Theme for 2012:
The 1861-1862 Floods: Informing Decisions 150 Years Later

Estimating Future Floods to Manage Flood Risk — Part 1

• Download presentation [PDF, 1.6 MB]
• Download presentation (with notes) [PDF, 1.7 MB]

• Listen to the presentation

Abstract:

The State of California in 2007 established the 200-year flood event as the minimum safety standard for protecting urban areas from flooding. The mandated 200-year event is a target threshold of flood peak and volume for a critical duration that will be used for flood management planning for current and future conditions. A successful flood risk management strategy for the 200-year event will be needed for continued local development in floodplains. A framework is needed to help define what a successful strategy will be for a given urban area.

Sacramento City Floods: 1849-1862

• Download presentation [PDF, 5.9 MB]
• Download presentation (with notes) [PDF, 1.4 MB]

• Listen to the presentation

Abstract:

The City of Sacramento sprung into existence on John Sutter's embarcadero in 1848 with the discovery of Gold on the American River. The discovery created a demand for a strategic location along the river to allow for the easy transport of people and goods toward the gold fields. The site, however, had its problems: It was intersected by two major rivers, on low land, with clear evidence of flooding, such as flotsam deposited in trees from past inundations. In short, it was not an ideal location for a permanent city. The desire of entrepreneurs to capitalize on the incoming flow of miners in need of goods and supplies to further their quest for gold, trumped any fears generated by Mother Nature. This was the beginning of Sacramento's problems with flooding. The two powerful rivers were both the lifeblood of the Sacramento and its most imminent threat. The city would be inundated with floods beginning in the winter of 1849-1850, with repeated flooding throughout the next decade. Each time, Sacramentans took actions to protect against flooding, including the construction of levees and minor street raising. It would take the flood of 1861-1862 to thrust the City into a new and frightening reality of the potential of Mother Nature. The storm would engulf the entire state, alter its economic base, and lead to the physical transformation of Sacramento's landscape. This presentation will explore the events leading up to the 1861-1862 flood, citizens' reactions to the flood, and explore why Sacramentans made the choices they did to maintain their city and explore how those choices still impact today's residents.

Understanding the Sacramento River Valley Before Levees and Dams

• Download presentation [PDF, 12.4 MB]

• Listen to the presentation

Abstract:

This presentation discusses three topics:

1. The geomorphic function of the Sacramento River system in the early 1800s
2. The historical and geomorphic context of the 1862 flood
3. How the Sacramento River Flood Control Project mimics the natural geomorphic function of the river system during floods

Historically, the lower Sacramento River lacked the capacity to convey seasonal floods and regularly overtopped its banks, sending water and sediment via a network of sloughs and crevasses into expansive flood basins on either side of the river. Prior to levees and dams, seasonal floods on the Sacramento River would regularly inundate the lowest parts of these flood basins, moderate floods would cause extensive flooding, and very large floods would create an 'inland sea', affecting over 2,000 square miles of the valley floor.

The 1862 flood was a very large flood that filled the Sacramento Valley flood basins. Although it was described as unprecedented by early settlers, most had lived in California for less than 15 years. Historical accounts from Spanish missions and Native Americans describe an earlier valley-filling flood in 1805. Subsequent valley-wide flooding in 1878 and again in 1907 suggests the 1862 flood was not an anomaly, but rather representative of very large magnitude floods that infrequently occur in the Sacramento Valley. The modern flood control system mimics the natural geomorphic function of the Sacramento River system by routing flood flows from the Sacramento and Feather Rivers through a network of flood basin bypasses.

Hydraulic Mining Sediment Impacts on American River Channel Morphology and Flood Stages

• Download presentation [PDF, 15.5 MB]
• Download presentation (with notes) [PDF, 4.9 MB]

• Listen to the presentation

Abstract:

The American River basin received 197 m³ of hydraulic mining sediment (HMS), mostly produced in the North Fork. Prior to the 1862 flood HMS accumulated in mountain tributaries, although changes in water quality were noticeable. The 1862 flood brought down tremendous volumes of sediment from the mountains, and initiated a prolonged period of sedimentation, flooding, and channel change in the lower American River (LAR). Historical evidence of geomorphic change are presented including cartography and hydrographic data from streamflow gages. Quantitative and spatial data are severely limited for presettlement or pre-1862 channel conditions. Topographic surveys of increasing resolution were done in the 1880s and in 1906. The 1906 survey provided a set of seven detailed topographic map sheets, ~30 cross sections, and a longitudinal profile for the LAR that constitute a comprehensive topographic data set suitable for geomorphic change detection.

After hydraulic mining was enjoined in 1884, the system underwent a long period of readjustments that continue to this day. Cross sections and flow stage data indicate that flow stages and the channel bed lowered ~2 m at the H Street Bridge between 1924 and 1983. This corresponded with the removal of midchannel sand bars, and is corroborated by ~7 m lowering of the longitudinal profile in the lower river between 1906 and 1998. Flow stages at the H Street and old Fair Oaks Bridge sites in the early 20th century were synchronous with licensed HMS production in the North Fork and closing of North Fork Dam in 1939. Apparently, channel-bed changes were in synch with mining and the closing of North Fork Dam. This suggests that the old Folsom Dam did not permanently arrest down-valley HMS transport. Channel changes attributable to recovery from HMS can be difficult to distinguish from changes caused by engineering works, such as dams, dredging, levees, and bank protection. Nevertheless, the legacy of HMS in the LAR remains strong and needs to be documented. HMS may contain high concentrations of mercury as has been shown elsewhere. The history of channel changes in the LAR should be thoroughly documented using field, historical, geochemical, GIS, and remote sensing methods to map and identify HMS and former channel positions.

Warning from the Past: The message, meteorology and myths from the Great West Coast flooding of 1861-1862

• Download presentation [PDF, 5.1 MB]

• Listen to the presentation

Abstract:

How bad can flooding get?

The greatest known and recorded widespread flooding, ever to impact the West Coast of the United States, occurred during the winter of 1861-1862. It was characterized by an extraordinarily wet weather pattern shifting from Oregon to California. That persistent and intense weather pattern produced flooding which, to this day, has never been matched.

The flooding was caused by synoptic weather patterns configuring air flow into the West Coast to produce strong atmospheric rivers, combined with a series of mid-latitude cyclones. The wet weather pattern shifted from north to the south, along the West Coast of the U.S., as winter unfolded. The soggy weather pattern initially struck Oregon, then moved south and stalled — pummeling northern California with biblical flooding. The moist pattern then shifted further south, finally causing extreme flooding into Southern California.

The author researched limited weather and historical accounts to reconstruct this series of storms and show you the impacts. You'll begin to understand the size and evolution of this epic flood event, while recognizing the lessons of history this "hydrologic warning" from the past can provide.

California Historical Rainfall Data and Modern Records

• Download presentation [PDF, 3.5 MB]
• Download presentation (with notes) [PDF, 1.8 MB]

• Listen to the presentation

Abstract:

[Abstract not available]

Physically-Based Estimation of Maximum Precipitation: Application to American River Basin for the 1996-1997 Storm

• Download presentation [PDF, 1.8 MB]
• Download paper [PDF, 1.1 MB]
• (Paper republished with permission of the author)

• Listen to the presentation

Abstract:

The presentation summarizes a paper published in the Journal of Hydrologic Engineering, April 2011, which proposed a methodology for maximum precipitation (MP) estimation that uses a physically-based numerical atmospheric model. As a case study, the model-based 72-h MP was estimated for the American River watershed (ARW) in California for the December 1996-January 1997 flood event.

Panel Discussion: Estimating Future Floods to Manage Flood Risk — Part 2

• Listen to the presentation

Moderator:

Panelists: