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A rationale for effective post-fire debris flow mitigation within forested terrain

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A rationale for effective post-fire debris flow mitigation within forested terrain
Geoenvironmental Disasters, Springer | May 25, 2018...
Summary
Watersheds recently burned by wildfires are recognized as having an increased susceptibility to debris flow occurrence. The great majority occur within the first 2...
Watersheds recently burned by wildfires are recognized as having an increased susceptibility to debris flow occurrence. The great majority occur within the first 2 years following wildfires. These debris flows are generated primarily through the process of progressive entrainment of material eroded from hillslopes and channels by surface runoff and appears independent of the vegetative community burned. The decreased likelihood of debris flows over time is linked to the restoration of hydrologic function as vegetative cover and soil infiltration functioning return to pre-fire conditions. An exception to this pattern of post-wildfire debris flow susceptibility occurs in burned drainage basins with forest cover. A second, later period of increased debris flow susceptibility due to infiltration-triggered landslides can occur in burned forested basins. This later period of debris flow susceptibility is largely attributable to the fire-induced tree mortality and subsequent decay of tree root networks decreasing soil strength on steep hillslopes which produces an increased likelihood of debris flow occurrence 3 to 10 or more years after the wildfire. Consequently, post-fire mitigation measures in forested terrain must address the risk posed by debris flows caused by progressive entrainment during the 2 years following the wildfire and debris flows due to infiltration-induced debris slides three or more years later. Mitigation for the later debris flows in forested terrain involves identification of areas with infiltration-induced debris slides coincident with concentrations of fire-killed trees. Timely reforestation of these areas after a wildfire limits the loss of soil strength from decaying roots.

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A shift from drought to extreme rainfall drives a stable landslide to catastrophic failure

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A shift from drought to extreme rainfall drives a stable landslide to catastrophic failure
Nature | February 7, 2019...
Summary
The addition of water on or below the earth’s surface generates changes in stress that can trigger both stable and unstable sliding of...

The addition of water on or below the earth’s surface generates changes in stress that can trigger both stable and unstable sliding of landslides and faults. While these sliding behaviours are well-described by commonly used mechanical models developed from laboratory testing (e.g., critical-state soilmechanics and rate-and-state friction), less is known about the field-scale environmental conditions orkinematic behaviours that occur during the transition from stable to unstable sliding. Here we use radarinterferometry (InSAR) and a simple 1D hydrological model to characterize 8 years of stable sliding of the Mud Creek landslide, California, UsA, prior to its rapid acceleration and catastrophic failure on May 20, 2017. Our results suggest a large increase in pore-fluid pressure occurred during a shift from historic drought to record rainfall that triggered a large increase in velocity and drove slip localization, overcoming the stabilizing mechanisms that had previously inhibited landslide acceleration. Given thepredicted increase in precipitation extremes with a warming climate, we expect it to become more common for landslides to transition from stable to unstable motion, and therefore a better assessmentof this destabilization process is required to prevent loss of life and infrastructure.

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A study of methods to estimate debris flow velocity

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A study of methods to estimate debris flow velocity
Landslides, Springer | September 16, 2019...
Summary
Debris flow velocities are commonly back-calculated from superelevation events which require subjective estimates of radii of curvature of bends in the debris flow...
Debris flow velocities are commonly back-calculated from superelevation events which require subjective estimates of radii of curvature of bends in the debris flow channel or predicted using flow equations that require the selection of appropriate rheological models and material property inputs. This research investigated difficulties associated with the use of these conventional velocity estimation methods. Radii of curvature estimates were found to vary with the extent of the channel investigated and with the scale of the media used, and back-calculated velocities varied among different investigated locations along a channel. Distinct populations of Bingham properties were found to exist between those measured by laboratory tests and those back-calculated from field data; thus, laboratory-obtained values would not be representative of field-scale debris flow behavior. To avoid these difficulties with conventional methods, a new preliminary velocity estimation method is presented that statistically relates flow velocity to the channel slope and the flow depth. This method presents ranges of reasonable velocity predictions based on 30 previously measured velocities.

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Age Determination of the Remaining Peat in the Sacramento–San Joaquin Delta, California, USA
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Age Determination of the Remaining Peat in the Sacramento–San Joaquin Delta, California, USA
U.S. Geological Survey (USGS) | October 9, 2007...
Summary
The Sacramento–San Joaquin Delta of California was once a 1,400 square kilometer (km2) tidal marsh, which contained a vast layer of peat ranging...
The Sacramento–San Joaquin Delta of California was once a 1,400 square kilometer (km2) tidal marsh, which contained a vast layer of peat ranging up to 15 meters (m) thick (Atwater and Belknap, 1980). Because of its favorable climate and highly fertile peat soils, the majority of the Delta was drained and reclaimed for agriculture during the late 1800s and early 1900s.

Drainage of the peat soils changed the conditions in the surface layers of peat from anaerobic (having no free oxygen present) to aerobic (exposed to the atmosphere). This change in conditions greatly increased the decomposition rate of the peat, which consists largely of organic (plant) matter. Thus began the process of land-surface subsidence, which initially was a result of peat shrinkage and compaction, and later largely was a result of oxidation by which organic carbon in the peat essentially vaporized to carbon dioxide (Deverel and others, 1998; Ingebritsen and Ikehara, 1999).

Because of subsidence, the land-surface elevation on farmed islands in the Delta has decreased from a few meters to as much as 8 m below local mean sea level (California Department of Water Resources, 1995; Steve Deverel, Hydrofocus, Inc., written commun., 2007).

The USGS, in collaboration with the University of California at Davis, and Hydrofocus Inc. of Davis, California, has been studying the formation of the Delta and the impact of wetland reclamation on the peat column as part of a project called Rates and Evolution of Peat Accretion through Time (REPEAT). The purpose of this report is to provide results on the age of the remaining peat soils on four farmed islands in the Delta.

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Beaches

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Beaches
Scientific American | August 1, 1960...
Summary
Beaches are natural playgrounds partly under the sun and partly under the sea where people can swim and surfboard, sun themselves and study other people. This human...
Beaches are natural playgrounds partly under the sun and partly under the sea where people can swim and surfboard, sun themselves and study other people. This human activity tends to obscure the fact that the beach itself is constantly in motion, quietly changing its configuration and restlessly shifting its position, grain by grain, until huge masses of sand have been moved. On a small scale and in a matter of hours the sand castles disappear and the footprints are erased; on a large scale, after days and months, the height of the sand around the rocks changes, the waves break in new places and the beach becomes broader or narrower. Indeed, over a period of years large quantities of sand may arrive or depart, posing complex problems of conservation for the people who want to enjoy the beach. This dynamic quality was incorporated by the late Columbia University physiographer Douglas W. Johnson into a definition: "A beach is a deposit of material which is in transit either alongshore or off-and-on shore." Thus three elements make a beach: a quantity of rocky material, a shore-line area in which it moves and a supply of energy to move it.

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Changing ecosystems: a brief ecological history of the Delta
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Changing ecosystems: a brief ecological history of the Delta
U.C. Davis Center for Watershed Sciences | February 15, 2010...
Summary
The San Francisco Estuary is a young estuary, about 6-10,000 years old in its present location. It became established during periods of high...
The San Francisco Estuary is a young estuary, about 6-10,000 years old in its present location. It became established during periods of high climatic variability (reflected in extreme floods and long droughts) compared to the relatively stable past 150 years. The Delta was formed as a huge freshwater marsh through the interaction of river inflow and the slow rise of sea level with the growth and decay of tules and other plants. This interaction resulted in the deposition of large amounts of organic matter, creating layers of peat that kept pace with sea level rise. These peat layers formed the soils of most of the present Delta ‘islands’, which were actually complex patches of floodable marsh.

The channels among the islands were historically shifting, winding distributaries of the entering rivers that moved inflowing water through the Delta, providing access to upstream areas for large runs of migratory fish. The movement and quality of water in these channels was strongly affected by tidal action. These attributes also created a complex of diverse and shifting habitats that supported a wide variety of functions for an ecological system in which there was no clear separation between aquatic and terrestrial components.

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County of San Bernardino Hydrology Manual

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County of San Bernardino Hydrology Manual
San Bernardino County | August 1, 1986...
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Data Measured on Water Collected from Eastern Mojave Desert, California

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Data Measured on Water Collected from Eastern Mojave Desert, California
U.S. Department of Energy (DOE) | August 18, 2017...
Summary
In March of 2000 field collection of water from the Eastern Mojave Desert resulted in the measurement of stable isotope, radiocarbon, tritium, and limited...
In March of 2000 field collection of water from the Eastern Mojave Desert resulted in the measurement of stable isotope, radiocarbon, tritium, and limited dissolved noble gases. This work was follow-on to previous studies on similar systems in southern Nevada associated with the Nevada Test Site (Davisson et al., 1999; Rose and Davisson, 2003). The data for groundwater from wells and springs was never formally published and is therefore tabulated in Table 1 in order to be recorded in public record. In addition 4 years of remote precipitation data was collected for stable isotopes and is included in Table 2. These studies, along with many parallel and subsequent ones using isotopes and elemental concentrations, are all related to the general research area of tracing sources and quantifying transport times of natural and man-made materials in the environment. This type of research has direct relevance in characterizing environmental contamination, understanding resource development and protection, designing early detection in WMD related terrorism, and application in forensics analysis.

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Distribution of Lakes in the United States

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Distribution of Lakes in the United States
Scientific American | June 12, 1880...
Summary
There are numerous lacustrine basins to be found in the States bordering the Pacific Ocean. As in other regions of the globe, their distribution is...
There are numerous lacustrine basins to be found in the States bordering the Pacific Ocean. As in other regions of the globe, their distribution is determined by the configuration of land, or, more specifically, by the forms of the great hydrographic basins in the interior of the continent; hence some general idea of the topography of the western portions of the United States is an essential preliminary.

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Estimating reservoir sedimentation rates at large spatialand temporal scales: A case study of California

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Estimating reservoir sedimentation rates at large spatialand temporal scales: A case study of California
Water Resources Research, American Geophysical Union (AGU) | December 25, 2009...
Summary
Previous reservoir sedimentation models have ignored two key factors for large spatial and temporal modeling of multiple reservoirs: trapping by upstream dams and decreasing sediment...
Previous reservoir sedimentation models have ignored two key factors for large spatial and temporal modeling of multiple reservoirs: trapping by upstream dams and decreasing sediment trapping as reservoirs fill. We developed a spreadsheet-based model that incorporates both factors. Using California as a case study, we used measured sedimentation rates to estimate sediment yields for distinct geomorphic regions and applied those rates to unmeasured reservoirs by region. Statewide reservoirs have likely filled with 2.1 billion m3 of sediment to date, decreasing total reservoir capacity by 4.5%. About 200 reservoirs have likely lost more than half their initial capacity to sedimentation.

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