Salt Marsh Accretion With and Without Deep Soil Subsidence as a Proxy for Sea-Level Rise

The relation between salt marsh accretion and flooding regime was quantified by statistical analysis of a unique dataset of accretion measurements using sedimentation-erosion bars, on three barrier islands in the Dutch Wadden Sea over a period of c. 15 years. On one of the islands, natural gas extraction caused deep soil subsidence, which resulted in gradually increasing flooding frequency, duration, and depth, and can thus be seen as a proxy for sea-level rise. Special attention was paid to effects of small-scale variation e.g., in distance to tidal creeks or marsh edges, elevation of the marsh surface, and presence of livestock. Overall mean accretion rate was 0.44 ± 0.0005 cm year−1, which significantly exceeded the local rate of sea-level rise of 0.25 ± 0.009 cm year−1. A multiple regression approach was used to detect the combined effect of flooding regime and the local environment. The most important flooding-related factors that enhance accretion are mean water depth during flooding and overall mean water depth, but local accretion strongly decreases with increasing distance to the nearest creek or to the salt marsh edge. Mean water depth during flooding can be seen as an indicator for storm intensity, while overall mean water depth is a better indicator for storm frequency. The regression parameters were used to run a simple model simulating the effect of various sea-level scenarios on accretion and show that, even under extreme scenarios of sea-level rise, these salt marshes can probably persist for the next 100 years, although the higher parts may experience more frequent inundation.

Integrity of risk indicators of hazardous natural processes (on the example of the Krasnodar Krai)

The problem of assessing risk indicators of hazardous natural processes as the basis for sustainable development of the region arises due to the peculiarities of the geological structure of the territory of Krasnodar Krai. The work is based on a comprehensive assessment of the geological conditions of the territory of Krasnodar Krai with the use of a systematic approach. A list of characteristic natural processes that pose the greatest danger to capital constructions was determined: in the mountainous part – erosion processes, on the plain – soil subsidence and associated landforms. Then, schematic maps were compiled and the geological component of the risk (its spatial-areal indicator) was determined. Subsequently, to compare these maps, overlay operations were performed, as a result of which the spatial characteristics of ARC/INFO layers were combined into a new layer and relational join of their attribute data was carried out. Adding the risks of each parameter made it possible to rank the territory into 4 zones according to the degree of integral risk of manifestation of natural processes.

Rate of Fen-Peat Soil Subsidence Near Drainage Ditches (Central Poland)

This study analyzed design depths (to), post-subsidence depths (t), shallowing magnitudes (d = to − t) and ratio values (d/t) of 12 drainage ditches in a fragment of the drained Solec fen-peat (central Poland) over a period of 47 years between 1967 and 2014. A significant decrease of the designed depth of the ditches to was shown, from the average designed value of 0.97 m to their average depth after subsidence, t = 0.71 m. The ratio (d/t) of 0.41, which is associated with the degree of organic matter decomposition, indicated medium degree of peat decomposition. The average values of bank and bottom subsidence of the ditches during the analyzed period, 1967–2014, were 0.43 m and 0.17 m, respectively. The values of the average annual rate of land surface subsidence in the vicinity of the ditches were varied and within the range of 0.09 cm year−1 to 1.70 cm year−1, with an average of 0.92 cm year−1. Two linear empirical equations were proposed to calculate the amount of subsidence and the average annual rate of subsidence of peat soil surface near the drainage ditch route, based on the knowledge of the initial thickness of the peat deposit. The results of calculations using the equations proposed by the authors were compared with calculations of the same parameters using 10 equations published in the literature. The results obtained using the proposed equations were mostly larger than those calculated with literature-published equations.

Degradation of Arable Soils in Central Yakutia: Negative Consequences of Global Warming for Yedoma Landscapes

Global warming, which is especially intensive (up to 0.08°C yr−1) in permafrost area of Central Yakutia, has dramatic consequences for scarce arable land resources in this region. In Yedoma landscapes, intense permafrost thawing on arable fields unprotected by forest vegetation transforms the surface microtopography with the formation of residual thermokarst mounds (byllars) of 6–10 m in diameter surrounded by a polygonal network of hollows of 0.3–1.5 m in depth above melting ice wedges. This process also takes place on former croplands abandoned in the recent decades because of socioeconomic reasons. It is accompanied by a significant transformation of the previously highly likely homogeneous soil cover composed of Cambic Turbic Cryosols (Sodic) into differentiated complexes of permafrost-affected Stagnic Cambisols or Calcic Solonetzes (Turbic) on the mounds and Calcic Stagnic Solonetzes (Turbic) in the microlows. Surface soil horizons on the mounds have a strongly to very strongly alkaline reaction (pH 8.5–9.5) and low (<2%) organic carbon content; a wavy line of effervescence is found at a depth of 15–30 cm. Soils in the microlows have a close to neutral reaction in the upper horizons (pH 6.2–7.5); higher organic carbon content (2–3%); more pronounced textural differentiation of the profile with the formation of typical natric Btn and, in some cases, overlying eluvial E horizons; deeper (50–60 cm) line of effervescence; and clear stagnic features in the lower part of the profile. In the case of shallow embedding by ice wedge, the lowermost part of the soil in the microlow is characterized by the low bulk density (1.04 g cm−3) because of the appearance of hollows after thawing of the ice-rich transient layer and melting of the top of ice wedges. This may be indicative of the further soil subsidence in the future and the appearance of initial thermokarst lakes (dyuedya) within the Yedoma terrain with its transformation into the alas type of landscape. Rapid thermokarst-driven development of microtopography followed by differentiation of the soil cover with increasing soil alkalinity on the microhighs and soil textural differentiation and overmoistening of deep layers in the microlows prevents the return of abandoned arable land to agriculture in Yedoma landscapes.

ANALISIS MODEL KEGAGALAN RUMAH 2 LANTAI AKIBAT NEGATIVE SKIN FRICTION DAN CURAH HUJAN YANG TINGGI

ABSTRACTOne of the problems that appear in a project is the presence of soft soil. In projects with soft soil types, it is necessary to manage the soil to increase the bearing capacity of soil. Soil subsidence on soft soil causes friction between the soil and the pile blanket, called the negative skin friction. Negative skin friction should not be neglected because it exerts a large enough force on the load that the pile must support. In addition, in designing an engineer must also pay attention to the optimal rainfall that will occur during the construction of a project and after that has an impact on the quality of the soil and foundation used. The topography of a project also needs to be considered, building a house on the edge of a slope can cause problems with slope instability. Increasing the load on the edge of the slope can reduce the safety factor of a slope. In this study, a modeling analysis will be carried out on a 2-story residential building that causes the house to collapse due to failure of the foundation design, the existence of negative frictional resistance on soft soil, and slope stability. ABSTRAKSalah satu permasalahan yang muncul pada suatu proyek adalah adanya tanah lunak. Pada proyek dengan jenis tanah lunak, perlu dilakukan perbaikan tanah untuk meningkatkan daya dukung tanah. Penurunan tanah pada tanah lunak menyebabkan gesekan antara tanah denan selimut tiang yang disebut fenomena tahanan friksi negatif. Tahanan friksi negatif tidak boleh diabaikan karena memberikan gaya yang cukup besar terhadap beban yang harus ditopang oleh tiang. Oleh karena itu, seorang insinyur harus memperhatikan dan mengetahui mengenai perilaku tanah lunak. Selain itu dalam mendesain, seorang insinyur juga harus memperhatikan mengenai curah hujan optimal yang akan terjadi selama pengerjaan suatu proyek dan setelahnya yang berdampak pada kualitas tanah dan fondasi yang digunakan. Topografi suatu proyek juga perlu diperhatikan, membangun rumah di tepi lereng dapat menyebabkan permasalahan pada ketidakstabilan lereng.

Coupling Interaction of Surrounding Soil-Buried Pipeline and Additional Stress in Subsidence Soil

In the process of underground resource exploitation, the induced surface subsidence easily leads to the deformation and failure of buried pipeline. And in the process of soil subsidence, the complex interaction between buried pipeline and surrounding soil occurs, which leads to deformation and additional stress in buried pipeline. In this paper, a laboratory test system is designed and developed to analyze the influence of buried depth, cohesion of soil, and angle of internal friction on stress, in order to obtain the deformation mechanism of pipe-soil and the pressure around the pipe and the distribution of additional axial stress along the pipeline. The research results show that in the process of subsidence, the synergistic deformation between the pipe and soil at both ends of the subsidence area is maintained, while there is a compressive nonsynergistic deformation zone in the soil at the top of the pipe, and the deformation zone in the cohesion-less soil and the cohesive soil presents a spire shape and an arch shape, respectively. Areas of maximum additional tensile and compressive stresses occur in the area of maximum curvature and the central position. In addition, the smaller the burial depth, the earlier the unloading phenomenon occurs; and the additional stress in buried pipe in cohesion-less soil is significantly less than that in cohesive soil, and the unloading phenomenon occurs earlier. The research results provide the basis for disaster prevention of buried petroleum transmission pipeline in subsidence process.

Conventional subsoil irrigation techniques do not lower carbon emissions from drained peat meadows

The focus of current water management in drained peatlands is to facilitate optimal drainage, which has led to soil subsidence and a strong increase in greenhouse gas (GHG) emissions. The Dutch land and water authorities proposed the application of subsoil irrigation (SSI) system on a large scale to potentially reduce GHG emissions, while maintaining high biomass production. Based on model results, the expectation was that SSI would reduce peat decomposition in summer by preventing groundwater tables (GWTs) from dropping below −60 cm. In 2017–2018, we evaluated the effects of SSI on GHG emissions (CO2, CH4, N2O) for four dairy farms on drained peat meadows in the Netherlands. Each farm had a treatment site with SSI installation and a control site drained only by ditches (ditch water level −60 / −90 cm, 100 m distance between ditches). The SSI system consisted of perforated pipes −70 cm from surface level with spacing of 5–6 m to improve drainage during winter–spring and irrigation in summer. GHG emissions were measured using closed chambers every 2–4 weeks for CO2, CH4 and N2O. Measured ecosystem respiration (Reco) only showed a small difference between SSI and control sites when the GWT of SSI sites were substantially higher than the control site (> 20 cm difference). Over all years and locations, however, there was no significant difference found, despite the 6–18 cm higher GWT in summer and 1–20 cm lower GWT in wet conditions at SSI sites. Differences in mean annual GWT remained low (< 5 cm). Direct comparison of measured N2O and CH4 fluxes between SSI and control sites did not show any significant differences. CO2 fluxes varied according to temperature and management events, while differences between control and SSI sites remained small. Therefore, there was no difference between the annual gap-filled net ecosystem exchange (NEE) of the SSI and control sites. The net ecosystem carbon balance (NECB) was on average 40 and 30 t CO2 ha−1 yr−1 in 2017 and 2018 on the SSI sites and 38 and 34 t CO2 ha−1 yr−1 in 2017 and 2018 on the control sites. This lack of SSI effect is probably because the GWT increase remains limited to deeper soil layers (60–120 cm depth), which contribute little to peat oxidation. We conclude that SSI modulates water table dynamics but fails to lower annual carbon emission. SSI seems unsuitable as a climate mitigation strategy. Future research should focus on potential effects of GWT manipulation in the uppermost organic layers (−30 cm and higher) on GHG emissions from drained peatlands.

Geophysical surveys integrated with rainfall data analysis for the study of soil piping phenomena occurred in a densely urbanized area in eastern Sicily

The occurrence of strong and abrupt rainfall, together with a wrong land use planning and an uncontrolled urban development, can constitute a risk for infrastructure and population. The water flow in the subsoil, under certain conditions, may cause underground cavities formation. This phenomena known as soil piping can evolve and generate the surface collapse. It is clear that such phenomena in densely urbanized areas represent an unpredictable and consistent risk factor, which can interfere with social activities. In this study a multidisciplinary approach aimed to obtain useful information for the mitigation of the risks associated with the occurrence of soil piping phenomena in urban areas has been developed. This approach is aimed at defining the causes of sudden soil subsidence events, as well as the definition of the extension and possible evolution of these instability areas. The information obtained from rainfall data analysis, together with a study of the morphological, geological and hydrogeological characteristics, have allowed us to evaluate the causes that have led to the formation of soil pipes. Furthermore, performance of 3D electrical resistivity surveys in the area affected by the instability have allowed us to estimate their extension in the subsoil and identifying the presence of further areas susceptible to instability.