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"Gomez, Basil"
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Research methods in geography : a critical introduction
This comprehensive textbook offers a conceptual and practical introduction to research methodology, data collection, and techniques used in both human and physical geography. It explores a full range of contemporary geographic techniques, including statistics, mathematical analysis, GIS, and remote sensing.
Book
Impact of Sea-Level Rise on the Hydrologic Landscape of the Mānā Plain, Kaua‘i
The Mānā Plain is a land apart, buffered from oceanographic influences by ~3–35 m high backshore deposits, and drained by an intricate, >100-y-old ditch system and modern, large-capacity pumps. Quantifying present and prospective inputs and outputs for the hydrologic landscape suggests that, although sea-level rise (SLR) will begin to impact ditch system operations in 2040, transient, event-based flooding caused by rainfall, not SLR induced, multi-mechanism flooding, will continue to pose the most immediate threat. This is because as sea level rises the ability of gravity flows to discharge storm runoff directly into the ocean will diminish, causing floodwater to pond in low-lying depressions. Estimates of the volume of water involved suggests the risk of flooding from surface water is likely to extend to 5.45 km2 of land that is presently ≤ 1 m above sea level. This land will not be permanently inundated, but weeks of pumping may be required to remove the floodwater. Increasing pumping capacity and preserving some operational ability to discharge storm runoff under the influence of gravity will enhance the ditch system’s resilience to SLR and ensure it continues to fulfill its primary functions, of maintaining the water table below the root zone and diverting storm runoff away from farmland, at least until the end of this century.
Journal Article
The Potential Rate of Bed-Load Transport
Averages of measurements made in three rivers characterized by a high availability of sediment in relation to runoff, and comparable data that represent the high end of the range of transport rates observed during three sets of laboratory experiments, confirm there is an upper, particle-size-dependent limit to bed-load transport efficiency. Incorporating the regression relation derived from these six diverse and unrelated data sets into R. A. Bagnold's classic formulation yields$i_{b} = ω$
$[0.0115\\cdotD_{50^{-0.51]/0.63$. This straightforward scale correlation can be used to estimate the potential rate of bed-load transport (for average conditions) in gravel-bed rivers when sediment transport is constrained neither by the supply of sediment to nor by the amount of sediment available in the channel. The independent application of this empirical limit formula to two rivers with applicable bed-load transport regimes reveals a good (± 10%) correspondence between average observed and predicted transport rates.
Journal Article
Geomorphic and Sedimentological Controls on the Effectiveness of an Extreme Flood
The 1993 flood on the Upper Mississippi River was a rare, large‐magnitude hydrological event. Field and aerial survey analyses and Landsat 5 Thematic Mapper data were used to appraise the thickness of overbank deposits on leveed and unleveed reaches. Results indicate that minimal (<5 mm) overbank sedimentation occurred, except in the immediate vicinity of a levee break. Unleveed sections also lacked overbank sedimentation. Little geomorphological or sedimentological evidence of this extreme event is likely to be preserved. This raises questions about the completeness of the stratigraphic record: in situations where wide floodplains with cohesive soils provide effective resistance and dissipate energy so that erosion is minimized, and/or sediment supply is limited by event timing or sequencing, a large flood may leave little or no substantive evidence of its occurrence.
Journal Article
Variable composition of particle-bound organic carbon in steepland river systems
The reported range (<10% to >90%) of modern particulate organic carbon (POC) in the suspended load of steepland rivers is at odds with the opinion that this class of river is an important source of ancient organic carbon. Analysis of all available data shows the composition of POC transported by steepland rivers is fundamentally determined by the relative contributions made by shallow hillslope erosion processes that mobilize soil‐derived modern organic carbon and deep‐seated erosion processes that release bedrock‐derived ancient organic carbon. Attribution of sources during a flood with a return period of >20 years in the Waipaoa River basin, New Zealand, serves to emphasize that by no means all of the POC originating from high‐yield steepland drainage basins is derived from sedimentary rocks. POC in the Waipaoa River is expected to be 14C‐depleted because gully erosion into bedrock ordinarily regulates suspended sediment yield across the entire range of flows. However, during this event the topsoil contribution was more important, ranging from 56% ± 9% on the rising limb to 16% ± 5% on the falling limb of the flood hydrograph and modern organic carbon accounted for 71% of the total POC yield. The amount of ancient organic carbon may be overestimated if the contribution topsoil makes to POC yield across the flood hydrograph is underestimated. Furthermore, to quantify the contribution made by different sources of organic matter in steepland drainage basins, it is necessary to consider the time‐varying signatures and relative contributions each erosion process makes to event POC yields.
Journal Article
Editorial: Centenary Essays
A series of invited essays will review the ideas and perspectives embedded in the literature on biogeography, climatology and geomorphology, three major subfields of physical geography. Under present conditions, when between 33 percent and 50 percent of Earth's surface has been transformed by human action, and when human beings are perceived to be the most important force shaping the planet, there has perhaps never been a better time for an integrative field of study to flourish.
Journal Article
ENSO/SAM interactions during the middle and late Holocene
A new chronology of large magnitude rainfall events derived from the continuous high-resolution Lake Tutira storm sediment record covers the last 6800 years and provides the first insight into changes in El Niño-Southern Oscillation (ENSO) teleconnections to the higher southern latitudes to be obtained from New Zealand. Synthesis with independent paleoclimate records from the tropical Pacific and Antarctica also reveals a millennial-scale waxing and waning of the teleconnections that were not visible in the narrow historical window previously used to view interactions between ENSO and the Southern Annular Mode (SAM). Consistent with modern ENSO behaviour, we find teleconnections to the Southwest Pacific varied throughout the middle and late Holocene, depending on the strength and phase of ENSO and the phase of the SAM. We suggest that precession-driven changes in the seasonal cycle of solar radiation exert a first-order control on the interaction between the two climate modes. Consequently, their present status may neither be indicative of conditions that prevailed earlier in the Holocene, nor of those that might be associated with future climate changes in the Southern Hemisphere extratropics.
Journal Article
Coherent rainfall response to middle- and late-Holocene climate variability across the mid-latitude South Pacific
Intercorrelated terrestrial and marine records from New Zealand, Chile and Argentina provide the first evidence of a coherent pan-Pacific response to the growing influence that El Niño-Southern Oscillation (ENSO) and multicentury variations in the interaction between ENSO and the Southern Annular Mode (SAM) exerted on rainfall in the Southern Hemisphere mid-latitudes during the middle and late Holocene. Rainfall is also strongly influenced by moisture originating from the prevailing southern westerly winds (SWW), and we find that the variations in rainfall forced by the interaction of ENSO and the SAM are superimposed on an underlying long-term trend induced by a temporal strengthening of the westerly circulation. We conclude that the evolution of rainfall across the South Pacific reflects the influence seasonal insolation exerts on: (1) ENSO/SAM interactions; and (2) the strength of the SWW.
Journal Article
Event suspended sediment characteristics and the generation of hyperpycnal plumes at river mouths; east coast continental margin, North Island, New Zealand
Steepland rivers draining small, coastal watersheds often have very high suspended sediment loads, but the event characteristics of suspended sediment concentration and yield in this class of river is not well documented. Continuous monitoring at four sites in the Waipaoa River basin, New Zealand, demonstrates that during individual and composite events, suspended sediment concentration versus water discharge relations typically show clockwise hysteresis and that event maximum concentration is poorly related to event peak discharge. The signature of different erosion processes is also imprinted on the event yield magnitude frequency distributions. Gully-dominated tributary basins produce relatively high yields at all frequencies, reflecting greater sediment availability, whereas in tributary basins, where shallow landsliding is the dominant erosion process, there is a steep increase in yields in relation to return period. We estimate that flood discharges from the Waipaoa River approach or exceed the critical suspended sediment concentration (∼40,000 mg L-1) for hyperpycnal plume generation (because of negative buoyancy) at the river mouth once every ∼40 yr, but in the neighboring Waiapu and Uawa Rivers, the threshold concentration may be exceeded once a year and two to three times a year, respectively.
Journal Article