Topographic Depressions Research Articles

Two-dimensional turbulence above topography: Vortices and potential vorticity homogenization.

The evolution of unforced and weakly damped two-dimensional turbulence over random rough topography presents two extreme states. If the initial kinetic energy [Formula: see text] is sufficiently high, then the topography is a weak perturbation, and evolution is determined by the spontaneous formation and mutual interaction of coherent axisymmetric vortices. High-energy vortices roam throughout the domain and mix the background potential vorticity (PV) to homogeneity, i.e., in the region between vortices, which is most of the domain, the relative vorticity largely cancels the topographic PV. If [Formula: see text] is low, then vortices still form but they soon become locked to topographic features: Anticyclones sit above topographic depressions and cyclones above elevated regions. In the low-energy case, with topographically locked vortices, the background PV retains some spatial variation. We develop a unified framework of topographic turbulence spanning these two extreme states of low and high energy. A main organizing concept is that PV homogenization demands a particular kinetic energy level [Formula: see text]. [Formula: see text] is the separator between high-energy evolution and low-energy evolution.

Topographic depressions can provide climate and resource microrefugia for biodiversity

Microrefugia are often located within topographically complex regions where stable environmental conditions prevail. Most of the studies concerning the distributions of climate change-sensitive species have emphasized the dominance of cold air pooling over other environmental factors, such as resource availability. There is a shortage of information on the relationships among topography-related microsite diversity, microclimate, resource availability, and species composition in microrefugia. To fill this knowledge gap, we studied the effects of microclimatic conditions and soil resources on plant species occurrence within and adjacent to 30 large topographic depressions (i.e., dolines) in two distant karst regions. Our results showed that both microclimate and soil resource availability may play a key role in maintaining climate change-sensitive species and biodiversity in dolines; therefore, they may simultaneously act as climate and resource microrefugia. Establishing climate-smart conservation priorities and strategies is required to maintain or increase the refugial capacity of such safe havens.

UAV-based approach for municipal solid waste landfill monitoring and water ponding issue detection using sensor fusion

Abstract Municipal solid waste (MSW) landfills need regular monitoring to ensure proper operations and meet environmental protection requirements. One requirement is to monitor landfill gas emissions from the landfill cover while another requirement is to monitor the potential settlement and damage to MSW landfill covers. Current surveying methods on a landfill cover are time- and labor-intensive and have limited spatial coverage. Landfill operators and researchers have developed unmanned aerial vehicle (UAV)-based monitoring over recent years; however, UAV-based automatic detection of water ponding in landfills has not been studied. Hence, this study proposes a UAV-based approach to monitor landfills and detect water ponding issues on covers by using multimodal sensor fusion. Data acquired from sensors mounted on a UAV were combined, leading to the creation of a ponding index (PI). This index was used to detect potential ponding sites or areas of topographical depression. The proposed approach has been applied in a case study of a closed MSW landfill before and after Hurricane Ian. A comparison between the generated PI map and a manual survey revealed a satisfactory performance with an IoU score of 70.74%. Hence, the utilization of UAV-based data fusing and the developed PI offers efficient identification of potential ponding areas.

Remote detection of upland surface water storage capacity in deglaciated terrain

AbstractA notable characteristic of terrain in non‐urbanized deglaciated areas of northeastern North America is the microtopography created by processes related to surficial geology, deglaciation and mechanical disturbances to surface materials from excavating events, most of which are caused by tree throw in the modern landscape. The features are often on the scale of 1–4 m across and decimetres to a metre in depth, appearing as ‘puddles’ during intense or high‐magnitude precipitation events. Generalized storage capacity values have been summarized in textbooks for varied landscape conditions, but surprisingly little information is available about how microtopography and related surface water storage varies in dominant physiographic settings in deglaciated landscapes defined by slope, surficial geology and land cover conditions. The increasing availability of elevation data at a horizontal resolution of 2 m or higher has made it possible to remotely evaluate differences in terrain elevation and quantify upland surface water storage capacity from relatively small topographic depressions. Here, we describe and quantify these topographic features in several coastal and inland watersheds in the state of Maine (USA) with measurements of depression volume calculated from digital elevation models (DEMs) using a pit filling approach. Results show that microtopographic storage capacity varies with slope and land cover conditions in deglaciated terrain of northeastern North America. Basin‐average surface water depression storage capacity estimates range from ~4 mm to as low as 0.2 mm. Human interventions such as clearing land for agriculture are associated with lower microtopographic surface water storage capacity than forested landscapes in the region.

Climatology of near-surface wind speed from observational, reanalysis and high-resolution regional climate model data over the Tibetan Plateau

As near-surface wind speed plays a role in regulating surface evaporation and thus the hydrological cycle, it is crucial to explore its spatio-temporal characteristics. However, in-situ measurements are scarce over the Tibetan Plateau, limiting the understanding of wind speed climate across this high-elevation region. This study explores the climatology of near-surface wind speed over the Tibetan Plateau by using for the first time homogenized observations together with reanalysis products and regional climate model simulations. Measuring stations across the center and the west of the plateau are at higher elevations and display higher mean and standard deviation, confirming that wind speed increases with increasing altitude. By exploring wind characteristics with a focus on seasonal cycle through cluster analysis, three regions of distinct wind regimes can be identified: (1) the central Tibetan Plateau, characterized by high elevation; (2) the eastern and the peripheral areas of the plateau; and (3) the Qaidam basin, a topographic depression strongly influenced by the blocking effect of the surrounding mountainous terrain. Notably, the ERA5 reanalysis, with its improvements in horizontal, vertical, and temporal spacing, model physics and data assimilation, demonstrates closer agreement to the measured wind conditions than its predecessor ERA-Interim. It successfully reproduces the three identified wind regimes. However, the newest ERA5-Land product does not show improvements compared to ERA5, most likely because they share most of the parametrizations. Furthermore, the two dynamical downscalings of ERA5 analyzed here fail to capture the observed wind statistics and exhibit notable biases and discrepancies also when investigating the diurnal variations. Consequently, these high-resolution downscaling products do not show add value in reproducing the observed climatology of wind speed compared to ERA5 over the Tibetan Plateau.

Collapse caldera walls: Mechanical controls on slope failure and morphology

Volcanic calderas are enclosed topographic depressions that are commonly delimited by steep annular cliffs (caldera walls). The walls represent degraded scarps of ring faults that accommodated caldera collapse. Here, we assess the mechanical controls on caldera wall morphology and failure by: (i) analysing slope properties of recently formed calderas; (ii) examining analytical solutions for slope failure; and (iii) simulating progressive slope failure via Distinct Element Method (DEM) numerical modelling. Average slope angles of the caldera walls in nature range from 20° to 65° and slope heights range from 99 m to 1080 m. Smaller slope heights are weakly tied to greater slope inclinations. Almost 60% of sampled caldera wall profiles show a steeper upper section and a gentler lower section, which in numerical models are reproduced as an upper slope comprising intact wall rock and a lower slope comprising failed material inclined at the angle of repose. Moreover, modelled material with a low angle of internal friction and low cohesion exhibits shear failure, whereas material with high friction and high cohesion shows tension cracking, buckling and toppling. The slope height and inclination data from the numerical models agree well with those in nature. The numerical model data correspond more closely to analytically-predicted failure planes than critical (i.e. limit equilibrium) slopes because they are short-lived and therefore unlikely to be sampled in either model or nature. If rock mass cohesions or friction angles constrained analytically from natural slopes are determined by assuming the slope is critical, they are likely to be underestimates. The homogeneous numerical models here give an estimated natural rock mass cohesion of 0.5 MPa or less. This is much lower than typical laboratory-scale cohesion values, and it highlights the importance of strength reduction when upscaling mechanical parameters from laboratory experiments for modelling slope stability and volcano deformation.

The Prados del Cervunal morainic complex: Evidence of a MIS 2 glaciation in the Iberian Central System synchronous to the global LGM

The area of Prados del Cervunal (PC) is an intra-morainic topographic depression located at 1800 m asl in the divide or interfluve between Garganta de Gredos and Garganta del Pinar valleys (Central Gredos; Iberian Central System, ICS). Both valleys, along with the adjacent Hoya Nevada, were occupied by glaciers during the Upper Pleistocene, leading to the development of the Prados del Cervunal moraine complexes studied in this work. Using cartographic methods and morphostratigraphic analysis, the three main glacial formations established in the Regional Chrono-Evolutionary Pattern for the ICS, Peripheral Deposits (PD), Principal Moraine (PM) and Internal Deposits (ID), have been identified and mapped in this area. The chronology of these formations has been implemented by Cosmic Ray Exposure (CRE) techniques using 10Be (new data) and 26Cl (previous data, recalculated in this work) in samples from morainic boulders. With these data, the following chrono-evolutionary sequence has been established: (stage 1) local-Maximum Ice Extent (MIE), dated in 25.0 ± 1.4 ka and corresponding to the maximum age obtained in these paleoglaciers; (stage 2) period of oscillations around the MIE, corresponding to the development of the PD Formation between ∼25 ka and ∼21 ka; (stage 3) period of readvance and stabilisation, dated after ∼21 ka (average age obtained for the PD moraines attached to PM moraines) and previous to ∼18 (minimum age obtained for a main crest of the PM formation); and (stage 4) onset of deglaciation dated around to ∼18 ka (average of ages obtained for the first main crest of the ID formation). During the stages of maximum ice expansion, these three glaciers formed an Ice field whose tongues were interconnected on the PC flat by an ice transfluence system (stages 1 and 2, Plateau Glacier Period). In later stages, the ice masses were partitioned, giving rise to valley glaciers and large moraines forming morainic complexes like those of PC (stages 2, 3 and 4, Valley Glaciers Period). The local MIE and onset of deglaciation stages in this area show a good fit with the ages stablished to global level for the global Last Glacial Maximum (LGM) and the onset of the Last Glacial Termination (Termination I). They also show good correlation at local (with other areas of the ICS), peninsular (with other Iberian mountains) and continental (some areas of the Alps and mountains of Central Europe) level. Finally, this evolutionary sequence and its correlations allowed us to adjust and validate some units of the Regional Chrono-Evolutionary Pattern model and propose the Gredos-Pinar-Cabeza Nevada glacial system as benchmark for the glaciation of Marine Isotope Stage (MIS) 2 in the Iberian Peninsula.

Statistical approach to identify variables predicting sulphide clay occurrence in southern Finland

Acid sulphate soil and sulphide-bearing sediments cause various challenges in construction projects and land use planning, as well as harmful environmental effects. Fine-grained sulphide sediments were mainly formed in coastal areas during the Litorina Sea water phase at approximately 7000 BP in the capital region of Finland, but not all these sediments contain sulphide clay. In this study, environmental and material property variables related to the depositional conditions of sulphide clay were selected for statistical analyses to find their association with the occurrence of sulphide. The datasets consisted of sulphide investigations by the City of Espoo, the City of Helsinki, and the Geological Survey of Finland. Statistically significant associations were found in the study area between the occurrence of sulphide and enumerative variables (i.e., sediment organic content, total clay depth, topographic class in the Litorina Sea phase, and water depth) in the Litorina Sea phase. Locations where sulphide clay is especially likely to occur consist of organic-rich (≥ 2%) thick clay (≥ 15 m) deposits in a topographically narrow depression with deep Litorina water (≥ 30 m), or where there is a moderate depth clay (3–5 m) in a local depression with shallow Litorina water (10–20 m). The best individual predictor for sulphide clay occurrence in the study area was found to be the sediment organic content, and, together with sediment water content, these variables very accurately predicted the occurrence of sulphide clay. In addition, clay depth is a very good predictor and, together with the topographic class narrow depression and the Litorina water depth or current elevation, can be used to predict sulphide occurrence.

Systematics and biogeography of Anoura cultrata (Mammalia, Chiroptera, Phyllostomidae): a morphometric, niche modeling, and genetic perspective, with a taxonomic reappraisal of the genus.

The nectar-feeding bats of the genus Anoura are widely distributed in the Neotropics, but are most speciose in the Andes. Anoura cultrata is a rare mid-elevation bat occurring in South and Central America. It is thought to be one of the few bat species exemplifying a latitudinal cline in body size. We address three systematic and biogeographic questions: 1) is the geographic variation in A. cultrata continuous, as argued to justify its current monotypic status? 2) do ecogeographic barriers to dispersal affect such variation? and 3) how do the genetic divergence and biogeography of the species compare to those of other members of the genus? To answer these questions, we used morphometric analyses, ecological niche modeling, and DNA barcoding. We divided the samples of A. cultrata into six geographic groups, delimited by topographic depressions separating mountain systems. We did not find significant correlations between body size and the geographic coordinates within five groups. Therefore, we conclude that ecogeographic barriers to dispersal between the regions occupied by such groups influenced morphometric variation in A. cultrata, and that despite its general north to south reduction in body size, the species does not show continuous clinal variation. A recent phylogenetic study of the genus Anoura concluded that it contains seven valid species. Our DNA barcoding analysis and morphological examination indicated that at least 10 species should be recognized, including A. peruana distinct from A. geoffroyi, and A. aequatoris and A. luismanueli distinct from A. caudifer. Moreover, we show that Central and South American populations of A. cultrata differ from each other at least at the subspecific level, thus we respectively refer to them as A. cultrata cultrata and as A. c. brevirostrum. Similarly, we refer to Central American and Mexican populations of 'A. geoffroyi' as A. peruana lasiopyga, and to their South American counterparts as A. p. peruana. The range of the latter subspecies reaches northeastern Venezuela. The Andes from southern Colombia to northern Peru appear to be the ancestral range of the genus.

From freshwater inflows to salt lakes and salt deposits in the Qaidam Basin, W China

The Qaidam basin in W China is an immense hyperarid intramontane basin with flat vast playas and salt lakes on the Qinghai-Tibet Plateau. The central basin is about 2800–2900 m a.s.l. elevation and enclosed by mountain ranges reaching > 5800 m in the Qilian Mountains and > 6200 m in the eastern Kunlun Mountains. The extensive playas of the basin are covered by gypsum or halite with very subordinate additional solids. In this contribution we report on the chemical composition of salt lakes and inflows to the Qaidam basin (analysis of 30 water samples collected in the summer of 2008 and 2009) together with the composition of 22 salt samples. Salt lakes and small salt ponds formed at topographic depressions. Some of the lakes cover > 300 km2 surface but are very shallow (1–2 m deep). Most salt lakes and salt ponds are NaCl dominated and contain typically 250–300 g kg−1 total dissolved solids (TDS). Some lakes are industrially used and produce KCl fertilizer, LiCl, and boron or are strongly modified by deep water produced in oil fields. Lakes along the borders to the high mountains are typically not fully saturated with halite. However, also these lakes lost most Ca and are drastically enriched in Mg and some lakes also in B and Li. The chemical development of the most natural salt lakes follows a path producing Ca-deficient water that ultimately precipitate Mg-bearing carbonates and chlorites in addition to halite upon evaporation. The salt lakes form by continuous and drastic evaporation of the waters supplied by the inflows to the lakes in the basin. All inflows carry considerable amounts of Cl and are characterized by very high Cl/Br ratios. These chemical characteristics suggest that the salt load of the inflows originates mostly from re-dissolved windblown halite deposited together with sand up to high altitudes in the bordering mountain ranges. Also, thermal waters ascending along deep faults along the Qilian Mountains carry considerable amounts of chloride. Their low Cl/Br ratio however suggests that most of the dissolved Na is derived from minerals of the basement rocks by fluid-rock interaction at T > 130 °C. The thermal fluids also carry considerable amounts of boron, indicating that co-precipitated borax in the salt lakes ultimately also derives from minerals in the basement rocks (tourmaline). Consequently, the presented data improve the understanding how the brines and salt lake waters develop from a wide range of chemically distinct low-TDS inflows and how the sequences of minerals precipitated upon evaporation in the Qaidam basin formed.

The interplay of bedrock fractures and glacial erosion in defining the present‐day land surface topography in mesoscopically isotropic crystalline rocks

AbstractThis paper addresses the effect of fractures within crystalline bedrock on glacial erosion processes in fast flowing hard bed glacier environments. In particular, we examine (i) whether the fracture type is critical for the capability of a glacier to erode the bedrock through quarrying/plucking processes and (ii) whether we can recognize specific fracture‐controlled erosion signatures from bedrock surface morphologies. We conducted an investigation within the northern part of the Åland Islands, southern Finland, where the ice‐flow direction (N–S) has remained constant through Late Pleistocene glaciations and where the bedrock is characterized by a lack of any mesoscopic anisotropies (such as foliation) and hence provides an optimal target to recognize the relationships between fractures and erosional morphologies. We characterized the fracture systems within the bedrock using both UAV‐acquired orthophotographs and standard field approaches and extrapolated the results to larger scales using LiDAR‐based digital elevation models. Our findings indicate that individual joints or shear fractures are associated with the development of minor vertical breaks along the bedrock surface. However, they do not provide sufficient mechanical weakness zones in the bedrock to allow effective glacial quarrying, even though their lengths can be relatively large (>50 m). By contrast, the linkage of several parallel shear fractures or the presence of larger faults with gouge‐bearing cores and well‐developed damage zones leads to localized disintegration of the rock material and the subsequent development of distinct topographic depressions along the bedrock surface. Consequently, the results allow predictions to be made about the bedrock features underlying the observed topographic signatures along the bedrock surface. Applied to the area of this investigation, abrasion associated with N–S‐directed glacial flows is responsible for the N–S‐oriented elongate but smooth fjord‐like megagrooves, whereas the more abrupt topographic breaks were generated by quarrying controlled by sub‐vertical, E–W‐trending zones of localized brittle deformation.

Productivity of Water Meadows under Haymaking in the Mid-Stream of the Ob River

The productivity of water meadows was studied in the middle stream of the Ob River by direct in situ measurements of the live and dead components of phytomass/biomass, the features of the active layer in natural ecosystems, and the patterns of plant organic matter and productivity (NPP) in different plant communities, micro-landscapes, and underlying soils. The study was conducted across different ecosystems along two profiles in the floodplain: (i) in the conditions of haymaking and (ii) in all natural ecosystems. The study revealed drastic changes in floristic composition at two profiles (catenas) both in the structure of plant communities and in productivity/NPP at different levels of the floodplain. The maximum diversity of vegetation was found in pristine natural ecosystems. Haymaking leads to an increase in the part of perennial turf grasses and sedges and decrease in the part of motley grasses. The maximum stocks of above-ground biomass (1450 g/m2) and below-ground biomass (3380 g/m2) were found in topographic depressions dominated by sedges. Haymaking causes pressure on the formation of root systems in dry and wet (swampy) meadows, which in turn leads to a decrease in the below-ground component of plant biomass. The total stock of plant phytomass/biomass increases from the upper points to the lower points in the floodplain profile: from 2991 to 4565 g/m2 with haymaking and from 3370 to 4060 g/m2 across the natural ecosystems. The NPP decreases by 12% in the upper and by 5% in the middle parts of the catena under haymaking, but it does not change in the lower part of catena as compared to all natural ecosystems.

Scour ponds from unusually large tsunamis on a beach-ridge plain in eastern Hokkaido, Japan

Scour ponds from unusually large tsunamis cut across the crest of a beach ridge in Kiritappu marsh, eastern Hokkaido. No fewer than ten of these ponds were imaged by photogrammetry as elongate topographic depressions as large as 5 m by 30 m. Sediments in these ponds are underlain by unconformities that were detected with ground-penetrating radar and observed directly in cores and a slice sample. Sediment deposits in the ponds contain peat and volcanic ash layers, the ages of which suggest that the scouring occurred during tsunamis generated by spatially extensive thrust ruptures along the southern Kuril trench, most recently during the early seventeenth century and its predecessor during the thirteenth–fourteenth century. Some of the ponds appear to have been formed during one tsunami and refreshed during later successors. This evidence of recurrent erosion suggests that the shoreline may retreat as part of earthquake-related cycles of coastal uplift and subsidence.

Morphodynamic Preservation of Fluvial Channel Belts

The fluvial sedimentary record is largely composed of deposits from relatively common flow events, rather than more catastrophic scour-and-fill events. At the scales of bedforms, such deposits are preserved within the stratigraphic record because they rapidly accumulate within, and are protected by, morphodynamic topographic depressions that occur naturally in the fluvial system as a result of feedbacks between flow, sediment transport, and topography. Examples include the preservation of ripples in front of dunes, dunes in front of bars, and bars within channels. Here, we used 3D seismic data that images preserved channel belts to test the hypothesis that alluvial-ridge basins, morphodynamic depressions formed between raised channel beds due to decreasing sedimentation rates away from channels in alluvial settings, are a source of topography driving channel-belt-scale preservation. Using the 3D seismic data, we measured the stratigraphic positions of channel belts, as well as their lengths, widths, sinuosities, and centerline orientations in the 3D seismic dataset. Results are consistent with well-preserved channel belts steered by alluvial-ridge-basin topography. Further, the thickness of the channel-belt interval exceeds the relief of any one alluvial-ridge basin, suggesting the volume records the filling of multiple alluvial-ridge basins and that the process is common. Characterizing the stratigraphic signature of alluvial-ridge basins is necessary for understanding contrasting fluvial architectures where external forcings prevented their formation.

The size of topographic depressions in a Sahelian savanna is a driver of woody vegetation diversity

In drylands, water availability is the main limiting factor for plant growth. Topographic depressions in the Sahel that reveal a more favorable water balance display greater tree diversity compared to their surroundings. However, the environmental factors that drive differences in botanical composition between depressions remain unknown. Here, we investigated the depression features, and the landscape and connectivity metrics responsible for woody vegetation composition in a savanna of Senegal. We mapped depressions in a 700 km2 area and inventoried woody vegetation in 61 depressions varying in area. Simple linear models were applied between (i) indicators of richness and botanical composition and (ii) depression attributes, landscape and connectivity metrics. We found that the area of a depression increased species richness. The number of vegetation strata and the presence of a temporary pond also positively influenced species richness. Yet, while large depressions always had high richness, some small depressions did too. We were not able to identify additional factors to explain this diversity between small depressions. In the context of decreasing richness and composition shift observed in the Sahel over recent decades, depressions, as biodiversity hotspots, are key elements in ecosystem functioning. Further studies are needed to understand other potential drivers of species diversity, such as soil water availability.

A topographic depression on the subducting Nazca plate controls the April 1st 2014 M8.1 Iquique earthquake rupture in Northern Chile

A topographic depression on the subducting Nazca plate controls the April 1st 2014 M8.1 Iquique earthquake rupture in Northern Chile

Impact of faulting in depocentres development, facies assemblages, drainage patterns, and provenance in continental half‐graben basins: An example from the Fanja Basin of Oman

AbstractFault throw gradients create transverse folding, and this can influence accommodation creation and sedimentary routing and infill patterns in extensional half‐graben basin. The Fanja half‐graben basin (Oman) offers an excellent outcrop of an alluvial fan succession displaying cyclical stacking and basin‐scale growth‐fold patterns. These unique conditions allow for an investigation of fault‐timing and accommodation development related to fault‐transverse folding. Our study combines geological mapping, structural analysis, sedimentary logging and correlation, and bulk mineralogical compositions. Mapping reveals that the basin is bounded by a regional‐scale fault, with local depocentres changing position in response to transverse syncline and anticline development ascribed to fault‐displacement gradients. The alluvial Qahlah Formation (Late Cretaceous) is unconformably overlying the Semail Ophiolite, and is in turn overlain by the marine Jafnayn Formation (Late Palaeocene). Facies and stratigraphic analysis allows for subdivision of the Qahlah Formation into four informal units, from base to top: (i) laterite in topographic depressions of the ophiolite, (ii) greenish pebbly sandstones, deriving from axially draining braided streams deposited in the low‐relief half‐graben basin. This green Qahlah grades vertically into the red Qahlah, formed by alluvial fanglomerates and floodplain mudstones, with drainage patterns changing from fault‐transverse to fault‐parallel with increasing distance to the main fault. The red Qahlah can be divided into (iii) the Wadi al Theepa member, found in a western basin depocentre, with higher immaturity and sand: mud ratio, suggesting a more proximal source, and (iv) the Al Batah member, located in the eastern part of the basin. The latter shows better sorting, a lower sand: mud ratio, and more prominent graded sub‐units. It also shows eastward expansion from an orthogonal monocline, ascribed to accommodation developed in a relay ramp. Changes in sedimentary facies and depositional patterns are consistent with differential mineralogical composition. The Green Qahlah is composed of quartz and lithic mafic rock fragments, sourced from the ophiolite and schists of the metamorphic basement. The Red Qahlah is composed of chert and kaolinite sourced from the Hawasina Nappe succession in the footwall of the master fault. These changes in source area are linked to unroofing of fault‐footwalls and domal structures during the extensional collapse of the Semail Ophiolite. The novelty of this study resides in linking sedimentology and fault‐displacement events controlling fault‐perpendicular folding, and its influence on depocentre generation and stratigraphic architecture. This is an approach seldom considered in seismic analysis, and rarely analysed in outcrop studies, thus placing the results from this study among the key outcrop‐based contributions to the field.

The Numerical Formulation of Simple Hysteretic Models to Simulate the Large‐Scale Hydrological Impacts of Prairie Depressions

AbstractTopographic depressions have large impacts on the hydrology, ecology, and biogeochemistry in prairie environments. Topographic depressions control the hydrological flow regime through their role in storing water from precipitation and snow melt, and the storage dynamics of topographic depressions affect the retention, transformations, and transport of sediment, carbon, and nutrients. The water stored in topographic depressions supports a diversity of animal and plant species. More generally, depressional wetlands are an integral component of global water, energy, and biogeochemical cycles. In this technical note, we present simple models to simulate hysteretic relationships between storage and contributing area. We consider both spatially distributed and spatially integrated models. The spatially distributed models (the ensemble‐depression model) explicitly simulate storage dynamics for a distribution of discrete depressions. In these spatially distributed models, the large‐scale storage‐contributing fraction relationships are an emergent property of the modeled system. The spatially integrated models (the meta‐depression model) parameterize the large‐scale storage‐discharge relationships. The spatially integrated models are formulated in a way to represent hysteretic behavior. We present a suite of numerical experiments and demonstrate that the ensemble‐depression and meta‐depression models have similar large‐scale behavior. The simple hysteretic models defined here are formulated in a way so that they can easily be incorporated in conventional hydrological models.

Double Shadows at the Lunar Poles

Topographic depressions within permanently shadowed regions (PSRs) on low-obliquity planetary bodies can be shielded not only from direct illumination, but also from scattered sunlight and thermal emission from nearby sunlit surfaces. We apply an illumination model to high-resolution topography data to produce the first map of double shadows at the lunar poles. The total doubly shadowed area resolved at the 30 m scale is 1.47 km2 in the northern hemisphere and 5.37 km2 in the southern hemisphere, predominantly contained within small craters on the floors of large permanently shadowed craters. In total, ∼0.04% of PSR area is permanently double shadowed, but the largest double shadows are nearly 600 m across, potentially large enough to be resolved in remote sensing temperature measurements. In the absence of secondary heating sources, double shadows are predicted to be significantly colder than singly shadowed areas and could sequester highly volatile compounds like carbon dioxide. Future in situ investigation of the regions identified in this work can elucidate the origin and distribution of the Moon’s most volatile deposits.

Impacts of channelization of River Bala, eastern Himalayan foothills, India

ABSTRACT Hard river engineering or channelization alters channel bathymetry and river morphology and invites multiple fluvio-hydrological hazards. The linear (72 m), concrete, low height (1.6 m), multipillars (20 pillars) bridge with concrete embankments and revetments has been constructed across and along the river Bala within the Himalayan foothill zone in the year 2017. As a result, the rate of siltation has been tremendously increased at the vicinity of the pillars of the bridge. The principal objectives are (i) to establish wrongly designed hard river engineering techniques and (ii) to find out the adverse effect of Bala bridge. Results showed that the highest rate of siltation was 0.55 m at the end of the monsoon in 2017 whereas the average of rate of siltation was 0.37 m between 2010 and 2017. If the rate of siltation is greater in a particular year, there is a high probability to divert the channel course. The thalweg line has tremendously shifted towards the right bank side. If the same condition persists for a long time, in near future (during monsoon) the river will avulse nearly 200 m right side on low lying topographic depression within the rich Buxa Tiger Reserve.