Valley Segments Research Articles

Refining the spatial and temporal signatures of creep and co-seismic slip along the southern San Andreas Fault using very high resolution UAS imagery and SfM-derived topography, Coachella Valley, California

The current interseismic period for an event on the Coachella Valley segment of the San Andreas Fault (SAF) is ~300 years, much greater than the best-estimated average recurrence interval of ~180 years, prompting questions regarding earthquake recurrence and fault behavior. Digital Surface Models (DSMs) generated using Structure-from-Motion-Multiview Stereo (SfM-MVS) techniques on unmanned aerial systems (UAS) imagery and very-high resolution UAS orthomosaics were used to identify and measure fault-related offsets of small geomorphic features and develop a model of late Holocene slip-per-event for the southern SAF (sSAF) in the Coachella Valley. We aim to better constrain slip estimates from recent earthquakes along the sSAF and combine new slip data with ages of past earthquakes from paleoseismic studies to understand earthquake recurrence. Slip-per-event for paleoearthquakes, which ruptured this segment of the sSAF, and the relationship between co-seismic slip events, creep or afterslip, and triggered slip were evaluated. Examination of offsets suggests that five (5) large, surface rupturing events produced average displacements of 2.6–3.1 m per event. Gaussian distribution analysis revealed small-scale offset clusters that we attribute to climate-modulated channel incision across the fault and subsequent creep. These offset clusters support a creep rate of ~3 mm/yr in the Mecca Hills averaged over the past ~160 years.

Dynamic models of earthquake rupture along branch faults of the eastern San Gorgonio Pass region in California using complex fault structure

AbstractGeologic data suggest that the Coachella Valley segment of the southern San Andreas fault (southern California, USA) is past its average recurrence time period. At its northern edge, this right-lateral fault segment branches into the Mission Creek and Banning strands of the San Andreas fault. Depending on how rupture propagates through this region, there is the possibility of a throughgoing rupture that could lead to the channeling of damaging seismic energy into the Los Angeles Basin. The fault structures and potential rupture scenarios on these two strands differ significantly, which highlights the need to determine which strand provides a more likely rupture path and the circumstances that control this rupture path. In this study, we examine the effect of different assumptions about fault geometry and initial stress pattern on the dynamic rupture process to test multiple rupture scenarios and thus investigate the most likely path(s) of a rupture that starts on the Coachella Valley segment. We consider three types of fault geometry based on the Southern California Earthquake Center Community Fault Model, and we create a three-dimensional finite-element mesh for each of them. These three meshes are then incorporated into the finite-element method code FaultMod to compute a physical model for the rupture dynamics. We use a slip-weakening friction law, and consider different assumptions of background stress, such as constant tractions and regional stress regimes with different orientations. Both the constant and regional stress distributions show that rupture from the Coachella Valley segment is more likely to branch to the Mission Creek than to the Banning fault strand. The fault connectivity at this branch system seems to have a significant impact on the likelihood of a throughgoing rupture, with potentially significant impacts for ground motion and seismic hazard both locally and in the greater Los Angeles metropolitan area.

How geomorphic context governs the influence of wildfire on floodplain organic carbon in fire‐prone environments of the western United States

AbstractWe draw on published studies of floodplain organic carbon storage, wildfire‐related effects on floodplains in temperate and high latitudes, and case studies to propose a conceptual model of the effects of wildfire on floodplain organic carbon storage in relation to climate and valley geometry. Soil organic carbon typically constitutes the largest carbon stock in floodplains in fire‐prone regions, although downed wood can contain significant organic carbon. We focus on the influence of wildfire on soil organic carbon and downed wood as opposed to standing vegetation to emphasize the geomorphic influences resulting from wildfire on floodplain organic carbon stocks. The net effect of wildfire varies depending on site‐specific characteristics including climate and valley geometry. Wildfire is likely to reduce carbon stock in steep, confined valley segments because increased water and sediment yields following fire create net floodplain erosion. The net effect of fire in partly confined valleys depends on site‐specific interactions among floodplain aggradation and erosion, and, in high‐latitude regions, permafrost degradation. In unconfined valleys in temperate latitudes, wildfire is likely to slightly increase floodplain organic carbon stock as a result of floodplain aggradation and wood deposition. In unconfined valleys in high latitudes underlain by permafrost, wildfire is likely in the short‐term to significantly decrease floodplain organic carbon via permafrost degradation and reduce organic‐layer thickness. Permafrost degradation reduces floodplain erosional resistance, leading to enhanced stream bank erosion and greater carbon fluxes into channels. The implications of warming climate and increased wildfires for floodplain organic carbon stock thus vary. Increasing wildfire extent, frequency, and severity may result in significant redistribution of organic carbon from floodplains to the atmosphere via combustion in all environments examined here, as well as redistribution from upper to lower portions of watersheds in the temperate zone and from floodplains to the oceans via riverine transport in the high‐latitudes. © 2019 John Wiley & Sons, Ltd.

Drainage system reorganization and late Quaternary tectonic deformation along the southern Dead Sea Transform – ADDENDUM

The Dead Sea Transform (DST) accounts for ~105 km of left-lateral slip between the Arabian plate and the Sinai subplate since the Miocene. Paleoseismic studies along the Arava Valley segment of the DST suggest that late Quaternary deformation has been primarily concentrated along the axis of the transform valley. Here, we examine late Quaternary changes in drainage system characteristics and attribute them to recent tectonic deformation in this region. Field-based geomorphic mapping, topographic cross sections, and optically stimulated luminescence (OSL) dating of fluvial deposits were used to map and date recent changes in the fluvial characteristics of catchments along the western margin of the southern Arava. Our results reveal coeval migration of channels, consistent with tectonically induced surface tilting caused by north–south compressional deformation along the western margin of the transform valley. OSL dating indicates this tilting was initiated in the late Pleistocene and continued at least into the mid-Holocene. The late Quaternary tectonic deformation along the southern Arava segment of the DST is distributed across a wider zone than previously considered and extends out to the margins of the transform valley. We associate the inferred wider deformation zone to possible changes in the geometry of motion along the DST.

Drainage system reorganization and late Quaternary tectonic deformation along the southern Dead Sea Transform

AbstractThe Dead Sea Transform (DST) accounts for ~105 km of left-lateral slip between the Arabian plate and the Sinai subplate since the Miocene. Paleoseismic studies along the Arava Valley segment of the DST suggest that late Quaternary deformation has been primarily concentrated along the axis of the transform valley. Here, we examine late Quaternary changes in drainage system characteristics and attribute them to recent tectonic deformation in this region. Field-based geomorphic mapping, topographic cross sections, and optically stimulated luminescence (OSL) dating of fluvial deposits were used to map and date recent changes in the fluvial characteristics of catchments along the western margin of the southern Arava. Our results reveal coeval migration of channels, consistent with tectonically induced surface tilting caused by north–south compressional deformation along the western margin of the transform valley. OSL dating indicates this tilting was initiated in the late Pleistocene and continued at least into the mid-Holocene. The late Quaternary tectonic deformation along the southern Arava segment of the DST is distributed across a wider zone than previously considered and extends out to the margins of the transform valley. We associate the inferred wider deformation zone to possible changes in the geometry of motion along the DST.

Evaluating Controls on Nutrient Retention and Export in Wide and Narrow Valley Segments of a Mountain River Corridor

AbstractOver the past few decades, nitrate‐nitrogen (NO3‐N) concentrations have increased within streams of the central Rockies, a pattern linked to regional N deposition trends. As NO3‐N concentrations increase, in‐stream biological demand may become saturated and stream N export may increase. In mountain landscapes, streams generally flow through steep, narrow valleys with limited riparian area and strong stream‐hillslope connectivity. Interspersed between the narrow valleys are wide segments where substantial floodplain riparian areas can develop. Here, we coupled measures of stream reach NO3‐N flux balances with nutrient enrichment experiments along two stream reaches of contrasting valley morphology in Rocky Mountain National Park. The stream reaches were (1) a narrow valley segment with limited floodplain riparian area and (2) a longitudinally adjacent (directly downstream) wide valley segment with extensive floodplain riparian area. We found that in‐stream biological uptake of added NO3‐N was limited in both segments, presumably as a consequence of saturating conditions. Assessment of mass flux indicated that the narrow valley segment was a consistent source of water and NO3‐N across flow states, while the wide segment was a sink at high flow and a source at low flow. Due to low in‐stream biological retention, gross gains and losses of water and NO3‐N to and from the stream exerted primary constraint on segment mass balances. Our results suggest that the exchange of water and nutrients between the stream and adjacent landscape can exert strong control on reach‐scale nutrient export, particularly in streams experiencing or approaching N saturation.

A forensic look into the lineament, vegetation, groundwater linkage: Study of Ranchi District, Jharkhand (India)

Lineaments have a genetic relationship with the formation of various topographic features, such as cliffs, slope breaks, narrow linear ridges, gorges and stream valley segments. The present study investigates the linkage between lineament, vegetation and groundwater. It explains an approach for lineaments extraction using shaded relief images from CartoDEM. The study area is Ranchi District, Jharkhand (India). Based on azimuth angle of the light source two shaded relief images (Lineament Analysis A with azimuth angles 0°, 45°, 90°, 135° and Lineament Analysis B with azimuth angles 180°, 225°, 270°, 315°) are created. Mann-Kendall (MK) method was used for positive and negative trend analysis in weather data over the study area. The proposed methodology is focused mainly on relationships between the extracted lineaments and multiple vegetation indices. Multiple vegetation indices on include the following: Difference Vegetation Index (DVI), Green Difference Vegetation Index (GDVI), Green Normalized Difference Vegetation Index (GNDVI), Normalized Difference Vegetation Index (NDVI), Ratio Vegetation Index (RVI) and Green Ratio Vegetation Index (GRVI), are generated from LANDSAT 5 Thematic Mapper (TM) satellite image. The NDVI and RVI maps had moderate correlation (R2) with lineament analysis A and B extracted from multi-directional images. Finally, results were validated for the study area by using Gravity Recovery and Climate Experiment (GRACE), and groundwater level data. Groundwater data shows indicative correlation with lineament maps (A & B). This analysis demonstrates the potential applicability of this methodology.

Grazing impacts on gully dynamics indicate approaches for gully erosion control in northeast Australia

AbstractDrainage network extension in semi‐arid rangelands has contributed to a large increase in the amount of fine sediment delivered to the coastal lagoon of the Great Barrier Reef, but gully erosion rates and dynamics are poorly understood. This study monitored annual erosion, deposition and vegetation cover in six gullies for 13 years, in granite‐derived soils of the tropical Burdekin River basin. We also monitored a further 11 gullies in three nearby catchments for 4 years to investigate the effects of grazing intensity. Under livestock grazing, the long‐term fine sediment yield from the planform area of gullies was 6.1 t ha‐1 yr‐1. This was 7.3 times the catchment sediment yield, indicating that gullies were erosion hotspots within the catchment. It was estimated that gully erosion supplied between 29 and 44% of catchment sediment yield from 4.5% of catchment area, of which 85% was derived from gully wall erosion. Under long‐term livestock exclusion gully sediment yields were 77% lower than those of grazed gullies due to smaller gully extent, and lower erosion rates especially on gully walls. Gully wall erosion will continue to be a major landscape sediment source that is sensitive to grazing pressure, long after gully length and depth have stabilised. Wall erosion was generally lower at higher levels of wall vegetation cover, suggesting that yield could be reduced by increasing cover. Annual variations in gully head erosion and net sediment yield were strongly dependent on annual rainfall and runoff, suggesting that sediment yield would also be reduced if surface runoff could be reduced. Deposition occurred in the downstream valley segments of most gullies. This study concludes that reducing livestock grazing pressure within and around gullies in hillslope drainage lines is a primary method of gully erosion control, which could deliver substantial reductions in sediment yield. Copyright © 2018 John Wiley & Sons, Ltd.

Influence of tributaries on the longitudinal patterns of benthic invertebrate communities

AbstractThere has been little effort to understand how tributaries influence mainstem rivers at large scales beyond the immediate influence of the tributary and downstream of the mixing zone. Such knowledge is needed to create breaks in stream networks that can aid in the classification of stream valley segments and conservation studies that rely on the delineation of zones. We use benthic invertebrate assemblages to infer longitudinal gradients and discontinuities and relate these patterns to confluence symmetry ratio (CSR; the size ratio of the tributary basin to the mainstem basin upstream of the confluence). In addition, we briefly explore reach and catchment‐scale environmental influences. We found evidence for both gradual and abrupt longitudinal changes in benthic invertebrate communities. There was not a smooth continuous gradient but a sawtooth pattern with an overarching trend. Two major discontinuities were found: one associated with a large CSR = 0.74 and reach scale factors including predominance of sand and an abundance of benthic organic matter that provided a unique habitat; and a second associated with a large CSR = 0.64 and a transition from coarse textured morainal deposits to glaciolacustrine deposits. There were synchronous additions of some benthic invertebrates (e.g., Eukiefferiella brehmi, Antocha, Hydropsyche morosa, and Oligochaeta) showing an affinity for downstream reaches, whereas others showed an affinity for headwater reaches (e.g., Simulium tuberosum, Baetis tricaudatus, and Micropsectra). Benthic invertebrate communities were driven by a combination of confluence symmetry ratio, landscape, and reach scale factors that can confound interpretation.

SH waves in a moon-shaped valley

The analytical solution of a two-dimensional moon-shaped alluvial valley embedded in an elastic half-space is analyzed for incident plane SH waves, using the wave function expansion and the Discrete Cosine Transform (DCT). A series of solutions with different depth-to-radius ratios have been computed, analyzed, and discussed. It is shown that amplification of incident motions along the thinning valley segment can be significant. The phenomena of combined action of the waves resulting from (a) turning (reversing the direction of propagation), (b) focusing, and (c) diffraction from the half space into the valley have been examined with an emphasis on the significance for surface-motion amplification and the power to damage man-made structures.

Beaver‐mediated lateral hydrologic connectivity, fluvial carbon and nutrient flux, and aquatic ecosystem metabolism

AbstractRiver networks that drain mountain landscapes alternate between narrow and wide valley segments. Within the wide segments, beaver activity can facilitate the development and maintenance of complex, multithread planform. Because the narrow segments have limited ability to retain water, carbon, and nutrients, the wide, multithread segments are likely important locations of retention. We evaluated hydrologic dynamics, nutrient flux, and aquatic ecosystem metabolism along two adjacent segments of a river network in the Rocky Mountains, Colorado: (1) a wide, multithread segment with beaver activity; and, (2) an adjacent (directly upstream) narrow, single‐thread segment without beaver activity. We used a mass balance approach to determine the water, carbon, and nutrient source‐sink behavior of each river segment across a range of flows. While the single‐thread segment was consistently a source of water, carbon, and nitrogen, the beaver impacted multithread segment exhibited variable source‐sink dynamics as a function of flow. Specifically, the multithread segment was a sink for water, carbon, and nutrients during high flows, and subsequently became a source as flows decreased. Shifts in river‐floodplain hydrologic connectivity across flows related to higher and more variable aquatic ecosystem metabolism rates along the multithread relative to the single‐thread segment. Our data suggest that beaver activity in wide valleys can create a physically complex hydrologic environment that can enhance hydrologic and biogeochemical buffering, and promote high rates of aquatic ecosystem metabolism. Given the widespread removal of beaver, determining the cumulative effects of these changes is a critical next step in restoring function in altered river networks.

Solving a Perplexing Scenic and Sage Creek Basin Drainage History Problem, Pennington County, South Dakota, USA

The escarpment-surrounded Sage Creek and Scenic Basins open in southeast directions toward the northeast and east oriented White River valley while their floors drain in a northwest direction to the northeast oriented Cheyenne River. Located in the South Dakota Badlands region the Sage Creek and Scenic Basins present an intriguing drainage history problem where key puzzle pieces also include the White and Cheyenne River valleys. The puzzle solution requires massive amounts of southeast oriented water to first erode as deep headcuts the east oriented White River valley segment and the two southeast-oriented Sage Creek and Scenic Basins prior to Cheyenne River valley headward erosion. The northeast oriented White River valley segment upstream from the east oriented White River valley segment (and from the Sage Creek and Scenic Basin location) next eroded headward across southeast oriented flow and was initiated by southeast oriented water flowing from the Scenic Basin that turned in a northeast direction to reach the east oriented White River downstream valley segment. Erosion of the Sage Creek and Scenic Basin headcuts abruptly ended when headward erosion of the northeast oriented Cheyenne River valley beheaded southeast oriented flow routes leading to the then actively eroding Sage Creek and Scenic Basin heacuts. Cheyenne River valley headward erosion in a southwest direction next captured massive southeast oriented flow then still moving to the newly eroded northeast oriented White River valley segment. Northwest oriented drainage developed on the Sage Creek and Scenic Basin floors when a flood surge or temporary dam caused water to fill the White River valley and to spill in a northwest direction across low points on the then abandoned Sage Creek and Scenic Basin headcut rims. This spillage eroded narrow northwest oriented valleys and drained water filling the two basins to the Cheyenne River valley while most of the ponded water drained in an east direction down the White River valley. The White River valley, Sage Creek and Scenic Basins, and the Cheyenne River valley were eroded by enormous quantities of southeast oriented water that also deeply eroded the entire South Dakota Badlands region.

Determining lateral offsets of rocks along the eastern part of the North Anatolian Fault Zone (Turkey) using spectral classification of satellite images and field measurements

ABSTRACTFault displacements are being measured by geological observations using the method of detecting and evaluating marker rocks. Thus, the length of total displacement in a fault zone relates to position detection of marker rocks. Due to limits of human eye, we used remote sensing data and terrestrial spectral measurements at 229 locations for measuring the total offset along the Kelkit Valley segment of the North Anatolian Fault Zone (NAFZ). We examined the lithology, especially ophiolites that are older than the fault zone and can be a good marker for detecting the total offset in the region. The Advanced Spaceborne Thermal Emission and Reflection Radiometer images are subjected to Spectral Angle Mapper (SAM) method. Principal component analysis, decorrelation stretching and geological map were used to compare the SAM results. Ophiolites on either side of the fault zone were clearly classified and identified with the SAM analysis. As a result of comparison of SAM with image enhancement methods and the geological map, we measured the total fault displacement on the NAFZ in the part of the Kelkit Valley. Along the fault zone to the north and south of the ophiolites providing a right lateral offset was measured as 90 ± 5 km.

Stratigraphic record of Pliocene-Pleistocene basin evolution and deformation within the Southern San Andreas Fault Zone, Mecca Hills, California

A thick section of Pliocene-Pleistocene nonmarine sedimentary rocks exposed in the Mecca Hills, California, provides a record of fault-zone evolution along the Coachella Valley segment of the San Andreas fault (SAF). Geologic mapping, measured sections, detailed sedimentology, and paleomagnetic data document a 3–5Myr history of deformation and sedimentation in this area. SW-side down offset on the Painted Canyon fault (PCF) starting ~3.7Ma resulted in deposition of the Mecca Conglomerate southwest of the fault. The lower member of the Palm Spring Formation accumulated across the PCF from ~3.0 to 2.6Ma during regional subsidence. SW-side up slip on the PCF and related transpressive deformation from ~2.6 to 2.3Ma created a time-transgressive angular unconformity between the lower and upper members of the Palm Spring Formation. The upper member accumulated in discrete fault-bounded depocenters until initiation of modern deformation, uplift, and basin inversion starting at ~0.7Ma.Some spatially restricted deposits can be attributed to the evolution of fault-zone geometric complexities. However, the deformation events at ca. 2.6Ma and 0.7Ma are recorded regionally along ~80km of the SAF through Coachella Valley, covering an area much larger than mapped fault-zone irregularities, and thus require regional explanations. We therefore conclude that late Cenozoic deformation and sedimentation along the SAF in Coachella Valley has been controlled by a combination of regional tectonic drivers and local deformation due to dextral slip through fault-zone complexities. We further propose a kinematic link between the ~2.6–2.3Ma angular unconformity and a previously documented but poorly dated reorganization of plate-boundary faults in the northern Gulf of California at ~3.3–2.0Ma. This analysis highlights the potential for high-precision chronologies in deformed terrestrial deposits to provide improved understanding of local- to regional-scale structural controls on basin formation and deformation along an active transform margin.

Sedimentological and ichnological implications of rapid Holocene flooding of a gently sloping mud‐dominated incised valley – an example from the Red River (Gulf of Tonkin)

AbstractThe Gulf of Tonkin coastline migrated at an average rate of ca 60 m year−1 landward during Holocene sea‐level rise (20 to 8 ka). Due to a combination of rapid coastline migration and undersupply of sand, neither coastal barriers nor tidal sand bars developed at the mouth of the Red River incised valley. Only a 30 to 80 cm thick sandy interval formed at the base of full‐marine deposits. Thus, the river mouth represented a mud‐dominated open funnel‐shaped estuary during transgression. At the base of the valley fill, a thin fluvial lag deposit marks a period of lowered sea‐level when the river did not reach geomorphic equilibrium and was thus prone to erosion. The onset of base‐level rise is documented by non‐bioturbated to sparsely bioturbated mud that occasionally contains pyrite indicating short‐term seawater incursions. Siderite in overlying deposits points to low‐salinity estuarine conditions. The open funnel‐shaped river mouth favoured upstream incursion of seawater that varied inversely to the seasonal strongly fluctuating discharge: several centimetres to a few tens of centimetres thick intervals showing marine or freshwater dominance alternate, as indicated by bioturbational and physical sedimentary structures, and by the presence of Fe sulphides or siderite, respectively. Recurrent short‐term seawater incursions stressed the burrowing fauna. The degree of bioturbation increases upward corresponding to increasing marine influence. The uppermost estuarine sediments are completely bioturbated. The estuarine deposits aggraded on average rapidly, up to several metres kyr−1. Siphonichnidal burrows produced by bivalves, however, document recurrent episodes of enhanced deposition (>0·5 m) and pronounced erosion (<1 m) that are otherwise not recorded. The slope of the incised valley affected the sedimentary facies. In steep valley segments, the marine transgressive surface (equivalent to the onset of full‐marine conditions) is accentuated by the Glossifungites ichnofacies, whereas in gently sloped valley segments the marine transgressive surface is gradational and bioturbated. Marine deposits are completely bioturbated.

Pennypack Creek Drainage Basin Erosion History: Bucks, Montgomery, and Philadelphia Counties, PA, USA

Topographic map evidence is used to interpret Pennypack Creek drainage basin erosion history in and north of the City of Philadelphia, Pennsylvania (USA). Southwest and west-southwest oriented through valleys crossing the south oriented Pennypack Creek drainage basin, barbed Pennypack Creek tributaries, and significant valley direction changes are used to determine that the Pennypack Creek valley eroded headward across massive southwest oriented floods. Initially floodwaters flowed on a low gradient topographic surface at least as high, if not higher, than the highest Pennypack Creek drainage basin elevations today. Shallow low gradient diverging and converging flow channels were eroded into the underlying bedrock surface predominantly along fault lines and other zones of easier to erode materials. Headward erosion of the much deeper Pennypack Creek valley across this anastomosing channel complex captured southwest oriented floodwaters and flow on northeast ends of beheaded channels was reversed so as to move toward the newly eroded and deeper Pennypack Creek valley. These reversed flow channels captured southwest oriented floodwaters still moving north of the actively eroding Pennypack Creek valley head. This captured water then moved in a northeast direction and eroded deep northeast oriented valleys headward from the newly eroded Pennypack Creek valley. These valleys today account for northeast and east oriented Pennypack Creek valley segments and northeast oriented (barbed) tributaries flowing to south oriented Pennypack Creek. The floodwater source cannot be determined from Pennypack Creek drainage basin evidence, but was from the northeast. Melting of a continental ice sheet could produce floods of sufficient volume and duration to overwhelm whatever drainage system previously existed and to erode new drainage basins in a manner similar to how the Pennypack Creek drainage basin was eroded.

Testing for longitudinal zonation of macroinvertebrate fauna along a small upland headwater stream in two seasons

AbstractThe effect of longitudinal zonation patterns and macroinvertebrate responses to changes in habitat characteristics have been given a lot of attention. But studies of changes in macroinvertebrate assemblages along small upland undisturbed watercourses are still lacking. The aim of the study is to analyse variability in macroinvertebrate communities between two different habitats/morphological sequences – shallow (riffle/run/step/) and deeper (pool) channel-bed morphological units on the background of the environmental parameters (local relief, slope, channel confinement ratio, channel-valley walls connectivity, floodplain continuity and channel abut, channel sinuosity and predominant land cover of riparian zone) of seven valley segments (functional process zones) in two seasons of the year (spring and autumn). The longitudinal-downstream gradient research was conducted on the semi-natural upland headwater brook in the Little Carpathians (9,330 m long, average gradient 2.8%) at 15 morphological sequences (30 sampling points). Each sampling point in spring as well as in autumn was characterised by mean flow velocity, discharge, water depth, channel width, channel bottom particle size, and flow types. Selected physico-chemical variables: pH, dissolved oxygen content (DO), oxygen saturation (DO %), temperature (t) conductivity and total dissolved solids (TDS) were measured directly in the field using the multisonde measuring device. Organisms were identified into the family level. The results showed that differences in zonation of benthic invertebrates between seasons are more apparent than seasonal variability between pools and riffles. Spring samples followed the increasing gradient of total dissolved solids downstream with characteristic families for upper and lower stretch. The disruption of macroinvertebrates zonation was more evident in autumn samples with greatest effects in pools. Based on RDA, the distribution of families was driven by three significant variables in riffles and four in pools. Alike environmental factors of pool sequences in the middle and upper reaches were responsible for similarity in macroinvertebrate structure. In conclusion, the distribution pattern of benthic invertebrates of the natural part of the small headwater stream in terms of abundance of macroinvertebrate families followed the longitudinal zonation in spring, but in autumn were the local habitat conditions more important.

Causes and mechanisms of the modification of the fluvial drainage basins

The relationship between the tectonic structure of the Ai–Ufa interfluve (Southern Urals), its morphology, the recent deformations, and the distribution of clastic material in the fluvial basins were studied. Geological interpretations are suggested for the problematic local areas of the drainage basins, whose structure and evolution are distinct from the model scenarios. The sedimentary regime of the river valleys is controlled, first of all, by their configuration and orientation of the valley segments relative to the tectonic zones, as well as by the amount of clastic material that is delivered by tributaries, the climate history of the fluvial basin, and its recent tectonic activity.

Geology of the Murcia Valley and Flood Plain Modifications in the Construction of the Circus Maximus, Rome, Italy

This paper presents a morphological and hydrogeological reconstruction of the Murcia Valley at the location of the great Roman stadium Circus Maximus in Rome. We reconstruct a valley segment using ERT (electrical resistivity tomography) and geoarchaeological drilling data that identified three main layers. The basal layer, with high resistivity values and convex shapes, is correlated to alluvial gravel and lithified silt‐clay sediments. The middle layer shows low‐to‐medium resistivity values extending to concavities between the basal convex shapes. The very low resistivity values of this middle layer characterize elliptical to circular morphologies and have been ascribed to the presence of water‐saturated clay‐silt and peaty sediments. The surface layer is characterized by widespread lateral inhomogeneity interpreted as anthropogenic fill. The data indicate a pre‐Roman anastomosed alluvial plain subsequently modified by human intervention. In an effort to reclaim the valley for construction of the Circus, the Romans utilized the natural topography and created a central embankment, later becoming the Spina, by filling depressions with sand taken from adjacent bars. Our study contributes to (1) knowledge of the pre‐Roman landscape, (2) understanding anthropogenic modification of the Murcia Valley flood plain, and (3) archaeological interpretation of the monument.

Sediment contributions from floodplains and legacy sediments to Piedmont streams of Baltimore County, Maryland

Disparity between watershed erosion rates and downstream sediment delivery has remained an important theme in geomorphology for many decades, with the role of floodplains in sediment storage as a common focus. In the Piedmont Province of the eastern USA, upland deforestation and agricultural land use following European settlement led to accumulation of thick packages of overbank sediment in valley bottoms, commonly referred to as legacy deposits. Previous authors have argued that legacy deposits represent a potentially important source of modern sediment loads following remobilization by lateral migration and progressive channel widening. This paper seeks to quantify (1) rates of sediment remobilization from Baltimore County floodplains by channel migration and bank erosion, (2) proportions of streambank sediment derived from legacy deposits, and (3) potential contribution of net streambank erosion and legacy sediments to downstream sediment yield within the Mid-Atlantic Piedmont.We calculated measurable gross erosion and deposition rates within the fluvial corridor along 40 valley segments from 18 watersheds with drainage areas between 0.18 and 155km2 in Baltimore County, Maryland. We compared stream channel and floodplain morphology from lidar-based digital elevation data collected in 2005 with channel positions recorded on 1:2400 scale topographic maps from 1959–1961 in order to quantify 44–46years of channel change. Sediment bulk density and particle size distributions were characterized from streambank and channel deposit samples and used for volume to mass conversions and for comparison with other sediment sources.Average annual lateral migration rates ranged from 0.04 to 0.19m/y, which represented an annual migration of 2.5% (0.9–4.4%) channel width across all study segments, suggesting that channel dimensions may be used as reasonable predictors of bank erosion rates. Gross bank erosion rates varied from 43 to 310Mg/km/y (median=114) and were positively correlated with drainage area. Measured deposition within channels accounted for an average of 46% (28–75%) of gross erosion, with deposition increasingly important in larger drainages. Legacy sediments accounted for 6–90% of bank erosion at individual study segments, represented about 60% of bank height at most exposures, and accounted for 57% (±16%) of the measured gross erosion. Extrapolated results indicated that first- and second-order streams accounted for 62% (±38%) of total streambank erosion from 1005km2 of northern Baltimore County. After accounting for estimated redeposition, extrapolated net streambank sediment yields (72Mg/km2/y) constituted 70% of estimated average Piedmont watershed yields (104Mg/km2/y). The results suggest that streambank sediments are a relatively large source of sediment from Piedmont tributaries to the Chesapeake Bay.