Stratification effects on shoaling internal solitary waves

This combined numerical/laboratory study investigates the effect of stratification form on the shoaling characteristics of internal solitary waves propagating over a smooth, linear topographic slope. Three stratification types are investigated, namely (i) thin tanh (homogeneous upper and lower layers separated by a thin pycnocline), (ii) surface stratification (linearly stratified layer overlaying a homogeneous lower layer) and (iii) broad tanh (continuous density gradient throughout the water column). It is found that the form of stratification affects the breaking type associated with the shoaling wave. In the thin tanh stratification, good agreement is seen with past studies. Waves over the shallowest slopes undergo fission. Over steeper slopes, the breaking type changes from surging, through collapsing to plunging with increasing wave steepness $A_w/L_w$ for a given topographic slope, where $A_w$ and $L_w$ are incident wave amplitude and wavelength, respectively. In the surface stratification regime, the breaking classification differs from the thin tanh stratification. Plunging dynamics is inhibited by the density gradient throughout the upper layer, instead collapsing-type breakers form for the equivalent location in parameter space in the thin tanh stratification. In the broad tanh profile regime, plunging dynamics is likewise inhibited and the near-bottom density gradient prevents the collapsing dynamics. Instead, all waves either fission or form surging breakers. As wave steepness in the broad tanh stratification increases, the bolus formed by surging exhibits evidence of Kelvin–Helmholtz instabilities on its upper boundary. In both two- and three-dimensional simulations, billow size grows with increasing wave steepness, dynamics not previously observed in the literature.

Risk Assessment of Pipeline Engineering Geological Disaster Based on GIS and WOE-GA-BP Models

Oil and gas pipelines are part of long-distance transportation projects which pass through areas with complex geological conditions and which are prone to geological disasters. Geological disasters significantly affect the safety of pipeline operations. Therefore, it is essential to conduct geological disaster risk assessments in areas along pipelines to ensure efficient pipeline operation, and to provide theoretical support for early warning and forecasting of geological disasters. In this study, the pipeline routes of the Sichuan-Chongqing and Western Hubei management offices of the Sichuan-East Gas Transmission Project were studied. Seven topographic factors—surface elevation, topographic slope, topographic aspect, plane curvature, stratum lithology, rainfall, and vegetation coverage index—were superimposed using the laying method with a total of eight evaluation indicators. The quantitative relationships between the factors and geological disasters were obtained using the geographic information system (GIS) and weight of evidence (WOE). The backpropagation neural network (BP) was optimised using a genetic algorithm (GA) to obtain the weight of each evaluation index. The quantified index was then utilized to identify the geological hazard risk zone along the pipeline. The results showed that the laying method, stratum lithology, and normalised difference vegetation index were the factors influencing hazards.

Location, location, location -- Considering relative catchment location to understand subsurface losses

The analysis of large samples of hydrologic catchments is regularly used to gain understanding of hydrologic variability and controlling processes. Several studies have pointed towards the problem that available catchment descriptors (such as mean topographic slope or average subsurface properties) are insufficient to capture hydrologically relevant properties. Here, we test the assumption that catchment location, i.e. the relative properties of catchments in relation to their surrounding neighbours, can provide additional information to reduce this problem. We test this idea in the context of Great Britain for a widely discussed problem, that of catchment water balance errors due to subsurface losses. We test three hypotheses while considering different locational aspects (1) location to coast, (2) location next a relevant neighbour and (3) location within the drainage basin, utilizing only basic and widely available geological and topographical information. We find that subsurface losses from catchments with a highly permeable geology connection to the coast are in order of 20% water balance error. We define a simple topographic-geologic index that is able to partially explain water balance issues between neighbours of highly permeable catchments. The results imply that location, geology and topography combine to define the differences of water balances of UK catchments compared to what we would expect from their climatic setting alone. The simple index defined here can easily be derived globally and tested regarding its wider applicability.

Effect of topographic slope on the export of nitrate in humid catchments

Excess export of nitrate to streams affects ecosystem structure and functions and has been an environmental issue attracting world-wide attention. The dynamics of catchment-scale solute export from diffuse nitrate sources can be explained by the activation and deactivation of dominant flow paths, as solute attenuation (including the degradation of nitrate) is linked to the age composition of outflow. Previous data driven studies suggested that catchment topographic slope has strong impacts on the age composition of streamflow and consequently on in-stream solute concentrations. However, the impacts have not been systematically assessed in terms of solute concentration levels and variation, particularly in humid catchments with strong seasonality in meteorological forcing. To fill this gap, we modeled the groundwater flow and nitrate transport for a cross-section of a small agricultural catchment in Central Germany. We used the fully coupled surface and subsurface numerical simulator HydroGeoSphere to model groundwater and overland flow as well as nitrate concentrations. We computed the water ages using numerical tracer experiments. To represent various topographic slopes, we additionally simulated ten synthetic cross-sections generated by modifying the mean slope from the real-world scenario while preserving the land surface micro-topography. Results suggest a three-class response of in-stream nitrate concentrations to topographic slope, from class 1 (slope > 1:60), via class 2 (1:100 < slope < 1:60), to class 3 (slope < 1:100). Flatter landscapes tend to produce higher in-stream nitrate concentrations within class 1 or class 3, however, not within class 2. Young streamflow fractions and nitrate concentrations decrease sharply when flatter landscapes are not able to maintain fast preferential discharge paths (e.g. seepage). The variation of in-stream concentrations, controlled by degradation variability rather than by nitrate source variability, shows a similar three-class response. Our results improve the understanding of nitrate export in response to topographic slope in temperate humid climates, with important implications for the management of stream water quality.

A Texas-specific VS30 map incorporating geology and VS30 observations

A Texas-specific [Formula: see text] map that uses geostatistical kriging integrated with a region-specific geologic proxy, field measurements of [Formula: see text], and P-wave seismogram estimates of [Formula: see text] is developed. The region-specific geologic proxy is used first to predict [Formula: see text] from the surface geologic conditions across the state, and then geostatistical kriging with an external drift is used to incorporate the local [Formula: see text] measurements/estimates into the map. Compared with the [Formula: see text] map of Texas developed from a topographic slope proxy, the Texas-specific [Formula: see text] map predicts larger [Formula: see text] values across much of Texas, except for the Gulf Coast region where the values are similar. The utilization of kriging brings the Texas-specific [Formula: see text] map into better agreement with the in situ measurements and estimates of [Formula: see text]. The sensitivity of predicted ground motions by ShakeMap to changes in [Formula: see text] values is evaluated with a scenario earthquake in the Dallas–Fort Worth area. The results suggest smaller predicted ground motions due to the generally larger values of [Formula: see text] in the Texas-specific [Formula: see text] map as compared to the [Formula: see text] from the topographic proxy.

Snow Cover Variability in the Greater Alpine Region in the MODIS Era (2000–2019)

Snow cover is particularly important in the Alps for tourism and the production of hydroelectric energy. In this study, we investigate the spatiotemporal variability in three snow cover metrics, i.e., the length of season (LOS), start of season (SOS) and end of season (EOS), obtained by gap-filling of MOD10A1 and MYD10A1, daily snow cover products of MODIS (Moderate-resolution Imaging Spectroradiometer). We analyze the period 2000–2019, evaluate snow cover patterns in the greater Alpine region (GAR) as a whole and further subdivide it into four subregions based on geographical and climate divides to investigate the drivers of local variability. We found differences both in space and time, with the northeastern region having generally the highest LOS (74 ± 4 days), compared to the southern regions, which exhibit a much shorter snow duration (48/49 ± 2 days). Spatially, the variability in LOS and the other metrics is clearly related to elevation (r2 = 0.85 for the LOS), while other topographic (slope, aspect and shading) and geographic variables (latitude and longitude) play a less important role at the MODIS scale. A high interannual variability was also observed from 2000 to 2019, as the average LOS in the GAR ranged between 41 and 85 days. As a result of high variability, no significant trends in snow cover metrics were seen over the GAR when considering all grid cells. Considering 500-m elevation bands and subregions, as well as individual grid points, we observed significant negative trends above 3000 m a.s.l., with an average of −17 days per decade. While some trends appeared to be caused by glacierized areas, removing grid cells covered by glaciers leads to an even higher frequency of grid cells with significant trends above 3000 m a.s.l., reaching 100% at 4000 m a.s.l. Trends are however to be considered with caution because of the limited length of the observation period.

A new tool to simulate ground shaking and earthquake losses

The main purpose of SISMOTOOL suite is Planning and Management of Seismic Emergencies face to a future earthquake. This tool is written in ARCGIS software executing a fast and efficient determination of the estimated damage scenarios (pre-process) and a correlation with the observed damage results (post-process). First of all, the tool allows to select the earthquake source parameters through a defined database; moreover, several attenuation laws can be chosen and they can be combined according to the study area features. In addition, the local site effects are characterized from Vs30 values, which have been achieved by: i) topographic slope as a proxy obtained from Digital Elevation Model; ii) considering Vs30 values acquired from active and/or passive empirical methods; iii) a combination of both procedures through empirical local correlation laws. In the second place, the elements exposed to risk are incorporated by an automatic extraction from the cadastral database after inputs has been refined. Thirdly, vulnerability and estimated losses can be determined either empirically (EMS98 scale and Vulnerability Index, Iv) or analytically (Capacity spectrum). Additionally, a vulnerability modifier is implemented to account soil-structure resonance. Finally, SISMOTOOL quantifies the epistemic uncertainties in the input parameters using a logic tree. Last, but not least, SISMOTOOL results have been validated through a representative seismic scenario: the 1910 Adra earthquake (southern Spain) with moment magnitude (Mw) 6.3 and macroseismic intensity VIII (EMS98 scale) proves the reliability of SISMOTOOL program.

Terrain Slope Effect on Forest Height and Wood Volume Estimation from GEDI Data

The Global Ecosystem Dynamics Investigation LiDAR (GEDI) is a new full waveform (FW) based LiDAR system that presents a new opportunity for the observation of forest structures globally. The backscattered GEDI signals, as all FW systems, are distorted by topographic conditions within their footprint, leading to uncertainties on the measured forest variables. In this study, we explore how well several approaches based on waveform metrics and ancillary digital elevation model (DEM) data perform on the estimation of stand dominant heights (Hdom) and wood volume (V) across different sites of Eucalyptus plantations with varying terrain slopes. In total, five models were assessed on their ability to estimate Hdom and four models for V. Results showed that the models using the GEDI metrics, such as the height at different energy quantiles with terrain data from the shuttle radar topography mission’s (SRTM) digital elevation model (DEM) were still dependent on the topographic slope. For Hdom, an RMSE increase of 14% was observed for data acquired over slopes higher than 20% in comparison to slopes between 10 and 20%. For V, a 74% increase in RMSE was reported between GEDI data acquired over slopes between 0–10% and those acquired over slopes higher than 10%. Next, a model relying on the height at different energy quantiles of the entire waveform (HTn) and the height at different energy quartiles of the bare ground waveform (HGn) was assessed. Two sets of the HGn metrics were generated, the first one was obtained using a simulated waveform representing the echo from a bare ground, while the second one relied on the actual ground return from the waveform by means of Gaussian fitting. Results showed that both the simulated and fitted models provide the most accurate estimates of Hdom and V for all slope ranges. The simulation-based model showed an RMSE that ranged between 1.39 and 1.66 m (between 26.76 and 39.26 m3·ha−1 for V) while the fitting-based method showed an RMSE that ranged between 1.26 and 1.34 m (between 26.78 and 36.29 m3·ha−1 for V). Moreover, the dependency of the GEDI metrics on slopes was greatly reduced using the two sets of metrics. As a conclusion, the effect of slopes on the 25-m GEDI footprints is rather low as the estimation on canopy heights from uncorrected waveforms degraded by a maximum of 1 m for slopes between 20 and 45%. Concerning the wood volume estimation, the effect of slopes was more pronounced, and a degradation on the accuracy (increased RMSE) of a maximum of 20 m3·ha−1 was observed for slopes between 20 and 45%.