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Articles 1 - 7 of 7
Full-Text Articles in Social and Behavioral Sciences
Dam Nation: A Geographic Census Of American Dams And Their Large-Scale Hydrologic Impacts, William L. Graf
Dam Nation: A Geographic Census Of American Dams And Their Large-Scale Hydrologic Impacts, William L. Graf
Faculty Publications
Newly available data indicate that darns fragment the fluvial system of the continental United States and that their impact on river discharge is several times greater than impacts deemed likely as a result of global climate change. The 75,000 dams in the continental United States are capable of storing a volume of water almost equaling one year's mean runoff, but there is considerable geographic variation in potential surface water impacts. In some western mountain and plains regions, darns can store more than 3 year's runoff, while in the Northeast and Northwest, storage is as little as 25% of the annual …
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 …
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. …
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.