Storms, Floods, and the Science of Atmospheric Rivers

American Geophysical Union (AGU) | August 9th, 2011

Imagine a stream of water thousands of kilometers long and as wide as the distance between New York City and Washington, D. C., flowing toward you at 30 miles perhour.

Imagine a stream of water thousands of kilometers long and as wide as the distance between New York City and Washington, D. C., flowing toward you at 30 miles perhour. No, this is not some hypothetical physics problem—it is a real river, carrying more water than 7–15 Mississippi Rivers combined. But it is not on land. It’s a river of water vapor in the atmosphere.

Stormwater Capture: Enhancing Recharge and Direct Use Through Data Collection

Southern California Water Coalition | April 26th, 2018

The purpose of this 2018 white paper update is to gain a better understanding of actual stormwater runoff capture volumes, costs, benefits, and project performa

The purpose of this 2018 white paper update is to gain a better understanding of actual stormwater runoff capture volumes, costs, benefits, and project performance across the region to inform future discussions. This white paper augments prior efforts and uses the most recent and best available stormwater project data. Previously in January 2012, the SCWC published its first white paper on stormwater titled Stormwater Capture: Opportunities to Increase Water Supplies in Southern California (SCWC 2012). The purpose of the 2012 white paper was to examine existing statewide policies, goals, and regional plans related to integrated stormwater management; trends, structure, and requirements of MS4 permits as they pertain to both opportunities and constraints to maximizing stormwater capture for water supply purposes; and the advantages and disadvantages of two strategies of stormwater management: onsite low impact development and regional stormwater capture and infiltration. Lastly, the 2012 white paper largely focused on conceptual stormwater projects and technical strategies for increasing stormwater capture. Since the 2012 white paper, many of the proposed projects were constructed and in operation. Other plans such as Metropolitan’s 2015 Integrated Resources Plan (MWD 2016), the City of Los Angeles’s Stormwater Capture Master Plan (LADWP 2015), and Los Angeles County Flood Control District’s LA Basin Study (LACFCD 2016) also estimated stormwater capture and costs. The SCWC saw an opportunity to evaluate the costs and benefits of these constructed stormwater capture projects and pursued a white paper update.

Stratigraphic Analysis of Corte Madera Creek Flood Control Channel Deposits

U.S. Geological Survey (USGS) | September 3rd, 2019

Sedimentation in a channel can reduce flood conveyance capability and potentially place nearby property and life at risk from flooding. In 1998, Marin County Public Works

Sedimentation in a channel can reduce flood conveyance capability and potentially place nearby property and life at risk from flooding. In 1998, Marin County Public Works dredged the concrete-lined segment of Corte Madera Creek, which drains a hilly and largely urbanized watershed that terminates in San Francisco Bay, California. From then through 2015, approximately 4,100 cubic meters of sand and gravel infilled the concrete-lined segment. Determining when and under what conditions this material was deposited informs dredging operations for the Corte Madera Creek Flood Control Project and increases understanding of sediment delivery timing and mechanisms from this and other San Francisco Bay tributaries. Two hypothesized scenarios were investigated: (1) complete flushing during high flows and re-deposition of channel fill afterward and (2) more steady, gradual channel infilling. Stratigraphic analysis of eight sediment cores collected from the flood-control channel deposits in August 2017 was used to identify the most likely scenario. In addition, sediment elevation profiles, grain-size data, and a one-dimensional hydrodynamic model were used to assess the potential for longitudinal-channel scour and deposition following the wet winter of water year 2017 in the intertidal reach of the concrete channel in Corte Madera Creek. Results indicated the channel is undergoing gradual infilling. Storm flows of water year 2017 did not completely scour the concrete channel fill. Sediment cores, stratigraphic analysis, and sediment elevation profiles indicated 0.23 meter of scour at the downstream end of the concrete-lined section and that roughly 0.5 meter of channel fill remained in the channel. The hydrodynamic model demonstrated that sediment deposition in the concrete channel is expected to start downstream from the point where the channel bed reaches mean lower low-water level. High flows can carry most of the sediment through this segment of channel, depositing the bed-material load downstream from the transition to a wide channel, where velocity and bed shear stress decrease abruptly. Although the storm flows of 2017 did not completely scour the channel fill, subsequent material deposited in the channel could be transported downstream from the concrete channel if the sediment elevation profile is in equilibrium with present (2019) mean sea level. A calibrated, coupled hydrodynamic-sediment transport model could be used to test the present equilibrium between sediment elevation profiles and mean sea level, such that additional sediment build-up in the concrete channel is remobilized during subsequent wet-season flows and deposited downstream from the concrete-lined segment.

Strum Und Drand – California’s Remarkable Storm-Drought Connection

International Association for Hydro-Environment Engineering and Research | May 31st, 2019

Storm and drought are essentially the whole story of water and life in California in ways that have always made hydro-environmental engineering a unique proposition th

Storm and drought are essentially the whole story of water and life in California in ways that have always made hydro-environmental engineering a unique proposition there. To begin with, California experiences larger year-to-year variations in precipitation than elsewhere in the US, with standard deviations of annual precipitation between 30-50% of long-term averages, compared to 10-30% nearly everywhere else. California’s annual precipitation totals routinely vary from as little as 50% to more than 200% of long-term averages, with those dry excursions forming our droughts. This extreme variability arises because California’s Mediterranean climate only provides a limited seasonal window of precipitation events, and within that period a small number of storms deliver most of the State’s precipitation each year. If a few extra large storms reach California in a given winter, we can have a very wet year indeed; if some are lacking, we face drought. But the storm-drought connection is deeper and more pervasive in California than anywhere else in the US.

Sustainable floodplains through large-scale reconnection to rivers

American Association for the Advancement of Science (AAAS) | December 11th, 2009

Flooding is the most damaging natural disaster worldwide, and the flood-vulnerable population is expected to grow in coming decades. Flood risks will likely increase beca

Flooding is the most damaging natural disaster worldwide, and the flood-vulnerable population is expected to grow in coming decades. Flood risks will likely increase because of both climate change and shifting land uses, such as filling of wetlands and expansion of impervious surfaces, that lead to more rapid precipitation runoff into rivers. In the United States, annual river flood losses continue to rise, punctuated by major events in the Midwest (1993, $30 billion in total costs; 2008, $15 billion) and California's Central Valley (1995 and 1997; $4 billion each event). Meanwhile, pressure to develop new housing in floodprone areas near rivers (floodplains) continues , even as levee-system maintenance is chronically underfunded.

Sustainable Water Management Strategy for Specialty Crop Expansion in the Sacramento Valley

Sacramento Area Council of Governments (SACOG) | June 26th, 2018

The Sacramento Area Council of Governments (SACOG) is an association of local governments in the six-county Sacramento Region of El Dorado, Placer, Sacramento, Sutter, Yo

The Sacramento Area Council of Governments (SACOG) is an association of local governments in the six-county Sacramento Region of El Dorado, Placer, Sacramento, Sutter, Yolo, and Yuba counties (excluding the Tahoe Basin in Placer and El Dorado counties) and the 22 cities therein. SACOG provides planning and funding for the region and serves as a forum for the study and resolution of regional issues. SACOG prepares the region’s long range plan which considers both transportation and land use. Through the lens of rural planning, SACOG has actively engaged in a Rural-Urban Connections Strategy (RUCS) Program that has studied ways to enhance rural economies and natural assets. The RUCS Program includes a scenario analysis modeling tool that links a parcel-level crop map with environmental and economic factors, including a comprehensive profile of per acre operational cost and return metrics for each crop. The study described in this report looks at how new agricultural crops and markets coupled with improved irrigation techniques will support new specialty crop acreage in the SACOG area. While new and improved irrigation techniques can result in better crop yields and decreased water demands, increases in irrigation efficiency also result in reduced groundwater recharge from irrigation return flows. SACOG received grant funding from the California Department of Food and Agriculture (CDFA) to evaluate the feasibility of recharging groundwater on agricultural lands within the SACOG portion of the Sacramento Valley to benefit specialty crop production. The primary goal of the project is to bring together a broad range of different factors impacting groundwater recharge and infiltration and to identify areas across the region that are most suited for strategic flooding of specialty crop fields; in other words, areas that will most efficiently and effectively facilitate recharge, while minimizing cost to the specialty crop producer. Ultimately, this feasibility information will be incorporated into SACOG’s RUCS model to evaluate the potential benefits of recharging groundwater on agricultural land for the benefit of specialty crops.

Synoptic conditions associated with cool season post-fire debris flows in the Transverse Ranges of southern California

Natural Hazards (Springer) | April 22nd, 2017

The Transverse Ranges of southern California often experience fire followed by flood. This sequence sometimes causes post-fire debris flows (PFDFs) that threaten life a

The Transverse Ranges of southern California often experience fire followed by flood. This sequence sometimes causes post-fire debris flows (PFDFs) that threaten life and property situated on alluvial fans. The combination of steep topography, highly erodible rock and soil, and wildfire, coupled with intense rainfall, can initiate PFDFs even in cases of relatively small storm rainfall totals. This study identifies common atmospheric conditions during which damaging PFDFs occur in the Transverse Ranges during the cool season, defined here as November–March. A compilation of 93 PFDF events during 1980–2014 triggered by 19 precipitation events is compared against previous studies of the events, reanalysis, precipitation, and radar data to estimate PFDF trigger times. Each event was analyzed to determine common atmospheric features and their range of values present at and preceding the trigger time. Results show atmospheric rivers are a dominant feature, observed in 13 of the 19 events. Other common features include low-level winds orthogonal to the Transverse Ranges and other conditions favorable for orographic forcing, a strong upper level jet south of the region, and moist-neutral static stability. Several events included closed low-pressure systems or narrow cold frontal rain bands. These findings can help forecasters identify more precisely the synoptic-scale atmospheric conditions required to produce PFDF-triggering rainfall and thus reduce uncertainty when issuing warnings.

Technical Report on Barriers: A part of the comprehensive survey of San Francisco Bay and tributaries, California

U.S. Army Corps of Engineers (USACE) | March 15th, 1963

The California Storm of January 1862

Quaternary Research (Elsevier) | September 2nd, 1996

The greatest storm in the written history of California struck the region in the winter of 1861–1862. The unusual weather began on Christmas Eve, 1861, and persisted fo

The greatest storm in the written history of California struck the region in the winter of 1861–1862. The unusual weather began on Christmas Eve, 1861, and persisted for some 45 days as a series of middle-latitude cyclones made landfall along the California coast. Episodes of very cold and very warm temperatures occurred both during the storm and in the spring of 1862 as meridional flow prevailed. Heavy precipitation swelled the Santa Ana River to more than triple the highest estimated discharge in this century. High water levels in coastal streams between Los Angeles and San Diego persisted into the spring. Lakes were created in the Los Angeles Basin and the Mojave Desert. Arroyos were cut. Sediments from the flood may be preserved in offshore basins.

The challenge of unprecedented floods and droughts in risk management

Nature Portfolio (Springer Nature) | August 3rd, 2022

Risk management has reduced vulnerability to floods and droughts globally, yet their impacts are still increasing. An improved understanding of the causes of changing imp

Risk management has reduced vulnerability to floods and droughts globally, yet their impacts are still increasing. An improved understanding of the causes of changing impacts is therefore needed, but has been hampered by a lack of empirical data. On the basis of a global dataset of 45 pairs of events that occurred within the same area, we show that risk management generally reduces the impacts of floods and droughts but faces difficulties in reducing the impacts of unprecedented events of a magnitude not previously experienced. If the second event was much more hazardous than the first, its impact was almost always higher. This is because management was not designed to deal with such extreme events: for example, they exceeded the design levels of levees and reservoirs. In two success stories, the impact of the second, more hazardous, event was lower, as a result of improved risk management governance and high investment in integrated management. The observed difficulty of managing unprecedented events is alarming, given that more extreme hydrological events are projected owing to climate change.