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Research about Colorado River, Grand Canyon

Source-linked reports with geographic coverage including Colorado River, Grand Canyon.

61 records · Page 4Linked to original sources
USGS1997

Debris flows in Grand Canyon National Park: Peak discharges, flow transformations, and hydrographs

Direct measurements of debris-flow hydrograph and flow behavior in remote drainage areas are rare. We infer hydrographs and flow behavior for recent debris flow in bedrock tributaries of the Colorado River from preserved stratigraphic relations, sedimentology and surface morphology of debris fans and evidence of flow-surface elevations. We propose that 3 types of debris-flow hydrographs occur in Grand Canyon: Type I flows have a single debris-flow peak followed by recessional 'hyperconcentrated flow' or streamflow; Type II flows have multiple debris-flow peaks with intervening 'hyperconcentrated flow' and (or) streamflow phases; and Type III flows begin as either Type I or Type II flows, but late-stage recessional streamflow is higher than the stage(s) of the debris-flow phase(s) and extensively reworks debris-flow deposits of buries them beneath streamflow sand and gravel. Field evidence shows that debris-flow peaks last for seconds to minutes, while recessional flows have durations of several hours to a day.

Arizona↗
USGS1997

Initiation of debris flows in tributaries of the Colorado River in Grand Canyon, Arizona

Debris flows are initiated in tributaries of the Colorado River in Grand Canyon when intense rainfall causes failures in colluvium and (or) bedrock. Most debris flows occur in the summer during localized convective thunderstorms with rainfall intensities as high as 40 mm/hr. Rarer and larger debris flows occur during unusually warm frontal storms in winter. Hourly precipitation data suggest that storms that cause debris flows terminate with a period of intense rainfall, a characteristic that complicates the use of daily rainfall records in assessing debris-flow hazard. Recurrence intervals for 1-day rainfall associated with 37 recent debris flows range from <1 to >50 years, with most <10 years. Recurrence intervals for the multi-day rainfall of storms associated with debris flows range from <1 to 158 years, but most were >10 years. The low recurrence intervals of debris-flow producing rainfalls, compared with the 10-50 yr recurrence intervals for most debris flows, underscores the co-dependence of debris-flow initiation on geologic factors, including bedrock type and antecedent soil-moisture conditions. The primary geologic factor influencing debris-flow initiation in Grand Canyon is the exposure of shale units at heights >100 m above the river. Exposed shale bedrock fails readily, either producing debris flows directly or contributing source material to wedges of colluvium that may fail later. Shales also provide silt- and clay-size particles that in part determine the rheological properties of debris flows.

Arizona↗
USGS1996

Initiation and frequency of debris flows in Grand Canyon, Arizona

Debris flows occur in 600 tributaries of the Colorado River in Grand Canyon, Arizona when intense precipitation causes slope failures in bedrock or colluvium. These slurries transport poorly sorted sediment, including very large boulders that form rapids at the mouths of tributaries and control the longitudinal profile of the Colorado River. Although the amount of rainfall on the days of historic debris flows typically is not unusual, the storm rainfall on consecutive days before the debris flows typically had recurrence intervals greater than 10 yrs. Four types of failure mechanisms initiate debris flows: bedrock failure (12 percent), failure of colluvial wedges by rainfall (21 percent), failure of colluvial wedges by runoff (the "firehose effect;" 36 percent), and combinations of these failure mechanisms (30 percent). Failure points are directly or indirectly associated with terrestrial shales, particularly the Permian Hermit Shale, shale units within the Permian Esplanade Sandstone of the Supai Group, and the Cambrian Bright Angel Shale. Shales either directly fail, produce colluvial wedges downslope that contain clay, or form benches that store poorly sorted colluvium in wedge-shaped deposits. Terrestrial shales provide the fine particles and clay minerals-particularly kaolinite and illite-essential to long-distance debris-flow transport, whereas marine shales mostly contain smectites, which inhibit debris-flow initiation. Using repeat photography, we determined whether or not a debris flow occurred in the last century in 164 of 600 tributaries in Grand Canyon. We used logistic regression to model the binomial frequency data using 21 morphometric and lithologic variables. The location of shale units, particularly the Hermit Shale, within the tributary is the most consistent variable related to debris-flow frequency in Grand Canyon. Other statistically significant variables vary with large scale changes in canyon morphology. Standard morphometric measures such as drainage-basin area, channel gradient, and aspect of the river corridor are the most significant variables in the narrow and deep eastern section of Grand Canyon. Measures of the location of source lithologies are more important in western Grand Canyon, which has broader and low-gradient drainages. Measures of geologic structure, and other standard hydrologic variates, were not significant. Our results show that the probability of debris-flow occurrence is highest in eastern Grand Canyon. Throughout Grand Canyon, the probability of debris-flow occurrence is highest in reaches of the Colorado River that trend south-southwest. This direction is significant because most summer storms originate from a southerly direction, and the maximum slope of the regional structure is to the southwest. The binomial frequency of debris flows is not random in Grand Canyon, and tributaries of similar debris-flow frequency are clustered in distinct reaches.

Arizona↗
USGS1993

Surficial geology, geomorphology, and erosion of archeologic sites along the Colorado River, eastern Grand Canyon, Grand Canyon National Park, Arizona

The average number of archeologic sites along the Colorado River in eastern Grand Canyon between River Miles 65-72 exceeds 12 km -1 ; the largest concentration from Glen Canyon Dam to the mouth of Grand Canyon. The sites are mostly of Anasazi affiliation, dating from the Pueblo Ito Pueblo II periods (A.D. 800-1200), although older sites of Basketmaker II affinity (about 200 B.C. to A.D. 400) and younger sites of Native American and Anglo affiliation are also present. All of the sites are closely associated with late-Holocene alluvial, debris-flow, and eolian deposits that accumulated in the river corridor during the past 2,500 years. The majority of sites occur on or beneath the surface of ancient alluvial deposits of the Colorado River, which form distinctive high terraces. Lateral shifts of the river extensively eroded these deposits and associated archeologic sites twice in prehistoric times, between A.D.300700 and between A.D. 1200-1400. In late historic times, numerous sites have been damaged or destroyed by erosion, which has accelerated since 1965-73. The daily operation of Glen Canyon Dam probably did not cause accelerated erosion in eastern Grand Canyon, although the presence of the dam indirectly effects erosion. Generally, sites are eroded by arroyo cutting in the short, ephemeral streams that drain the terraces of the river corridor. These streams are small; 90 percent have catchment area less than 20,000-30,000 m 2 and channel length of less than 300-400 m. Driven by excessive rainfall, arroyo cutting deepens, widens, and expands the channel system. The extent of arroyo cutting is related to past and present depositional levels of the river, which are local baselevels of erosion. The post-dam level is 3-4 m below the lowest pre-dam level; this decrease resulted from elimination of the annual flood and a six-fold reduction of sediment load. Eighty percent of tributary streams end above or on the post-dam depositional level, but during large runoff the channels are free to extend upslope as well as downslope toward the river. These channels will eventually extend downslope to the river, where the channel gradient will be lowered 3-4 m. Arroyo cutting will be intensified until channel gradients adjust to the post-dam baselevel.

Arizona↗
USGS1969

Stratified rocks of the Grand Canyon

The record of the earth's history in the walls of the Grand Canyon has been deciphered through hard work by many people during the past 100 years. Much still remains unsolved. John Wesley Powell's contributions were of a pioneering type, though he was not the first to discuss the rocks of the Grand Canyon. Far more important than his own observations and deductions in the field of stratigraphic geology was his tremendous influence upon the work of his associates and his successors. This chapter traces the evolution of thought concerning the stratified rocks of the Grand Canyon and summarizes present concepts of stratigraphic history as recorded in the walls of the canyon. A brief summary of available data and conclusions on each of the principal sedimentary units is presented.

Arizona↗
USGS1969

The rapids and the pools - Grand Canyon

Through the Grand Canyon the Colorado drops in elevation about 2,200 feet in 280 miles; most of this drop occurs in rapids that account for only 10 percent of the distance. Despite the importance of rapids, there are no waterfalls. Depth measurements made at 1/10-mile intervals show that the bed profile is highly irregular, but the apparent randomness masks an organized alternation of deeps and shallows. Measurement of the age of a lava flow that once blocked the canyon near Toroweap shows that no appreciable deepening of the canyon has taken place during the last million years. It is reasoned that the river has had both the time and the ability to eliminate the rapids. The long-continued existence and the relative straightness of the longitudinal profile indicate that the river maintains a state of quasi-equilibrium which provides the hydraulic requirements for carrying the debris load brought in from upstream without continued erosion of the canyon bed. The maintenance of the alternating pools and rapids seems to be a necessary part of this poised or equilibrium condition.

Arizona↗