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Articles 1 - 14 of 14
Full-Text Articles in Physical Sciences and Mathematics
The Science And Practice Of River Restoration, Ellen E. Wohl, Stuart N. Lane, Andrew C. Wilcox
The Science And Practice Of River Restoration, Ellen E. Wohl, Stuart N. Lane, Andrew C. Wilcox
Geosciences Faculty Publications
River restoration is one of the most prominent areas of applied water-resources science. From an initial focus on enhancing fish habitat or river appearance, primarily through structural modification of channel form, restoration has expanded to incorporate a wide variety of management activities designed to enhance river process and form. Restoration is conducted on headwater streams, large lowland rivers, and entire river networks in urban, agricultural, and less intensively human-altered environments. We critically examine how contemporary practitioners approach river restoration and challenges for implementing restoration, which include clearly identified objectives, holistic understanding of rivers as ecosystems, and the role of restoration …
Rapid Reservoir Erosion, Hyperconcentrated Flow, And Downstream Deposition Triggered By Breaching Of 38 M Tall Condit Dam, White Salmon River, Washington, Andrew C. Wilcox, Jim E. O'Connor, Jon J. Major
Rapid Reservoir Erosion, Hyperconcentrated Flow, And Downstream Deposition Triggered By Breaching Of 38 M Tall Condit Dam, White Salmon River, Washington, Andrew C. Wilcox, Jim E. O'Connor, Jon J. Major
Geosciences Faculty Publications
Condit Dam on the White Salmon River,Washington, a 38m high dam impounding a large volume (1.8 million m3) of fine-grained sediment (60% sand, 35% silt and clay, and 5% gravel), was rapidly breached in October 2011. This unique dam decommissioning produced dramatic upstream and downstream geomorphic responses in the hours and weeks following breaching. Blasting a 5 m wide hole into the base of the dam resulted in rapid reservoir drawdown, abruptly releasing ~1.6 million m3 of reservoir water, exposing reservoir sediment to erosion, and triggering mass failures of the thickly accumulated reservoir sediment. Within 90 min …
Climate And Topographic Controls On Simulated Pasture Production In A Semiarid Mediterranean Watershed With Scattered Tree Cover, J. Lozano-Parra, Marco P. Maneta, S. Schnabel
Climate And Topographic Controls On Simulated Pasture Production In A Semiarid Mediterranean Watershed With Scattered Tree Cover, J. Lozano-Parra, Marco P. Maneta, S. Schnabel
Geosciences Faculty Publications
Natural grasses in semiarid rangelands constitute an effective protection against soil erosion and degradation, are a source of natural food for livestock and play a critical role in the hydrologic cycle by contributing to the uptake and transpiration of water. However, natural pastures are threatened by land abandonment and the consequent encroachment of shrubs and trees as well as by changing climatic conditions. In spite of their ecological and economic importance, the spatiotemporal variations of pasture production at the decadal–century scales over whole watersheds are poorly known.We used a physically based, spatially distributed ecohydrologic model applied to a 99.5 ha …
Understanding Greenland Ice Sheet Hydrology Using An Integrated Multi-Scale Approach, A. K. Rennermalm, S. E. Moustafa, J. Mioduszewski, V. W. Chu, R. R. Forster, B. Hagedorn, Joel T. Harper, T. L. Mote, D. A. Robinson, C. A. Shuman, L. C. Smith, M. Tedesco
Understanding Greenland Ice Sheet Hydrology Using An Integrated Multi-Scale Approach, A. K. Rennermalm, S. E. Moustafa, J. Mioduszewski, V. W. Chu, R. R. Forster, B. Hagedorn, Joel T. Harper, T. L. Mote, D. A. Robinson, C. A. Shuman, L. C. Smith, M. Tedesco
Geosciences Faculty Publications
Improved understanding of Greenland ice sheet hydrology is critically important for assessing its impact on current and future ice sheet dynamics and global sea level rise. This has motivated the collection and integration of in situ observations, model development, and remote sensing efforts to quantify meltwater production, as well as its phase changes, transport, and export. Particularly urgent is a better understanding of albedo feedbacks leading to enhanced surface melt, potential positive feedbacks between ice sheet hydrology and dynamics, and meltwater retention in firn. These processes are not isolated, but must be understood as part of a continuum of processes …
Dynamically Downscaled Winter Precipitation Over Complex Terrain Of The Central Rockies Of Western Montana, Usa, Nicholas Loren Silverman, Marco P. Maneta, S.-H. Chen, Joel T. Harper
Dynamically Downscaled Winter Precipitation Over Complex Terrain Of The Central Rockies Of Western Montana, Usa, Nicholas Loren Silverman, Marco P. Maneta, S.-H. Chen, Joel T. Harper
Geosciences Faculty Publications
We evaluate the results of dynamically downscaled winter precipitation over Western Montana using the weather research and forecasting (WRF) model through comparison with estimates from the observationally based parameter-elevation regressions on independent slopes model (PRISM). Seven years (six winters) from 2000 to 2006 are simulated at 4 km resolution to assess the similarities and differences between the two models as well as the implications for hydrologic modeling. Inherent biases in both approaches are apparent, highlighting the difficulty in climate model validation. Results show general agreement between the two models in the spatial distribution of winter precipitation. A principal component analysis …
Compressional And Em Wave Velocity Anisotropy In A Temperate Glacier Due To Basal Crevasses, And Implications For Water Content Estimation, John Bradford, Joshua Nichols, Joel T. Harper, Toby W. Meierbachtol
Compressional And Em Wave Velocity Anisotropy In A Temperate Glacier Due To Basal Crevasses, And Implications For Water Content Estimation, John Bradford, Joshua Nichols, Joel T. Harper, Toby W. Meierbachtol
Geosciences Faculty Publications
We have conducted a series of experiments designed to investigate elastic and electromagnetic (EM) velocity anisotropy associated with a preferentially aligned fracture system on a temperate valley glacier in south-central Alaska, USA. Measurements include a three-dimensional compressional wave (P-wave) seismic reflection survey conducted over a 300 m x 300 m survey patch, with uniform source grid and static checkerboard receiver pattern. Additionally, we acquired a multiazimuth, multi-offset, polarimetric groundpenetrating radar (GPR) reflection experiment in a wagon-wheel geometry with 94 degrees of azimuthal coverage. Results show azimuthal variation in the P-wave normal-moveout velocity of less than 3% (3765 and 3630 ms …
Monitoring Glacier Surface Seismicity In Time And Space Using Rayleigh Waves, T. D. Mikesell, K. Van Wijk, M. M. Haney, J. H, Bradford, H. P. Marshall, Joel T. Harper
Monitoring Glacier Surface Seismicity In Time And Space Using Rayleigh Waves, T. D. Mikesell, K. Van Wijk, M. M. Haney, J. H, Bradford, H. P. Marshall, Joel T. Harper
Geosciences Faculty Publications
Sliding glaciers and brittle ice failure generate seismic body and surface wave energy characteristic to the source mechanism. Here we analyze continuous seismic recordings from an array of nine short-period passive seismometers located on Bench Glacier, Alaska (USA) (61.033N, 145.687W). We focus on the arrival-time and amplitude information of the dominant Rayleigh wave phase. Over a 46-hour period we detect thousands of events using a cross-correlation based event identification method. Travel-time inversion of a subset of events (7% of the total) defines an active crevasse, propagating more than 200 meters in three hours. From the Rayleigh wave amplitudes, we estimate …
Thermal Tracking Of Meltwater Retention In Greenland’S Accumulation Area, Neil F. Humphrey, Joel T. Harper, W. Tad Pfeffer
Thermal Tracking Of Meltwater Retention In Greenland’S Accumulation Area, Neil F. Humphrey, Joel T. Harper, W. Tad Pfeffer
Geosciences Faculty Publications
Poorly understood processes controlling retention of meltwater in snow and firn have important implications for Greenland Ice Sheet’s mass balance and flow dynamics. Here we present results from a 3 year (2007-2009) field campaign studying firn thermal profiles and density structure along an 85 km transect of the percolation zone of west Greenland. We installed one or two thermistor strings at 14 study sites, each string having 32 sensors spaced between 0 and 10 m depth. Data from our network of over 500 sensors were collected at 15-60 min intervals for 1-2 years, thereby recording the thermal signature of meltwater …
Georadar-Derived Estimates Of Firn Density In The Percolation Zone, Western Greenland Ice Sheet, Joel Brown, John Bradford, Joel T. Harper, W. Tad Pfeffer, Neil Humphrey, Ellen Mosley-Thompson
Georadar-Derived Estimates Of Firn Density In The Percolation Zone, Western Greenland Ice Sheet, Joel Brown, John Bradford, Joel T. Harper, W. Tad Pfeffer, Neil Humphrey, Ellen Mosley-Thompson
Geosciences Faculty Publications
Greater understanding of variations in firn densification is needed to distinguish between dynamic and melt-driven elevation changes on the Greenland ice sheet. This is especially true in Greenland’s percolation zone, where firn density profiles are poorly documented because few ice cores are extracted in regions with surface melt.We used geoader to investigate firn density variations with depth along an about 70 km transect through a portion of the accumulation area in western Greenland that partially melts. We estimated electromagnetic wave velocity by inverting reflection travel times picked from common midpoint gathers. We followed a procedure designed to find the simplest …
Timing Of Present And Future Snowmelt From High Elevations In Northwest Montana, Bonnie Jean Gillan, Joel T. Harper, Johnnie N. Moore
Timing Of Present And Future Snowmelt From High Elevations In Northwest Montana, Bonnie Jean Gillan, Joel T. Harper, Johnnie N. Moore
Geosciences Faculty Publications
The sensitivity of snowmelt-driven water supply to climate variability and change is difficult to assess in the mountain west, where strong climatic gradients coupled with complex topography are sampled by sparse ground measurements. We developed a model which ingests daily satellite imagery and meteorological data and is suitable for areas >1000 km2, yet captures spatial variability of snow accumulation and melt in steep mountain terrain.We applied the model for the years 2000–2008 to a 2900 km2 snowmelt-dominated watershed in NW Montana. We found that >25% of the basin’s snow water equivalent (SWE) accumulates above the highest measurement station and >70% …
Complex Dielectric Permittivity Measurements From Ground-Penetrating Radar Data To Estimate Snow Liquid Water Content In The Pendular Regime, John H. Bradford, Joel T. Harper, Joel Brown
Complex Dielectric Permittivity Measurements From Ground-Penetrating Radar Data To Estimate Snow Liquid Water Content In The Pendular Regime, John H. Bradford, Joel T. Harper, Joel Brown
Geosciences Faculty Publications
Monitoring the snow water equivalent (SWE) is critical to effective management of water resources in many parts of the world that depend on the mountain snowpack for water storage. There are currently no methods to remotely sense SWE with accuracy over large lateral distances in the steep and often forested terrain of mountain basins. Previous studies have shown that measurements of ground-penetrating radar (GPR) velocity can provide accurate estimates of SWE in dry snow. Introduction of liquid water into the snowpack results in a three-phase system that cannot be accurately characterized with GPR velocity alone. We show that measuring the …
Air Compression As A Mechanism For The Underdamped Slug Test Response In Fractured Glacier Ice, Toby W. Meierbachtol, Joel T. Harper, Neil Humphrey, Jeremy Shaha, John Bradford
Air Compression As A Mechanism For The Underdamped Slug Test Response In Fractured Glacier Ice, Toby W. Meierbachtol, Joel T. Harper, Neil Humphrey, Jeremy Shaha, John Bradford
Geosciences Faculty Publications
Artificial perturbations of borehole water levels, known as slug tests, are a useful means of characterizing the glacier hydrologic system. Slug tests were performed on Bench Glacier, Alaska, in 21 boreholes over three field seasons during the transition from a winter to a summer drainage mode. Fifty-four slug tests were conducted, with water level monitoring in up to five boreholes adjacent to the slugged borehole. Seven of the slug tests were performed in conjunction with dye dispersion tests to identify water pathways within the slugged borehole following perturbation. Nearly 60% of monitored adjacent boreholes showed a hydraulic connection to the …
Two Modes Of Accelerated Glacier Sliding Related To Water, Joel T. Harper, Neil Humphrey, W. T. Pfeffer, Brian Lazar
Two Modes Of Accelerated Glacier Sliding Related To Water, Joel T. Harper, Neil Humphrey, W. T. Pfeffer, Brian Lazar
Geosciences Faculty Publications
We present the first glacier-wide detailed measurement of basal effective pressure and related observations including bed separation to elucidate the role of water in sliding. The hard bedded glacier instrumented in our study exhibited two phases of accelerated sliding motion apparently driven by separate mechanisms. The first acceleration phase (up to 5 fold increase in speed) was closely tied to an increase in bed separation. The faster second phase (up to 9 fold increase in speed) was related to an unusually high level of connectivity of subglacial waters. We infer the first mode was related to cavity opening and the …
High Altitude Himalayan Climate Inferred From Glacial Ice Flux, Joel T. Harper, Neil Humphrey
High Altitude Himalayan Climate Inferred From Glacial Ice Flux, Joel T. Harper, Neil Humphrey
Geosciences Faculty Publications
Glaciological processes are modeled to investigate precipitation patterns and the resulting mass flux of snow and ice across Himalayan topography. Our model tracks the accumulation and ablation of snow and ice and the transport of snow and ice across the topography by glacier motion. We investigate high elevation precipitation on the Annapurna Massif by comparing the existing ice cover with model-simulated glaciers produced by a suite of different precipitation scenarios. Our results suggest that precipitation reaches a maximum level well below the elevation of the highest peaks. Further, essentially no snow accumulates on the topography above an elevation of 6200–6300 …