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Articles 361 - 371 of 371
Full-Text Articles in Geography
Issues Concerning Phreatophyte Clearing, Revegetation, And Water Savings Along The Gila River, Arizona, William L. Graf, Duncan T. Patten, Bonnie Turner
Issues Concerning Phreatophyte Clearing, Revegetation, And Water Savings Along The Gila River, Arizona, William L. Graf, Duncan T. Patten, Bonnie Turner
Faculty Publications
A detailed analysis of the published results of the U. S. Geological Survey Phreatophyte Project conducted in the area of interest for the Corps of Engineers Camelsback Dam study provides the following results. It appears that the figure of 18.53 inches per year for water savings from phreatophyte clearing along the Gila River in southeast Arizona should not be used for predicting potential water salvage because of large sampling errors, measurement errors, and the inherent variability of the natural processes of evapotranspiration. An extensive literature review shows that no dependable values are available for the Gila River project area. It …
A Probabilistic Approach To The Spatial Assessment Of River Channel Instability, William L. Graf
A Probabilistic Approach To The Spatial Assessment Of River Channel Instability, William L. Graf
Faculty Publications
The deterministic approach to the analysis of river channel instability has not proved to be a completely useful basis for geographic predictions of channel behavior. Economic estimates for benefits of structural channel control projects commonly account for flood inundation, but in arid and semiarid regions these estimates are incomplete because they fail to take into account destructive channel migration and erosion. As a solution, a method whereby historical records of channel locations are reduced to spatially defined probabilistic functions allows calculation of the probability that given parcels of near-channel terrain will be destroyed by erosion. The probability of erosion for …
Variability Of Sediment Removal In A Semi-Arid Watershed, William L. Graf
Variability Of Sediment Removal In A Semi-Arid Watershed, William L. Graf
Faculty Publications
Field and documentary data from Walnut Gulch Watershed, an instrumented semiarid drainage basin of approximately 150 km2 (57 mi2) in southeastern Arizona, show that 83% of the alluvium removed from the basin during a 15‐year erosion episode beginning about 1930 was excavated from the highest‐order stream. The amount of alluvium removed in the erosion episode would have been equal to a covering of about 4 cm (1.6 in) over the entire basin. The rate of sediment removal during the erosion episode was 18 times greater than the rate of present channel sediment transport. Production of sediment from slopes and channel …
Channel Instability In A Braided Sand Bed River, William L. Graf
Channel Instability In A Braided Sand Bed River, William L. Graf
Faculty Publications
The Gila River of central Arizona is representative of braided, sand bed rivers in alluvial valleys that have inherent unstable behavior and destructive channel migration. The 112-year record of channel conditions along a portion of the Gila River provides data for the construction of locational probability maps for main flow channels. Zones of stability and hazardous instability alternate with each other at 3.2 km (2 mi) intervals. During the past century the overall sinuosity of the main flow channel has remained close to 1.18, despite numerous changes in actual location. Spatial and temporal variation of sinuosity have occurred in subreaches …
The Effect Of Dam Closure On Downstream Rapids, William L. Graf
The Effect Of Dam Closure On Downstream Rapids, William L. Graf
Faculty Publications
The force of flowing water and the resistance of the largest boulder provide a means of evaluation of the stability of rapids in canyon rivers. Field measurements and calculations show that the closure of Flaming Gorge Dam, Utah, has had a significant effect on the stability of rapids in the canyons of the Green River in Dinosaur National Monument 68 km (42 mi) downstream from the dam. The reduction in peak flows by the dam has limited the competence of the river to move boulders deposited in the main channel by tributary processes, landslides, and prehistoric floods. Before the dam …
The Distribution Of Glaciers In The American Rocky Mountains, William L. Graf
The Distribution Of Glaciers In The American Rocky Mountains, William L. Graf
Faculty Publications
No abstract provided.
Network Characteristics In Suburbanizing Streams, William L. Graf
Network Characteristics In Suburbanizing Streams, William L. Graf
Faculty Publications
Analysis of hydrologic, geomorphic, and suburbanization data from a small instrumented drainage basin near Iowa City, Iowa, indicates that channel networks are radically altered when suburban development overtakes a drainage basin. Changes in channel networks are such that the network becomes much more efficient in collecting water quickly, so that lag time and kurtosis of storm hydrographs are altered to produce the familiar flash floods of urban areas. The data show that network changes are closely associated with lag time and kurtosis of storm hydrographs and suggest that corrective measures should be concentrated on the internal links of the network. …
Cirques As Glacier Locations, William L. Graf
Cirques As Glacier Locations, William L. Graf
Faculty Publications
A comparison between the 319 cirques that contain glaciers and a sample of 240 empty cirques in the Rocky Mountains shows that in the present climatic situation, landforms are strong factors in determining the locations of glaciers. An optimum glacier location is a large cirque facing northeast, with a planimetric shape of width greater than length, high steep walls, a pass located to the windward, and a peak to the southwest. Glaciers survive in the present climatic conditions because of a geomorphic feedback system, whereby glaciers are protected by cirque forms that owe their morphology to glacial processes.
The Impact Of Suburbanization On Fluvial Geomorphology, William L. Graf
The Impact Of Suburbanization On Fluvial Geomorphology, William L. Graf
Faculty Publications
Analysis of aerial photography for the period 1950–1971 and field data collected from 1970 to 1974 indicate that in the Denver area suburban development has caused significant changes in fluvial systems. By first introducing large quantities of sediment and later by increasing surface runoff, suburban development leads to an expansion of floodplains followed by downcutting of streams. As areas of suburban development increase, greater percentages of stream lengths are dominated by transportation, and lesser percentages are dominated by erosion and deposition.
Quantitative Analysis Of Pinedale Landforms, Beartooth Mountains, Montana And Wyoming, William L. Graf
Quantitative Analysis Of Pinedale Landforms, Beartooth Mountains, Montana And Wyoming, William L. Graf
Faculty Publications
The spatial distribution of terminal moraines in alpine valleys can be quantitatively described using distance/regression models. Surface parameters indicative of age may also be numerically analyzed. Evaluation of postglacial modification of valley sides between terminal moraines provides an additional indicator of relative age of valley segments. Analysis of the geomorphology of alpine features in the upper Rock Creek drainage in the southeastern Beartooth Mountains, Montana, shows that glaciers in this area deposited evidence of two Bull Lake, four Pinedale, and two Neo glacial advances.
The Geomorphology Of The Glacial Valley Cross Section, William L. Graf
The Geomorphology Of The Glacial Valley Cross Section, William L. Graf
Faculty Publications
Several alpine valley systems in the southeastern Beartooth Mountains, Montana and Wyoming, have been examined using techniques similar to methods of stream system analysis. The general equation y = a x**b is the most adequate mathematical model for the cross valley profile; b values range between 1.5 and 2.0, indicating a parabolic form. As intensity of erosion increases in the glacial valley system, the b value also increases, indicating relatively deeper and narrower valley cross sections. The law of stream numbers, the law of stream lengths, and the bifurcation ratio, derived from fluvial geomorphology, are also applicable in glacial geomorphology.