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David J. Topping

Publications and source records attributed to David J. Topping.

81 records · Page 5Linked to original sources
USGS2005

Sedimentology and stratigraphy of the Palisades, Lower Comanche, and Arroyo Grande areas of the Colorado River Corridor, Grand Canyon, Arizona

This report analyzes various depositional environments in three archaeologically significant areas of the Colorado River corridor in Grand Canyon. Archaeological features are built on and buried by fluvial, aeolian, and locally derived sediment, representing a complex interaction between geologic and cultural history. These analyses provide a basis for determining the potential influence of Glen Canyon Dam operations on selected archaeological sites and thus for guiding dam operations in order to facilitate preservation of cultural resources. This report presents initial results of a joint effort between geologists and archaeologists to evaluate the significance of various depositional processes and environments in the prehistoric formation and modern preservation of archaeological sites along the Colorado River corridor in Grand Canyon National Park. Stratigraphic investigations of the Palisades, Lower Comanche, and Arroyo Grande areas of Grand Canyon yield detailed information regarding the sedimentary history at these locations. Reconstruction of past depositional settings is critical to a thorough understanding of the geomorphic and stratigraphic evolution of these three archaeologically significant areas. This examination of past sedimentary environments allows the relative significance of fluvial, aeolian, debris-fan, and slope-wash sedimentary deposits to be identified at each site. In general the proportion of fluvial sediment (number and thickness of flood deposits) is shown to decrease away from the river, and locally derived sediment becomes more significant. Flood sequences often occur as 'couplets' that contain a fluvial deposit overlain by an interflood unit that reflects reworking of fluvial sediment at the land surface by wind and local runoff. Archaeological features are built on and buried by sediment of various depositional environments, implying a complex interaction between geologic and cultural history. Such field analysis, which combines geological and archaeological information and techniques, can provide a basis for future determination of the effects of Glen Canyon Dam operations on selected areas of the river corridor. This knowledge is essential to the development of preservation strategies for cultural resources in Grand Canyon.

Scientific Investigations Report↗
USGS2003

Computation and analysis of the instantaneous-discharge record for the Colorado River at Lees Ferry, Arizona — May 8, 1921, through September 30, 2000

A gaging station has been operated by the U.S. Geological Survey at Lees Ferry, Arizona, since May 8, 1921. In March 1963, Glen Canyon Dam was closed 15.5 miles upstream, cutting off the upstream sediment supply and regulating the discharge of the Colorado River at Lees Ferry for the first time in history. To evaluate the pre-dam variability in the hydrology of the Colorado River, and to determine the effect of the operation of Glen Canyon Dam on the downstream hydrology of the river, a continuous record of the instantaneous discharge of the river at Lees Ferry was constructed and analyzed for the entire period of record between May 8, 1921, and September 30, 2000. This effort involved retrieval from the Federal Records Centers and then synthesis of all the raw historical data collected by the U.S. Geological Survey at Lees Ferry. As part of this process, the peak discharges of the two largest historical floods at Lees Ferry, the 1884 and 1921 floods, were reanalyzed and recomputed. This reanalysis indicates that the peak discharge of the 1884 flood was 210,000±30,000 cubic feet per second (ft 3 /s), and the peak discharge of the 1921 flood was 170,000±20,000 ft 3 /s. These values are indistinguishable from the peak discharges of these floods originally estimated or published by the U.S. Geological Survey, but are substantially less than the currently accepted peak discharges of these floods. The entire continuous record of instantaneous discharge of the Colorado River at Lees Ferry can now be requested from the U.S. Geological Survey Grand Canyon Monitoring and Research Center, Flagstaff, Arizona, and is also available electronically at http://www.gcmrc.gov. This record is perhaps the longest (almost 80 years) high-resolution (mostly 15- to 30-minute precision) times series of river discharge available. Analyses of these data, therefore, provide an unparalleled characterization of both the natural variability in the discharge of a river and the effects of dam operations on a river. Following the construction and quality-control checks of the continuous record of instantaneous discharge, analyses of flow duration, sub-daily flow variability, and flood frequency were conducted on the pre- and post-dam parts of the record. These analyses indicate that although the discharge of the Colorado River varied substantially prior to the closure of Glen Canyon Dam in 1963, operation of the dam has caused changes in discharge that are more extreme than the pre-dam natural variability. Operation of the dam has eliminated flood flows and base flows, and thereby has effectively "flattened" the annual hydrograph. Prior to closure of the dam, the discharge of the Colorado River at Lees Ferry was lower than 7,980 ft 3 /s half of the time. Discharges lower than about 9,000 ft 3 /s were important for the seasonal accumulation and storage of sand in the pre-dam river downstream from Lees Ferry. The current operating plan for Glen Canyon Dam no longer allows sustained discharges lower than 8,000 ft 3 /s to be released. Thus, closure of the dam has not only cut off the upstream supply of sediment, but operation of the dam has also largely eliminated discharges during which sand could be demonstrated to accumulate in the river. In addition to radically changing the hydrology of the river, operation of the dam for hydroelectric-power generation has introduced large daily fluctuations in discharge. During the pre-dam era, the median daily range in discharge was only 542 ft 3 /s, although daily ranges in discharge exceeding 20,000 ft 3 /s were observed during the summer thunderstorm season. Relative to the pre-dam period of record, dam operations have increased the daily range in discharge during all but 0.1 percent of all days. The post-dam median daily range in discharge, 8,580 ft 3 /s, exceeds the pre-dam median discharge of 7,980 ft 3 /s. Operation of the dam has also radically changed the frequency of floods on the Colorado River at Lees Ferry. The frequency of floods with peak discharges larger than about 29,000 ft 3 /s has greatly decreased, while the frequency of smaller floods, with peak discharges between 18,500 and 29,000 ft 3 /s, has increased substantially. Operation of the dam has greatly extended the duration of smaller floods; for example, each of the four longest periods of sustained flows in excess of 18,500 ft 3 /s occurred after closure of the dam.

Arizona↗
USGS2003

U.S. Geological Survey research on surrogate measurements for suspended sediment

The U.S. Geological Survey is evaluating potentially useful surrogate instruments and methods for inferring the physical characteristics of suspended sediments. Instruments operating on bulk acoustic, bulk and digital optic, laser, and pressure-differential technologies are being tested in riverine and laboratory settings for their usefulness to Federal agencies toward providing quantifiably reliable information on bed-material and bed-topography characteristics, and on concentrations, size distributions and transport rates of sediments in suspension and as bedload. The efficacy of four suspended-sediment surrogate technologies has been demonstrated to varying degrees of success in Kansas, Florida, Arizona, and Puerto Rico.

Arizona;Florida;Kansas↗
USGS2001

Quantifying the relative importance of flow regulation and grain size regulation of suspended sediment transport α and tracking changes in grain size of bed sediment β

To predict changes in sediment transport, it is essential to know whether transport is regulated mainly by changes in flow or by changes in grain size of sediment on the bed. In flows where changes in suspended sediment transport are regulated purely by changes in flow (grain size of bed sediment is constant), increases in flow strength cause increases in both concentration and grain size of sediment in suspension (because stronger flows are able to suspend more sediment and coarser grains). Under this constraint of constant grain size of bed sediment concentration and median diameter of suspended sediment are positively correlated. In contrast, where transport is regulated purely by changes in grain size of sediment on the bed, concentration and median diameter of suspended sediment are negatively correlated (because increasing the median diameter of the bed sediment causes the concentration to decrease while causing the median grain size in suspension to increase). Where both flow strength and grain size on the bed are free to vary, the relation between concentration and grain size in suspension can be used to quantify the importance of grain size regulation relative to flow regulation of sediment transport, a measure defined as α. To predict sediment transport in systems that are regulated dominantly by changes in grain size on the bed, it is more useful to measure sediment input events or changes in grain size on the bed than to measure changes in flow. More commonly, grain size of bed sediment may be secondary to flow in regulating transport but may, nevertheless, be important. The relative coarseness of bed sediment (β) can be measured directly or, like α, can be calculated from measurements of concentration and grain size of suspended sediment.

Water Resources Research↗
USGS2000

Colorado River sediment transport: 1. Natural sediment supply limitation and the influence of Glen Canyon Dam

Analyses of flow, sediment‐transport, bed‐topographic, and sedimentologic data suggest that before the closure of Glen Canyon Dam in 1963, the Colorado River in Marble and Grand Canyons was annually supply‐limited with respect to fine sediment (i.e., sand and finer material). Furthermore, these analyses suggest that the predam river in Glen Canyon was not supply‐limited to the same degree and that the degree of annual supply limitation increased near the head of Marble Canyon. The predam Colorado River in Grand Canyon displays evidence of four effects of supply limitation: (1) seasonal hysteresis in sediment concentration, (2) seasonal hysteresis in sediment grain size coupled to the seasonal hysteresis in sediment concentration, (3) production of inversely graded flood deposits, and (4∥ development or modification of a lag between the time of a flood peak and the time of either maximum or minimum (depending on reach geometry) bed elevation. Analyses of sediment budgets provide additional support for the interpretation that the predam river was annually supply‐limited with respect to fine sediment, but it was not supply‐limited with respect to fine sediment during all seasons. In the average predam year, sand would accumulate and be stored in Marble Canyon and upper Grand Canyon for 9 months of the year (from July through March) when flows were dominantly below 200–300 m 3 /s; this stored sand was then eroded during April through June when flows were typically higher. After closure of Glen Canyon Dam, because of the large magnitudes of the uncertainties in the sediment budget, no season of substantial sand accumulation is evident. Because most flows in the postdam river exceed 200–300 m 3 /s, substantial sand accumulation in the postdam river is unlikely.

Colorado River, Glen Canyon Dam↗
USGS2000

Colorado River sediment transport: 2. Systematic bed‐elevation and grain‐size effects of sand supply limitation

The Colorado River in Marble and Grand Canyons displays evidence of annual supply limitation with respect to sand both prior to [ Topping et al , this issue] and after the closure of Glen Canyon Dam in 1963. Systematic changes in bed elevation and systematic coupled changes in suspended‐sand concentration and grain size result from this supply limitation. During floods, sand supply limitation either causes or modifies a lag between the time of maximum discharge and the time of either maximum or minimum (depending on reach geometry) bed elevation. If, at a cross section where the bed aggrades with increasing flow, the maximum bed elevation is observed to lead the peak or the receding limb of a flood, then this observed response of the bed is due to sand supply limitation. Sand supply limitation also leads to the systematic evolution of sand grain size (both on the bed and in suspension) in the Colorado River. Sand input during a tributary flood travels down the Colorado River as an elongating sediment wave, with the finest sizes (because of their lower settling velocities) traveling the fastest. As the fine front of a sediment wave arrives at a given location, the bed fines and suspended‐sand concentrations increase in response to the enhanced upstream supply of finer sand. Then, as the front of the sediment wave passes that location, the bed is winnowed and suspended‐sand concentrations decrease in response to the depletion of the upstream supply of finer sand. The grain‐size effects of depletion of the upstream sand supply are most obvious during periods of higher dam releases (e.g., the 1996 flood experiment and the 1997 test flow). Because of substantial changes in the grain‐size distribution of the bed, stable relationships between the discharge of water and sand‐transport rates (i.e., stable sand rating curves) are precluded. Sand budgets in a supply‐limited river like the Colorado River can only be constructed through inclusion of the physical processes that couple changes in bed‐sediment grain size to changes in sand‐transport rates.

Colorado River, Grand Canyon↗