rainfall—typically referred to as ‘dry lightning’—is a major source of wildfire ignition in central and northern California. Despite being rare, dry lightning outbreaks have resulted in destructive fires in this region due to the intersection of dense, dry vegetation and a large population living adjacent to fire-prone lands. Since thunderstorms are much less common in this region relative to the interior West, the climatology and drivers of dry lightning have not been widely investigated in central and northern California. Using daily gridded lightning and precipitation observations (1987–2020) in combination with atmospheric reanalyses, we characterize the climatology of dry lightning and the associated meteorological conditions during the warm season (May–October) when wildfire risk is highest. Across the domain, nearly half (∼46%) of all cloud-to-ground lightning flashes occurred as dry lightning during the study period. We find that higher elevations (>2000 m) receive more dry lightning compared to lower elevations (

Modeling the impact of future rainfall changes on the effectiveness of urban stormwater control measures

Springer Nature | February 19th, 2024

The convergence of urban expansion, deteriorating infrastructure, and a changing climate will escalate the risks of stormwater pollution and urban flooding in the coming

The convergence of urban expansion, deteriorating infrastructure, and a changing climate will escalate the risks of stormwater pollution and urban flooding in the coming decades. Using outputs from an ensemble of global climate models to drive a high spatial resolution stormwater model, we analyzed climate change impacts on urban stormwater runoff and control measures for 23 cities across the United States. Runoff model outputs for two future emissions scenarios ending in 2055 were compared against a historical scenario to assess changes. All cities showed increases in average annual stormwater runoff, with changes up to 30% over the next 30 years due to a greater frequency of high intensity storm events. Runoff model outputs showed substantial variation across cities with untreated stormwater runoff increasing by as much as 48%. Patterns of future runoff impacts within cities will affect the performance of distributed treatment strategies such as Green Stormwater Infrastructure (GSI) to meet municipal water quality improvement and runoff reduction goals. Results indicate that adoption of adaptable design standards and decision support tools that readily accommodate projected precipitation changes are critical for supporting more resilient designs of stormwater control measures.