<p> This study was conducted to provide an improved understanding of the dynamics of river islands and to investigate the role of islands in regulating sediment flux within the fluvial system. </p><p> The study showed that the islands in entrenched geomorphic subreaches of the MSR form, erode, and reform in locations controlled by lateral constrictions. The geometry of the islands adjust on a decadal or even longer time scale in response to a disturbance or changes in water and sediment supply, and thus, the islands form part of a temporal and spatial continuum of bedforms. The formation of the islands regulates sediment flux through the reach. </p><p> The study reach of the Middle Snake River (MSR) in Idaho contains over 300 islands within approximately 200 km between Swan Falls Dam and Brownlie Reservoir. The hydrology of the study reach has been significantly altered by upstream dams on the mainstem and dams on tributaries within the study reach. </p><p> Data used in the study include: (1) historical aerial photos (1938/1939) and topographic maps (c1894-1906), (2) topographic and bathymetric survey data collected in 1997 through 1999, (3) flow measurements from 1911 to present, (4) bed material samples, (5) morphostratigraphic mapping of 194 islands and (6) stratigraphic soil profile data collected on 95 islands. The soil profile data included soil stratigraphy, soil samples (used for sediment gradations and pollen analyses), pedological descriptions, historical artifacts and charcoal fragments (used for carbon dating). A previously developed 1-dimensional hydraulic model of the study reach was used to evaluate the hydraulic conditions along MSR and to calculate the overtopping discharges of the islands. </p><p> Comparison of historical aerial and topographic data with 2012 aerial photography showed evidence of the growth and erosion of islands and reworking of island chains to form new configurations, illustrating the dynamic nature of the islands over the last approximately 100 years. The historical document review also showed that the location of almost all larger islands and island groups are controlled by lateral constrictions such as tributary fans. </p><p> Soil profile data, pollen analyses, historical artifacts and radiocarbon dating of soil charcoal were used to determine the approximate age of islands and to evaluate the erosional and depositional activity of the islands. The soil profile data showed an extreme range in age at some islands where the gravel platform of the islands is old (circa 7,000 years), but the overlying sediments are young (on the order of hundreds of years). </p><p> Two-dimensional sediment-transport models were developed to evaluate the baseline conditions and simulate island development. Baseline conditions modeling showed the gravel- to cobble-sized material forming the core of the islands is not mobilized under the current hydrology. The islands formed in response to more recent floods from silt-sand sized sediment supply, which explains the relatively young soils overlying older gravel cores. </p><p> Modeling results showed that: (1) the island geometry adjusts to a disturbance or a change in sediment supply, (2) the formation of islands regulates sediment flux, and (3) the islands form, erode, and reform in the same general locations, which supports the study hypotheses that islands form part of a temporal and spatial continuum of bedforms.</p>

<p> Recharge areas for most springs are rarely known because they can be sourced from proximal, shallow, atmospheric sources or long-travelled, deep, regional aquifers and alteration along the flow path is common. Stable isotopic (¹⁸O and ²H) geochemistry of springs water can provide indications of relative flow path distance. Locally sourced springs generally have an isotopic signature similar to the isotopic values of local precipitation for that region and elevation. Springs with a different isotopic composition than local meteoric inputs likely have non-local recharge, representing a regional source. Exceptions to this rule include springs in karst terrain, geothermal locations, or travertine-rich groundwater systems, where other physical or geochemical processes influence the isotopic signature of the water. In this study, we tested local vs. regional sourcing using springs isotopic data from regional studies across Western North America in Arizona, Nevada, and Alberta. These regional study sites included the Basin and Range, Transition Zone, Colorado Plateau, Cordillera, Interior Plains physiographic regions, and lowland to montane aquifers. The combination of location-specific physical data with stable isotopic groundwater data provides an effective method for flow path determination at springs with similar flow and chemistry. Springs from Arizona were found to be a mix of regional and local recharge, those from Nevada were locally sourced, and Alberta's springs are generally sourced from regional flow systems. </p><p> Springs provide a truly unique ecosystem where groundwater first daylights, mixes with surface waters, and both plants and animals find refuge. Variability of springs type (the springs geomorphic properties) can have profound effects on all aspects of a groundwater spring. Water chemistry may exert significant changes on vegetation, which in turn modify the springs ecology. Changes in vegetation composition and density can also change erosion rates and channel morphology, thereby altering geomorphology. Analyses of data from southern Nevada and Alberta, Canada housed in an extensive springs database of western North America were interpreted to determine the interconnectedness of geochemistry, geomorphology, and vegetation cover. Using various statistical techniques, the opposite variables were significant in the two field areas. In the Spring Mountains the highest elevation clusters had the highest plant species diversity and the fewest spheres of discharge. In Alberta the clusters with average elevation, neither highest nor lowest, were the groups with the highest plant species diversity and most variability in geomorphic surface types.</p>

<p> Wildfires dramatically affect hydrologic processes including runoff and erosion, which in turn can impact society. Disturbance by fire creates ecosystem heterogeneity, prompting many species to adapt to fire cycles. Human impacts have altered fire frequency and affected natural systems to the point that additional landscape-scale disturbances may cause a disruption in ecosystem form and function. The altered ecosystems and increased development in forests may exacerbate post-fire impacts, affecting more of the population in fire-prone regions. </p><p> The following three studies will improve our understanding and management of post-fire impacts on stream channel processes. A catchment in eastern Arizona where runoff data were collected between 1962 and 1983 was subsequently burned by a wildfire in 2011. The direct comparison of pre and post-fire runoff showed that the fire made runoff more rapid, increased peak discharge rates, and compressed the time scale of storm hydrographs. These results can help improve post-fire runoff modeling and management efforts. </p><p> The second topic addressed the scaling of sediment delivery across hillslope and small catchment scales. Erosion data used in this study were from the Arizona site and five other sites across the western US. Results from five of the six sites showed that sediment delivery significantly decreased with increasing spatial extent, while the lack of trend at the sixth site illustrates the variability in erosion responses across ecosystems. The relationships developed in this study will help improve estimates of sediment delivery rates at the small-catchment scale using more easily acquired data from small plots. </p><p> The third study addressed whether straw bale check dams reduce post-fire sediment yields or affect ephemeral stream channel morphology. A series of laboratory flume experiments based on measured post-fire field conditions showed that check dams can store sediment from initial runoff events, but that a large number of check dams would be needed to reduce post-fire sediment yields. The stored sediment reduced the local channel gradient, but the check dams did not otherwise affect the channel morphology. These data and field observations were used to develop a check dam classification system that can be applied in ephemeral streams in burned or unburned areas.</p>

<p> Fluvial suspended sediment is a master variable affecting a wide range of fluvial and coastal environmental processes, and dominating the terrestrial mass flux to the oceans. Although it has long been recognized that relationships between suspended sediment concentration and discharge are not stationary in small, mountainous rivers over time scales from hours to decades, most studies continue to assume stationarity. This collection of studies directly addresses the issue of non-stationarity in the suspended sediment &ndash;discharge relationship of the Salinas River, central California, and examines the progression of abandoned channel fill sequences in the Eel River Estuary of northern California. </p><p> Preceding these studies is a methodological analysis of the pretreatment of fluvial and marsh sediments for particle size analysis. Pretreatment of sediment with hydrogen peroxide to remove organic constituents and aid deflocculation is a common component of particle size analyses of terrestrial and marine sediments. The first chapter presents the quantitatively determined effect of a range of treatment levels on particle size distribution among four sediment types representing a range of mineral/organic particle size distributions, organic content and particle characterization (charcoal or detrital plant material). </p><p> The following three chapters examine the effects of antecedent basin conditions on the suspended sediment &ndash; discharge relationship in the Salinas River. In chapter two, forty-five years of suspended sediment data from the lower Salinas and 80 years of hydrologic data were used to construct hydrologic descriptors of basin preconditioning and test the effects of these preconditions on suspended sediment behavior. Fine (diameter (<i>D</i>) &lt; 63 &mu;m) and sand sized (<i>D</i> > 63 &mu;m) sediment were found to respond differently to antecedent hydrologic conditions. Fine sediment was most sensitive to flushing flows of moderate discharge (10 &ndash; 20x mean discharge (<i>Q_mean</i>) that led to lower subsequent fine sediment concentrations, while sand concentrations were generally decreased by periods of drought and longer elapsed time since a wide range of discharges acting as maintenance flows. </p><p> Chapter three examines the interannual to decadal scale persistence of suspended sediment &ndash; discharge relationship states in the lower Salinas River, assesses the role of antecedent hydrologic conditions in controlling these patterns, and addresses their relationship to El Ni&ntilde;o Southern Oscillation (ENSO) climatic states. The decadal scale variability in suspended sediment behavior was influenced by interannual to decadal scale fluctuations in hydrologic characteristics, including: elapsed time since small (&sim; 0.1x Qmean), and moderate (&sim; 10x Qmean) threshold discharge values, the number of preceding days that low/no flow occurred, and annual water yield. El Ni&ntilde;o climatic activity was found to have little effect on decadal-scale fluctuations in the fine suspended sediment &ndash; discharge relationship due to low or no effect on the frequency of moderate to low discharge magnitudes, annual precipitation, and water yield. However, sand concentrations generally increased in El Ni&ntilde;o years due to the increased frequency of moderate to high magnitude discharge events, which generally increase sand supply. </p><p> Chapter four brings to bear the decadal scale persistence of suspended sediment - discharge behavior, the effects of antecedent hydrologic conditions, and ENSO influences on the estimation of inter-decadal scale sediment flux from the Salinas River. The longer sampling records employed in this study and incorporation of decadal scale behavior or antecedent hydrologic conditions resulted in average annual load estimates of 2.1 or 2.4 Mt, in comparison to earlier estimates of &sim; 3.3 Mt by previous researchers. El Ni&ntilde;o years dominated the sediment budget by producing on average ten times more sediment than non-El Ni&ntilde;o years. </p><p> Chapter five proposes a modification of the current generic model for abandoned channel fill stratigraphy produced in unidirectional flow river reaches to incorporate seasonal tidal deposition. This work was based on evidence from two consecutive abandoned channel fill sequences in Ropers Slough of the lower Eel River Estuary. Planform geomorphic characteristics derived from these images were used in conjunction with sub-cm resolution stratigraphic analyses to describe the depositional environment processes and their resultant sedimentary deposits. The abandoned channel fill sequences appeared to differ due to the topographic steering of bed sediment transport and deposition previously identified in rivers experiencing only unidirectional flow, while also expressing the seasonal dichotomy of fluvial and tidal deposits.</p>

Thesis (M.S.)--University of California, Santa Cruz, 1995. / Typescript. Includes bibliographical references (leaves 143-147).

Thesis (Ph. D.)--Florida State University, 2006. / Advisor: James B. Elsner, Florida State University, College of Social Sciences, Dept. of Geography. Title and description from dissertation home page (Sept. 19, 2006). Document formatted into pages; contains x, 90 pages. Includes bibliographical references.

<p> Landslides pose a persistent threat to El Salvador's population, economy and environment. Government officials share responsibility in managing this hazard by alerting populations when and where landslides may occur as well as developing and enforcing proper land use and zoning practices. This thesis addresses gaps in current knowledge between identifying precisely when and where slope failures may initiate and outlining the extent of the potential debris inundation areas. Improvements on hazard maps are achieved by considering a series of environmental variables to determine causal factors through spatial and temporal analysis techniques in Geographic Information Systems and remote sensing. The output is a more dynamic tool that links high resolution geomorphic and hydrological factors to daily precipitation. Directly incorporable into existing decision support systems, this allows for better disaster management and is transferable to other developing countries.</p>

Physical erosion can mobilise particulate organic carbon (POC) from vegetation and soil, representing an export of primary productivity from ecosystems, and a lateral transfer of carbon recently-derived from the atmosphere. These carbon transfers are thought to be enhanced in mountain forests where erosion rates are high. However, the rates and controls on POC transfer remain poorly constrained, as does the impact of POC export on carbon cycling at regional and global scales. This thesis takes an interdisciplinary approach to address this issue, using remote sensing, river geochemistry, river hydrology, and geomorphic mapping in the Kosñipata Valley, in the Central Andes of Peru. Its main aims are to: 1) estimate stream discharge throughout the year and to evaluate the water balance and sources; 2) quantify the source of riverine POC, accounting for POC derived from sedimentary rocks (POC_fossil) to examine the POC eroded from soils and vegetation (POC_non-fossil); 3) quantify river POC yields; 4) assess the hillslope processes that erode POC; and 5) assess how POC export impacts the carbon balance of mountain forest, and how fluvial transfer impacts the wider carbon cycle. Stream flow was monitored from January 2010 to February 2011 at two newly installed river gauging stations in the Kosñipata Valley at 2250 m (Wayqecha, 48.5 km²) and 1360 m (San Pedro, 164.4 km²). Then annual water balance for the San Pedro catchment was quantified. Rainfall inputs of 3028 mm and cloud water inputs of 308 ± 97 mm were balanced by outputs via stream runoff (2721 mm) and actual evapotranspiration (907 mm), leaving a residual of -294 ± 97 mm (< ~10 % of water inputs). The source of POC in river suspended sediment samples was quantified using radiocarbon (Δ¹⁴C, ‰), stable carbon isotopes, and the nitrogen to carbon ratio. This revealed that river POC_non-fossil was sourced from very young organic carbon in the valley (Δ¹⁴C ~50 ‰) and that POC_fossil comprised 43 % of total POC. Combining the hydrometric measurements with river samples, annual particulate load fluxes were quantified. The vast majority (73 % to 77 %) of the annual suspended sediment transfer and POC (both POC_fossil and POC_non-fossil) occurred in the wet season over a period of 4 months. The suspended sediment yield for the valley (960 – 1200 t km^-2 yr^-1) was consistent with those for the Andean portion of the Madre de Dios River into which the Kosñipata River drains. The river POC_non-fossil yield was 5.2 – 6.9 tC km^-2 yr^-1. Landslides are likely to have played an important role in the mobilisation of POC_non-fossil. A detailed landslide mapping using 25 years of remote sensing data revealed that on average 0.09 % of the valley per year is impacted by this mass-wasting process. These landslides mobilise ~28 tC km^-2 yr^-1 of soil and vegetation valley-wide. The discrepancy between the landslide erosional flux and fluvial POCnon-fossil export suggests an important fraction of the POCnon-fossil harvested by landslides is either exported as coarse debris (not quantified in the fluvial POC_non-fossil flux), remains buried onsite, or is degraded and respired onsite. Landslides also played an important ecosystem function, turning over some sections of the mountain forest within ~625 years, with a 1200 year valley-wide mean. On the basin scale, the Madre de Dios River drains ~ 6 % of the Amazonian Andes. This study enables estimation of the delivery of POC to the lowland Amazon Basin. Using the observation that POC_non-fossil and POC_fossil fluxes were closely linked with suspended sediment transfer, total yields of ~0.22 MtC yr^-1 and ~0.17 MtC yr^-1, respectively, were estimated from this section of the Andes. The export of POC_non-fossil from mountain forests by rivers represents 0.4 – 1.0 % yr^-1 of the net primary productivity of Andean forest and so even if only a small portion of this is buried in sedimentary deposits, it may promote the Andes as a carbon sink. These results demonstrate the long-term influence of erosional processes in the cycling of carbon in the Amazon Basin.