Geology topics
Research about Colorado River, Grand Canyon
Source-linked reports with geographic coverage including Colorado River, Grand Canyon.
Evaluation of airborne thermal-infrared image data for monitoring aquatic habitats and cultural resources within the Grand Canyon
This study examined thermal-infrared (TIR) image data acquired using the airborne Advanced Thematic Mapper (ATM) sensor in the afternoon of July 25th, 2000 over a portion of the Colorado River corridor to determine the capability of these 100-cm resolution data to address some biologic and cultural resource requirements for GCMRC. The requirements investigated included the mapping of warm backwaters that may serve as fish habitats and the detection (and monitoring) of archaeological structures and natural springs that occur on land. This report reviews the procedure for calibration of the airborne TIR data to obtain surface water temperatures and shows the results for various river reaches within the acquired river corridor. With respect to mapping warm backwater areas, our results show that TIR data need to be acquired with a gain setting that optimizes the range of temperatures found within the water to increase sensitivity of the resulting data to a level of 0.1 °C and to reduce scan-line noise. Data acquired within a two-hour window around maximum solar heating (1:30 PM) is recommended to provide maximum solar heating of the water and to minimize cooling effects of late-afternoon shadows. Ground-truth data within the temperature range of the warm backwaters are necessary for calibration of the TIR data. The ground-truth data need to be collected with good locational accuracy. The derived water-temperature data provide the capability for rapid, wide-area mapping of warm-water fish habitats using a threshold temperature for such habitats. The collected daytime TIR data were ineffective in mapping (detecting) both archaeological structures and natural springs (seeps). The inability of the daytime TIR data to detect archaeological structures is attributed to the low thermal sensitivity (0.3 °C) of the collected data. The detection of subtle thermal differences between geologic materials requires sensitivities of at least 0.1 °C, which can be obtained by most TIR sensors using an appropriate gain setting. Simultaneous data collection for both land and water purposes can be achieved using sensors that collect TIR data in two separate channels, each channel using a gain setting most appropriate for land or water. The detection of archaeological structures and natural water seeps would also be improved by collection of data after sunset, which would require a separate data acquisition from that providing surface water temperature data and therefore additional cost. At this point, the cost for acquiring TIR data is quite high ($620/river-km) compared to the potential benefits of the data, unless reflected-wavelength data are also collected that can satisfy other GCMRC protocol requirements (such as mapping riparian vegetation). This is especially true if multiple data acquisitions are required during the year for temporal analyses of backwater areas. The cost for these data cannot be totally mitigated by its ability to partly replace the need for ground surveys of backwaters because calibration of the TIR data will require some ground-truth data from warm backwater areas (in addition to low-temperature main-stem data). However, the airborne data can provide a product that cannot be approached by ground surveys, that being an instantaneous (2 hour) map of surface water temperature over a 160-km stretch of the Grand Canyon.
Effects of a test flood on fishes of the Colorado River in Grand Canyon, Arizona
A beach/habitat-building flow (i.e., test flood) of 1274 m 3 /s, released from Glen Canyon Dam down the Colorado River through Grand Canyon, had little effect on distribution, abundance, or movement of native fishes, and only short-term effects on densities of some nonnative species. Shoreline and backwater catch rates of native fishes, including juvenile humpback chub ( Gila cypha ), flannelmouth suckers ( Catostomus latipinnis ), and bluehead suckers ( C. discobolus ), and all ages of speckled dace ( Rhinichthys osculus ), were not significantly different before and after the flood. Annual spring spawning migrations of flannelmouth suckers into the Paria River and endangered humpback chub into the Little Colorado River (LCR) took place during and after the flood, indicating no impediment to fish migrations. Pre-spawning adults staged in large slack water pools formed at the mouths of these tributaries during the flood. Net movement and habitat used by nine radio-tagged adult humpback chub during the flood were not significantly different from prior observations. Diet composition of adult humpback chub varied, but total biomass did not differ significantly before, during, and after the flood, indicating opportunistic feeding for a larger array of available food items displaced by the flood. Numbers of nonnative rainbow trout ( Oncorhynchus mykiss ) <152 mm total length decreased by ∼8% in electrofishing samples from the dam tailwaters (0–25 km downstream of the dam) during the flood. Increased catch rates in the vicinity of the LCR (125 km downstream of the dam) and Hell's Hollow (314 km downstream of the dam) suggest that these young trout were displaced downstream by the flood, although displacement distance was unknown since some fish could have originated from local populations associated with intervening tributaries. Abundance, catch rate, body condition, and diet of adult rainbow trout in the dam tailwaters were not significantly affected by the flood, and the flood did not detrimentally affect spawning success; catch of young-of-year increased by 20% in summer following the flood. Post-flood catch rates of nonnative fathead minnows ( Pimephales promelas ) in shorelines and backwaters, and plains killifish ( Fundulus zebrinus ) in backwaters decreased in the vicinity of the LCR, and fathead minnows increased near Hell's Hollow, suggesting that the flood displaced this nonnative species. Densities of rainbow trout and fathead minnows recovered to pre-flood levels eight months after the flood by reinvasion from tributaries and reproduction in backwaters. We concluded that the flood was of insufficient magnitude to substantially reduce populations of nonnative fishes, but that similar managed floods can disadvantage alien predators and competitors and enhance survival of native fishes.
Sediment delivery by ungaged tributaries of the Colorado River in Grand Canyon
No abstract available.
Monitoring of coarse sediment inputs to the Colorado River In Grand Canyon
No abstract available.
Techniques for estimating sediment yield of ungaged tributaries on the southern Colorado Plateau
Numerous regional sediment transport data are used to evaluate three techniques for estimating streamflow sediment yield from ungaged tributaries of the Colorado River in Grand Canyon. These techniques include: (1) a regression equation relating drainage area to sediment yield for all relevant sediment-yield data from northern Arizona, (2) an empirical relation developed by Renard (1972) selected from 8 potentially relevant methods, and (3) a new procedure that combines regional flood-frequency analysis with sediment-rating curves. Results based on techniques (1) and (2) are not significantly different. The third technique requires numerous assumptions, most notably that sediment yield on a decadal average can be described by several floods of recurrence intervals of 2 yr, 5 yr, and 10 yr described by regional flood-frequency relations. Using data collected at gaging stations, we develop a relation between peak discharge and total-event sediment yield derived from hydrographs and sediment-rating curves. This third technique produces sediment yield estimates comparable to those of the regional data regression and Renard (1972) relations and may be a more robust technique for estimating sediment yield when streamflow data are available.
Linkage between grain-size evolution and sediment depletion during Colorado River floods
No abstract available.
Modeling of sand movement storage in the Colorado River through the Grand Canyon
Explore the source record for details and available documents.
Reworking of aggraded debris fans by the 1996 controlled flood on the Colorado River in Grand Canyon National Park, Arizona
Debris flows from 600 tributaries in Grand Canyon periodically deposit poorly sorted sediment on debris fans along the Colorado River between Lakes Powell and Mead. Before regulation, stable fans and rapids along the river resulted from the interaction of tributary debris flows and large, mainstem floods. Floods in the Colorado River maintained fans and rapids as highly-reworked deposits of boulders and cobbles. After the closure of Glen Canyon Dam in 1963, decreases in stage and stream power associated with reduced annual peak flows drastically reduced the amount of debris-fan reworking. Previous research has shown that modest powerplant releases from Glen Canyon Dam, particularly in combination with tributary floods, can significantly rework aggraded debris fans. These limited flows have entrained boulders up to 1 mo in diameter, although discharges greatly exceeding the maximum powerplant release (946 m 3 /s) would be required to completely remove most aggraded fans. From 1987 through 1995, debris flows constricted the Colorado River at the mouths of at least 25 tributary canyons in Grand Canyon National Park, Arizona, creating 2 new rapids and narrowing at least 9 existing riffles or rapids. The highest peak discharge on the Colorado River in Grand Canyon between 1986 and 1996 was 960 m 3 /s in January 1993. In March-April 1996, we studied the effects of a 7-day flood release that peaked at 1,370 m 3 /s on 18 recently aggraded debris fans downstream from Glen Canyon Dam. The largest changes occurred at Badger and Lava Falls rapids, 38 and 312 km downstream from the dam, respectively; several other aggraded debris fans were only slightly changed. Areas of aggraded debris fans decreased by 2 to 42 percent; only the debris fan at Bedrock Rapid, which is controlled by a large bedrock outcrop, increased in area owing to deposition of reworked sediment on the downstream margin. Volumes decreased on 7 of 9 debris fans by 3 to 34 percent. The distal margins of most recently aggraded debris fans became armored with a lag of cobbles and boulders, and the width of the reworked zone on most debris fans increased by 4 to 30 m. Constriction of the river decreased at 11 of 18 debris fans, although some rapids, such as Tanner Rapid, became slightly more constricted at low discharges owing to changes in stage-discharge relations. Velocities on the left and right sides of Lava Falls Rapid decreased by about half, but velocities increased in three other rapids (e.g., Badger Creek Rapid). Stream power per unit width decreased in 9 of 10 rapids because of decreases in water-surface fall and widening of the rapids. Changes in the sizes of upper pool sand bars were inconsistent, although separation bars downstream from the reworked debris fan generally increased in size. The amount of stream power generated by the controlled flood greatly affected the variability of reworking among the 18 debris fans. For a given discharge, mainstem reworking is expected to vary with channel and debris-fan geometry, the initial particle-size distribution of the deposit, and distance from the dam. The elapsed time between debris flow and the controlled flood also was important because larger particles at older deposits became interlocked, imbricated, and (or) sutured together during smaller dam releases combined with tributary floods in January 1993 and August 1994. The effectiveness of future floods of similar magnitude in reworking debris fans will depend in part on the release history and extent of armoring in the period between the debris flow and the flood. If reworking of debris fans is a criterion for design of future controlled floods, our data support release of a higher peak discharge of shorter duration shortly after constricting debris flows occur.
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.
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.
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.